polyhydroxyalkanoates

Abstract

The present disclosure relates to polyhydroxyalkanoates, methods of their production, and their uses.

Description

POLYHYDROXYALKANOATESRELATED APPLICATION

[0001] The present application claims priority from Australian Provisional Patent Application No 2024903130 filed on 27 September 2024, the contents of which are incorporated herein by reference in their entirety.FIELD

[0002] The present disclosure relates to polyhydroxyalkanoates. The present disclosure also relates to methods of producing the polyhydroxyalkanoates, and their uses.BACKGROUND

[0003] The growth of polymer-based products, particularly packaging, has resulted in significant non- biodegradable waste, prompting a search for environmentally friendly alternatives amid the plastic pollution crisis. Ideal materials would be biodegradable in various natural environments, derived from renewable resources, and exhibit competitive mechanical properties compared to traditional petroleum-based plastics. In this context, bioplastics present an attractive alternative due to their potential to meet these criteria while reducing environmental impact.

[0004] Polyhydroxyalkanoates (PHAs) are a promising class of biodegradable polyesters that are produced by microorganisms using renewable feedstocks. Unlike bioplastics that rely on fossil fuels, PHAs can biodegrade in diverse environments, including soil and water, making them ideal for applications in biomedicine and food packaging due to their low toxicity and biocompatibility.

[0005] The mechanical properties and / or processability of common PHAs can hamper their practical application. For example, poly(3-hydroxybutyrate) (P3HB), a common homopolymer PHA, is relatively stiff and brittle with quite poor impact strength. Furthermore, the melting temperature of PHB is about 180° C, which is close to its decomposition temperature ranging from 200-300° C, resulting in a narrow viable processing window. In contrast, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), a common copolymer PHA, is less brittle and offers a wider processing window relative to PHB, particularly for PHBV with higher 3-hydroxyvalerate content. However, it has an extremely low melt strength and undergoes strain thinning during extensional flow, making it not well suited for producing thin films used extensively in packaging applications and commonly produced by blown film extrusion.

[0006] An opportunity therefore remains to develop biodegradable polymers that exhibit an improved balance between biodegradability, processability and physical properties. It would be advantageous to provide biodegradable polymers having one or more of these properties; or which may provide a useful alternative to existing biodegradable polymers.

[0007] Any reference to background art herein is not to be construed as an admission that such art constitutes common general knowledge in Australia or elsewhere.SUMMARY

[0008] The present inventors have undertaken extensive research and have developed the PHA block copolymers described herein. Advantageously, PHA block copolymers of the present disclosure were found tohave favourable mechanical properties which can render them more suitable for use in soft and flexible film applications.

[0009] Accordingly, in a first aspect, the present disclosure provides a polyhydroxyalkanoate block copolymer comprising a first block, a second block and optionally one or more further blocks, wherein each of the blocks have a number average molecular weight (Mn) of at least about 20 kDa, and wherein the first block and the second block are not the same.

[0010] In some embodiments of the first aspect, the first block and the second block are composed of different polymerised monomers. In some embodiments, the first block and the second block are composed of the same polymerised monomers but in different amounts.

[0011] In a second aspect, the present disclosure provides a method of producing a polyhydroxyalkanoate block copolymer comprising a first block, and a second block, and optionally one or more further blocks, the method comprising: reacting a first precursor block comprising at least one reactive end group and a second precursor block comprising at least one reactive end group to thereby provide a coupled first block and second block, wherein the each of the precursor blocks have a number average molecular weight (Mn) of at least about 20 kDa, and wherein the first precursor block and the second precursor block are not the same.

[0012] In some embodiments of the second aspect, the first precursor block and the second precursor block are composed of different polymerised monomers. In some embodiments, the first precursor block and the second precursor block are composed of the same polymerised monomers but in different amounts.

[0013] The polyhydroxyalkanoate block copolymer produced by, or obtained by, the second aspect may be a polyhydroxyalkanoate block copolymer of the first aspect.

[0014] In a third aspect, the present disclosure provides the use of the polyhydroxyalkanoate block copolymer of the first aspect, or produced by, or obtained by, the method of the second aspect, in a film or a coating.

[0015] In a fourth aspect, the present disclosure provides a film comprising the polyhydroxyalkanoate block copolymer of the first aspect, or produced by, or obtained by the method of the second aspect.

[0016] The present inventors have undertaken extensive research and have developed the PHA polymer compositions comprising crosslinked and optionally grafted PHA polymers described herein. Advantageously, PHA polymer compositions of the present disclosure were found to have favourable properties which can render them more suitable for use in soft and flexible film applications.

[0017] Accordingly, in a fifth aspect, the present disclosure provides a polyhydroxyalkanoate (PHA) polymer composition comprising a crosslinked and optionally grafted PHA polymer, formed by reactive blending of a mixture comprising at least one PHA polymer, an initiator and optionally a mono-reactive grafting agent.

[0018] In a sixth aspect, the present disclosure provides a method of producing a PHA polymer composition comprising a crosslinked and optionally grafted PHA polymer, the method comprising: reactive blending of a mixture comprising at least one PHA polymer, an initiator and optionally a mono- reactive grafting agent to thereby provide the PHA polymer composition.

[0019] In some embodiments of the sixth aspect, the PHA polymer composition is a PHA block copolymer composition comprising a crosslinked and optionally grated PHA block copolymer, and the method comprises: reacting one or more PHA polymers, a glycolytic agent, a glycolysis catalyst, and a multi isocyan ate compound to thereby provide a PHA block copolymer; and reactive blending of a mixture comprising the PHA block polymer, an initiator and optionally a mono- reactive grafting agent to thereby provide the PHA block copolymer composition.

[0020] The PHA polymer composition produced by, or obtained by, the sixth aspect may be a PHA polymer composition of the fifth aspect.

[0021] In a seventh aspect, the present disclosure provides the use of the PHA polymer composition of the fifth aspect, or produced by, or obtained by, the method of the sixth aspect, in a film.

[0022] In an eighth aspect, the present disclosure provides a film comprising the PHA polymer composition of the fifth aspect, or produced by, or obtained by, the method of the sixth aspect.

[0023] In a ninth aspect, the present disclosure provides a film composition comprising: a polyhydroxyalkanoate block copolymer of the first aspect, or produced by, or obtained by, the method of the second aspect; and a PHA polymer composition of the fifth aspect, or produced by, or obtained by, the method of the sixth aspect.

[0024] In a tenth aspect, the present disclosure provides the use of the film composition of the ninth aspect for producing a film.

[0025] It will be appreciated that the embodiments of each aspect of the present disclosure may equally be applied to each other aspect, mutatis mutandis.BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 . Screw configuration of Prism twin screw extruder.

[0027] Figure 2. Screw configuration of Entek twin screw extruder.

[0028] Figure 3. Schematic of film blowing die.

[0029] Figure 4. Transient extensional viscosity of PHBV materials: a) 185°C & 0.1 s1, b) 190°C & 0.1 s1, c) 185°C & 1 S'1, d) 190°C & 1 S'1.

[0030] Figure 5. DSC thermogram of 2nd heat scan of PHBV materials. Offset for clarity. Samples (top to bottom): PBHV; Extruded PBHV; 0.2° / <rP-PHBV; 0.2° / <rP-PHBV-UDA; and 5° / <rPHBV-BPMS.

[0031] Figure 6. Film blowing of a) 0.2° / <rP-PHBV-UDA and b) 5° / <rPHBV-BPMS materials.

[0032] Figure 7. Transient extensional viscosity of a) unmodified P3HB4HB measured at 170°C, 175 °C or 180°C and a strain rate of 0.1 s1, b) crosslinked P3HB4HB material measured at 180°C, 185°C, 190°C, 195°C or 210°C and a strain rate of 0.1 s1.

[0033] Figure 8. Photos of a) film blowing of crosslinked P3HB4HB material, b) crosslinked P3HB4HB blown film, c) heat-sealed crosslinked P3HB4HB film packaging.

[0034] Figure 9. Transient extensional viscosity of crosslinked blend of PHBV (1 mol% 3HV) and P3HB4HB (30 mol% 4HB) (50:50 wt.% of each) measured at 205°C or 210°C and a strain rate of 0.1 s1.

[0035] Figure 10. Transient extensional viscosity of crosslinked P3HB4HB block copolymer measured at 172°C and a strain rate of 0.1 s1.DETAILED DESCRIPTION

[0036] Reference will now be made in detail to certain embodiments of the present disclosure. While the present disclosure will be described in conjunction with the embodiments, it will be understood that the intention is not to limit the present disclosure to those embodiments. On the contrary, the present disclosure is intended to cover all alternatives, modifications, and equivalents, which may be included within the scope of the present disclosure as defined by the claims.

[0037] One skilled in the art will recognize many methods and materials similar or equivalent to those described herein, which could be used in the practice of the present disclosure. The present disclosure is in no way limited to the methods and materials described. It will be understood that the present disclosure extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the present disclosure.

[0038] All publications referred to herein are incorporated by reference in their entirety.

[0039] For the purposes of interpreting this specification, terms used in the singular will also include the plural and vice versa. Throughout this disclosure, unless specifically stated otherwise or the context requires otherwise, reference to a single step, composition of matter, group of steps or group of compositions of matter shall be taken to encompass one and a plurality (i.e., one or more) of those steps, compositions of matter, groups of steps or groups of compositions of matter. Thus, as used herein, the singular forms “a”, “an” and “the” include plural aspects unless the context clearly dictates otherwise. For example, reference to “a” includes a single as well as two or more; reference to “an” includes a single as well as two or more; reference to “the” includes a single as well as two or more and so forth.

[0040] The term “and / or”, e.g., “X and / or Y” shall be understood to mean either “X and Y” or “X or Y” and shall be taken to provide explicit support for both meanings or for either meaning.

[0041] Unless otherwise indicated, the terms “first,” “second,” etc. are used herein merely as labels, and are not intended to impose ordinal, positional, or hierarchical requirements on the items to which these terms refer. Moreover, reference to a “second” item does not require or preclude the existence of lower-numbered item (e.g., a “first’ item) and / or a higher-numbered item (e.g., a “third” item).

[0042] As used herein, the phrase “at least one of’ or “one or more of’ when used with a list of items, means different combinations of one or more of the listed items may be used and only one of the items in the list may be needed. The item may be a particular object, thing, or category. In other words, “at least one of’ means any combination of items or number of items may be used from the list, but not all of the items in the list may be required. For example, “at least one of item A, item B, and item C” may mean item A; item A and item B; item B; item A, item B, and item C; or item B and item C. In some cases, “at least one of item A, item B, and item C” may mean, for example and without limitation, two of item A, one of item B, and ten of item C; four of item B and seven of item C; or some other suitable combination.

[0043] As used herein, the term “about’, unless stated to the contrary, typically refers to a range of up to + / - 10% of the designated value, and includes smaller ranges therein, for example + / - 5% or + / - 1 % of the designated value.

[0044] It is to be appreciated that certain features that are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any sub-combination.

[0045] Throughout the present specification, various aspects and components of the disclosure can be presented in a range format. The range format is included for convenience and should not be interpreted as an inflexible limitation on the scope of the present disclosure. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range, unless specifically indicated. For example, description of a range such as from 1 to 5 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 5, from 3 to 5 etc., as well as individual and partial numbers within the recited range, for example, 1, 2, 3, 4, 5, 5.5 and 6, unless where integers are required or implicit from context. This applies regardless of the breadth of the disclosed range. Where specific values are required, these will be indicated in the specification.

[0046] Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.Polyhydroxyalkanoate block copolymers

[0047] PHAs typically exhibit excellent biodegradability, their physical properties and / or processability can limit their practical application. Modifications, such as creating random copolymers, have been shown to enhance the properties of PHAs but may yield materials that are not readily available in desirable forms. Another approach involves combining different PHAs through physical blending or block-copolymer formation to improve performance.

[0048] While biological methods for synthesizing block-copolymers exist, they often involve complex processes and product mixtures. Chemical synthesis offers greater control and variety, but research into the chemical synthesis of PHA block copolymers has been limited. Most studies have focused on isocyanate chemistry using low molecular weight hydroxy-terminated PHAs (Mn < 4 kDa) as starting materials, with few evaluating the mechanical properties of the resulting products.

[0049] The present disclosure provides polyhydroxyalkanoate block copolymers comprising a first block, a second block and optionally one or more further blocks. It will be understood that the polyhydroxyalkanoate having a "block copolymer" structure means the polyhydroxyalkanoate comprises at least two polyhydroxyalkanoate polymer blocks that are coupled together.

[0050] The present inventors have identified that the polyhydroxyalkanoate block copolymers of the present disclosure may be suitable for use in polymer-based products such as packaging. Advantageously, polyhydroxyalkanoate block copolymers of the present disclosure were found to have favourable mechanicalproperties, for example favourable elongation at break and tensile strength, which can render them more suitable for use in soft and flexible film applications.

[0051] An important feature of the polyhydroxyalkanoate block copolymers of the present disclosure is that each of the blocks have a number average molecular weight (Mn) of at least about 20 kDa. The use of relatively high molecular weight polymer blocks may advantageously impart favourable mechanical properties which can render the polyhydroxyalkanoate block copolymers more suitable for industrial soft film applications, such as thermoplastic applications like film blowing.

[0052] There is no particular limitation on the molecular weight of each of the blocks of the polyhydroxyalkanoate block copolymers of the present disclosure, provided that the number average molecular weight (Mn) of each of the blocks is at least about 20 kDa. The number average molecular weight of each polymer block (e.g. the first block, the second block, and / or the optional one or more additional blocks) may independently range from about 20 kDa to about 300 kDa, and all combinations and sub-combinations of ranges therein. The number average molecular weight of each polymer block may be at least about 20 kDa, at least about 30 kDa, at least about 40 kDa, at least about 50 kDa, at least about 60 kDa, at least about 70 kDa, at least about 80 kDa, at least about 90 kDa, at least about 100 kDa, at least about 110 kDa, at least about 120 kDa, at least about 130 kDa, at least about 140 kDa, or at least about 150 kDa. The number average molecular weight of each polymer block may be up to about 300 kDa, up to about 290 kDa, up to about 280 kDa, up to about 270 kDa, up to about 260 kDa, up to about 250 kDa, up to about 240 kDa, up to about 230 kDa, up to about 220 kDa, up to about 210 kDa, up to about 200 kDa, up to about 190 kDa, up to about 180 kDa, up to about 170 kDa, up to about 160 kDa, or up to about 150 kDa. Any minimum and maximum value may be combined to form a range, provided the range is between 20 kDa to 300 kDa. In some embodiments, the number average molecular weight of each polymer block independently ranges from about 20 kDa to about 300 kDa, from about 20 kDa to about 250 kDa, from about 20 kDa to about 200 kDa, from about 20 kDa to about 150 kDa, from about 20 kDa to about 125 kDa, from about 20 kDa to about 100 kDa, from about 30 kDa to about 100 kDa, from about 40 kDa to about 100 kDa, or from about 50 kDa to about 100 kDa.

[0053] Another important feature of the polyhydroxyalkanoate block copolymer of the present disclosure is that first block and the second block are not the same. That is, the first block and the second block are constitutionally different. The coupling of two different polymer blocks may advantageously allow for induced microphase separation of the polymer blocks. Accordingly, the first block and the second block may phase separate when they are not covalently coupled. Without wishing to be bound by theory, the present inventors hypothesise that the different compositions of the polymer blocks promotes solid state microphase separation of the polymer blocks, which is constrained due to their covalent coupling. This coupling in turn limits or prevents macrophase separation of the polymer blocks. The induced microphase separation is believed to impart a unique morphology, contributing to the favourable mechanical properties of the polyhydroxyalkanoate block copolymer.

[0054] In some embodiments, the first block and the second block are composed of different polymerised monomers, thereby making them constitutionally different. In these embodiments, it is believed that the differencein polymerised monomer composition may impart the polymer blocks with different material properties which may allow for induced microphase separation.

[0055] In some embodiments, the first block and the second block are composed of the same polymerised monomers but in different amounts, thereby making them constitutionally different. In these embodiments, it is believed that the difference in polymerised monomer content may impart the polymer blocks with different material properties which may allow for induced microphase separation.

[0056] A polymer block within the polyhydroxyalkanoate block copolymer of the present disclosure may be composed of any suitable polymerised monomer(s). Examples of suitable polymerised monomers include one or more of 3-hydroxybutyrate (3HB), 3-hydroxyvalerate (3HV), 4-hydroxybutyrate (4HB), and 3-hydroxyhexanoate (HHx). In some embodiments, each polymer block (e.g. the first block, the second block, and / or the optional one or more additional blocks) independently comprises at least one polymerised monomer selected from 3- hydroxybutyrate, 3-hydroxyvalerate, 4-hydroxybutyrate, and 3-hydroxyhexanoate.

[0057] Any suitable polymer block may be used within the polyhydroxyalkanoate block copolymer of the present disclosure. Examples of suitable polymer blocks include poly(3-hydroxybutyrate) (PHB), poly(3- hydroxyvalerate) (PHV), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co-4- hydroxybutyrate) (P3HB4HB), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx).

[0058] In some embodiments, each polymer block (e.g. the first block, the second block, and / or the optional one or more additional blocks) is independently selected from polymer blocks of poly(3-hydroxybutyrate), poly(3- hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). In some embodiments, each polymer block is independently selected from polymer blocks of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3- hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). In some embodiments, each polymer block is independently a polymer block of poly(3-hydroxybutyrate-co-3- hydroxyvalerate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

[0059] In some embodiments, the first block or the second block is a polymer block of poly(3-hydroxybutyrate- co-3-hydroxyvalerate). In some embodiments, the first block is a polymer block of poly(3-hydroxybutyrate-co-3- hydroxyvalerate). In some embodiments, the second block is a polymer block of poly(3-hydroxybutyrate-co-3- hydroxyvalerate).

[0060] In some embodiments, the first block or the second block is a polymer block of poly(3-hydroxybutyrate- co-4-hydroxybutyrate). In some embodiments, the first block is a polymer block of poly(3-hydroxybutyrate-co-4- hydroxybutyrate). In some embodiments, the second block is a polymer block of poly(3-hydroxybutyrate-co-4- hydroxybutyrate).

[0061] In some embodiments, the first block is a polymer block of poly(3-hydroxybutyrate-co-3- hydroxyvalerate) and the second block is a polymer block of poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

[0062] In embodiments where the first block and the second block are composed of different polymerised monomers, the first block and the second block may be independently selected from polymer blocks of poly(3- hydroxybutyrate), poly(3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), provided that the first block and the second block are not the same. In some embodiments, the first block and the second block are independently selected from polymer blocks of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3- hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). In some embodiments, the first block and the second block are independently a polymer block of poly(3-hydroxybutyrate- co-3-hydroxyvalerate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

[0063] In embodiments where the first block and the second block are composed of the same polymerised monomers but in different amounts, the first block and the second block may both be selected from polymer blocks of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and poly(3- hydroxybutyrate-co-3-hydroxyhexanoate). In some embodiments, the first block and the second block are both selected from poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3- hydroxyhexanoate). In some embodiments, the first block and the second block are both not polymer blocks of poly(3-hydroxybutyrate-co-3-hydroxyvalerate).

[0064] It will be appreciated by persons skilled in the art that any polymer blocks which are copolymer blocks are composed of two or more polymerised monomers, with the total content of the polymerised monomers equalling 100 mol%. For example, the polymer block poly(3-hydroxybutyrate-co-3-hydroxyvalerate) is composed of polymerised monomers of 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV), each of which may be present in amounts ranging from 1-99 mol%, provided that their combined content equals 100 mol%. Similarly, the polymer block poly(3-hydroxybutyrate-co-4-hydroxybutyrate) is composed of polymerised monomers of 3- hydroxybutyrate (3HB) and 4-hydroxybutyrate (4HB), each of which may be present in amounts ranging from 1- 99 mol%, provided that their combined content equals 100 mol%. The content of a polymerised monomer within a polymer block may be determined by methods known in the art, for example by nuclear magnetic resonance spectroscopy analysis.

[0065] In some embodiments, a polymer block of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) has a 3- hydroxyvalerate content of about 1 mol%, about 5 mol%, about 10 mol%, about 15 mol%, about 20 mol%, about 25 mol%, about 30 mol%, about 35 mol%, about 40 mol%, about 45 mol%, about 50 mol%, about 55 mol%, about 60 mol%, about 65 mol%, about 70 mol%, about 75 mol%, about 80 mol%, about 85 mol%, about 90 mol%, about 95 mol%, or about 99 mol%. In some embodiments, a polymer block of poly(3-hydroxybutyrate-co-3- hydroxyvalerate) has a 3-hydroxyvalerate content of about 1 mol%.

[0066] In some embodiments, a polymer block of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) has a 4- hydroxybutyrate content of about 1 mol%, about 5 mol%, about 10 mol%, about 15 mol%, about 20 mol%, about 25 mol%, about 30 mol%, about 35 mol%, about 40 mol%, about 45 mol%, about 50 mol%, about 55 mol%, about 60 mol%, about 65 mol%, about 70 mol%, about 75 mol%, about 80 mol%, about 85 mol%, about 90 mol%, about 95 mol%, or about 99 mol%. In some embodiments, a polymer block of poly(3-hydroxybutyrate-co-4- hydroxybutyrate) has a 4-hydroxybutyrate content of about 15 mol%. In some embodiments, a polymer block of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) has a 4-hydroxybutyrate content of about 30 mol%.

[0067] In some embodiments, a polymer block of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) has a 3- hydroxyhexanoate content of about 1 mol%, about 5 mol%, about 10 mol%, about 15 mol%, about 20 mol%, about 25 mol%, about 30 mol%, about 35 mol%, about 40 mol%, about 45 mol%, about 50 mol%, about 55 mol%, about 60 mol%, about 65 mol%, about 70 mol%, about 75 mol%, about 80 mol%, about 85 mol%, about 90 mol%, about 95 mol%, or about 99 mol%. In some embodiments, a polymer block of poly(3-hydroxybutyrate-co-3- hydroxyhexanoate) has a 3-hydroxyhexanoate content of about 15 mol%.

[0068] In embodiments where the first block and the second block are composed of different polymerised monomers, any one or more of the following may apply: the first block and the second block differ in their 3-hydroxybutyrate (3HB) content by at least about 15 mol%, at least about 20 mol%, at least about 25 mol%, at least about 30 mol%, at least about 35 mol%, at least about 40 mol%, or at least about 45 mol%, for example where one of the first block and the second block is a polymer block of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate- co-4-hydroxybutyrate) or poly(3-hydroxybutyrate-co-3-hydroxyhexanoate); the first block and the second block differ in their 3-hydroxyvalerate (3HV) content by at least about 15 mol%, at least about 20 mol%, at least about 25 mol%, at least about 30 mol%, at least about 35 mol%, at least about 40 mol%, or at least about 45 mol%, for example where one of the first block and the second block is a polymer block of poly(3-hydroxyvalerate) or poly(3-hydroxybutyrate-co-3-hydroxyvalerate); the first block and the second block differ in their 4-hydroxybutyrate (4HB) content by at least about 15 mol%, at least about 20 mol%, at least about 25 mol%, at least about 30 mol%, at least about 35 mol%, at least about 40 mol%, or at least about 45 mol%, for example where one of the first block and the second block is a polymer block of poly(3-hydroxybutyrate-co-4-hydroxybutyrate); the first block and the second block differ in their 3-hydroxyhexanoate (HHx) content by at least about 15 mol%, at least about 20 mol%, at least about 25 mol%, at least about 30 mol%, at least about 35 mol%, at least about 40 mol%, or at least about 45 mol%, for example where one of the first block and the second block is a polymer block of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

[0069] In embodiments where the first block and the second block are composed of different polymerised monomers, any one or more of the following may apply: the first block and the second block differ in their 3-hydroxybutyrate (3HB) content in a range from about 15 mol%to about 100 mol%, from about 15 mol%to about 85 mol%, from about 15 mol%to about 70 mol%, from about 30 mol% to about 100 mol%, from about 30 mol% to about 85 mol%, or from about 30 mol% to about 70 mol%, for example where one of the first block and the second block is a polymer block of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) or poly(3- hydroxybutyrate-co-3-hydroxyhexanoate); the first block and the second block differ in their 3-hydroxyvalerate (3HV) content in a range from about 15 mol%to about 100 mol%, from about 15 mol%to about 85 mol%, from about 15 mol%to about 70 mol%, from about 30 mol% to about 100 mol%, from about 30 mol% to about 85 mol%, or from about 30 mol% to about 70mol%, for example where one of the first block and the second block is a polymer block of poly(3-hydroxyvalerate) or poly(3-hydroxybutyrate-co-3-hydroxyvalerate); the first block and the second block differ in their 4-hydroxybutyrate (4HB) content in a range from about 15 mol%to about 100 mol%, from about 15 mol%to about 85 mol%, from about 15 mol%to about 70 mol%, from about 30 mol% to about 100 mol%, from about 30 mol% to about 85 mol%, or from about 30 mol% to about 70 mol%, for example where one of the first block and the second block is a polymer block of poly(3-hydroxybutyrate- co-4-hydroxybutyrate); the first block and the second block differ in their 3-hydroxyhexanoate (HHx) content in a range from about 15 mol% to about 100 mol%, from about 15 mol% to about 85 mol%, from about 15 mol% to about 70 mol%, from about 30 mol%to about 100 mol%, from about 30 mol%to about 85 mol%, or from about 30 mol% to about 70 mol%, for example where one of the first block and the second block is a polymer block of poly(3- hydroxybutyrate-co-3-hydroxyhexanoate).

[0070] In embodiments where the first block and the second block are composed of the polymerised monomers but in different amounts, any one or more of the following may apply: the first block and the second block differ in their 3-hydroxybutyrate (3HB) content by at least about 15 mol%, at least about 20 mol%, at least about 25 mol%, at least about 30 mol%, at least about 35 mol%, at least about 40 mol%, or at least about 45 mol%, for example where both of the first block and the second block are polymer blocks of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) or poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), preferably polymer blocks of poly(3-hydroxybutyrate-co-4- hydroxybutyrate) or poly(3-hydroxybutyrate-co-3-hydroxyhexanoate); the first block and the second block differ in their 3-hydroxyvalerate (3HV) content by at least about 15 mol%, at least about 20 mol%, at least about 25 mol%, at least about 30 mol%, at least about 35 mol%, at least about 40 mol%, or at least about 45 mol%, for example where both of the first block and the second block are polymer blocks of poly(3-hydroxybutyrate-co-3-hydroxyvalerate); the first block and the second block differ in their 4-hydroxybutyrate (4HB) content by at least about 15 mol%, at least about 20 mol%, at least about 25 mol%, at least about 30 mol%, at least about 35 mol%, at least about 40 mol%, or at least about 45 mol%, for example where both of the first block and the second block are polymer blocks of poly(3-hydroxybutyrate-co-4-hydroxybutyrate); the first block and the second block differ in their 3-hydroxyhexanoate (HHx) content by at least about 15 mol%, at least about 20 mol%, at least about 25 mol%, at least about 30 mol%, at least about 35 mol%, at least about 40 mol%, or at least about 45 mol%, for example where both of the first block and the second block are polymer blocks of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

[0071] In embodiments where the first block and the second block are composed of the polymerised monomers but in different amounts, any one or more of the following may apply: the first block and the second block differ in their 3-hydroxybutyrate (3HB) content in a range from about 15 mol%to about 100 mol%, from about 15 mol%to about 85 mol%, from about 15 mol%to about 70 mol%, from about 30 mol% to about 100 mol%, from about 30 mol% to about 85 mol%, or from about 30 mol% to about 70mol%, for example where both of the first block and the second block are polymer blocks of poly(3- hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) or poly(3- hydroxybutyrate-co-3-hydroxyhexanoate), preferably polymer blocks of poly(3-hydroxybutyrate-co-4- hydroxybutyrate) or poly(3-hydroxybutyrate-co-3-hydroxyhexanoate); the first block and the second block differ in their 3-hydroxyvalerate (3HV) content in a range from about 15 mol%to about 100 mol%, from about 15 mol%to about 85 mol%, from about 15 mol%to about 70 mol%, from about 30 mol% to about 100 mol%, from about 30 mol% to about 85 mol%, or from about 30 mol% to about 70 mol%, for example where both of the first block and the second block are polymer blocks of poly(3- hydroxybutyrate-co-3-hydroxyvalerate); the first block and the second block differ in their 4-hydroxybutyrate (4HB) content in a range from about 15 mol%to about 100 mol%, from about 15 mol%to about 85 mol%, from about 15 mol%to about 70 mol%, from about 30 mol% to about 100 mol%, from about 30 mol% to about 85 mol%, or from about 30 mol% to about 70 mol%, for example where both of the first block and the second block are polymer blocks of poly(3- hydroxybutyrate-co-4-hydroxybutyrate); the first block and the second block differ in their 3-hydroxyhexanoate (HHx) content in a range from about 15 mol% to about 100 mol%, from about 15 mol% to about 85 mol%, from about 15 mol% to about 70 mol%, from about 30 mol%to about 100 mol%, from about 30 mol%to about 85 mol%, or from about 30 mol%to about 70 mol%, for example where both of the first block and the second block are polymer blocks of poly(3- hydroxybutyrate-co-3-hydroxyhexanoate).

[0072] The polyhydroxyalkanoate block copolymer may be described as having an AB block copolymer structure, where A and B respectively represent the first and second blocks.

[0073] The polyhydroxyalkanoate block copolymer of the present disclosure may optionally comprise one or more further blocks, in addition to the first and second blocks. That is, the polyhydroxyalkanoate block copolymer comprises at least two blocks, and may optionally comprise one or more further blocks. For example, the polyhydroxyalkanoate block copolymer may comprise or consist of two, three, four, five, six, seven, eight, nine, ten or more blocks. It will be understood that first and second blocks of the polyhydroxyalkanoate block copolymer may be at any position (e.g. at an end or in the middle of the block copolymer) and in any order (e.g. in forward or reverse sequence), provided that they are adjacent. That is, the polyhydroxyalkanoate block copolymer of the present disclosure requires at least two adjacent blocks that are not the same.

[0074] In some embodiments, the polyhydroxyalkanoate block copolymer further comprises a third block. In some embodiments, the first block and third block are the same. For example, the polyhydroxyalkanoate block copolymer may have an ABA block copolymer structure. In some embodiments, the second block and the third block are the same. For example, the polyhydroxyalkanoate block copolymer may have an ABB block copolymer structure. In some embodiments, the first, second and third blocks are not the same. For example, the polyhydroxyalkanoate block copolymer may have an ABC block copolymer structure.

[0075] In some embodiments, the polyhydroxyalkanoate block copolymer further comprises a fourth block. In some embodiments, the first and fourth block are the same. For example, the polyhydroxyalkanoate blockcopolymer may have an ABAA or ABBA block copolymer structure. In some embodiments, the second block and fourth block are the same. For example, the polyhydroxyalkanoate block copolymer may have an ABAB or ABBB block copolymer structure. In some embodiments, the first, second and fourth block are not the same.

[0076] In some embodiments, the polyhydroxyalkanoate block copolymer further comprises a fifth block. In some embodiments, the first block and fifth block are the same. For example, the polyhydroxyalkanoate block copolymer may have an ABAAA, ABABA, ABBAA or ABBBA block copolymer structure. In some embodiments, the second block and the fifth block are the same. For example, the polyhydroxyalkanoate block copolymer may have an ABAAB, ABABB, ABBAB or ABBBB block copolymer structure. In some embodiments, the first, second and fifth blocks are not the same.

[0077] In some embodiments, the polyhydroxyalkanoate block copolymer is a di-block copolymer consisting of a first block and a second block. In some embodiments, the polyhydroxyalkanoate block copolymer is a triblock copolymer consisting of a first block, a second block and a third block.

[0078] The polymer blocks of the polyhydroxyalkanoate block copolymer of the present disclosure may be coupled to each other directly via a linking group, or indirectly via a linking moiety.

[0079] In some embodiments, the polymer blocks of the polyhydroxyalkanoate block copolymer are directly attached via a linking group. As used herein, the term “linking group” refers to a functional group that covalently attaches two adjacent blocks. The linking group may be formed by reacting a reactive end group of a precursor polymer block (e.g. a first precursor block) with a complementary reactive end group of another precursor block (e.g. a second precursor block), as described herein. Examples of suitable linking groups include ester (-C(=O)O- ), ether (-O-), urethane (-OC(=O)NH-), amide (-C(=O)NH-), thioether (-S-), and thioester (-C(=O)S-). In some embodiments, the linking group is selected from an ester, amide and urethane. In some embodiments, the linking group is an ester.

[0080] In some embodiments, the polymer blocks of the polyhydroxyalkanoate block copolymer are indirectly attached via a linking moiety. As used herein, the term “linking moiety” refers to a chemical moiety that covalently attaches two or more blocks. The linking moiety may be formed by reacting two or more reactive groups of a precursor linking moiety with a complementary reactive end group of at least two precursor blocks (e.g. a first precursor block and a second precursor block), so as to provide a linker moiety attached to two or more blocks (e.g. a first block and a second block), as described herein. Any suitable linking moiety may be used. The linking moiety may be attached to the at least two blocks by any suitable functional group, for example an ester, ether, urethane, amide, thioether, or thioester, preferably a urethane. In some embodiments, the linking moiety is a urethane linking moiety, that is, the linking moiety is attached to the at least two blocks (e.g. a first block and a second block) by urethane groups. In some embodiments, the linking moiety is selected from an ester linking moiety, an ether linking moiety, a urethane linking moiety, an amide linking moiety, a thioether linking moiety, or a thioester linking moiety.

[0081] In some embodiments, the linking moiety is the reaction product of a precursor linking moiety selected from:a diisocyanate compound, for example selected from hexamethylene diisocyanate (HDI), L-lysine diisocyanate ethyl ester (LDI) and trimethyl hexamethylene diisocyanate (TMDI); a bis- or multi-functional hydroxy compound, for example selected from dihydroxy compounds such as ethylene glycol, aromatic hydroxy compounds such as a hydroquinone or catechol, and multi-arm ethylene glycol oligomers such as short 3-arm or 4-arm hydroxy-polyethylene glycols; a bis- or multi-functional amino compound, for example selected from lower alkyl alpha, omegadiamines such as 1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane and 1,6- diaminohexane, branched diamines such as 1,2-diaminopropane, aromatic diamines such as p- phenylenediamine, multi-arm compounds such as tris(2-aminoethyl)amine and short 3-arm or 4-arm aminopolyethylene glycols, and lysine; a bis- or multi-functional thiol compound, for example selected from aliphatic or aromatic thiol compounds such as benzene-1 ,2-dithiol and propane-1, 3-dithiol, and substituted thiols such as dithiothreitol and multi-arm short thio-polyethylene glycols; and a bis- or multi-functional carboxylic acid compound, for example selected from multi-arm short carboxypolyethylene glycols, lower aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, and glutaric acid, and aromatic dicarboxylic acids such as terephthalic acid and benzenetricarboxylic acid.

[0082] As used herein, the term “multi-functional compound” means the compound has at least 2 functional groups (for example 2-6 functional groups, or 2-4 functional groups or 2 functional groups) that can participate in a reaction with a complementary reactive group.

[0083] In some embodiments, the linking moiety is the reaction product of a diisocyanate compound. In some embodiments, the diisocyanate compound is selected from hexamethylene diisocyanate (HDI), L-lysine diisocyanate ethyl ester (LDI) and trimethyl hexamethylene diisocyanate (TMDI). In some embodiments, the linking moiety is the reaction product of hexamethylene diisocyanate (HDI). In some embodiments, the linking moiety is -OC(=O)NH-(CH2)6-NHC(=O)O-.

[0084] There is no particular limitation on the molecular weight of the polyhydroxyalkanoate block copolymer of the present disclosure. The number average molecular weight (Mn) of the polyhydroxyalkanoate block copolymer may range from about 30 kDa to about 600 kDa, and all combinations and sub-combinations of ranges therein. The number average molecular weight of the polyhydroxyalkanoate block copolymer may be at least about 30 kDa, at least about 40 kDa, at least about 60 kDa, at least about 80 kDa, at least about 100 kDa, at least about 120 kDa, at least about 140 kDa, at least about 160 kDa, at least about 180 kDa, at least about 200 kDa, at least about 220 kDa, at least about 240 kDa, at least about 260 kDa, at least about 280 kDa, or at least about 300 kDa. The number average molecular weight of the polyhydroxyalkanoate block copolymer may be up to about 600 kDa, up to about 580 kDa, up to about 560 kDa, up to about 540 kDa, up to about 520 kDa, up to about 500 kDa, up to about 480 kDa, up to about 460 kDa, up to about 440 kDa, up to about 420 kDa, up to about 400 kDa, up to about 380 kDa, up to about 360 kDa, up to about 340 kDa, up to about 320 kDa, or up to about 300 kDa. Any minimum and maximum value may be combined to form a range, provided the range is between 30 kDa to 600 kDa. In some embodiments, the number average molecular weight of the polyhydroxyalkanoateblock copolymer ranges from about 30 kDa to about 550 kDa, about 30 kDa to about 500 kDa, about 30 kDa to about 450 kDa, about 30 kDa to about 400 kDa, about 30 kDa to about 350 kDa, about 30 kDa to about 300 kDa, about 30 kDa to about 250 kDa, about 30 kDa to about 220 kDa, or from about 40 kDa to about 220 kDa, or from about 60 kDa to about 220 kDa, or from about 40 kDa to about 160 kDa.

[0085] The number average molecular weight (Mn) of a polyhydroxyalkanoate block copolymer or a polymer block may be determined by any method known in the art, for example using gel permeation chromatography (GPC) using a refractometer detector.

[0086] The polyhydroxyalkanoate block copolymer of the present disclosure may be produced by, or obtained by, the method described herein.

[0087] Advantageously, as described herein and shown in the Examples, polyhydroxyalkanoate block copolymers of the present disclosure may exhibit favourable mechanical properties, including elongation at break, tensile strength and / or tensile toughness, which can improve their suitability for soft and flexible film applications. It will be appreciated that the ideal mechanical properties of a polyhydroxyalkanoate block copolymer can depend on the intended application. In some embodiments, the polyhydroxyalkanoate block copolymer of the present disclosure exhibits an elongation at break of at least about 75%, at least about 100%, at least about 125%, or at least about 150%. In some embodiments, the polyhydroxyalkanoate block copolymer exhibits a tensile toughness of at least about 40 MJ / m3. In some embodiments, the polyhydroxyalkanoate block copolymer exhibits a tensile strength of at least about 7 MPa.Methods of production

[0088] The present disclosure also provides a method of producing a polyhydroxyalkanoate block copolymer comprising a first block, and a second block, and optionally one or more further blocks. The produced polyhydroxyalkanoate block copolymer may be the polyhydroxyalkanoate block copolymer described herein.

[0089] The method comprises a step of reacting a first precursor block comprising at least one reactive end group and a second precursor block comprising at least one reactive end group to thereby provide a coupled first block and second block, wherein the each of the precursor polymer blocks have a number average molecular weight (Mn) of at least about 20 kDa, and wherein the first precursor block and the second precursor block are not the same. Such covalent coupling takes place through reaction between complimentary reactive functional groups. It will be understood that the first and second precursor blocks respectively correspond to the first and second blocks of a produced polyhydroxyalkanoate block copolymer. The first and second blocks can become directly attached through the reaction of the reactive end groups of the precursor polymer blocks with each other (forming a linking group between the first and second blocks), or indirectly attached a linking moiety through the reaction of the reactive end groups of the precursor polymer blocks with a precursor linking moiety, as described herein.

[0090] In some embodiments, the first precursor block and the second precursor block are composed of different polymerised monomers. In some embodiments, the first precursor block and the second precursor block are composed of the same polymerised monomers but in different amounts.

[0091] It will be appreciated by persons skilled in the art that the block copolymer structure of the produced polyhydroxyalkanoate block copolymer may depend on the number of reactive end groups present on the precursor polymer blocks. By way of example only: reacting a first precursor block comprising one reactive end group and a second precursor block comprising one reactive end group can produce a di-block copolymer, for example having an AB block copolymer structure; reacting a first precursor block comprising two reactive end groups and a second precursor block comprising one reactive end groups can produce di-block and tri-block copolymers, for example having AB, ABA and ABB block copolymer structures; and reacting a first precursor block comprising two reactive end groups and a second precursor block comprising two reactive end groups can produce di-block and tri-block copolymers, for example having AB, ABA and ABB block copolymer structures, as well as multi-block copolymers, for example having ABAB, ABABA and other block copolymer structures as described herein.

[0092] The first precursor block and the second precursor block may be provided in any suitable ratio, for example to achieve a desired block copolymer structure. In some embodiments, the first precursor block and the second precursor block are provided in a molar ratio ranging from about 10:1 to about 1 :10, and all combinations and sub-combinations of ranges therein. The first precursor block and the second precursor block may be provided in a molar ratio of about 10:1, about 5:1, about 2:1, about 1 :1, about 1 :2, about 1 :5, or about 1 :10. Any minimum and maximum value may be combined to form a range, provided the range is between 10:1 to about 1 :10. In some embodiments, the first precursor block and the second precursor block are provided in a molar ratio ranging from about 5:1 to about 1 :5.

[0093] There is no particular limitation on the molecular weight of the precursor polymer blocks, provided that the number average molecular weight (Mn) of each of the precursor polymer blocks is at least about 20 kDa. The number average molecular weight of each precursor polymer block (e.g. the first precursor block and the second precursor block) may independently range from about 20 kDa to about 300 kDa, and all combinations and subcombinations of ranges therein. The number average molecular weight of each precursor polymer block may be at least about 20 kDa, at least about 30 kDa, at least about 40 kDa, at least about 50 kDa, at least about 60 kDa, at least about 70 kDa, at least about 80 kDa, at least about 90 kDa, at least about 100 kDa, at least about 110 kDa, at least about 120 kDa, at least about 130 kDa, at least about 140 kDa, or at least about 150 kDa. The number average molecular weight of each precursor polymer block may be up to about 300 kDa, up to about 290 kDa, up to about 280 kDa, up to about 270 kDa, up to about 260 kDa, up to about 250 kDa, up to about 240 kDa, up to about 230 kDa, up to about 220 kDa, up to about 210 kDa, up to about 200 kDa, up to about 190 kDa, up to about 180 kDa, up to about 170 kDa, up to about 160 kDa, or up to about 150 kDa. Any minimum and maximum value may be combined to form a range, provided the range is between 20 kDa to 300 kDa. In some embodiments, the number average molecular weight of each precursor polymer block independently ranges from about 20 kDa to about 300 kDa, from about 20 kDa to about 250 kDa, from about 20 kDa to about 200 kDa, from about 20 kDa to about 150 kDa, from about 20 kDa to about 125 kDa, from about 20 kDa to about 100 kDa, from about 30 kDa to about 100 kDa, from about 40 kDa to about 100 kDa, or from about 50 kDa to about 100 kDa.

[0094] As used herein, the term “reactive end group” refers to a reactive group present at an end of a precursor polymer block used to prepare the polyhydroxyalkanoate block copolymer. A precursor polymer block (e.g. a first precursor block or a second precursor block) may comprise one reactive end group, or may comprise two reactive end groups which may be the same or different, preferably the same.

[0095] The reactive end groups of a precursor polymer block (e.g. the first and second precursor blocks) may be any suitable reactive group capable of reacting with a complementary reactive group to form a covalent attachment. Examples of suitable reactive end groups include hydroxy, halogen, thiol, carboxylic acid, amine, epoxide, isocyanate and acid chloride. In some embodiments, the at least one reactive end group of the first precursor block and the at least one reactive end group of the second precursor are independently selected from a hydroxy, halogen, thiol, carboxylic acid, amine, epoxide, isocyanate and acid chloride.

[0096] The at least one reactive end group of one precursor block (e.g. a first precursor block) may be different to the reactive end group of another precursor block (e.g. a second precursor block), for example in embodiments where the reactive end groups of a first and second precursor block react with each other to form a functional group that covalently attaches the two blocks. In some embodiments, the at least one reactive end group of the first precursor block and the at least one reactive end group of the second precursor are not the same. In some embodiments, the at least one reactive end group of the first precursor block and the at least one reactive end group of the second precursor are complementary. In some embodiments, the at least one reactive end group of the first precursor block is a hydroxy, and the at least one reactive end group of the second precursor is a carboxylic acid or acid chloride. In some embodiments, the at least one reactive end group of the first precursor block is a carboxylic acid or acid chloride, and the at least one reactive end group of the second precursor is a hydroxy.

[0097] The at least one reactive end group of one precursor block (e.g. a first precursor block) may be the same as the reactive end group of another precursor block (e.g. a second precursor block), for example in embodiments where the reactive end groups of a first and second precursor block react with two or more reactive groups of a precursor linking moiety to provide a linker moiety that covalently attaches the two blocks. In some embodiments, the at least one reactive end groups of both the first precursor block and the second precursor block are hydroxy groups.

[0098] In some embodiments, the at least one reactive end group of the first precursor block and the at least one reactive end group of the second precursor block react to form a linking group, such that the first block and the second block are directly attached via the linking group. The linking group may be any suitable linking group, including those described herein. In some embodiments, the linking group is selected from an ester (-C(=O)O-), ether (-O-), urethane (-OC(=O)NH-), amide (-C(=O)NH-), thioether (-S-), and thioester (-C(=O)S-). In some embodiments, the linking group is selected from an ester, amide and urethane. In some embodiments, the linking group is an ester.

[0099] A coupling agent may be used to promote the reaction to form a linking group, for example by activating a reactive end group. Any suitable coupling agents known in the art may be used. Examples of suitable coupling agents include: carbodiimide compounds, for example 1 -ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) anddicyclohexylcarbodiimide (DCC); imidazole compounds, for example cabonyldiimidazole (CDI); and acyl halide forming agents, for example thionyl chloride, oxalyl chloride and phosphorus oxychloride.

[0100] In embodiments where the linking group is an ester (e.g. formed by reaction of a carboxylic acid and a hydroxy), the coupling agent may be a carbodiimide compound, which may be ethyl-3-(3- dimethylaminopropyl)carbodiimide or dicyclohexylcarbodiimide, preferably ethyl-3-(3- dimethylaminopropyl)carbodiimide. In embodiments where the linking group is an amide (e.g. formed by reaction of a carboxylic acid and an amine), the coupling agent may be an imidazole compound, which may be cabonyldiimidazole, or an acyl halide forming agent, which may be selected from thionyl chloride, oxalyl chloride and phosphorus oxychloride. In embodiments where the linking group is a thioester (e.g. formed by reaction of a carboxylic acid and a thiol), the coupling agent may be an acyl halide forming agent, which may be selected from thionyl chloride, oxalyl chloride and phosphorus oxychloride.

[0101] In some embodiments, the at least one reactive end group of the first precursor block and the at least one reactive end group of the second precursor block react with a precursor linking moiety comprising two or more reactive groups, such that the first block and the second block are indirectly attached via a linking moiety.

[0102] As used herein, the term “precursor linking moiety” refers to a chemical moiety comprising two or more (e.g. 3, 4, 5, 6 or more) reactive groups that can react with the reactive end groups of precursor polymer blocks (e.g. the first and second precursor blocks) to form a covalent attachment. It will be understood that the precursor linking moiety corresponds to the linking moiety of a produced polyhydroxyalkanoate block copolymer, where the linking moiety becomes attached to two or more polymer blocks (e.g. a first block and a second block) through the reaction of the reactive end groups of the respective precursor blocks (e.g. a first precursor block and a second precursor block) with the two or more reactive groups of the precursor linking moiety. The linking moiety may be any suitable linking moiety, including those described herein.

[0103] The precursor linking moiety may be first reacted with one of the precursor polymer blocks (e.g. the first precursor block), followed by the resulting adduct being reacted with the other of the two precursor polymer blocks (e.g. the second precursor block). Alternatively, the first and second polymer block may be both reacted with the precursor linking moiety.

[0104] A precursor linking moiety may be a di-functional moiety comprising two reactive groups, or a multifunctional moiety comprising three or more reactive groups. The reactive groups of the precursor linking moiety may be the same or different, preferably the same.

[0105] The two or more reactive groups of the precursor linking moiety may be any suitable reactive groups capable of reacting with a complementary reactive end group of a precursor polymer block (e.g. a first precursor block or a second precursor block) to form a covalent attachment. Examples of suitable reactive groups include hydroxy, halogen, thiol, carboxylic acid, amine, epoxide, isocyanate and acid chloride. In some embodiments, the two or more reactive groups of the precursor linking moiety are selected from any one or more of hydroxy, thiol, carboxylic acid, amine, isocyanate and acid chloride. In some embodiments, the two or more reactive groups of the precursor linking moiety are urethane groups.

[0106] In some embodiments, the precursor linking moiety comprising two or more reactive groups is selected from: a diisocyanate compound, for example selected from hexamethylene diisocyanate (HDI), L-lysine diisocyanate ethyl ester (LDI) and trimethyl hexamethylene diisocyanate (TMDI); a bis- or multi-functional hydroxy compound, for example selected from dihydroxy compounds such as ethylene glycol, aromatic hydroxy compounds such as a hydroquinone or catechol, and multi-arm ethylene glycol oligomers such as short 3-arm or 4-arm hydroxy-polyethylene glycols; a bis- or multi-functional amino compound, for example selected from lower alkyl alpha, omegadiamines such as 1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane and 1,6- diaminohexane, branched diamines such as 1,2-diaminopropane, aromatic diamines such as p- phenylenediamine, multi-arm compounds such as tris(2-aminoethyl)amine and short 3-arm or 4-arm aminopolyethylene glycols, and lysine; a bis- or multi-functional thiol compound, for example selected from aliphatic or aromatic thiol compounds such as benzene-1 ,2-dithiol and propane-1, 3-dithiol, and substituted thiols such as dithiothreitol and multi-arm short thio-polyethylene glycols; and a bis- or multi-functional carboxylic acid compound, for example selected from multi-arm short carboxypolyethylene glycols, lower aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, and glutaric acid, and aromatic dicarboxylic acids such as terephthalic acid and benzenetricarboxylic acid.

[0107] In some embodiments, the precursor linking moiety comprising two or more reactive groups is a diisocyanate compound. In some embodiments, the diisocyanate compound is selected from hexamethylene diisocyanate (HDI), L-lysine diisocyanate ethyl ester (LDI) and frimethyl hexamethylene diisocyanate (TMDI). In some embodiments, the precursor linking moiety comprising two or more reactive groups is hexamethylene diisocyanate (HDI).

[0108] The produced polyhydroxyalkanoate block copolymer may optionally comprise one or more further blocks, in addition to the first and second blocks, as described herein. That is, the produced polyhydroxyalkanoate block copolymer comprises at least two blocks, and may optionally comprise one or more further blocks. For example, the produced polyhydroxyalkanoate block copolymer may comprise or consist of two, three, four, five, six, seven, eight, nine, ten or more blocks.

[0109] In some embodiments, the produced polyhydroxyalkanoate block copolymer comprises a third block. In these embodiments, the method comprises a further step of reacting a third precursor block comprising at least one reactive end group and the second precursor block comprising at least one reactive end group to thereby provide a coupled second block and third block. It will be understood that the third precursor block corresponds to the third block of a produced polyhydroxyalkanoate block copolymer, which becomes attached to the second block through the reaction of the reactive end groups of the precursor polymer blocks.

[0110] In some embodiments, the first precursor block and the third precursor block are the same. For example, the produced polyhydroxyalkanoate block copolymer may have an ABA block copolymer structure. In some embodiments, the second precursor block and the third precursor block are the same. For example, theproduced polyhydroxyalkanoate block copolymer may have an ABB block copolymer structure. In some embodiments, the first, second and third blocks are not the same. For example, the produced polyhydroxyalkanoate block copolymer may have an ABC block copolymer structure

[0111] In some embodiments, the at least one reactive end group of a precursor polymer block (e.g. a first precursor block or a second precursor block) is selected from a hydroxy, oxazoline, oxazinone, halogen, thiol, carboxylic acid, amine, epoxide, isocyanate and acid chloride. In some embodiments, the two or more reactive groups of the precursor linking moiety are selected from any one or more of a hydroxy, oxazoline, oxazinone, halogen, thiol, carboxylic acid, amine, epoxide, isocyanate and acid chloride.

[0112] By way of example only, suitable complementary reactive functional groups can include isocyanate with alcohol; alcohol with carboxylic acid; alcohol with acid chloride; alcohol with epoxide; amine with epoxide; amine with carboxylic acid; amine with acid chloride; halogen with alcohol; halogen with carboxylic acid; thiol with carboxylic acid; thiol with epoxide; thiol with acid chloride; and thiol with carboxylic acid.

[0113] In embodiments of the method of the present disclosure, the reaction of the precursor polymer blocks (e.g. the first and second precursor blocks) may take place in a solvent. Examples of suitable solvents in which that reaction takes place include chloroform, 1,2-dichloroethane and diglyme. Such reaction in solvent will generally take place at a temperature ranging from room temperature up to the boiling point of the solvent used.

[0114] In embodiments of the method of the present disclosure, the reaction of the precursor polymer blocks (e.g. the first and second precursor blocks) may be performed by melt processing. Melt processing may be performed using techniques / equipment known to those skilled in the art. For example, melt processing may be performed using conventional melt extrusion equipment. Such reaction via melt processing will generally take place at a temperature ranging from about 140°C to about 190°C.

[0115] A precursor polymer block used in the method of the present disclosure may be composed of any suitable polymerised monomer(s). Examples of suitable polymerised monomers include one or more of 3- hydroxybutyrate, 3-hydroxyvalerate, 4-hydroxybutyrate, and 3-hydroxyhexanoate. In some embodiments, each precursor polymer block (e.g. the first precursor block and the second precursor block) independently comprises at least one polymerised monomer selected from 3-hydroxybutyrate, 3-hydroxyvalerate, 4-hydroxybutyrate, and 3-hydroxyhexanoate.

[0116] Any suitable precursor polymer block may be used in the method of the present disclosure. Examples of suitable precursor polymer blocks include poly(3-hydroxybutyrate) (PHB), poly(3-hydroxyvalerate) (PHV), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx).

[0117] In some embodiments, each precursor polymer block (e.g. the first precursor block and the second precursor block) is independently selected from polymer blocks of poly(3-hydroxybutyrate), poly(3- hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). In some embodiments, each precursor polymer block is independently selected from polymer blocks of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3- hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). In someembodiments, each precursor polymer block is independently a polymer block of poly(3-hydroxybutyrate-co-3- hydroxyvalerate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

[0118] In some embodiments, the first precursor block or the second precursor block is a polymer block of poly(3-hydroxybutyrate-co-3-hydroxyvalerate). In some embodiments, the first precursor block is a polymer block of poly(3-hydroxybutyrate-co-3-hydroxyvalerate). In some embodiments, the second precursor block is a polymer block of poly(3-hydroxybutyrate-co-3-hydroxyvalerate).

[0119] In some embodiments, the first precursor block or the second precursor block is a polymer block of poly(3-hydroxybutyrate-co-4-hydroxybutyrate). In some embodiments, the first precursor block is a polymer block of poly(3-hydroxybutyrate-co-4-hydroxybutyrate). In some embodiments, the second precursor block is a polymer block of poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

[0120] In some embodiments, the first precursor block is a polymer block of poly(3-hydroxybutyrate-co-3- hydroxyvalerate) and the second precursor block is a polymer block of poly(3-hydroxybutyrate-co-4- hydroxybutyrate).

[0121] In embodiments where the first precursor block and the second precursor block are composed of different polymerised monomers, the first precursor block and the second precursor block may be independently selected from polymer blocks of poly(3-hydroxybutyrate), poly(3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3- hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3- hydroxyhexanoate), provided that the first precursor block and the second precursor block are not the same. In some embodiments, the first precursor block and the second precursor block are independently selected from polymer blocks of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). In some embodiments, the first precursor block and the second precursor block are independently a polymer block of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

[0122] In embodiments where the first precursor block and the second precursor block are composed of the same polymerised monomers but in different amounts, the first precursor block and the second precursor block may both be selected from polymer blocks of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3- hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). In some embodiments, the first precursor block and the second precursor block are both selected from poly(3- hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

[0123] In some embodiments, the first precursor block and the second precursor block are both not polymer blocks of poly(3-hydroxybutyrate-co-3-hydroxyvalerate).

[0124] In some embodiments, a precursor polymer block of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) has a 3-hydroxyvalerate content of about 1 mol%, about 5 mol%, about 10 mol%, about 15 mol%, about 20 mol%, about 25 mol%, about 30 mol%, about 35 mol%, about 40 mol%, about 45 mol%, about 50 mol%, about 55 mol%, about 60 mol%, about 65 mol%, about 70 mol%, about 75 mol%, about 80 mol%, about 85 mol%, about 90 mol%, about 95 mol%, or about 99 mol%. In some embodiments, a precursor polymer block of poly(3-hydroxybutyrate- co-3-hydroxyvalerate) has a 3-hydroxyvalerate content of about 1 mol%.

[0125] In some embodiments, a precursor polymer block of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) has a 4-hydroxybutyrate content of about 1 mol%, about 5 mol%, about 10 mol%, about 15 mol%, about 20 mol%, about 25 mol%, about 30 mol%, about 35 mol%, about 40 mol%, about 45 mol%, about 50 mol%, about 55 mol%, about 60 mol%, about 65 mol%, about 70 mol%, about 75 mol%, about 80 mol%, about 85 mol%, about 90 mol%, about 95 mol%, or about 99 mol%. In some embodiments, a precursor polymer block of poly(3-hydroxybutyrate- co-4-hydroxybutyrate) has a 4-hydroxybutyrate content of about 15 mol%. In some embodiments, a precursor polymer block of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) has a 4-hydroxybutyrate content of about 30 mol%.

[0126] In some embodiments, a precursor polymer block of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) has a 3-hydroxyhexanoate content of about 1 mol%, about 5 mol%, about 10 mol%, about 15 mol%, about 20 mol%, about 25 mol%, about 30 mol%, about 35 mol%, about 40 mol%, about 45 mol%, about 50 mol%, about 55 mol%, about 60 mol%, about 65 mol%, about 70 mol%, about 75 mol%, about 80 mol%, about 85 mol%, about 90 mol%, about 95 mol%, or about 99 mol%. In some embodiments, a precursor polymer block of poly(3- hydroxybutyrate-co-3-hydroxyhexanoate) has a 3-hydroxyhexanoate content of about 15 mol%.

[0127] In embodiments where the first precursor block and the second precursor block are composed of different polymerised monomers, any one or more of the following may apply: the first precursor block and the second precursor block differ in their 3-hydroxybutyrate (3HB) content by at least about 15 mol%, at least about 20 mol%, at least about 25 mol%, at least about 30 mol%, at least about 35 mol%, at least about 40 mol%, or at least about 45 mol%, for example where one of the first precursor block and the second precursor block is a polymer block of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3- hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) or poly(3-hydroxybutyrate-co-3- hydroxyhexanoate); the first precursor block and the second precursor block differ in their 3-hydroxyvalerate (3HV) content by at least about 15 mol%, at least about 20 mol%, at least about 25 mol%, at least about 30 mol%, at least about 35 mol%, at least about 40 mol%, or at least about 45 mol%, for example where one of the first precursor block and the second precursor block is a polymer block of poly(3-hydroxyvalerate) or poly(3-hydroxybutyrate-co-3- hydroxyvalerate); the first precursor block and the second precursor block differ in their 4-hydroxybutyrate (4HB) content by at least about 15 mol%, at least about 20 mol%, at least about 25 mol%, at least about 30 mol%, at least about 35 mol%, at least about 40 mol%, or at least about 45 mol%, for example where one of the first precursor block and the second precursor block is a polymer block of poly(3-hydroxybutyrate-co-4-hydroxybutyrate); the first precursor block and the second precursor block differ in their 3-hydroxyhexanoate (HHx) content by at least about 15 mol%, at least about 20 mol%, at least about 25 mol%, at least about 30 mol%, at least about 35 mol%, at least about 40 mol%, or at least about 45 mol%, for example where one of the first precursor block and the second precursor block is a polymer block of poly(3-hydroxybutyrate-co-3- hydroxyhexanoate).

[0128] In embodiments where the first precursor block and the second precursor block are composed of different polymerised monomers, any one or more of the following may apply: the first precursor block and the second precursor block differ in their 3-hydroxybutyrate (3HB) content in a range from about 15 mol% to about 100 mol%, from about 15 mol% to about 85 mol%, from about 15 mol% to about 70 mol%, from about 30 mol%to about 100 mol%, from about 30 mol%to about 85 mol%, or from about 30 mol% to about 70 mol%, for example where one of the first precursor block and the second precursor block is a polymer block of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3- hydroxybutyrate-co-4-hydroxybutyrate) or poly(3-hydroxybutyrate-co-3-hydroxyhexanoate); the first precursor block and the second precursor block differ in their 3-hydroxyvalerate (3HV) content in a range from about 15 mol% to about 100 mol%, from about 15 mol% to about 85 mol%, from about 15 mol% to about 70 mol%, from about 30 mol%to about 100 mol%, from about 30 mol%to about 85 mol%, or from about 30 mol% to about 70 mol%, for example where one of the first precursor block and the second precursor block is a polymer block of poly(3-hydroxyvalerate) or poly(3-hydroxybutyrate-co-3-hydroxyvalerate); the first precursor block and the second block differ in their 4-hydroxybutyrate (4HB) content in a range from about 15 mol%to about 100 mol%, from about 15 mol% to about 85 mol%, from about 15 mol%to about 70 mol%, from about 30 mol%to about 100 mol%, from about 30 mol%to about 85 mol%, or from about 30 mol% to about 70 mol%, for example where one of the first precursor block and the second precursor block is a polymer block of poly(3-hydroxybutyrate-co-4-hydroxybutyrate); the first precursor block and the second precursor block differ in their 3-hydroxyhexanoate (HHx) content in a range from about 15 mol% to about 100 mol%, from about 15 mol% to about 85 mol%, from about 15 mol% to about 70 mol%, from about 30 mol% to about 100 mol%, from about 30 mol% to about 85 mol%, or from about 30 mol% to about 70 mol%, for example where one of the first precursor block and the second precursor block is a polymer block of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

[0129] In embodiments where the first precursor block and the second precursor block are composed of the polymerised monomers but in different amounts, any one or more of the following may apply: the first precursor block and the second precursor block differ in their 3-hydroxybutyrate (3HB) content by at least about 15 mol%, at least about 20 mol%, at least about 25 mol%, at least about 30 mol%, at least about 35 mol%, at least about 40 mol%, or at least about 45 mol%, for example where both of the first precursor block and the second precursor block are polymer blocks of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3- hydroxybutyrate-co-4-hydroxybutyrate) or poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), preferably polymer blocks of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) or poly(3-hydroxybutyrate-co-3-hydroxyhexanoate); the first precursor block and the second precursor block differ in their 3-hydroxyvalerate (3HV) content by at least about 15 mol%, at least about 20 mol%, at least about 25 mol%, at least about 30 mol%, at least about 35 mol%, at least about 40 mol%, or at least about 45 mol%, for example where both of the first precursor block and the second precursor block are polymer blocks of poly(3-hydroxybutyrate-co-3-hydroxyvalerate); the first precursor block and the second precursor block differ in their 4-hydroxybutyrate (4HB) content by at least about 15 mol%, at least about 20 mol%, at least about 25 mol%, at least about 30 mol%, at least about35 mol%, at least about 40 mol%, or at least about 45 mol%, for example where both of the first precursor block and the second precursor block are polymer blocks of poly(3-hydroxybutyrate-co-4-hydroxybutyrate); the first precursor block and the second precursor block differ in their 3-hydroxyhexanoate (HHx) content by at least about 15 mol%, at least about 20 mol%, at least about 25 mol%, at least about 30 mol%, at least about 35 mol%, at least about 40 mol%, or at least about 45 mol%, for example where both of the first precursor block and the second precursor block are polymer blocks of poly(3-hydroxybutyrate-co-3- hydroxyhexanoate).

[0130] In embodiments where the first precursor block and the second precursor block are composed of the polymerised monomers but in different amounts, any one or more of the following may apply: the first precursor block and the second precursor block differ in their 3-hydroxybutyrate (3HB) content in a range from about 15 mol% to about 100 mol%, from about 15 mol% to about 85 mol%, from about 15 mol% to about 70 mol%, from about 30 mol%to about 100 mol%, from about 30 mol%to about 85 mol%, or from about 30 mol% to about 70 mol%, for example where both of the first precursor block and the second precursor block are polymer blocks of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4- hydroxybutyrate) or poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), preferably polymer blocks of poly(3- hydroxybutyrate-co-4-hydroxybutyrate) or poly(3-hydroxybutyrate-co-3-hydroxyhexanoate); the first precursor block and the second precursor block differ in their 3-hydroxyvalerate (3HV) content in a range from about 15 mol% to about 100 mol%, from about 15 mol% to about 85 mol%, from about 15 mol% to about 70 mol%, from about 30 mol%to about 100 mol%, from about 30 mol%to about 85 mol%, or from about 30 mol% to about 70 mol%, for example where both of the first precursor block and the second precursor block are polymer blocks of poly(3-hydroxybutyrate-co-3-hydroxyvalerate); the first precursor block and the second precursor block differ in their 4-hydroxybutyrate (4HB) content in a range from about 15 mol% to about 100 mol%, from about 15 mol% to about 85 mol%, from about 15 mol% to about 70 mol%, from about 30 mol%to about 100 mol%, from about 30 mol%to about 85 mol%, or from about 30 mol% to about 70 mol%, for example where both of the first precursor block and the second precursor block are polymer blocks of poly(3-hydroxybutyrate-co-4-hydroxybutyrate); the first precursor block and the second precursor block differ in their 3-hydroxyhexanoate (HHx) content in a range from about 15 mol% to about 100 mol%, from about 15 mol% to about 85 mol%, from about 15 mol% to about 70 mol%, from about 30 mol% to about 100 mol%, from about 30 mol% to about 85 mol%, or from about 30 mol% to about 70 mol%, for example where both of the first precursor block and the second precursor block are polymer blocks of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

[0131] The first and second precursor polymer blocks used in the method of the present disclosure can advantageously be sourced by any suitable means. For example, polyhydroxyalkanoates are often produced through biosynthetic pathways using microorganisms, for example through bacterial fermentation of sugars or lipids. The biosynthesis of polyhydroxyalkanoates is well known to those skilled in the art and conventional techniques / apparatus / reagents etc. for their production can advantageously be employed to provide for the first and second precursor blocks. For example, poly(3-hydroxybutyrate) can be readily accumulated in microbialcultures fed glucose or acetic acid, while poly(3-hydroxybutyrate-co-3-hydroxyvalerate), with high (>20%) 3- hydroxyvaleric acid content, can be readily accumulated in microbial cultures fed with feedstocks high in propionic and / or valeric acid.

[0132] Alternatively, the first and second precursor blocks may be prepared using known chemical synthesis techniques, for example from beta-lactones, functional cyclic esters and cyclic diolides.

[0133] Depending on the desired molecular weight of the polyhydroxyalkanoate block copolymer to be produced, the first and second precursor blocks may be sourced and used as sourced.

[0134] Alternatively, a precursor polyhydroxyalkanoate may be sourced and processed to undergo a reduction in its molecular weight and optionally attachment of a chain scission agent or residue thereof in order to provide for a precursor polymer block (e.g. one or both of the first precursor block and the second precursor block). The reaction between the precursor polyhydroxyalkanoate and the chain scission agent may be performed in solvent or by melt processing.

[0135] For example, a precursor polyhydroxyalkanoate may be reacted with a chain scission agent to promote a reduction in its molecular weight to provide for one or both of the first and second polymer blocks. Depending on the chain scission agent used, the resulting first and second precursor blocks may derive an end group from the chain scission agent or a residue thereof, which may function as a coupling agent between the first and second polymer blocks.

[0136] As used herein, the term “precursor polyhydroxyalkanoate” refers to a polyhydroxyalkanoate that is reacted with a chain scission agent to produce a precursor polymer block (e.g. a first and / or second precursor block) for use in accordance with the method of the present disclosure.

[0137] As used herein, the term “chain scission agent’ refers to a compound that can react with and reduce the molecular weight of a polyhydroxyalkanoate. In addition to performing a chain scission task, the chain scission agent or residue thereof may also become covalently attached to a terminal end of the so formed precursor polymer block, and may also function as a reactive end group in a subsequent coupling reaction. The chain scission agent may be a single compound or a combination of two or more compounds.

[0138] When promoting a reduction in the molecular weight of the precursor polyhydroxyalkanoate, the chain scission agent or residue thereof may or may not become covalently coupled to the so formed precursor polymer block.

[0139] Where the chain scission agent does not become covalently coupled to the so formed precursor polymer block, the role of that agent is purely chain scission. The resulting precursor polymer block(s) (e.g. one or both of the first and second precursor polymer blocks) can then be used in the method of the present disclosure and be covalently coupled as described herein. In these embodiments, the resulting precursor polymer block(s) may have the required at least one reactive end group, or may be further reacted to provide the at least one reactive end group using techniques known in the art.

[0140] Examples of such chain scission agents include inorganic acids (e.g. HCI), inorganic bases (e.g. KOH, NaOH), and peroxides.

[0141] Where the chain scission agent or a residue thereof does become covalently coupled to the so formed precursor polymer block, the role of that agent is first chain scission and then chain coupling.

[0142] In one embodiment, the chain scission agent or a residue thereof that becomes covalently coupled to the so formed precursor polymer block does not comprise a reactive group. For example, a mono-functional alcohol (e.g. methanol) may be reacted with a polyhydroxyalkanoate to reduce its molecular weight and covalently couple to the so formed precursor polymer block (e.g. one of the first or the second precursor polymer blocks) to form an adduct. The adduct does not comprise a reactive group derived from a functionality of the chain scission agent. Examples of such chain scission agents include mono functional alcohol (e.g. methanol), amine (e.g. methyl or ethylamine) and thiol (e.g. benzyl mercaptans) compounds. In these embodiments, the resulting precursor polymer block(s) may have the required at least one reactive end group, or may be further reacted to provide the at least one reactive end group using techniques known in the art.

[0143] In another embodiment, the chain scission agent or a residue thereof that becomes covalently coupled to the so formed precursor polymer block comprises a reactive group. In these embodiments, the precursor linking moiety as described herein may form part of a polymer block through the chain scission reaction. For example, a multi-functional alcohol (e.g. ethylene glycol) may be reacted with a polyhydroxyalkanoate to reduce its molecular weight and covalently couple to the so formed precursor polymer block (e.g. one of the first or the second precursor polymer blocks) to provide an adduct. The adduct will carry a terminal residue from the multi-functional alcohol and present a hydroxyl end group that can function to couple with a reactive end group of other precursor polymer block. When such a chain scission agent becomes covalently coupled to a precursor polymer block (e.g. a first precursor block), it can take on the role of a precursor linking moiety which the other precursor polymer block (e.g. a second precursor block) can be coupled. Examples of such chain scission agents include multifunctional alcohols, multi-functional amines and multi-functional thiols, such as those described herein in relation to the precursor linking moiety.

[0144] Those skilled in the art will appreciate that depending on the circumstances the multi-functional compounds described herein may function solely as a precursor linking moiety, or first as a chain scission agent followed by a chain coupling agent.

[0145] In some embodiments, a precursor polymer block (e.g. one or both of the first and second precursor blocks) is prepared by reacting a chain scission agent with a precursor polyhydroxyalkanoate to reduce its molecular weight. In some embodiments, a precursor polymer block (e.g. one or both of the first and second precursor blocks) is prepared by reacting a chain scission agent with a polyhydroxyalkanoate to reduce its molecular weight and provide an adduct of the so formed precursor polymer block which does not comprise a reactive group derived from a functionality of the chain scission agent.

[0146] In some embodiments, a precursor polymer block (e.g. one or both of the first and second precursor blocks) is prepared by reacting a chain scission agent with a polyhydroxyalkanoate to reduce its molecular weight and provide an adduct of the so formed precursor polymer block comprising a reactive group derived from a functionality of the chain scission agent.

[0147] In some embodiments, the precursor polyhydroxyalkanoate is reacted with a chain scission agent in a solvent. Examples of suitable solvents in which that reaction takes place include chloroform, 1,2-dichloroethane and diglyme. Such reaction in solvent will generally take place at a temperature ranging from room temperature up to the boiling point of the solvent used.

[0148] In some embodiments, the precursor polyhydroxyalkanoate is reacted with a chain scission agent by melt processing the precursor polyhydroxyalkanoate together with the chain scission agent. Melt processing the precursor polyhydroxyalkanoate with the chain scission agent may be performed using techniques / equipment known to those skilled in the art. For example, melt processing may be conveniently performed using conventional melt extrusion equipment. Such reaction via melt processing will generally take place at a temperature ranging from about 140°C to about 190°C. In embodiments, the precursor polyhydroxyalkanoate is reacted with a chain scission agent to provide a first and / or second precursor polymer block having at least one hydroxy end group.

[0149] Where the first and second precursor blocks are produced through reaction of a precursor polyhydroxyalkanoate with a chain scission agent, each of the first and second precursor blocks will generally be produced separately.

[0150] The present disclosure also provides a polyhydroxyalkanoate block copolymer produced by, or obtained by, the method of the present disclosure.Applications

[0151] As described herein, the polyhydroxyalkanoate block copolymers of the present disclosure may advantageously be suitable for use in polymer-based products such as packaging. The polyhydroxyalkanoate block copolymers may also be suitable for use in other polymer-based products such as coatings.

[0152] Accordingly, the present disclosure provides the use of the polyhydroxyalkanoate block copolymer described herein, or produced by, or obtained by, the method described herein, in a film. The film may be produced by extrusion, injection moulding or film blowing.

[0153] The present disclosure provides the use of the polyhydroxyalkanoate block copolymer described herein, or produced by, or obtained by, the method described herein, in a coating. The coating may be an extrusion coating or a solvent cast coating.

[0154] The present disclosure further provides a film or a film composition comprising the polyhydroxyalkanoate block copolymer described herein, or produced by, or obtained by, the method described herein. The film may be produced by extrusion, injection moulding or film blowing. The film composition may be for use in the production of a film by extrusion, injection moulding or film blowing.

[0155] The present disclosure further provides a coating or a coating composition comprising the polyhydroxyalkanoate block copolymer described herein, or produced by, or obtained by, the method described herein. The coating may be an extrusion coating or a solvent cast coating. The coating composition may be for use in extrusion coating or solvent cast coating.Crosslinked polyhydroxyalkanoate polymers

[0156] The present disclosure also provides polyhydroxyalkanoate (PH A) polymer compositions comprising a crosslinked and optionally grafted PHA polymer. The crosslinked and optionally grafted PHA polymer is formedby reactive blending of a mixture comprising at least one PHA polymer, an initiator and optionally a mono-reactive grafting agent.

[0157] The inventors have identified that the PHA polymer compositions of the present disclosure may be suitable for use in polymer-based products such as packaging. Advantageously, PHA polymer compositions of the present disclosure were found to have favourable rheological properties, for example strain hardening behaviour, which can render them more suitable for use in soft and flexible film applications, including thermoplastic applications such as film blowing.

[0158] The mixture used to form the crosslinked and optionally grafted PHA polymer comprises at least one PHA polymer. The at least one PHA polymer may be a single PHA polymer, a blend of two or more PHA polymers, or a PHA block-copolymer. In some embodiments, the at least one PHA polymer is a single PHA polymer. In some embodiments, the at least one PHA polymer is a blend of two or more PHA polymers. The ratio of two or more PHA polymers may be suitably selected, for example, depending on the desired application of the PHA polymer composition. In some embodiments, the at least one PHA polymer is a blend of two PHA polymers. The two PHA polymers may be present in a weight ratio (wt%:wt%) ranging from about 99:1 to about 1 :99, and all combinations and sub-combinations of ranges therein. In some embodiments, the two PHA polymers are present in a weight ratio (wt%:wt%) of about 99:1, about 95:5, about 90:10, about 85: 15, about 80:20, about 75:25, about 70:30, about 65:35, about 60:40, about 55:45, about 50:50, about 45:55, about 40:60, about 35:65, about 30:70, about 25:75, about 20:80, about 15:85, about 10:90, about 5:95, or about 1 :99. In some embodiments, the at least one PHA polymer is a PHA block-copolymer. The PHA block copolymer may be a polyhydroxyalkanoate block copolymer of the present disclosure.

[0159] The PHA polymer may be composed of any suitable polymerised monomer(s). Examples of suitable polymerised monomers include one or more of 3-hydroxybutyrate (3HB), 3-hydroxyvalerate (3HV), 4- hydroxybutyrate (4HB), and 3-hydroxyhexanoate (HHx). In some embodiments, the at least one PHA polymer comprises at least one polymerised monomer selected from 3-hydroxybutyrate, 3-hydroxyvalerate, 4- hydroxybutyrate, and 3-hydroxyhexanoate.

[0160] In some embodiments, the at least one PHA polymer comprises or is poly(3-hydroxybutyrate), poly(3- hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

[0161] It will be appreciated by persons skilled in the art that any polymer blocks which are copolymer blocks are composed of two or more polymerised monomers, with the total content of the polymerised monomers equalling 100 mol%. For example, the polymer block poly(3-hydroxybutyrate-co-3-hydroxyvalerate) is composed of polymerised monomers of 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV), each of which may be present in amounts ranging from 1-99 mol%, provided that their combined content equals 100 mol%. Similarly, the polymer block poly(3-hydroxybutyrate-co-4-hydroxybutyrate) is composed of polymerised monomers of 3- hydroxybutyrate (3HB) and 4-hydroxybutyrate (4HB), each of which may be present in amounts ranging from 1- 99 mol%, provided that their combined content equals 100 mol%. The content of a polymerised monomer withina polymer block may be determined by methods known in the art, for example by nuclear magnetic resonance spectroscopy analysis.

[0162] In some embodiments, a polymer block of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) has a 3- hydroxyvalerate content of about 1 mol%, about 5 mol%, about 10 mol%, about 15 mol%, about 20 mol%, about 25 mol%, about 30 mol%, about 35 mol%, about 40 mol%, about 45 mol%, about 50 mol%, about 55 mol%, about 60 mol%, about 65 mol%, about 70 mol%, about 75 mol%, about 80 mol%, about 85 mol%, about 90 mol%, about 95 mol%, or about 99 mol%. In some embodiments, a polymer block of poly(3-hydroxybutyrate-co-3- hydroxyvalerate) has a 3-hydroxyvalerate content of about 1 mol%.

[0163] In some embodiments, a polymer block of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) has a 4- hydroxybutyrate content of about 1 mol%, about 5 mol%, about 10 mol%, about 15 mol%, about 20 mol%, about 25 mol%, about 30 mol%, about 35 mol%, about 40 mol%, about 45 mol%, about 50 mol%, about 55 mol%, about 60 mol%, about 65 mol%, about 70 mol%, about 75 mol%, about 80 mol%, about 85 mol%, about 90 mol%, about 95 mol%, or about 99 mol%. In some embodiments, a polymer block of poly(3-hydroxybutyrate-co-4- hydroxybutyrate) has a 4-hydroxybutyrate content of about 15 mol%. In some embodiments, a polymer block of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) has a 4-hydroxybutyrate content of about 30 mol%.

[0164] In some embodiments, a polymer block of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) has a 3- hydroxyhexanoate content of about 1 mol%, about 5 mol%, about 10 mol%, about 15 mol%, about 20 mol%, about 25 mol%, about 30 mol%, about 35 mol%, about 40 mol%, about 45 mol%, about 50 mol%, about 55 mol%, about 60 mol%, about 65 mol%, about 70 mol%, about 75 mol%, about 80 mol%, about 85 mol%, about 90 mol%, about 95 mol%, or about 99 mol%. In some embodiments, a polymer block of poly(3-hydroxybutyrate-co-3- hydroxyhexanoate) has a 3-hydroxyhexanoate content of about 15 mol%.

[0165] In some embodiments, the at least one PHA polymer is a single PHA polymer, which is selected from poly(3-hydroxybutyrate), poly(3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3- hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). In some embodiments, the at least one PHA polymer is poly(3-hydroxybutyrate-co-3-hydroxyvalerate) or poly(3- hydroxybutyrate-co-4-hydroxybutyrate).

[0166] In some embodiments, the at least one PHA polymer is a blend of two or more PHA polymers, which are independently selected from poly(3-hydroxybutyrate), poly(3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3- hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3- hydroxyhexanoate). In some embodiments, the at least one PHA polymer is a blend of two PHA polymers, which are independently selected from poly(3-hydroxybutyrate), poly(3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3- hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3- hydroxyhexanoate). In some embodiments, the at least one PHA polymer is a blend of poly(3-hydroxybutyrate- co-3-hydroxyvalerate) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

[0167] In some embodiments, the at least one PHA polymer is a PHA block copolymer, which comprises one or polymer blocks independently selected from poly(3-hydroxybutyrate), poly(3-hydroxyvalerate), poly(3- hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). In some embodiments, the at least one PHA polymer is a PHA block copolymer composed of polymer blocks of poly(3-hydroxybutyrate-co-4-hydroxybutyrate). In some embodiments, the at least one PHA polymer is a PHA block copolymer of the present disclosure.

[0168] In embodiments wherein the at least one PHA polymer is a PHA block copolymer, the PHA block copolymer may be formed by reaction of one or more PHA polymers, a glycolytic agent, a glycolysis catalyst, and a multiisocyanate compound. In some embodiments, the PHA block copolymer is formed prior to the reactive blending. In some embodiments, the PHA block copolymer is formed during the reactive blending.

[0169] Any suitable glycolytic agent, glycolysis catalyst and / or multiisocyanate compound may be used to form the PHA block copolymer, including those known in the art and described herein. The term “multiisocyanate compound” will be understood to mean a compound comprising two or more isocyanate functional groups. Examples of suitable glycolytic agents include polyols such as ethylene glycol (EG) and glycerol. In some embodiments, the glycolytic agent is ethylene glycol. Examples of suitable glycolysis catalysts include organotin catalysts (e.g. dibutyltin dilaurate, stannous octanoate), bismuth / zinc catalysts (e.g. bismuth neodecanoate, zinc acetate), mercury catalysts (e.g. phenylmercuric acid), ferric chelate catalysts (e.g. ferric acetylacetonate), zirconium chelate catalysts (e.g. Zn(AcAc)4), tertiary amine catalysts (e.g. triethylamine, DABCO (1,4- diazabicyclo[2.2.2]octane)), amidine / amine catalysts (e.g. amino alcohols, 1,8-Diazabicyclo[5.4.0]undec-7-ene), acid catalysts (e.g. Methanesulfonic Acid (MSA), Trifluoromethanesulfonic Acid (TFMSA), and Dimethyl Hydrogen Phosphate (DMHP)), and base catalysts (e.g. potassium alkoxides, phenolates). In some embodiments, the glycolysis catalyst is an organotin catalyst, preferably dibutyltin dilaurate (DBTDL). Examples of suitable multi isocyan ate compounds include diisocyanate compounds (e.g. hexamethylene diisocyanate (HDI), L-lysine diisocyanate ethyl ester (LDI), trimethyl hexamethylene diisocyanate (TMDI)). In some embodiments, the multi isocyan ate compound is hexamethylene diisocyanate (HDI).

[0170] There is no particular limitation on the molecular weight of the at least one PHA polymer. The number average molecular weight (Mn) of the at least one PHA polymer may be from about 80 kDa to about 10,000 kDa, and all combinations and sub-combinations of ranges therein. In some embodiments, the number average molecular weight of the at least one PHA polymer may be from about 80 kDa to about 1,500 kDa, or from about 100 kDa to about 1,000 kDa, or from about 100 kDa to about 500 kDa.

[0171] The at least one PHA polymer may be present in the mixture in any suitable amount. In some embodiments, the at least one PHA polymer is provided in an amount of about 99.70 wt% to about 99.99 wt%, based on the total amount of the at least one PHA polymer and the initiator, and all combinations and subcombinations of ranges therein. For example, the at least one PHA polymer may be present in an amount of about 99.70 wt%, about 99.71 wt%, about 99.72 wt%, about 99.73 wt%, about 99.74 wt%, about 99.75 wt%, about 99.76 wt%, about 99.77 wt%, about 99.78 wt%, about 99.79 wt%, about 99.80 wt%, about 99.81 wt%, about 99.82 wt%, about 99.83 wt%, about 99.84 wt%, about 99.85 wt%, about 99.86 wt%, about 99.87 wt%, about 99.88 wt%, about 99.89 wt%, about 99.90 wt%, about 99.91 wt%, about 99.92 wt%, about 99.93 wt%, about 99.94 wt%, about 99.95 wt%, about 99.96 wt%, about 99.97 wt%, about 99.98 wt%, or about 99.99 wt%. Any two amount may be combined to form a range, provided the range is between 99.70 wt% to 99.99 wt%. In some embodiments, the atleast one PHA polymer is provided in an amount of from about 99.7 wt% to about 99.9 wt%, or about 99.75 wt% to about 99.9 wt%, or about 99.8 wt% to about 99.9 wt%. In some embodiments, the at least one PHA polymer is provided in an amount of about 99.8 wt%.

[0172] The mixture used to form the crosslinked and optionally grafted PHA polymer comprises an initiator. Examples of suitable initiators include dicumyl peroxide, t-amyl-2-ethylhexyl peroxycarbonate, 1,1-bis(t- butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy) hexane, 2,5-dimethyl-2,5-di(t-amyl peroxy) hexane, 2,5-bis(t-butylperoxy)-2,5-dimethylhexane, 2,5-dimethyl-di(t-butylperoxy)hexyne-3, di-t-butyl peroxide, benzoyl peroxide, di-t-amyl peroxide, t-butyl cumyl peroxide, n-butyl-4,4-bis(t-butylperoxy)valerate, 1,1- d i (t-buty lperoxy)-3, 3, 5-tri methy l-cyclohexane, 1 , 1 -di(t-butylperoxy)cyclohexane, 1 , 1 -di(t-amylperoxy)- cyclohexane, 2,2-di(t-butylperoxy)butane, ethyl-3,3-di(t-butylperoxy)butyrate, 2,2-di(t-amylperoxy)propane, ethyl- 3,3-di(t-amylperoxy)butyrate, t-butylperoxy-acetate, t-amylperoxyacetate, t-butylperoxybenzoate, t- amylperoxybenzoate, di-t-butyldiperoxyphthalate, and combinations thereof. In some embodiments, the initiator is an organic peroxide. In some embodiments, the initiator is dicumyl peroxide (DCP).

[0173] The initiator may be present in any suitable amount for providing a crosslinked and optionally grafted PHA polymer. In some embodiments, the initiator is provided in an amount of from about 0.01 wt% to about 0.30 wt%, based on the total amount of the at least one PHA polymer and the initiator, and all combinations and subcombinations of ranges therein. The inventors have surprisingly found that this weight range of initiator can prevent excessive crosslinking of the PHA polymer, which may result in gels and undesirable polymer properties for processing and end use applications. Advantageously, as shown in the Examples, this weight range of initiator can allow the formed PHA polymer composition to be suitable for producing a film, including a blown film. The initiator may be provided in an amount of from about 0.01 wt%, about 0.02 wt%, about 0.03 wt%, about 0.04 wt%, about 0.05 wt%, about 0.06 wt%, about 0.07 wt%, about 0.08 wt%, about 0.09 wt%, about 0.10 wt%, about 0.11 wt%, about 0.12 wt%, about 0.13 wt%, about 0.14 wt%, about 0.15 wt%, about 0.16 wt%, about 0.17 wt%, about 0.18 wt%, about 0.19 wt%, about 0.20 wt%, about 0.21 wt%, about 0.22 wt%, about 0.23 wt%, about 0.24 wt%, about 0.25 wt%, about 0.26 wt%, about 0.27 wt%, about 0.28 wt%, about 0.29 wt%, or about 0.30 wt%. Any two amounts may be combined to form a range, provided the range is between 0.01 wt% to 0.30 wt%. In some embodiments, the initiator is provided in an amount of from about 0.10 wt% to about 0.3 wt%, or about 0.10 to about 0.25 wt%, or about 0.10 to about 0.20 wt%. In some embodiments, the initiator is provided in an amount of about 0.20 wt%. The initiator may be dicumyl peroxide.

[0174] In some embodiments, the initiator is provided in an amount of from about 0.0032 mol% to about 0.096 mol%, based on the total amount of the at least one PHA polymer at the initiator. The initiator may be provided in an amount of from about 0.0032 mol%, about 0.0064 mol%, about 0.0096 mol%, about 0.013 mol%, about 0.016 mol%, about 0.019 mol%, about 0.022 mol%, about 0.026 mol%, about 0.029 mol%, about 0.032 mol%, about 0.035 mol%, about 0.038 mol%, about 0.042 mol%, about 0.045 mol%, about 0.048 mol%, about 0.051 mol%, about 0.054 mol%, about 0.058 mol%, about 0.061 mol%, about 0.064 mol%, about 0.067 mol%, about 0.07 mol%, about 0.074 mol%, about 0.077 mol%, about 0.08 mol%, about 0.083 mol%, about 0.086 mol%, about 0.09 mol%, about 0.093 mol%, or about 0.096 mol%. Any two amounts may be combined to form a range, providedthe range is between 0.0032 mol% to 0.096 mol%. In some embodiments, the initiator is provided in an amount of from about 0.032 mol%to about 0.096 mol%, or about 0.032 mol%to about 0.08 mol%, or about 0.10 to about 0.064 mol%. In some embodiments, the initiator is provided in an amount of about 0.064 mol%.

[0175] The mixture used to form the crosslinked and optionally grafted PHA polymer may optionally comprise a mono-reactive grafting agent. It will be appreciated that the mono-reactive grafting agent, when present, allows for grafting of the agent to the at least one PHA polymer to provide a grafted PHA polymer. The term “mono- reactive grafting agent’ will be understood to mean a grafting agent comprising only one reactive group capable of grafting to the at least one PHA polymer. Beneficially, using a mono-reactive grafting agent can prevent crosslinking of PHA polymer(s) via the grafting agent, which can occur with multi-functional grafting agents and may result in gels and undesirable polymer properties for processing and end use applications.

[0176] In some embodiments, the mono-reactive grafting agent comprises an unsaturated functional group as the reactive group. The unsaturated functional group may be an alkene, which may be a terminal alkene. In some embodiments, the mono-reactive grafting agent comprises a Ce-Cis alkene, which may be optionally substituted. Examples of optional substituents include polar groups, such as -COOH, -OH, and -NH2, which may be used to modify the hydrophilicity of the one or more PHA polymers. In some embodiments, the mono-reactive grafting agent is selected from undecenoic acid, dodecene and octeadecene. In some embodiments, the mono-reactive grafting agent is undecenoic acid.

[0177] The mono-reactive grafting agent may be present in any suitable amount for providing a grafted PHA polymer. In some embodiments, the mono-reactive grafting agent is provided in an amount of from about 0.1 wt% to about 5.0 wt%, based on the total amount of the at least one PHA polymer and the mono-reactive grafting agent, and all combinations and sub-combinations of ranges therein. The mono-reactive grafting agent may be provided in an amount of about 0.1 wt%, about 0.2 wt%, about 0.3 wt%, about 0.4 wt%, about 0.5 wt%, about 0.6 wt%, about 0.7 wt%, about 0.8 wt%, about 0.9 wt%, about 1 .0 wt%, about 1 .1 wt%, about 1 .2 wt%, about 1 .3 wt%, about 1 .4 wt%, about 1 .5 wt%, about 1 .6 wt%, about 1 .7 wt%, about 1 .8 wt%, about 1 .9 wt%, about 2.0 wt%, about 2.1 wt%, about 2.2 wt%, about 2.3 wt%, about 2.4 wt%, about 2.5 wt%, about 2.6 wt%, about 2.7 wt%, about 2.8 wt%, about 2.9 wt%, about 3.0 wt%, about 3.1 wt%, about 3.2 wt%, about 3.3 wt%, about 3.4 wt%, about 3.5 wt%, about 3.6 wt%, about 3.7 wt%, about 3.8 wt%, about 3.9 wt%, about 4.0 wt%, about 4.1 wt%, about 4.2 wt%, about 4.3 wt%, about 4.4 wt%, about 4.5 wt%, about 4.6 wt%, about 4.7 wt%, about 4.8 wt%, about 4.9 wt%, or about 5.0 wt%. Any two amounts may be combined to form a range, provided the range is between 0.1 wt% to 5.0 wt%. In some embodiments, the mono-reactive grafting agent is provided in an amount of 0.1 wt% to about 2.0 wt%, or from about 0.1 wt% to about 1 .0 wt%, or from about 0.1 wt% to about 0.5 wt%. In some embodiments, the mono-reactive grafting agent is provided in an amount of about 0.2 wt%. The mono- reactive grafting agent may be undecenoic acid.

[0178] In some embodiments, the mono-reactive grafting agent is provided in an amount of from about 0.047 mol% to about 2.4 mol%, based on the total amount of the at least one PHA polymer and the mono-reactive grafting agent, and all combinations and sub-combinations of ranges therein. The mono-reactive grafting agent may be provided in an amount of about 0.047 mol%, about 0.094 mol%, about 0.14 mol%, about 0.19 mol%,about 0.23 mol%, about 0.28 mol%, about 0.33 mol%, about 0.38 mol%, about 0.42 mol%, about 0.47 mol%, about 0.52 mol%, about 0.56 mol%, about 0.61 mol%, about 0.66 mol%, about 0.7 mol%, about 0.75 mol%, about 0.8 mol%, about 0.85 mol%, about 0.89 mol%, about 0.94 mol%, about 0.99 mol%, about 1 mol%, about 1.1 mol%, about 1 .2 mol%, about 1 .3 mol%, about 1 .4 mol%, about 1 .5 mol%, about 1 .6 mol%, about 1 .7 mol%, about 1.8 mol%, about 1.9 mol%, about 2 mol%, about 2.1 mol%, about 2.2 mol%, about 2.3 mol%, or about 2.4 mol%. Any two amounts may be combined to form a range, provided the range is between 0.047 mol% to 2.4 mol%. In some embodiments, the mono-reactive grafting agent is provided in an amount of 0.047 mol% to about 0.94 mol%, or from about 0.047 mol% to about 0.47 mol%, or from about 0.047 mol% to about 0.24 mol%.

[0179] Advantageously, as demonstrated in the Examples, the mixture does not require any additional agents in order to provide a composition suitable for producing a film, including for film blowing applications. Accordingly, in some embodiments, the mixture consists of the at least one PHA polymer, the initiator and optionally the mono- reactive grafting agent. In some embodiments, the mixture consists of the at least one PHA polymer, the initiator and the mono-reactive grafting agent. In some embodiments, the mixture consists of the at least one PHA polymer and the initiator. In this context, the term “consists of’ will be understood to mean that the mixture includes only the recited components and no additional components.

[0180] In some embodiments, the mixture does not comprise one or more additives, which may be selected from a chain extender, a plasticiser, a clarifier, a nucleating agent, a thermal stabiliser, an oxidative stabiliser, an inorganic filler, an anti-slip agent, a compatabiliser, and a blocking agent.

[0181] In some embodiments, the mixture does not comprise a solvent. In some embodiments, the mixture is not provided in a solvent.

[0182] The crosslinked and optionally grafted PHA polymer is formed by reactive blending of the mixture described herein. The reactive blending may be performed by any suitable process and / or apparatus, including those known in the art and described herein. In some embodiments, the reactive blending is performed via melt mixing. In some embodiments, the reactive blending is performed using a melt mixer. In some embodiments, the reactive blending is performed via reactive extrusion. In some embodiments, the reactive blending is performed using an extruder, such as a twin-screw extruder. The screw profile of the extruder may use a combination of forward and reverse mixing zones, which may advantageously enhance mixing of the components and / or reduce the duration (residence time) required for the reactive blending. The temperature profile of the extruder may comprise a reducing temperature profile, which may also advantageously enhance mixing of the components and / or reduce the duration (residence time) required for the reactive blending.

[0183] The reactive blending may be performed for any suitable duration to provide the crosslinked and optionally grafted PHA polymer. In some embodiments, the reactive blending is performed for a duration of from about 1 minute to about 12 minutes, and all combinations and sub-combinations of ranges therein. The reactive blending may be performed for a duration of about 1 minute, about 2 minutes, about 3 minutes, about 4 minutes, about 5 minutes, about 6 minutes, about 7 minutes, about 8 minutes, about 9 minutes, about 10 minutes, about 11 minutes, or about 12 minutes. Any two values may be combined to form a range, provided the range is between 1 minute to 12 minutes. In some embodiments, the reactive blending is performed for a duration of from about 1minute to about 6 minutes, or from about 1 minute to about 5 minutes, or from 1 minute to about 4 minutes, or from about 1 minute to about 3 minutes. In some embodiments, the reactive blending is performed for a duration of about 3 minutes.

[0184] The reactive blending may be performed at a temperature, or within a temperature range, suitable to provide the crosslinked and optionally grafted PHA polymer. The temperature, or temperature range, may be suitably selected depending on the at least one PHA polymer and / or the at least one initiator used in the mixture. In some embodiments, the reactive blending is performed at a temperature (or within a temperature range) of from about 160 °C to about 190 °C, and all combinations and sub-combinations of ranges therein. The reactive blending may be performed at a temperature of about 160 °C, about 161 °C, about 162 °C, about 163 °C, about 164 °C, about 165 °C, about 166 °C, about 167 °C, about 168 °C, about 169 °C, about 170 °C, about 171 °C, about 172 °C, about 173 °C, about 174 °C, about 175 °C, about 176 °C, about 177 °C, about 178 °C, about 179 °C, about 180 °C, about 181 °C, about 182 °C, about 183 °C, about 184 °C, about 185 °C, about 186 °C, about 187 °C, about 188 °C, about 189 °C, or about 190 °C. Any two values may be combined to form a range, provided the range is between 160 °C to 190 °C. In some embodiments, the reactive blending is performed at a temperature of from about 165 °C to about 190 °C, or from about 166 °C to about 190 °C, or from about 165 °C to about 175 °C, or from about 166 °C to about 175 °C, or from about 160 °C to about 175 °C, or from about 161 °C to about 175 °C, or from about 160 °C to about 170 °C, or from about 161 °C to about 170 °C. In some embodiments, the reactive blending is performed at a temperature of about 170 °C.

[0185] The reactive blending may be performed at a screw speed suitable for providing the crosslinked and optionally grafted PHA polymer. The screw speed may be suitably selected depending on the apparatus used. In some embodiments, the reactive blending is performed at a screw speed of from about 20 rpm to about 160 rpm, and all combinations and sub-combinations of ranges therein. The reactive blending may be performed at a screw speed of about 20 rpm, about 25 rpm, about 30 rpm, about 35 rpm, about 40 rpm, about 45 rpm, about 50 rpm, about 55 rpm, about 60 rpm, about 65 rpm, about 70 rpm, about 75 rpm, about 80 rpm, about 85 rpm, about 90 rpm, about 95 rpm, about 100 rpm, about 110 rpm, about 120 rpm, about 130 rpm, about 140 rpm, about 150 rpm, or about 160 rpm. Any two values may be combined to form a range, provided the range is between 20 rpm about 160 rpm. In some embodiments, the reactive blending is performed at a screw speed of from about 80 to about 160 rpm. In some embodiments, the reactive blending is performed at a screw speed of about 100 rpm, or about 160 rpm. In some embodiments, the reactive blending is performed at a screw speed of from about 20 to about 100 rpm, or from about 20 to about 60 rpm, or from about 20 to about 40 rpm, or from about 3o to about 40 rpm. In some embodiments, the reactive blending is performed at a screw speed of about 30 rpm. In some embodiments, the reactive blending is performed at a screw speed of about 40 rpm.

[0186] The PHA polymer composition comprises a crosslinked and optionally grafted PHA polymer. The crosslinked and optionally grafted PHA polymer may be partially crosslinked, that is, a portion of the PHA polymer used may be crosslinked. The extent of crosslinking may be characterised by the gel content (insoluble portion) of the PHA polymer composition, which assumes that the insoluble portion is crosslinked PHA polymer. The gel content of the PHA polymer composition may be measured by any suitable method, including those known in theart, for example by Soxhlet extraction. In some embodiments, the PHA polymer composition has a gel content of no more than about 5 wt%, no more than about 4 wt%, no more than about 3 wt%, no more than about 2 wt%, or no more than about 1 wt%.

[0187] The PHA polymer composition may advantageously exhibit properties that make it suitable for producing a film, including for film blowing applications. The inventors have identified that PHA polymer compositions that exhibit strain hardening behaviour in extensional flow are likely to be suitable for film blowing. In some embodiments, the PHA polymer composition exhibits strain hardening in a measurement of extensional viscosity at a temperature within the range of from about 150 °C to about 210 °C, and all combinations and subcombinations of ranges therein. In some embodiments, the PHA polymer composition exhibits strain hardening in a measurement of extensional viscosity at a temperature within the range of from about 160 °C to about 200 °C, or from about 170 °C to about 195 °C. The inventors have also identified that PHA polymers that exhibit strain hardening over a wider temperature range may be more suitable for film flowing. In some embodiments, the PHA polymer composition exhibits strain hardening in a measurement of extensional viscosity over a temperature range spanning at least about 10 °C, at least about 15 °C, at least about 20 °C, at least about 25 °C, or at least about 30 °C.

[0188] The PHA polymer composition of the present disclosure may be produced by, or obtained by, the methods described herein.Methods of production

[0189] The present disclosure also provides methods of producing a PHA polymer composition comprising a crosslinked and optionally grafted PHA polymer. The produced PHA polymer composition may be the PHA polymer composition described herein.

[0190] The method comprises a step of reactive blending of a mixture comprising at least one PHA polymer, an initiator and optionally a mono-reactive grafting agent to thereby provide the PHA polymer composition. It will be appreciated that the reactive blending allows reaction of the at least one PHA polymer and the initiator such that crosslinking and optional grafting of the at least one PHA polymer occurs.

[0191] The at least one PHA polymer may be a single PHA polymer, a blend of two or more PHA polymers, or a PHA block-copolymer. In some embodiments, the at least one PHA polymer is a single PHA polymer. In some embodiments, the at least one PHA polymer is a blend of two or more PHA polymers. The ratio of two or more PHA polymers may be suitably selected, for example, depending on the desired application of the PHA polymer composition. In some embodiments, the at least one PHA polymer is a blend of two PHA polymers. The two PHA polymers may be present in a weight ratio (wt%:wt%) ranging from about 99: 1 to about 1 : 99, and all combinations and sub-combinations of ranges therein. In some embodiments, the two PHA polymers are present in a weight ratio (wt%:wt%) of about 99:1, about 95:5, about 90:10, about 85:15, about 80:20, about 75:25, about 70:30, about 65:35, about 60:40, about 55:45, about 50:50, about 45:55, about 40:60, about 35:65, about 30:70, about 25:75, about 20:80, about 15:85, about 10:90, about 5:95, or about 1 :99. In some embodiments, the at least one PHA polymer is a PHA block-copolymer. The PHA block copolymer may be a polyhydroxyalkanoate block copolymer of the present disclosure.

[0192] The PH A polymer may be composed of any suitable polymerised monomer(s). Examples of suitable polymerised monomers include one or more of 3-hydroxybutyrate (3HB), 3-hydroxyvalerate (3HV), 4- hydroxybutyrate (4HB), and 3-hydroxyhexanoate (HHx). In some embodiments, the at least one PHA polymer comprises at least one polymerised monomer selected from 3-hydroxybutyrate, 3-hydroxyvalerate, 4- hydroxybutyrate, and 3-hydroxyhexanoate.

[0193] In some embodiments, the at least one PHA polymer comprises or is poly(3-hydroxybutyrate), poly(3- hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

[0194] In some embodiments, a polymer block of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) has a 3- hydroxyvalerate content of about 1 mol%, about 5 mol%, about 10 mol%, about 15 mol%, about 20 mol%, about 25 mol%, about 30 mol%, about 35 mol%, about 40 mol%, about 45 mol%, about 50 mol%, about 55 mol%, about 60 mol%, about 65 mol%, about 70 mol%, about 75 mol%, about 80 mol%, about 85 mol%, about 90 mol%, about 95 mol%, or about 99 mol%. In some embodiments, a polymer block of poly(3-hydroxybutyrate-co-3- hydroxyvalerate) has a 3-hydroxyvalerate content of about 1 mol%.

[0195] In some embodiments, a polymer block of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) has a 4- hydroxybutyrate content of about 1 mol%, about 5 mol%, about 10 mol%, about 15 mol%, about 20 mol%, about 25 mol%, about 30 mol%, about 35 mol%, about 40 mol%, about 45 mol%, about 50 mol%, about 55 mol%, about 60 mol%, about 65 mol%, about 70 mol%, about 75 mol%, about 80 mol%, about 85 mol%, about 90 mol%, about 95 mol%, or about 99 mol%. In some embodiments, a polymer block of poly(3-hydroxybutyrate-co- 4-hydroxybutyrate) has a 4-hydroxybutyrate content of about 15 mol%. In some embodiments, a polymer block of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) has a 4-hydroxybutyrate content of about 30 mol%.

[0196] In some embodiments, a polymer block of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) has a 3- hydroxyhexanoate content of about 1 mol%, about 5 mol%, about 10 mol%, about 15 mol%, about 20 mol%, about 25 mol%, about 30 mol%, about 35 mol%, about 40 mol%, about 45 mol%, about 50 mol%, about 55 mol%, about 60 mol%, about 65 mol%, about 70 mol%, about 75 mol%, about 80 mol%, about 85 mol%, about 90 mol%, about 95 mol%, or about 99 mol%. In some embodiments, a polymer block of poly(3-hydroxybutyrate- co-3-hydroxyhexanoate) has a 3-hydroxyhexanoate content of about 15 mol%.

[0197] In some embodiments, the at least one PHA polymer is a single PHA polymer, which is selected from poly(3-hydroxybutyrate), poly(3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3- hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). In some embodiments, the at least one PHA polymer is poly(3-hydroxybutyrate-co-3-hydroxyvalerate) or poly(3- hydroxybutyrate-co-4-hydroxybutyrate).

[0198] In some embodiments, the at least one PHA polymer is a blend of two or more PHA polymers, which are independently selected from poly(3-hydroxybutyrate), poly(3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3- hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3- hydroxyhexanoate). In some embodiments, the at least one PHA polymer is a blend of two PHA polymers, which are independently selected from poly(3-hydroxybutyrate), poly(3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and poly(3- hydroxybutyrate-co-3-hydroxyhexanoate). In some embodiments, the at least one PHA polymer is a blend of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

[0199] In some embodiments, the at least one PHA polymer is a PHA block copolymer, which comprises one or polymer blocks independently selected from poly(3-hydroxybutyrate), poly(3-hydroxyvalerate), poly(3- hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and poly(3- hydroxybutyrate-co-3-hydroxyhexanoate). In some embodiments, the at least one PHA polymer is a PHA block copolymer composed of polymer blocks of poly(3-hydroxybutyrate-co-4-hydroxybutyrate). In some embodiments, the at least one PHA polymer is a PHA block copolymer of the present disclosure.

[0200] In embodiments wherein the at least one PHA polymer is a PHA block copolymer, the PHA block copolymer may be formed by reaction of one or more PHA polymers, a glycolytic agent, a glycolysis catalyst, and a multiisocyanate compound.

[0201] Accordingly, in some embodiments, the PHA polymer composition is a PHA block copolymer composition comprising a crosslinked and optionally grafted PHA block copolymer, and the method comprises: reacting one or more PHA polymers, a glycolytic agent, a glycolysis catalyst, and a multi isocyan ate compound to thereby provide a PHA block copolymer; and reactive blending of a mixture comprising the PHA block polymer, an initiator and optionally a mono- reactive grafting agent to thereby provide the PHA block copolymer composition.

[0202] In some embodiments, the reacting step and reactive blending step are performed simultaneously. In some embodiments, the reacting step and reactive blending step are performed sequentially. In some embodiments, the reacting step is performed prior to the reactive blending step.

[0203] Any suitable glycolytic agent, glycolysis catalyst and / or multiisocyanate compound may be used to form the PHA block copolymer, including those known in the art and described herein. The term “multiisocyanate compound” will be understood to mean a compound comprising two or more isocyanate functional groups. Examples of suitable glycolytic agents include polyols such as ethylene glycol (EG) and glycerol. In some embodiments, the glycolytic agent is ethylene glycol. Examples of suitable glycolysis catalysts include organotin catalysts (e.g. dibutyltin dilaurate, stannous octanoate), bismuth / zinc catalysts (e.g. bismuth neodecanoate, zinc acetate), mercury catalysts (e.g. phenylmercuric acid), ferric chelate catalysts (e.g. ferric acetylacetonate), zirconium chelate catalysts (e.g. Zn(AcAc)4), tertiary amine catalysts (e.g. triethylamine, DABCO (1,4- diazabicyclo[2.2.2]octane)), amidine / amine catalysts (e.g. amino alcohols, 1,8-Diazabicyclo[5.4.0]undec-7-ene), acid catalysts (e.g. Methanesulfonic Acid (MSA), Trifluoromethanesulfonic Acid (TFMSA), and Dimethyl Hydrogen Phosphate (DMHP)), and base catalysts (e.g. potassium alkoxides, phenolates). In some embodiments, the glycolysis catalyst is an organotin catalyst, preferably dibutyltin dilaurate (DBTDL). Examples of suitable multi isocyan ate compounds include diisocyanate compounds (e.g. hexamethylene diisocyanate (HDI), L-lysine diisocyanate ethyl ester (LDI), trimethyl hexamethylene diisocyanate (TMDI)). In some embodiments, the multi isocyan ate compound is hexamethylene diisocyanate (HDI).

[0204] There is no particular limitation on the molecular weight of the at least one PHA polymer. The number average molecular weight (Mn) of the at least one PHA polymer may be from about 80 kDa to about 10,000 kDa, and all combinations and sub-combinations of ranges therein. In some embodiments, the number average molecular weight of the at least one PHA polymer may be from about 80 kDa to about 1,500 kDa, or from about 100 kDa to about 1,000 kDa, or from about 100 kDa to about 500 kDa.

[0205] The at least one PHA polymer may be present in the mixture in any suitable amount. In some embodiments, the at least one PHA polymer is provided in an amount of about 99.70 wt% to about 99.99 wt%, based on the total amount of the at least one PHA polymer and the initiator, and all combinations and subcombinations of ranges therein. For example, the at least one PHA polymer may be present in an amount of about 99.70 wt%, about 99.71 wt%, about 99.72 wt%, about 99.73 wt%, about 99.74 wt%, about 99.75 wt%, about 99.76 wt%, about 99.77 wt%, about 99.78 wt%, about 99.79 wt%, about 99.80 wt%, about 99.81 wt%, about 99.82 wt%, about 99.83 wt%, about 99.84 wt%, about 99.85 wt%, about 99.86 wt%, about 99.87 wt%, about 99.88 wt%, about 99.89 wt%, about 99.90 wt%, about 99.91 wt%, about 99.92 wt%, about 99.93 wt%, about 99.94 wt%, about 99.95 wt%, about 99.96 wt%, about 99.97 wt%, about 99.98 wt%, or about 99.99 wt%. Any two amount may be combined to form a range, provided the range is between 99.70 wt% to 99.99 wt%. In some embodiments, the at least one PHA polymer is provided in an amount of from about 99.7 wt% to about 99.9 wt%, or about 99.75 wt% to about 99.9 wt%, or about 99.8 wt% to about 99.9 wt%. In some embodiments, the at least one PHA polymer is provided in an amount of about 99.8 wt%.

[0206] The initiator may be any initiator suitable to allow crosslinking and optional grafting of the at least one PHA polymer. Examples of suitable initiators include dicumyl peroxide, t-amyl-2-ethylhexyl peroxycarbonate, 1,1- bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy) hexane, 2,5-dimethyl-2,5-di(t- amyl peroxy) hexane, 2,5-bis(t-butylperoxy)-2,5-dimethylhexane, 2,5-dimethyl-di(t-butylperoxy)hexyne-3, di-t- butyl peroxide, benzoyl peroxide, di-t-amyl peroxide, t-butyl cumyl peroxide, n-butyl-4,4-bis(t- butylperoxy)valerate, 1 , 1 -d i(t-buty lperoxy)-3, 3, 5-tri methy l-cyclohexane, 1 , 1 -di(t-butylperoxy)cyclohexane, 1,1- di(t-amylperoxy)-cyclohexane, 2,2-di(t-butylperoxy)butane, ethyl-3,3-di(t-butylperoxy)butyrate, 2,2-di(t- amylperoxy)propane, ethyl-3,3-di(t-amylperoxy)butyrate, t-butylperoxy-acetate, t-amylperoxyacetate, t- butylperoxybenzoate, t-amylperoxybenzoate, di-t-butyldiperoxyphthalate, and combinations thereof. In some embodiments, the initiator is an organic peroxide. In some embodiments, the initiator is dicumyl peroxide (DCP).

[0207] The initiator may be present in any suitable amount for providing a crosslinked and optionally grafted PHA polymer. In some embodiments, the initiator is provided in an amount of from about 0.01 wt% to about 0.30 wt%, based on the total amount of the at least one PHA polymer and the initiator, and all combinations and subcombinations of ranges therein. The inventors have surprisingly found that this weight range of initiator can prevent excessive crosslinking of the PHA polymer, which may result in gels and undesirable polymer properties for processing and end use applications. Advantageously, as shown in the Examples, this weight range of initiator can allow the formed PHA polymer composition to be suitable for producing a film, including a blown film. The initiator may be provided in an amount of from about 0.01 wt%, about 0.02 wt%, about 0.03 wt%, about 0.04 wt%, about 0.05 wt%, about 0.06 wt%, about 0.07 wt%, about 0.08 wt%, about 0.09 wt%, about 0.10 wt%, about 0.11wt%, about 0.12 wt%, about 0.13 wt%, about 0.14 wt%, about 0.15 wt%, about 0.16 wt%, about 0.17 wt%, about 0.18 wt%, about 0.19 wt%, about 0.20 wt%, about 0.21 wt%, about 0.22 wt%, about 0.23 wt%, about 0.24 wt%, about 0.25 wt%, about 0.26 wt%, about 0.27 wt%, about 0.28 wt%, about 0.29 wt%, or about 0.30 wt%. Any two amounts may be combined to form a range, provided the range is between 0.01 wt% to 0.30 wt%. In some embodiments, the initiator is provided in an amount of from about 0.10 wt% to about 0.3 wt%, or about 0.10 to about 0.25 wt%, or about 0.10 to about 0.20 wt%. In some embodiments, the initiator is provided in an amount of about 0.20 wt%. The initiator may be dicumyl peroxide.

[0208] In some embodiments, the initiator is provided in an amount of from about 0.0032 mol% to about 0.096 mol%, based on the total amount of the at least one PHA polymer at the initiator. The initiator may be provided in an amount of from about 0.0032 mol%, about 0.0064 mol%, about 0.0096 mol%, about 0.013 mol%, about 0.016 mol%, about 0.019 mol%, about 0.022 mol%, about 0.026 mol%, about 0.029 mol%, about 0.032 mol%, about 0.035 mol%, about 0.038 mol%, about 0.042 mol%, about 0.045 mol%, about 0.048 mol%, about 0.051 mol%, about 0.054 mol%, about 0.058 mol%, about 0.061 mol%, about 0.064 mol%, about 0.067 mol%, about 0.07 mol%, about 0.074 mol%, about 0.077 mol%, about 0.08 mol%, about 0.083 mol%, about 0.086 mol%, about 0.09 mol%, about 0.093 mol%, or about 0.096 mol%. Any two amounts may be combined to form a range, provided the range is between 0.0032 mol% to 0.096 mol%. In some embodiments, the initiator is provided in an amount of from about 0.032 mol%to about 0.096 mol%, or about 0.032 mol%to about 0.08 mol%, or about 0.10 to about 0.064 mol%. In some embodiments, the initiator is provided in an amount of about 0.064 mol%.

[0209] The mixture used to form the crosslinked and optionally grafted PHA polymer may optionally comprise a mono-reactive grafting agent. It will be appreciated that the mono-reactive grafting agent, when present, allows for grafting of the agent to the at least one PHA polymer to provide a grafted PHA polymer.

[0210] In some embodiments, the mono-reactive grafting agent comprises an unsaturated functional group as the reactive group. The unsaturated functional group may be an alkene, which may be a terminal alkene. In some embodiments, the mono-reactive grafting agent comprises a Ce-Cis alkene, which may be optionally substituted. Examples of optional substituents include polar groups, such as -COOH, -OH, and -NH2. In some embodiments, the mono-reactive grafting agent is selected from undecenoic acid, dodecene and octeadecene. In some embodiments, the mono-reactive grafting agent is undecenoic acid.

[0211] The mono-reactive grafting agent may be present in any suitable amount for providing a grafted PHA polymer. In some embodiments, the mono-reactive grafting agent is provided in an amount of from about 0.1 wt% to about 5.0 wt%, based on the total amount of the at least one PHA polymer and the mono-reactive grafting agent, and all combinations and sub-combinations of ranges therein. The mono-reactive grafting agent may be provided in an amount of about 0.1 wt%, about 0.2 wt%, about 0.3 wt%, about 0.4 wt%, about 0.5 wt%, about 0.6 wt%, about 0.7 wt%, about 0.8 wt%, about 0.9 wt%, about 1 .0 wt%, about 1 .1 wt%, about 1 .2 wt%, about 1 .3 wt%, about 1 .4 wt%, about 1 .5 wt%, about 1 .6 wt%, about 1 .7 wt%, about 1 .8 wt%, about 1 .9 wt%, about 2.0 wt%, about 2.1 wt%, about 2.2 wt%, about 2.3 wt%, about 2.4 wt%, about 2.5 wt%, about 2.6 wt%, about 2.7 wt%, about 2.8 wt%, about 2.9 wt%, about 3.0 wt%, about 3.1 wt%, about 3.2 wt%, about 3.3 wt%, about 3.4 wt%, about 3.5 wt%, about 3.6 wt%, about 3.7 wt%, about 3.8 wt%, about 3.9 wt%, about 4.0 wt%, about 4.1 wt%,about 4.2 wt%, about 4.3 wt%, about 4.4 wt%, about 4.5 wt%, about 4.6 wt%, about 4.7 wt%, about 4.8 wt%, about 4.9 wt%, or about 5.0 wt%. Any two amounts may be combined to form a range, provided the range is between 0.1 wt% to 5.0 wt%. In some embodiments, the mono-reactive grafting agent is provided in an amount of 0.1 wt% to about 2.0 wt%, or from about 0.1 wt% to about 1 .0 wt%, or from about 0.1 wt% to about 0.5 wt%. In some embodiments, the mono-reactive grafting agent is provided in an amount of about 0.2 wt%. The mono- reactive grafting agent may be undecenoic acid.

[0212] In some embodiments, the mono-reactive grafting agent is provided in an amount of from about 0.047 mol% to about 2.4 mol%, based on the total amount of the at least one PHA polymer and the mono-reactive grafting agent, and all combinations and sub-combinations of ranges therein. The mono-reactive grafting agent may be provided in an amount of about 0.047 mol%, about 0.094 mol%, about 0.14 mol%, about 0.19 mol%, about 0.23 mol%, about 0.28 mol%, about 0.33 mol%, about 0.38 mol%, about 0.42 mol%, about 0.47 mol%, about 0.52 mol%, about 0.56 mol%, about 0.61 mol%, about 0.66 mol%, about 0.7 mol%, about 0.75 mol%, about 0.8 mol%, about 0.85 mol%, about 0.89 mol%, about 0.94 mol%, about 0.99 mol%, about 1 mol%, about 1.1 mol%, about 1 .2 mol%, about 1 .3 mol%, about 1 .4 mol%, about 1 .5 mol%, about 1 .6 mol%, about 1 .7 mol%, about 1.8 mol%, about 1.9 mol%, about 2 mol%, about 2.1 mol%, about 2.2 mol%, about 2.3 mol%, or about 2.4 mol%. Any two amounts may be combined to form a range, provided the range is between 0.047 mol% to 2.4 mol%. In some embodiments, the mono-reactive grafting agent is provided in an amount of 0.047 mol% to about 0.94 mol%, or from about 0.047 mol% to about 0.47 mol%, or from about 0.047 mol% to about 0.24 mol%.

[0213] In some embodiments, the mixture consists of the at least one PHA polymer, the initiator and optionally the mono-reactive grafting agent. In some embodiments, the mixture consists of the at least one PHA polymer, the initiator and the mono-reactive grafting agent. In some embodiments, the mixture consists of the at least one PHA polymer and the initiator. In this context, the term “consists of’ will be understood to mean that the mixture includes only the recited components and no additional components.

[0214] In some embodiments, the mixture does not comprise one or more additives, which may be selected from a chain extender, a plasticiser, a clarifier, a nucleating agent, a thermal stabiliser, an oxidative stabiliser, an inorganic filler, an anti-slip agent, a compatabiliser, and a blocking agent.

[0215] In some embodiments, the mixture does not comprise a solvent. In some embodiments, the mixture is not provided in a solvent.

[0216] The reactive blending may be performed by any suitable process and / or apparatus, including those known in the art and described herein. In some embodiments, the reactive blending is performed via melt mixing. In some embodiments, the reactive blending is performed using a melt mixer. In some embodiments, the reactive blending is performed via reactive extrusion. In some embodiments, the reactive blending is performed using an extruder, such as a twin-screw extruder. The screw profile of the extruder may use a combination of forward and reverse mixing zones. The temperature profile of the extruder may comprise a reducing temperature profile.

[0217] The reactive blending may be performed for any suitable duration to provide the crosslinked and optionally grafted PHA polymer. In some embodiments, the reactive blending is performed for a duration of from about 1 minute to about 12 minutes, and all combinations and sub-combinations of ranges therein. The reactiveblending may be performed for a duration of about 1 minute, about 2 minutes, about 3 minutes, about 4 minutes, about 5 minutes, about 6 minutes, about ? minutes, about 8 minutes, about 9 minutes, about 10 minutes, about 11 minutes, or about 12 minutes. Any two values may be combined to form a range, provided the range is between 1 minute to 12 minutes. In some embodiments, the reactive blending is performed for a duration of from about 1 minute to about 6 minutes, or from about 1 minute to about 5 minutes, or from 1 minute to about 4 minutes, or from about 1 minute to about 3 minutes. In some embodiments, the reactive blending is performed for a duration of about 3 minutes.

[0218] The reactive blending may be performed at a temperature, or within a temperature range, suitable to provide the crosslinked and optionally grafted PHA polymer. The temperature, or temperature range, may be suitably selected depending on the at least one PHA polymer and / or the at least one initiator used in the mixture. In some embodiments, the reactive blending is performed at a temperature (or within a temperature range) of from about 160 °C to about 190 °C, and all combinations and sub-combinations of ranges therein. The reactive blending may be performed at a temperature of about 160 °C, about 161 °C, about 162 °C, about 163 °C, about 164 °C, about 165 °C, about 166 °C, about 167 °C, about 168 °C, about 169 °C, about 170 °C, about 171 °C, about 172 °C, about 173 °C, about 174 °C, about 175 °C, about 176 °C, about 177 °C, about 178 °C, about 179 °C, about 180 °C, about 181 °C, about 182 °C, about 183 °C, about 184 °C, about 185 °C, about 186 °C, about 187 °C, about 188 °C, about 189 °C, or about 190 °C. Any two values may be combined to form a range, provided the range is between 160 °C to 190 °C. In some embodiments, the reactive blending is performed at a temperature of from about 165 °C to about 190 °C, or from about 166 °C to about 190 °C, or from about 165 °C to about 175 °C, or from about 166 °C to about 175 °C, or from about 160 °C to about 175 °C, or from about 161 °C to about 175 °C, or from about 160 °C to about 170 °C, or from about 161 °C to about 170 °C. In some embodiments, the reactive blending is performed at a temperature of about 170 °C.

[0219] The reactive blending may be performed at a screw speed suitable for providing the crosslinked and optionally grafted PHA polymer. The screw speed may be suitably selected depending on the apparatus used. In some embodiments, the reactive blending is performed at a screw speed of from about 20 rpm to about 160 rpm, and all combinations and sub-combinations of ranges therein. The reactive blending may be performed at a screw speed of about 20 rpm, about 25 rpm, about 30 rpm, about 35 rpm, about 40 rpm, about 45 rpm, about 50 rpm, about 55 rpm, about 60 rpm, about 65 rpm, about 70 rpm, about 75 rpm, about 80 rpm, about 85 rpm, about 90 rpm, about 95 rpm, about 100 rpm, about 110 rpm, about 120 rpm, about 130 rpm, about 140 rpm, about 150 rpm, or about 160 rpm. Any two values may be combined to form a range, provided the range is between 20 rpm about 160 rpm. In some embodiments, the reactive blending is performed at a screw speed of from about 80 to about 160 rpm. In some embodiments, the reactive blending is performed at a screw speed of about 100 rpm, or about 160 rpm. In some embodiments, the reactive blending is performed at a screw speed of from about 20 to about 100 rpm, or from about 20 to about 60 rpm, or from about 20 to about 40 rpm, or from about 30 to about 40 rpm. In some embodiments, the reactive blending is performed at a screw speed of about 30 rpm. In some embodiments, the reactive blending is performed at a screw speed of about 40 rpm.

[0220] The produced crosslinked and optionally grafted PHA polymer may be partially crosslinked, that is, a portion of the PHA polymer used may be crosslinked. In some embodiments, the PHA polymer composition has a gel content of no more than about 5 wt%, no more than about 4 wt%, no more than about 3 wt%, no more than about 2 wt%, or no more than about 1 wt%.

[0221] The produced PHA polymer composition may advantageously exhibit properties that make it suitable for producing a film, including for film blowing applications. In some embodiments, the produced PHA polymer composition exhibits strain hardening in a measurement of extensional viscosity at a temperature within the range of from about 150 °C to about 210 °C, and all combinations and sub-combinations of ranges therein. In some embodiments, the produced PHA polymer composition exhibits strain hardening in a measurement of extensional viscosity at a temperature within the range of from about 160 °C to about 200 °C, or from about 170 °C to about 195 °C. In some embodiments, the produced PHA polymer composition exhibits strain hardening in a measurement of extensional viscosity over a temperature range spanning at least about 10 °C, at least about 15 °C, at least about 20 °C, at least about 25 °C, or at least about 30 °C.

[0222] The present disclosure also provides a PHA polymer composition produced, or obtained by, by a method of the present disclosure.Applications

[0223] As described herein, the PHA polymer compositions of the present disclosure may advantageously be suitable for use in polymer-based products such as packaging. The PHA polymer compositions may also be suitable for use in other polymer-based products such as coatings.

[0224] Accordingly, the present disclosure provides the use of the PHA polymer composition described herein, or produced by, or obtained by, the method described herein, in a film. The film may be produced by extrusion, injection moulding or film blowing. In some embodiments, the film is produced by film blowing. The film blowing may be performed at a temperature at which the PHA polymer composition exhibits strain hardening.

[0225] The present disclosure also provides the use of the PHA polymer composition described herein, or produced by, or obtained by, the method described herein, in a coating. The coating may be an extrusion coating or a solvent cast coating.

[0226] The present disclosure further provides a film or a film composition comprising the PHA polymer composition described herein, or produced by, or obtained by, the method described herein. The film may be produced by extrusion, injection moulding or film blowing. In some embodiments, the film is produced by film blowing. The film composition may be for use in the production of a film by extrusion, injection moulding or film blowing. In some embodiments, the film is for use in the production of a film by film blowing. The film blowing may be performed at a temperature at which the PHA polymer composition exhibits strain hardening.

[0227] The present disclosure further provides a coating or a coating composition comprising the PHA polymer composition described herein, or produced by, or obtained by, the method described herein. The coating may be an extrusion coating or a solvent cast coating. The coating composition may be for use in extrusion coating or solvent cast coating.

[0228] Advantageously, as described herein and shown in the Examples, films produced from the PHA polymer compositions of the present disclosure may exhibit favourable mechanical properties, including elongation at break, tensile strength and / or tensile toughness, which can improve their suitability for soft and flexible film applications. It will be appreciated that the ideal mechanical properties can depend on the intended application. In some embodiments, a film produced from the PHA polymer composition of the present disclosure exhibits an elongation at break of at least about 50%, for example from about 50% to about 1000%. In some embodiments, a film produced from the PHA polymer composition of the present disclosure exhibits a tensile strength of at least about 20 MPa, for example from about 20 MPa to about 50 MPa. In some embodiments, a film produced from the PHA polymer composition of the present disclosure exhibits a toughness of at least about 1.5 MJ / m3, for example from about 1.5 MJ / m3to about 100 MJ / m3.Film compositions

[0229] The present disclosure also provides a film composition comprising: a polyhydroxyalkanoate block copolymer described herein, or produced by, or obtained by, the method described herein; and a PHA polymer composition described herein, or produced by, or obtained by the method described herein.

[0230] The film composition may be for use in the production of a film by extrusion, injection moulding or film blowing. In some embodiments, the film is for use in the production of a film by film blowing. The film blowing may be performed at a temperature at which the PHA polymer composition exhibits strain hardening.

[0231] The present disclosure provides the use of the film composition for producing a film. The film may be produced by extrusion, injection moulding or film blowing. In some embodiments, the film is produced by film blowing. The film blowing may be performed at a temperature at which the PHA polymer composition exhibits strain hardening.

[0232] The present disclosure also provides a film comprising: a polyhydroxyalkanoate block copolymer described herein, or produced by, or obtained by, the method described herein; and a PHA polymer composition described herein, or produced by, or obtained by, the method described herein.

[0233] The film may be produced by extrusion, injection moulding or film blowing. In some embodiments, the film is produced by film blowing. The film blowing may be performed at a temperature at which the PHA polymer composition exhibits strain hardening.

[0234] The film may advantageously exhibit favourable mechanical properties, including elongation at break, tensile strength and / or tensile toughness, which can improve its suitability for soft and flexible film applications. It will be appreciated that the ideal mechanical properties can depend on the intended application. In some embodiments, the film exhibits an elongation at break of at least about 50%, for example from about 50% to about 1000%. In some embodiments, the film exhibits a tensile strength of at least about 20 MPa, for example fromabout 20 MPa to about 50 MPa. In some embodiments, the film exhibits a toughness of at least about 1 .5 MJ / m3, for example from about 1 .5 MJ / m3to about 100 MJ / m3.

[0235] It will be appreciated by persons skilled in the art that numerous variations and / or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.EXAMPLESMaterial characterisationNuclear magnetic resonance spectroscopy (NMR)

[0236] Quantitative1H high resolution one-dimensional NMR spectra were acquired at 298 K in deuterated chloroform (CDCh) (10 mg / mL) on Bruker Advance 700 spectrometers. The number of scans was set to 512. The relative peak intensities of1H-NMR spectra were determined using TopSpin 3.6.0 (Bruker) software. Chemical shifts were referenced to the residual proton peak of CDCh at 7.26 ppm.Gel permeation chromatography (GPC)

[0237] The number-average molar mass (Mn), weight-average molar mass (Mw), and dispersity (£)) of the PHA copolymers were determined by GPC, using an Agilent 1260 Infinity II Multidetector GPC System. Samples were dissolved in HPLC grade chloroform (~ 3 mg / mL) followed by filtration using polytetrafluoroethylene syringe filters (0.22 pm, Kinesis, ESF-PT-13-022). A column set consisting of a guard column (Agilent PLgel (10 pm, 7.5 mm x 50 mm)) followed by 3 x Agilent PLgel MIXED-B (10 pm, 7.5 mm x 300 mm) columns in series were used. The columns were kept at 30°C. A refractometer, at 30°C, was used to detect the signals. A chloroform flow rate of 1 mL / min was used for the analysis. The apparatus was calibrated with narrowly distributed molecular weight polystyrene standards and PS-H EasiVial calibration standards (PL2010-0201). The Mark-Houwink-Sakurada (MHS) relation and specific MHS parameters (K and a) were used to correct the molar mass. The following Mark- Houwink constants for PHB in chloroform, K = 7.7 x 103mL / g and a = 0.82, were used.Differential scanning calorimetry (DSC)

[0238] DSC analysis was performed on a TA instrument Q2000 under nitrogen flow (50 mL / min) with sample masses of 2-4 mg in sealed aluminium pans. A multi-step heating / cooling profile was employed with the following steps: 1) Equilibrate at 25°C followed by heating to 185°C with a 10°C / min ramp, keeping isothermal at 185°C for 0.2 min; 2) Cooling from 185°C to -70°C with a 10°C / min ramp, keeping isothermal at -70°C for 5 min; 3) Heating from -70°C to 185°C with a 10°C ramp; 4) Cooling from 185°C to -70°C with a 40°C / min ramp; 5) Heating to 80°C with a 20°C / min ramp. The first heating cycle was used to determine melting temperatures Tmand melting enthalpy AHm, while the first cooling cycle was used to determine the crystallisation temperatures Tc. Glass transition temperatures Tgwere determined from the final heating cycle. Data analysis was performed using TA Universal Analysis softwareMechanical property assessment

[0239] Tensile testing of block-copolymers as well as starting materials and blends were performed according to the ISO 527 standard using a universal testing machine Instron 5543 quipped with a 50 N load cell and pneumatic grips. Samples were razor cut using a stainless-steel template into rectangular shape with average film thickness of 0.1-0.15 mm measured via Tecloc gauge, according to ASTM D882. Sample dimensions were 5 mm width and 40 mm sample length, with a 20 mm grip distance.

[0240] Tensile testing of each polymer sample was repeated on 5 specimens, at a grip separation speed of 2 mm / min until fracture. The tensile modulus was determined from the slope of initial low strain in the elastic regime of curves, and the tensile toughness was calculated as an integrated area under the curve.Preparation of films for mechanical testing

[0241] Thin films for mechanical testing were prepared via solvent casting into flat glass petri dishes. For the preparation of solvent cast films, 1 g of polymer sample was dissolved in 12 mL of HPLC grade chloroform at 80°C (~5 wt%) until well dissolved. For blends of the starting block materials, 1 g of overall sample was dissolved, comprised of a 1 :1 molar ratio of both copolymers. After dissolution, the sample was allowed to cool down to room temperature and filtered through a fine pore metal mesh into a glass petri dish. The dish was covered with a glass cover and aluminium foil and the solvent slowly evaporated in a fume hood over the course of several days. The resulting film was dried under vacuum at room temperature overnight and left in the open environment for two weeks before testing.Example 1 : PHBV (1 mol%3HV)-b-P3HB4HB (30 mol% 4HB) block copolymer coupled using diisocyanate precursor linking moiety HDIMaterials

[0242] PHBV random copolymer with 1% 3HV content was purchased from TianAn Biopolymer (Ningbo, China) at a molecular weight of Mn = 116 kDa, Mw = 442 kDa and a dispersity of D = 3.8. P3HB4HB with high 4HB content was purchased from CJ Biomaterials (South Korea) with a molecular weight of Mn = 166 kDa, Mw = 325 kDa and a dispersity of D = 1.95. The 4HB content was determined via1H NMR analysis to be approximately 30 mol%. P3HB4HB with 15 mol% 4HB content was purchased from PHABuilder (China) with a molecular weight of Mn = 100 kDa, Mw = 255 kDa and a dispersity of D = 2.6.

[0243] HPLC grade chloroform, tin(ll)-ethylhexanoate (stannous octoate, 92.5-100%), hexamethylene diisocyanate (HDI, puriss., >99.0% (GC)), diethyl ether (AR grade), and diethyl glycol dimethyl ether (diglyme, anhydrous) were purchased from Merck Life Science Pty Ltd and used as received. 1,2-dichloroethane (anhydrous 99.8%) was purchased from Merck Life Science Pty Ltd and dried over 3A mol sieves for at least 24h before use. Ethylene glycol (anhydrous, 99.8%) and dibutyltin dilaurate (95 %) were purchased from Sigma- Aldrich Pty Ltd and used as received. Methanol (AR grade) was produced by ChemSupply and supplied by the UQ Science Store and used as received. Deuterated chloroform (99.8%) was purchased from NovaChem and used as received.Synthesis of PHBV(1%HV)-b-P3HB4HB(30%4HB) block-copolymers

[0244] PHA-b-PHA block-copolymers were synthesised using hydroxy-terminated PHBV (1 mol% 3HV) and hydroxy-terminated P3HB4HB (30 mol% 4HB) of varying molecular weights. Hydroxy-terminated PHAs were produced following a previously described transesterification protocol (Mai et al, Polymer Degradation and Stability, 2002, 205, 110123). In general, commercially available PHAs with a molecular weight of Mn= 116 kDa (PHBV) and Mn= 166 kDa (P3HB4HB) respectively were dissolved in diglyme at 140°C under argon atmosphere. Subsequently, dibutyltin dilaurate and an excess of ethylene glycol was added and the reaction mixture was stirred at 140°C until the desired molecular weight was obtained. In the case of both PHAs, Mnof ~ 90kDa was reached after approximately 5-6 minutes of reaction time, while Mnof 40-50kDa was achieved after 20 minutes reaction time. Finally, the reaction was quenched by pouring into a large volume of ice-cold water and the precipitate was filtered off, washed with methanol, and dried at 80°C in vacuum.

[0245] To prepare for the block-copolymer reaction, the glassware was dried in a vacuum oven at 100°C overnight and then connected to a Schlenk line setup and allowed to cool down under a dynamic vacuum. The solvent used was anhydrous 1,2-dichloroethane which was additionally dried over 3A mol sieves (10% w / v) for at least 24 h before use.

[0246] Hydroxy-terminated PHAs were dried at 80°C under vacuum overnight before use, then transferred into the pre-dried 3-neck reaction vessel fitted with a reflux condenser and rubber septum, connected to the Schlenk line and the PHA containing vessel was then evacuated and flushed with argon gas three times. After the last evacuation / flushing cycle of the solid PHA starting materials, the reaction setup was kept under a constant argon flow and dried 1,2-dichloroethane was added via syringe through the septum to a PHA concentration of up to 200 mg / mL. The reaction mixture was then heated to 100°C and stirred under reflux until full dissolution of the PHAs. Subsequently, the solution was allowed to cool down to 65°C and stannous octoate (0.8 l / mL solvent) and hexamethylene diisocyanate (HDI, 2.2 mol eq NCO:OH) were added to the reaction mixture. The solution was stirred under argon flux at 65°C for 6 h. The reaction was quenched by precipitating into a cold mixture of diethyl ethenmethanol 20:1 v / v and the precipitate was filtered, rinsed with methanol, and dried at80°C in vacuum before analysis.

[0247] The final molecular weights of the block materials, their blend and the coupled block copolymer are provided in Table 1. The block-copolymer Mn and Mw values are approximately double those of the starting materials, indicating that predominantly di-blocks had formed. Although the presence of PHBV and P3HB4HB ‘homopolymers’ cannot be excluded - either from unreacted material or from coupling of PHBV with PHBV and P3HB4HB with P3HB4HB chains, respectively - the differences in mechanical properties compared to blends of the starting materials support the assumption that the majority of the polymers formed consists of A-B type PHBV- b-P3HB4HB block-copolymer. Since the dispersity of the block-copolymer products remained relatively low and unchanged, a wide mixture of multi-blocks is not expected. In addition, an excess of diisocyanate can lead to the formation of allophanate groups, resulting in side-products and crosslinking of the polymer chains. However, such products generally form insoluble gels and the allophanate groups can be detected with NMR spectroscopy. Gelatinous or insoluble components were generally not observed during the workup and filtration of the productand no allophanate groups where visible in the product NMR spectra, indicating no significant by-product formation or crosslinking had occurred.Table i .Thermal properties

[0248] The thermal properties of the prepared block copolymers were compared to the raw starting materials (Mn= 41 kDa for PHBV and Mn= 48kDa for P3HB4HB), a PHBV / P3HB4HB blend (Mn= 50 kDa, molar ratio PHBV and P3HB4HB of 1 :1), and a random copolymer P3HB4HB with 15% 4HB content and a molecular weight of Mn= 100kDa. The thermal properties are provided in Table 2.Table 2.^calculated based on 100% crystalline PHB with AHm of 146 J / g (Barham, P. J., et al., Journal of Materials Science 19, 2781-2794 (1984)).

[0249] P3HB4HB (30% 4HB content) showed a minor melting peak at considerably lower temperatures than PHBV (83°C vs. 173°C) with almost negligible melting enthalpy of 2.5 J / g (vs. 95.4 J / g for PHBV). Blending the materials did not lead to a significant decrease in Tm, with both blends (Blende and Blendsok) sitting at around 171 °C. The block-copolymer also showed only a minor decrease in melting temperature to Tm=169°C. However, the decrease in melting enthalpies from pure PHBV to blend to block copolymer (99.2 J / g (PHBV) - 47.3 J / g (PHBV / P3HB4HB blend90k) - 36.8 J / g (PHBV-b-P3HB4HB block)) indicates a decrease in crystallinity with the introduction of 4HB into the mixture and additional decrease during block-copolymer formation. This is particularly evident for blocks, where the covalent linkages tying the blocks together limits the possibility of complete chain migration into a macrophase separated domain, so that the effects on thermal properties are more pronouncedwhen P3HB4HB and PHBV were covalently linked in the block copolymer rather than simply combined in a physical blend.

[0250] Comparing the block-copolymer to the random copolymer P3HB4HB-15 (15 mol% 4HB) containing a comparable 3HB:4HB ratio, the melting enthalpy of the block copolymer sits between those of the blend and the P3HB4HB-15, indicating a lower crystallinity for the random copolymer, while the Tgof the random copolymer is considerably higher than both blend and block. Since the 4HB units are known act as crystal defects in the copolymer and can therefore disrupt the crystallinity of the PHB, it seems reasonable that the random copolymer exhibited considerably smaller crystalline areas, regularly disrupted by 4HB units, compared to the blockcopolymer where the 4HB-induced disruption would be more localised on one (P3HB4HB) block.Mechanical properties

[0251] The mechanical properties of the prepared block copolymers were compared to the as-purchased starting materials PHBV (1 mol% HV, Mn= 116 kDa) and P3HB4HB (30 mol% 4HB, Mn= 166 kDa), the as- purchased random copolymer P3HB4HB with comparable 4HB content (15 mol% 4HB, Mn = 100 kDa), as well as to PHBV / P3HB4HB blends with comparable molecular weights (Mn= 50 kDa and Mn= 90 kDa, molar ratio 1 :1). The mechanical properties are provided in Table 3.Table 3.

[0252] Comparing the mechanical properties of the 50 / 50 blends of polymers with different molecular weights - blend50k using the same materials as employed for the block copolymer formation (PHBV-OHsok and P3HB4HB- 30-OH50k), and blendOOk using materials of molecular weights similar to the resulting block copolymer (PHBV- OHgok and P3HB4HB-30-OHgok) - it can be seen that the molecular weights of the PHAs influenced the mechanical properties of the resulting blend, indicated by an increase in elongation at break and toughness of the material when going from 50 kDa to 90 kDa molecular weight of the blend. Although the molecular weight nearly doubled from 50 to 90 kDa, both blends remain in a relatively low molecular weight range, and the resulting changes in mechanical properties were not particularly significant. In contrast, when compared to the block-copolymer which has a similar molecular weight (Mn= 80 kDa), the changes in mechanical properties between blend and block become apparent. Notably, the elongation at break remained below 85% for both blends, while it exceeded 600% elongation for the block copolymer. A similarly dramatic increase was observed in the overall toughness of the block copolymer, exceeding 50 MJ / m3for the block-copolymer, compared to values below 5 MJ / m3for the 30mol%4HB P3HB4HB and PHBV starting materials as well as both blends. The block copolymer showed a slightly elevated modulus compared to the blends.

[0253] Comparison of the PHBV-b-P3HB4HB block-copolymer to a random P3HB4HB copolymer containing a comparable overall 4HB content of approximately 15 mol% shows some clear differences, especially in elongation at break and material toughness. While the measured tensile strengths were approximately the same, the elongation at break for the block copolymer was roughly double that of the random copolymer, leading to a corresponding increase in toughness from ~20 to 50 MJ / m3. The block copolymer also had an increased modulus compared to P3HB4HB-15, which has the same 4HB content, and was the highest modulus among the samples, reaching 408.8 MPa.Example 2: PHBV (1 mol%3HV)-b-P3HB4HB (30 mol% 4HB) block copolymer coupled using diisocyanate precursor linking moiety HDI

[0254] Experiments in this study were performed using PHBV (1%HV) and P3HB4HB (30% 4HB) as building blocks. Building blocks of different molecular weights were synthesised by basic hydrolysis to obtain COOH- terminated PHA and glycolysis / transesterification with ethylene glycol to obtain OH-terminated PHA. Building blocks with Mn = 18-20kDa and 40-50kDa were investigated. The diisocyanate precursor linking moiety used was hexamethylene diisocyanate (HDI) at a molar ratio of 2.2 eq.

[0255] The general procedure was as follows: PHBV and P3HB4HB as well as the used glassware were dried in the vacuum oven at least over night to remove traces of water. Dichloroethane (DCE) was used as a solvent and dried before use. The experiments were performed on a Schlenk line under argon gas. PHBV and P3HB4HB were added to DCE and stirred at 100°C until fully dissolved. The reaction mixture was cooled to 65°C. Stannous octoate as catalyst (0.8 uL / mL DCE) and HDI (2.2 eq) were added and the reaction mixture was stirred for 6 h. Subsequently, the product was recovered through precipitation in a cold diethyl ethenmethanol (20:1) mixture and following filtration.

[0256] Success of the coupling reaction was determined by gel permeation chromatography (GPC) to determine increase in molecular weight. The molecular weights of building blocks, non-coupled mix of starting materials, and coupled block copolymers are provided in Table 4.Table 4.

[0257] Samples were submited to mechanical testing for tensile strength and elongation at break compared to a non-chemically bound mixture of the starting materials where possible. Maximum tensile strength and elongation at break for non-coupled and coupled block copolymers are provided in Table 5.

[0258] All coupled PHA-PHA block copolymer samples showed an increase in molecular weight (Mnas well as Mw) compared to their non-coupled mix of staring materials, indicating the coupling had been successful and block-copolymers were been produced (Figure 1). Regarding mechanical testing, small molecular weight mixtures (20kDa, uncoupled “blends” of the starting material) were not successfully solvent cast or did not produce films stable enough for mechanical testing therefore no direct comparison to the coupled materials could be made. All coupled samples were able to be solvent cast and tested for their mechanical properties, indicating an improvement of casting ability and mechanical properties compared to their non-coupled blends. Especially for products of the 40+50kDa coupling, significant increases in elongation at break compared to pure PHBV (-3-5%) and of tensile strength compared to pure P3HB4HB (~ 0.5 MPa) were observed. The coupling of 50+75kDa starting blocks also showed a significant increase in elongation and toughness compared to their uncoupled blend. Example 3: PHBV (1 mol%3HV)-b-P3HB4HB (30 mol% 4HB) block copolymer coupled using carbodiimide coupling agent

[0259] Experiments in this study were performed using PHBV (1%HV) and P3HB4HB (30% 4HB) as building blocks. Building blocks of different molecular weights were synthesised by basic hydrolysis to obtain COOH- terminated PHA and glycolysis / transesterification with ethylene glycol to obtain OH-terminated PHA. Both PHA- end group combinations were successfully coupled: PHBV-COOH with P3HB4HB-OH as well as PHBV-OH with P3HB4HB-COOH.

[0260] Building blocks with Mn = 24-26kDa, 30-35kDa, and 81kDa were investigated. Carbodiimide coupling agents used were N-ethyl-N’-(3-dimethylamino-propyl)carbodiimide hydrochloride (EDC.HCI) and dicyclohexylcarbodiimide (DCC) with 4-dimethylaminopyridine (DMAP) as catalyst either alone or in combination with N-hydroxysuccinimide (NHS).

[0261] The general synthesis procedure was as follows: PHBV and P3HB4HB were combined in a 1 :1 molar ratio and dissolved in chloroform at 70°C, then cooled down in an ice bath. 0.2 eq of DMAP was added, followed by dropwise addition of 2-10 eq of an EDC solution in chloroform (5 mg / mL). The reaction mixture was removedfrom the ice bath and allowed to warm to room temperature and was stirred between 10-48 h. Subsequently, the product was recovered through precipitation in cold methanol and filtration.

[0262] Success of the coupling reaction has been determined by gel permeation chromatography (GPC) to determine increase in molecular weight. The molecular weights of building blocks, non-coupled mix of starting materials, and coupled block copolymers are provided in Table 6.Table 6.Example 4: Free radical crosslinked and optionally grafted PHBV using peroxide initiatorMaterials and methods

[0263] Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) in powder form (ENMAT Y1000), which was purchased from TianAn Biopolymer, China (M _n= 140 kg / mol, M _W= 461 kg / mol and D = 3.3, 1 mol% 3HV, by 1 H-NMR, Tm = 172°C, Tc = 103°C). Dicumyl peroxide (DCP) (98% grade) and undecenoic acid (UDA) (98% grade) were obtained from Sigma-Aldrich and used as-is. Commercial melt strength enhancer (Paraloid™ BPMS- 265) was supplied by Rohm and Haas Chemical (Thailand) Ltd and used as is.Prism twin-screw extrusion

[0264] Reactive extrusion of the PHBV formulations were prepared on the Prism extruder using a two-step process, consisting of dry mixing followed by melt compounding. PHBV was first dried in fan-forced oven at 60°C for 3 days. The formulations, as described further below, were mechanically mixed in a container (size depending on volume of formulation). A co-rotating twin screw extruder with a diameter of 16 mm and a length- to-diameter ratio of 40:1 was used for melt compounding. A screw speed of the 100 rpm and a temperature profile as described further below was used for the extrusion of PHBV. The pre-mixed blends were fed into the extruder using a flood feeding technique to pack the barrel. The screw configuration, shown in Figure 1, was chosen to allow for sufficient mixing of the materials and appropriate residence time. A double strand die with diameter of 3 mm were used and the material was fed into a Scheer strand pelletiser at a feed rate and rotor speed of 14 after all extrusion was completed.Entek twin-screw extrusion

[0265] Reactive extrusion of the PHBV formulations were prepared on the Entek extruder using a two-step process, consisting of dry mixing followed by melt compounding. PHBV was first dried in fan-forced oven at 60°C for 3 days. The formulations, as described further below, were mechanically mixed in a container (size depending on volume of formulation). A co-rotating twin screw extruder with a diameter of 27 mm and a length-to-diameterratio of 40:1 was used for melt compounding. A volumetric vibratory feeder was used to feed the material into the extruder. The feed rate was set at 3 kg / hour. A screw speed of the 160 rpm and a temperature profile as described further below was used for extrusion of PHBV. The pre-mixed blends were fed into the extruder using a flood feeding technique to pack the barrel. The screw configuration, shown in Figure 2, was chosen to allow for sufficient mixing of the materials and residence time. A triple circular strand die with diameter of 5 mm were used for this extruder and the material was fed in-line into a Scheer strand pelletiser with a feed roll rate and rotor speed of 14.Collin hot compression moulding (also known as melt pressing, MP)

[0266] A Collin lab P300S compression moulder was used to prepare samples for rheology, mechanical and SAXS / WAXS characterisation. The material (~1 g) was added to the centre of the mould and the prepared plate set was placed to the compression moulder. The method proceeded as follows: 1) ramp from 40°C to 180°C at 35°C / min at 0 bar, 2) isothermal at 180°C for 20 seconds at 1 bar and degas, 3) isothermal at 180°C for 10 seconds at 5 bar and degas, 4) isothermal at 180° for 50 seconds at 40 bar, 5) ramp from 180°C to 40°C at 50°C at 40 bar, 6) isothermal at 40°C for 90 seconds at 40 bar. The film was retrieved from the mould and aged for a minimum of 2 weeks prior to testing.Film blowing extrusion

[0267] The film blowing extrusion was conducted on a laboratory scale film blowing tower equipped with an Axon single screw extruder with a screw diameter of 25 mm and a screw length of 625 mm. The extruder was set at 32 rpm, which results in an approximate throughput of 2 kg / hour of material.

[0268] The temperature profile of the film blowing extruder was altered until the formation of a stable bubble. The temperatures were recorded when a stable bubble was able to be formed for at least 5 minutes.Differential scanning calorimetry (DSC)

[0269] DSC analysis was performed using a TA instrument Q2500. Samples of 4-6 mg in sealed aluminium pans were analysed under nitrogen flow (50 mL / min) using a heat-isothermal-cool-heat-cool measuring cycle as follows: 1) Equilibrate at 25°C, then heat up from 25°C to T-maxwith a 10°C / ramp and keep isothermal for 0.1 minute to erase the thermal history; 2) Cool down to -70°C with a 10°C / min ramp and keep isothermal for 5 minutes; 3) Heat up from -70°C to T-maxwith a 10°C / min ramp; 4) Cool down to -70° with a 50°C / min ramp; 5) Heat up from -70°C to 40°C. The T-maxis polymer dependent and approximately 10°C higher than the literature melting temperature of the polymer; T-maxfor PHBV is 185°C. The melting temperature (Tm) and enthalpy of melting (A / 7m) were determined from the first heating cycle since the rheological testing requires an understanding of the polymer properties as processed, without erasing the thermal history, while the crystallisation temperature (Tc), was determined from the first cooling scan. The glass transition temperature, Tg, and second melting temperature (Tm„ 2nd) was determined from the 2ndheating cycle, where the latter provides information on the inherent thermal properties of the polymer. A fast quench was applied during the final cooling cycle in an attempt to observe the glass transition temperature (Tg) of the PHA materials during the final heating cycle. Data were analysed using TA Universal Analysis software.Gel permeation chromatography (GPC)

[0270] The number-average molecular mass (Mn), weight-average molecular mass (Mw), and dispersity (£)) were determined by GPC, using an Agilent 1260 Infinity II. Samples were dissolved in HPLC grade chloroform (2.5 mg / mL) followed by filtration using polytetrafluoroethylene syringe filters (0.22 m, Kinesis, ESF-PT-13-022). A column set consisting of a guard column (Agilent PL-gel (10 pm, 7.5 mm x 50 mm)) followed by 3 x Agilent PL gel MIXED-B (10 pm, 7.5 mm x 300 mm) columns in series was used. The columns were kept at 30°C. A refractometer, at 30°C, was used to detect the signals. A chloroform flow rate of 1 mL / min was used for the analysis. Narrowly distributed molecular weight polystyrene standards and PS-H EasiVial calibration standards (PL2010-0201) were used for calibration. The Mark-Houwink-Sakurada (MHS) relation and specific MHS parameters (K and a) were used to correct the molecular mass. The following Mark-Houwink constants were used for PHBV: K= 7.7 x 103mL / g and a = 0.82.Nuclear Magnetic Resonance (NMR)

[0271] Modified PHBV (~15 mg) was dissolved in CDCh (1 mL) and transferred to an NMR tube through a polytetrafluoroethylene syringe filter (0.22 pm, Kinesis, ESF-PT-13-022). The CDCh peak was referenced to 5H 7.26 ppm for1H NMR and to 5c 77.2 ppm for13C NMR. The chemical structure of the modified-PHAs was investigated using a combination of1H,13C, and HMBC experiments on a Bruker Avance 700 MHz spectrometer with cryoprobe.1H NMR spectral data were acquired at 298 K with 4 dummy scans followed by 32 scans over a spectral width of 11 ppm with a relaxation time of 3.13 seconds. HMBC spectral data was acquired at 298K with 16 dummy scans followed by 18 scans over a spectral width of 11 ppm and 200 ppm for1H and13C, respectively. A DOSY experiment was completed on the Bruker Avance 900 MHz spectrometer with a cryoprobe. DOSY spectra data was acquired at 298K with 4 dummy scans followed by 16 scans over a spectral width of 12 ppm. The chemical shifts and relative peak intensities were determined using MestReNova software. Extensional rheology

[0272] Extensional rheology measurements were performed on an Xpansion Instruments Sentmanat Extensional Rheometer (SER) Universal Testing Platform, model SER-3, specifically designed for the use on a TA Instruments Discovery Hybrid Rheometer host system. Samples were prepared by hot compression moulding, following by cutting fixed width strips (12.7 x 10 mm, length x width) using a blade cutter. The Environmental Test Chamber (ETC) was pre-heated to various temperatures depending on the melting temperature of the polymer type and extended beyond their melting temperature for measuring a temperature window of strain hardening. The specimens were loaded onto pre-heated drums and allowed to equilibrate at the test temperature for 60 seconds, while undergoing a pre-stretch at a strain rate of 0.01 s1to account for the difference in solid and melt density. The testing was conducted at various strain rates and repeated in triplicate. After testing, the sample was allowed to cool and removed from the drums. The drums were wiped clean with a soft and disposable laboratory wipe to remove any sample residue. The transient extensional rheology (77^), was calculated by using TA Trios Software.Predicting the Linear Viscoelastic (LVE) envelope

[0273] Some biodegradable polymers are sensitive to thermal degradation after prolonged periods of time at temperatures near their melting temperature. This creates difficulty when attempting to reach steady state forrheological measurements because their equilibrium viscosity is constantly changing. Due to this, oscillatory measurements in conjunction with the Generalised Maxwell Model (GMM) to determine the LVE envelope were avoided due to their extended experiment time. Therefore, in this thesis, a method was developed to predict the LVE envelope based on the GMM with four elements, according to Laun’s method (Bourg et al., 2021; Laun, 1978).

[0274] The start-up uniaxial extensional flow of a polymer melt will follow the LVE envelope if the polymer acts as a Newtonian fluid. It only deviates when experiencing strain hardening or thinning behaviour. Therefore, the early data points of the uniaxial start-up extensional test superimpose the LVE envelope and can be used to predict the LVE envelope in its entirety. Minimising the sum of square differences between the extensional viscosity data and the predicted LVE envelope by changing the four elements in the GMM (through an iterative Excel Solver process) allows the LVE envelope to be determined.

[0275] To do this, the GMM is fitted to 10 evenly distributed data points between 0.11 s to 3.33 s of the startup extensional flow test (e = 0.1 s1). Data points are excluded where there are clear outliers to the neighbouring data points and hence the predicted LVE envelope. Outliers are commonly observed early on in a uniaxial extensional flow test due to the sagging of the sample during melting and the initial stretch takes up the slack of the sample.

[0276] It is noted that the LVE envelope in this study is not a true value but is predictive based on the uniaxial start-up extensional viscosity of the polymer during the extensional viscosity test. Thus, the predicted LVE envelope is purely representative and used solely for the calculation of the degree of strain hardening.Quantifying the degree of strain hardening

[0277] To quantify the extent of strain hardening, the degree of strain hardening can be calculated. This is achieved by determining the ratio between the measured extensional viscosity and the predicted LVE envelope at a specified time, as shown in Equation 1 . This measure offers a quantitative assessment of the strain hardening behaviour exhibited by the polymer.Degree of strain hardening = hE ( > ) / hEp( (1)is the predicted transient extensional viscosity of the LVE envelope at a specific time (f) and r]f (t, e) is the measured transient extensional viscosity of the strain test at a specific time (f) and strain rate (e).Tensile test

[0278] Tensile tests were performed according to ASTM D882, determining tensile properties of thin films. All tests were completed on an Instron 5543 universal testing machine (Instron, Massachusetts, USA) fitted with a 500 N electronic load cell. Each sample was cut with a razor blade and with dimensions 10 x 60 mm and measured with a digital calliper prior to testing. The tensile test was performed at a rate of 2 mm / min until fracture of the sample, at least 4 replicates were measured.Sample preparation and extrusion

[0279] Two types of extruders were utilised for batch formulation in this study. The Prism twin-screw compound extruder (16 mm screw diameter) was used for smaller scale testing of PHBV formulations. To manufacture sufficient material for film blowing an Entek twin-screw compound extruder (27 mm screw diameter) was used. The formulations used for this study are described in Table 7 for the Prism extruder and Table 8 for the Entek extruder. The temperature profiles for the extrusion of the PHBV materials are detailed in Table 9. Paraloid™ BPMS-265 melt strength enhancer was added via smaller feeder after calibration. The Axon film blowing extruder and tower was used for demonstration of film blowing. The temperature profile for film blowing of PHBV materials is detailed in Table 9. The films were prepared by Collin hot compression moulding.Table 7. PHBV formulations for Prism extruder.Table 8. PHBV formulations for Entek extruder.Table 9. Temperature profile for extruders.Characterisation and methods

[0280] Extensional rheology, differential scanning calorimetry (DSC) and gel permeation chromatography(GPC) were measured as described above.Soxhlet extraction

[0281] Gel content was measured based on the ASTM D2765 standard using Soxhlet extraction. PHBV formulation (~0.3 g) was placed inside a weighed stainless-steel mesh cage of 150 mesh (100 micron). This stainless-steel mesh cage was then placed in refluxing chloroform for 6 hours before being dried under vacuumat 70°C overnight and reweighed to determine the gel content of the PHBV formulation.Calculation of film blowing strain rate

[0282] The strain rate of the film blowing extrusion process can be approximated based on the die dimensions (Figure 3), film dimensions at frost line and throughput of extruder. Due to no obvious frost line being present for the 5%-PHBV-BPMS formulation the strain rate is calculated on the 0.2%-P-PHBV-UDA, and it would be expected to be similar due to the throughput of the extruder remaining constant between materials.

[0283] Area of die exitADie(cm2) = n(R - R )ADie = 1.622 cm2AB= 0.130 cm2where RB is the radius of the bubble at the FLH.

[0285] Calculation of polymer flowThe density of semi crystalline materials in the melt can be approximated using 80% of solid density of the polymer: 0.8g pm= 1.02 r cm3where pmis the density of molten PHBV.

[0286] Die flowThe throughput of the extruder is approximately Output flow (Output flow = 0.434

[0287] Frost line height flow

[0288] Average strain ratewhere f is the velocity at the frost line height and Vois the velocity of the polymer at the die.

[0289] Velocity at the diecmVD= 0.335 — s

[0290] Velocity at the frost line heightVFLH= 3.34 — s

[0291] Therefore:Average strain rateAverage strain rate = 0.14 s-1

[0292] Understanding the average strain rate during the pilot film-blowing demonstration assists with scaling up to larger extrusion and film production processes, as well as refining the screening methodology for measuring the polymer's extensional rheology. The strain rate provides insights into the appropriate conditions for evaluating the polymer’s extensional behaviour, helping predict its performance during the film-blowing process. Furthermore, targeting specific blow-up and take-up ratios to achieve a known strain rate at which the polymer exhibits strain hardening, can further enhance the efficiency and quality of film production.Calculation of film blowing strain rate

[0293] The maximum blow-up ratio was calculated from the widest section of the film that was able to be blown prior to the bubble breaking.

[0294] Maximum blow-up ratioDBBURmax= —UD

[0295] The average film thickness was calculated at the same position of where the maximum BUR was measured. The film thickness at 8 points around the circumference of the tube was measured and averaged.Results and discussionPrism twin-screw extrusion

[0296] Reactive extrusion was conducted in a twin-screw prism extruder at 0.2% by weight of both peroxide and undecenoic acid. From this, minor grafting, amounting to 0.4 mol%, was detected in 0.2%-P-PHBV-UDA via1H NMR spectroscopy.

[0297] To discern the relative contributions of crosslinking versus branching, a formulation consisting of peroxide and PHBV alone was prepared. In industrial applications, a commercial melt strength enhancer is often employed to enhance the melt strength and extensional rheological properties of polymers. Therefore, an additional formulation was prepared, blending 5 wt% of a commercial melt strength enhancer with PHBV, to serve as a comparison against both neat and modified PHBV.Extensional rheology

[0298] The PHBV formulations were pelletised and then processed into sheets via melt pressing for extensional rheology testing. The objective was to assess whether the reactively extruded grafted PHBV exhibits enhanced extensional rheology and strain hardening, thereby facilitating the film blowing process. Figure 4 presents the extensional rheology results at 185°C and 190°C, with strain rates of 0.1 s1and 1 s1. PHBV exhibited strain thinning behaviour across all temperatures and strain rates. Both modified PHBVs, however, demonstrated strain hardening behaviour at 185°C and a strain rate of 0.1 s1. Notably, 0.2%-P-PHBV did not exhibit strain hardening under any other testing conditions. Interestingly, 0.2%-P-PHBV-UDA showed strain hardening across all conditions, suggesting that the addition of the branching agent (UDA) positively influenced the extensional flow behaviour of the material. The dramatic rise in extensional viscosity for the grafted sample at 185°C and a strain rate of 1 s1arises from tension adjustment of the sample at the beginning of the test. The strain rate of the extensional rheology test can be related to the maximum take-up ratio (TUR) and blow-up ratio (BUR) the material can endure during film blowing. A higher strain rate correlates to a higher TUR and BUR and permits the manufacturer of thinner films. The temperature window for extensional rheology testing can be related to the temperature profile suitable for film blowing the polymer.Scale-up extrusion

[0299] The strain hardening behaviour observed in the modified PHBV materials suggests their suitability for film blowing applications. Consequently, the reaction was scaled up using an Entek extruder to produce sufficient material for film blowing trials. The pilot-scale film blowing tower typically requires a minimum of 1 kg of material to adjust the parameters and achieve a stable bubble. For comparison, the 5%-PHBV-BPMS formulation was also processed for film blowing trials.

[0300] During extrusion, noticeable processing differences were observed among the various formulations. An in-line pelletiser was used in series with the extruder to maintain a continuous process. However, challenges arose with PHBV, which lacked the melt strength necessary to be fed into the pelletiser, resulting in premature breakage of the strands. The addition of 5% Paraloid™ BPMS-265 and the peroxide / branching agent significantly improved both the extrusion process and in-line pelletisation, allowing the system to run continuously for an hour without interruption.Thermal properties

[0301] The thermal properties of the extruded materials are summarised in Table 10. A small reduction in melting temperature (2ndheating scan) was observed for the chemically modified PHBVs compared to neat PHBV. A further decrease in melting temperature was noted for 0.2%-P-PHBV-UDA compared to 0.2%-P-PHBV, indicating that grafting has influenced the melting behaviour of the polymer. Additionally, a reduction in crystallinitywas observed for the reactively extruded PHBV. The crystallinity measured by DSC for the non-grafted and grafted reactive extruded PHBVs was 60% and 52%, respectively, compared to 65% for neat PHBV.Table 10. Thermal properties of PHBV formulations processed in the Entek extruder.

[0302] The melting temperature of the melt strength-enhanced PHBV formulation increased slightly to 173.5°C, compared to 171.8°C for neat PHBV. Paraloid™ BPMS-265, a non-reactive high molecular weight acrylic copolymer, caused a slight increase in the peak melting temperature when used in a 5% formulation. The 2ndheating scan thermograms, shown in Figure 5, illustrates the melting behaviour of the materials. Molecular weight analysis

[0303] The weight average molecular weight (Mw) and number average molecular weight (Mn) of the PHBV materials were measured and are shown in Table 11 . A reduction in Mwand Mnwas measured for the reactively extruded PHBVs compared to neat PHBV. The reduction in molecular weight is attributed to polymer chain scission caused by thermal degradation. The approximate 25% reduction in Mwis comparable to, if not less than, the reductions reported in similar reactive extrusion processes in literature (Lemes et al., 2016; Pilon & Kelly, 2016).Table 11. Molecular weight of PHBV materials.Film blowing of reactively extruded modified PHBV

[0304] Film blowing of the materials was conducted as described above. Attempts to film blow PHBV were unsuccessful, resulting in significant sagging and bubble collapse. The 0.2%-P-PHBV showed some improvement in apparent melt strength, but a stable bubble could not be consistently achieved. This correlates to the extensional rheology of the material, where strain hardening was only achievable over a narrow temperature window and at low strain rates. In contrast, 0.2%-P-PHBV-UDA exhibited a notable increase in melt strength,allowing for the formation of a stable bubble (Figure 6, a). This material successfully underwent continuous film blowing for 30 minutes. The 5%-PHBV-BPMS also produced a stable bubble, but it could not be expanded into a larger bubble. This limitation is hypothesised to be related to the crystallisation behaviour of the films. The 0.2%-P-PHBV-UDA bubble demonstrated clear transparency of the molten polymer, which was malleable and allowed for expansion, with the frost line of the bubble also visible. In contrast, the 5%-PHBV-BPMS, which was also able to be film blown (Figure 6, b), crystallised rapidly upon exiting the die, restricting bubble expansion and resulting in a lower blow-up ratio and thicker film (T able 12), where the blow-up ratio is defined as the ratio of the flat bubble diameter of the film to the diameter of the die. Polymers that can accommodate high blow-up ratios are more resilient in the film blowing process and can be processed across a broader range of parameters. The strain rate of the film blowing process was approximated to be 0.14 s1, which is comparable to other strain rates reported in the literature (Muke et al., 2003; Helmut Munstedt et al., 2005). This further supports the use of extensional rheology to determine the propensity of the materials to be film blown as the testing extension rates are comparable to the rates of film blowing.Table 12. Average film thickness and maximum blow-up ratio of PHBV materials subjected to film blowing.Sample Average film thickness (pm) Maximum blow-up ratio (BUR)PHBV NA NAExample 5: Free radical crosslinked P3HB4HB using peroxide initiator

[0305] Experiments in this study were performed using P3HB4HB (15 mol% 4HB, Mw ~210 kDa).Sample preparation

[0306] P3HB4HB (15 mol% 4HB) (2000 g) was pre-dried under vacuum at 80°C overnight. Dicumyl peroxide (6 g, 0.2 wt%) was added to acetone (~20 mL) and poured over the pre-dried P3HB4HB powder. The contents were mixed thoroughly and placed in a stainless-steel tray in a vacuum oven at 60°C to remove the acetone.

[0307] The Prism extruder temperature profiles was set (from hopper to die: 155°C, 165°C, 165°C, 165°C, 170°C, 170°C, 175°C, 170°C, 165°C, 160°C) and a screw speed of 40 rpm. The loaded P3HB4HB powder was added to the extruder, and the extruded strands were pelletized. The partially crosslinked P3HB4HB pellets were dried under vacuum at 80°C overnight.

[0308] The film blowing extruder temperature profile was set (from hopper to die: 160°C, 170°C, 170°C, 175°C, 180°C, 175°C, 175°C). The extruder screw speed was set 40 rpm. The pre-dried and DCP loaded P3HB4HB pellets was added to the extruder and extruded into thin films.Extensional rheology

[0309] Pre-dried and DCP loaded P3HB4HB pellets (~4 g) were added to a stainless-steel mould with a stainless-steel lidding plate added on top. The plates are placed into a hot melt press preheated to 175°C and compressed for 3 minutes at 100 bar and cooled down to 40°C over 3 minutes. The partially crosslinked P3HB4HBsheet is cut using a razor blade into 1 cm x 1.2 cm strips for extensional rheology testing. For comparison, unmodified P3HB4HB was also assessed.

[0310] The results are shown in Figure 7. The strain hardening curves show that unmodified P3HB4HB lacks strain hardening behaviour, which correlates with its inability to be film blown. In contrast, the partially crosslinked P3HB4HB material exhibits clear strain hardening across a wide temperature range, enabling stable bubble formation during film blowing.

[0311] A photo of the film bubble and the final transparent film product are shown in Figure 8 to visually confirm the process and highlight its suitability for packaging applications.Example 6: Free radical crosslinked PHBV and P3HB4HB blends and using peroxide initiator

[0312] Experiments in this study were performed using a blend of PHBV (1 mol% 3HV) and of P3HB4HB (30 mol% 4HB) at 50:50 wt.% of each. These were prepared as blends and cross-linked via melt mixing using a Rheomix melt mixer. Once taken out of the melt mixer, the samples were subjected to extensional rheology, and their mechanical properties were assessed.Sample preparation

[0313] PHA polymer blend: The desired amounts of PHBV (1 mol% 3HV) and P3HB4HB (30 mol% 4HB) were weighed out.

[0314] Initiator loading: The desired amount of peroxide was weighed out (typically 0.2 wt%). The peroxide was then added to acetone at low volume (typically ~10mL) for dissolution. The acetone solution was then poured over each of the PHAs while mechanically mixing. The PHA / peroxide mixture was then placed into a vacuum oven to remove the acetone and any residual water.

[0315] Melt mixing: The melt mixer was set up and heating started at 170°C. Once at the required temperature, the RPM was set to 30. The PHA / peroxide mixture was then added and the materials compressed into the melt mixing chamber using the ram. Melting and mixing was allowed for 30 seconds. The ram was then released. Mixing was continued for 3 minutes and 30 seconds. Mixing and heating was then turned off and the sample retrieved.

[0316] Film blowing extrusion: Film blowing extrusion was conducted following the procedure in Example 4.Extensional rheology

[0317] To measure the extensional rheology the material is taken from the Rheomix and directly melt pressed at ~175°C under 100 bar of pressure for 5 minutes. The results are shown in Figure 9.Mechanical properties

[0318] The mechanical properties of the blown film at two thicknesses are summarised in Table 13.Table 13.Example 7: P3HB4HB block copolymerisation with free radical crosslinkingSample preparation

[0319] P3HB4HB (15% 4HB) was dried in a stainless-steel tray under vacuum at 80°C overnight prior to sample preparation.

[0320] P3HB4HB (59 g) was added to a plastic bucket and DBTDL (0.3 g) was dissolved in acetone (10 mL) and pour in two batches over the P3HB4HB with vigorous mechanical mixing after each addition. The contents of the bucket were poured onto a stainless-steel tray and dried under vacuum at 60°C for at least one night (materialA). Dicumyl peroxide (1.2 g) was dissolved in acetone (~5 mL) and added to P3HB4HB (1 g) (material D) in a specimen jar and mixed thoroughly with a spatula.

[0321] Immediately before the experiment commenced, P3HB4HB (1 g) and anhydrous EG (0.15 g) (materialB), P3HB4HB (1 g) and hexamethylene diisocyanate (1.1 g) (material C) were placed in a specimen jar and mixed thoroughly with a spatula.Glycolysis, block copolymerisation and partial crosslinking

[0322] The Rheomix melt mixer was turned on and set to 170°C, 30 minutes prior to the start of the experiment. After reaching 170°C, the screw speed was set to 30 rpm and the P3HB4HB / DBTDL mixture (material A) was added to the hopper of the melt mixer. The material was pushed down with the ram. After 30 seconds of melting and mixing, the P3HB4HB / EG mixture (material B) was added and pushed down with the ram to ensure incorporation into the melt. After 10 minutes of glycolysis reaction, the P3HB4HB / HDI mixture (material C) was added and pushed down with the ram to ensure incorporation into the melt. After an additional 1 minute, the P3HB4HB / DCP mixture (material D) was added to the melt and pushed down with the ram to ensure incorporation into the melt. The reaction proceeded for an additional 2 minutes and then the mixing and heating was stopped. Some of the material (~5 g) was immediately transferred to a stainless-steel plate where it was melt pressed at 175°C for 3 minutes and then cooled to 40°C at 80°C / min.Extensional rheology testing

[0323] Samples were cut (~1 .2 cm x 1 cm) from the melt pressed sheet for extensional rheology testing. The oven was preheated to 172°C for 10 minutes. The sample was added onto the drums, and the test was started once the oven temperature reached 172°C again. The total test runs for approximately 2 minutes, which includes pre-stretch, stretch relaxation and stretching.

[0324] The extensional rheology of the sample was measured at 172°C and a stain rate of 0.1 s1. The results are shown in Figure 10. The sample demonstrated pronounced strain hardening behaviour, indicating a material which is suitable for film blowing. The temperature of 172°C was the only temperature tested for this material as this is slightly higher than the melting temperature of the PHA material.ITEMLISED LIST OF EMBODIMENTSS1 . A polyhydroxyalkanoate block copolymer comprising a first block, a second block and optionally one or more further blocks, wherein each of the blocks have a number average molecular weight (Mn) of at least about 20 kDa, and wherein the first block and the second block are not the same.2. The polyhydroxyalkanoate block copolymer according to item 1 , wherein the first block and the second block are composed of different polymerised monomers.3. The polyhydroxyalkanoate block copolymer according to item 1 , wherein the first block and the second block are composed of the same polymerised monomers but in different amounts.4. The polyhydroxyalkanoate block copolymer according to any one of the preceding items, wherein the first block and the second block independently comprise at least one polymerised monomer selected from 3- hydroxybutyrate, 3-hydroxyvalerate, 4-hydroxybutyrate, and 3-hydroxyhexanoate.5. The polyhydroxyalkanoate block copolymer according to any one of the preceding items, wherein the first block and the second block are independently selected from polymer blocks of poly(3-hydroxybutyrate), poly(3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4- hydroxybutyrate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), preferably selected from polymer blocks of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and poly(3- hydroxybutyrate-co-3-hydroxyhexanoate).6. The polyhydroxyalkanoate block copolymer according to any one of the preceding items, wherein one or both of the following apply: the first block or the second block is a polymer block of poly(3-hydroxybutyrate-co-3-hydroxyvalerate); the first block or the second block is a polymer block of poly(3-hydroxybutyrate-co-4-hydroxybutyrate). the first block or the second block is a polymer block of poly(3-hydroxybutyrate-co-3-hydroxyvalerate); the first block or the second block is a polymer block of poly(3-hydroxybutyrate-co-4-hydroxybutyrate).7. The polyhydroxyalkanoate block copolymer according to any one of the preceding items, wherein the polyhydroxyalkanoate block copolymer comprises a third block, preferably wherein the first block and third block are the same.8. The polyhydroxyalkanoate block copolymer according to any one of the preceding items, wherein the polymer blocks of the polyhydroxyalkanoate block copolymer are directly attached via a linking group, preferably wherein the linking group is selected from an ester, ether, urethane, amide, thioether, and thioester.9. The polyhydroxyalkanoate block copolymer according to any one of the preceding items, wherein the polymer blocks of the polyhydroxyalkanoate block copolymer are indirectly attached via a linking moiety, preferably wherein the linking moiety is the reaction product of a precursor linking moiety selected from: a diisocyanate compound, for example selected from hexamethylene diisocyanate (HDI), L-lysine diisocyanate ethyl ester (LDI) and trimethyl hexamethylene diisocyanate (TMDI); a bis- or multi-functional hydroxy compound, for example selected from dihydroxy compounds such as ethylene glycol, aromatic hydroxy compounds such as a hydroquinone or catechol, and multi-arm ethylene glycol oligomers such as short 3-arm or 4-arm hydroxy-polyethylene glycols;a bis- or multi-functional amino compound, for example selected from lower alkyl alpha, omegadiamines such as 1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane and 1,6- diaminohexane, branched diamines such as 1,2-diaminopropane, aromatic diamines such as p- phenylenediamine, multi-arm compounds such as tris(2-aminoethyl)amine and short 3-arm or 4-arm aminopolyethylene glycols, and lysine; a bis- or multi-functional thiol compound, for example selected from aliphatic or aromatic thiol compounds such as benzene-1 ,2-dithiol and propane-1, 3-dithiol, and substituted thiols such as dithiothreitol and multi-arm short thio-polyethylene glycols; and a bis- or multi-functional carboxylic acid compound, for example selected from multi-arm short carboxypolyethylene glycols, lower aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, and glutaric acid, and aromatic dicarboxylic acids such as terephthalic acid and benzenetricarboxylic acid.10. A method of producing a polyhydroxyalkanoate block copolymer comprising a first block, and a second block, and optionally one or more further blocks, the method comprising: reacting a first precursor block comprising at least one reactive end group and a second precursor block comprising at least one reactive end group to thereby provide a coupled first block and second block, wherein the each of the precursor blocks have a number average molecular weight (Mn) of at least about 20 kDa, and wherein the first precursor block and the second precursor block are not the same.11 . The method according to item 10, wherein: the first precursor block and the second precursor block are composed of different polymerised monomers, or the first precursor block and the second precursor block are composed of the same polymerised monomers but in different amounts.12. The method according to item 10 or item 11, wherein the produced polyhydroxyalkanoate block copolymer is the polyhydroxyalkanoate block copolymer as defined in any one of items 1 to 9.13. The method according to any one of items 10 to 12, wherein the first precursor block and the second precursor block are provided in a molar ratio of about 10:1, 5:1, 2:1, 1 :1, 1 :2, 1:5, or 1 :10.14. The method according to any one of items 10 to 13, wherein the at least one reactive end group of the first precursor block and the at least one reactive end group of the second precursor are independently selected from a hydroxy, halogen, thiol, carboxylic acid, amine, epoxide, isocyanate and acid chloride.15. The method according to any one of items 10 to 14, wherein the at least one reactive end group of the first precursor block and the at least one reactive end group of the second precursor react to form a linking group, such that the first block and the second block are directly attached via the linking group, preferably wherein the linking group is selected from an ester, ether, urethane, amide, thioether, and thioester.16. The method according to any one of items 10 to 14, wherein the at least one reactive end group of the first precursor block and the at least one reactive end group of the second precursor react with a precursor linking moiety comprising two or more reactive groups, such that the first block and the second block are indirectly attached via a linking moiety.17. The method according to items 16, wherein the two or more reactive groups of the precursor linking moiety are selected from any one or more of hydroxy, thiol, carboxylic acid, amine, isocyanate and acid chloride, preferably wherein the two or more reactive groups of the precursor linking moiety are the same.18. The method according to item 16 or item 17, wherein the precursor linking moiety comprising two or more reactive groups is selected from: a diisocyanate compound, for example selected from hexamethylene diisocyanate (HDI), L-lysine diisocyanate ethyl ester (LDI) and trimethyl hexamethylene diisocyanate (TMDI); a bis- or multi-functional hydroxy compound, for example selected from dihydroxy compounds such as ethylene glycol, aromatic hydroxy compounds such as a hydroquinone or catechol, and multi-arm ethylene glycol oligomers such as short 3-arm or 4-arm hydroxy-polyethylene glycols; a bis- or multi-functional amino compound, for example selected from lower alkyl alpha, omegadiamines such as 1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane and 1,6- diaminohexane, branched diamines such as 1,2-diaminopropane, aromatic diamines such as p- phenylenediamine, multi-arm compounds such as tris(2-aminoethyl)amine and short 3-arm or 4-arm aminopolyethylene glycols, and lysine; a bis- or multi-functional thiol compound, for example selected from aliphatic or aromatic thiol compounds such as benzene-1 ,2-dithiol and propane-1, 3-dithiol, and substituted thiols such as dithiothreitol and multi-arm short thio-polyethylene glycols; and a bis- or multi-functional carboxylic acid compound, for example selected from multi-arm short carboxypolyethylene glycols, lower aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, and glutaric acid, and aromatic dicarboxylic acids such as terephthalic acid and benzenetricarboxylic acid.19. The method according to any one of items 10 to 18, wherein the produced polyhydroxyalkanoate block copolymer comprises a third block and the method further comprises: reacting a third precursor block comprising at least one reactive end group and the second precursor block comprising at least one reactive end group to thereby provide a coupled second block and third block, preferably wherein the third precursor polymer block and first precursor polymer block are the same.20. The method according to any one of items 10 to 19, wherein the reaction takes place in a solvent or by melt processing.21. The method according to any one of items 10 to 20, wherein the first precursor block and the second precursor block are independently prepared by reacting a chain scission agent with a precursor polyhydroxyalkanoate to reduce its molecular weight.22. The polyhydroxyalkanoate block copolymer produced by, or obtained by, the process according to any one of items 10 to 21.23. Use of the polyhydroxyalkanoate block copolymer according to any one of items 1 to 9, or produced by, or obtained by, the method according to any one of items 10 to 21, in a film or a coating.24. A film comprising the polyhydroxyalkanoate block copolymer according to any one of items 1 to 9, or produced by, or obtained by, the method according to any one of items 10 to 21 .25. The use according to item 23 or the film according to item 24, wherein the film is produced by extrusion, injection moulding or film blowing.26. A PHA polymer composition comprising a crosslinked and optionally grafted PHA polymer, formed by reactive blending of a mixture comprising at least one PHA polymer, an initiator and optionally a mono-reactive grafting agent.27. The PHA polymer composition of item 26, wherein the at least one PHA polymer is a single PHA polymer, a blend of two or more PHA polymers, or a PHA block-copolymer.28. The PHA polymer composition of item 26 or item 27, wherein the at least one PHA polymer comprises at least one polymerised monomer selected from 3-hydroxybutyrate, 3-hydroxyvalerate, 4-hydroxybutyrate, and 3-hydroxyhexanoate.29. The PHA polymer composition of any one of items 26 to 28, wherein the at least one PHA polymer comprises or is selected from poly(3-hydroxybutyrate), poly(3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3- hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3- hydroxyhexanoate).30. The PHA polymer composition of any one of items 26 to 29, wherein the at least one PHA polymer comprises or is poly(3-hydroxybutyrate-co-3-hydroxyvalerate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate).31 . The PHA polymer composition of any one of items 26 to 30, wherein the at least one PHA polymer has an average molecular weight of about 80 kDa to about 10,000 kDa.32. The PHA polymer composition of any one of items 26 to 31 , wherein the at least one PHA polymer is provided in an amount of about 99.70 wt% to about 99.99 wt%, based on the total amount of the at least one PHA polymer and the initiator.33. The PHA polymer composition of any one of items 26 to 32, wherein the at least one PHA polymer is a PHA block copolymer, which is formed by reaction of one or more PHA polymers, a glycolytic agent, a glycolysis catalyst, and a multi isocyan ate compound.34. The PHA polymer composition of item 33, wherein one or more of the following apply: the glycolytic agent is ethylene glycol (EG) or glycerol; the glycolysis catalyst is selected from an organotin catalyst (e.g. dibutyltin dilaurate, stannous octanoate), a bismuth / zinc catalyst (e.g. bismuth neodecanoate, zinc acetate), a mercury catalyst (e.g. phenylmercuric acid), a ferric chelate catalyst (e.g. ferric acetylacetonate), a zirconium chelate catalyst (e.g. Zn(AcAc)4), a tertiary amine catalyst (e.g. triethylamine, DABCO (1 ,4-diazabicyclo[2.2.2]octane)), an amidine / amine catalyst (e.g. amino alcohols, 1,8-Diazabicyclo[5.4.0]undec-7-ene), an acid catalyst (e.g. Methanesulfonic Acid (MSA), Trifluoromethanesulfonic Acid (TFMSA), and Dimethyl Hydrogen Phosphate (DMHP)), and a base catalyst (e.g. potassium alkoxides, phenolates); the multiisocyanate compound is a diisocyanate compound (e.g. hexamethylene diisocyanate (HDI), L-lysine diisocyanate ethyl ester (LDI), trimethyl hexamethylene diisocyanate (TMDI)).35. The PHA polymer composition of item 33 or item 34, wherein the PHA block copolymer is formed prior to, or during, the reactive blending.36. The PHA polymer composition of any one of items 26 to 35, wherein the initiator is selected from dicumyl peroxide, t-amyl-2-ethylhexyl peroxycarbonate, 1 ,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5- dimethyl-2,5-di(t-butylperoxy) hexane, 2,5-dimethyl-2,5-di(t-amyl peroxy) hexane, 2,5-bis(t-butylperoxy)-2,5- dimethylhexane, 2,5-dimethyl-di(t-butylperoxy)hexyne-3, di-t-butyl peroxide, benzoyl peroxide, di-t-amyl peroxide, t-butyl cumyl peroxide, n-butyl-4,4-bis(t-butylperoxy)valerate, 1 , 1 -di(t-butylperoxy)-3,3,5-trimethyl- cyclohexane, 1 , 1 -di(t-butylperoxy)cyclohexane, 1 , 1 -di(t-amylperoxy)-cyclohexane, 2,2-d i (t-buty lperoxy)butane, ethyl-3,3-di(t-butylperoxy)butyrate, 2,2-di(t-amylperoxy)propane, ethyl-3,3-di(t-amylperoxy)butyrate, t- butylperoxy-acetate, t-amylperoxyacetate, t-butylperoxybenzoate, t-amylperoxybenzoate, di-t- buty Idiperoxyphthalate, and combinations thereof.37. The PHA polymer composition of any one of items 26 to 36, wherein the initiator is an organic peroxide.38. The PHA polymer composition of any one of items 26 to 37, wherein the initiator is dicumyl peroxide.39. The PHA polymer composition of any one of items 26 to 38, wherein the initiator is provided in an amount of about 0.01 wt% to about 0.30 wt%, based on the total amount of the at least one PHA polymer and the initiator.40. The PHA polymer composition of any one of items 26 to 39, wherein the initiator is provided in an amount of about 0.0032 mol% to about 0.096 mol%, based on the total amount of the at least one PHA polymer at the initiator.41 . The PHA polymer composition of any one of items 26 to 40, wherein the mono-reactive grafting agent comprises an unsaturated functional group as a reactive group.42. The PHA polymer composition of item 41, wherein the unsaturated functional group is an alkene, preferably a terminal alkene.43. The PHA polymer composition of item 41 or item 42, wherein the mono-reactive grafting agent comprises an Ce-Cis alkene, which may be optionally substituted.44. The PHA polymer composition of any one of items 26 to 43, wherein the mono-reactive grafting agent is selected from undecanoic acid, dodecene and octeadecene.45. The PHA polymer composition of any one of items 26 to 44, wherein the mono-reactive grafting agent is provided in an amount of about 0.1 wt% to about 5.0 wt%, based on the total amount of the at least one PHA polymer and the mono-reactive grafting agent.46. The PHA polymer composition of any one of items 26 to 45, wherein the mono-reactive grafting agent is provided in an amount of about 0.0470 mol% to about 2.3500 mol%, based on the total amount of the at least one PHA polymer and the mono-reactive grafting agent.47. The PHA polymer composition of any one of items 26 to 46, wherein the mixture consists of the at least one PHA polymer, the initiator and optionally the mono-reactive grafting agent.48. The PHA polymer composition of any one of items 26 to 47, wherein the mixture does not comprise one or more additives selected from: a chain extender, a plasticiser, a clarifier, a nucleating agent, a thermal stabiliser, an oxidative stabiliser, an inorganic filler, an anti-slip agent, a compatabiliser, and a blocking agent.49. The PHA polymer composition of any one of items 26 to 48, wherein the mixture does not comprise a solvent.50. The PHA polymer composition of any one of items 26 to 49, wherein the reactive blending is performed using a melt mixer.51 . The PHA polymer composition of any one of items 26 to 50, wherein the reactive blending is performed via melt mixing.52. The PHA polymer composition of any one of items 26 to 49, wherein the reactive blending is performed using a twin screw extruder.53. The PHA polymer composition of any one of items 26 to 49 and 52, wherein the reactive blending is performed via reactive extrusion.54. The PHA polymer composition of any one of items 26 to 53, wherein the reactive blending is performed for a duration of about 1 minutes to about 12 minutes.55. The PHA polymer composition of any one of items 26 to 54, wherein the reactive blending is performed at a temperature of about 160 °C to about 190 °C.56. The PHA polymer composition of any one of items 26 to 55, wherein the reactive blending is performed using a screw speed of about 20 rpm to about 160 rpm, preferably a screw speed of about 20 rpm to about 60 rpm.57. The PHA polymer composition of any one of items 26 to 56, wherein the crosslinked and optionally grafted PHA polymer exhibits a gel content of no more than about 5 wt%.58. The PHA polymer composition of any one of items 26 to 57, wherein the PHA polymer composition exhibits strain hardening in a measurement of extensional viscosity at a temperature within the range of from about 150 °C to about 210 °C and a strain rate of 0.1 s-1.59. A method of producing a PHA polymer composition comprising a crosslinked and optionally grafted PHA polymer, the method comprising: reactive blending of a mixture comprising at least one PHA polymer, an initiator and optionally a mono-reactive grafting agent to thereby provide the PHA polymer composition.60. The method of item 59, wherein the produced PHA polymer composition is the PHA polymer composition as defined in any one of items 26 to 58.61 . The method of item 59 or item 60, wherein the at least one PHA polymer is a single PHA polymer, a blend of two or more PHA polymers, or a PHA block-copolymer.62. The method of any one of items 59 to 61 , wherein the PHA polymer composition is a PHA block copolymer composition comprising a crosslinked and optionally grafted PHA block copolymer, and the method comprises:reacting one or more PHA polymers, a glycolytic agent, a glycolysis catalyst, and a multiisocyanate compound to thereby provide a PHA block copolymer; and reactive blending of a mixture comprising the PHA block polymer, an initiator and optionally a mono- reactive grafting agent to thereby provide the PHA block copolymer composition.63. The method of item 62, wherein one or more of the following apply: the glycolytic agent is ethylene glycol (EG) or glycerol; the glycolysis catalyst is selected from an organotin catalyst (e.g. dibutyltin dilaurate, stannous octanoate), a bismuth / zinc catalyst (e.g. bismuth neodecanoate, zinc acetate), a mercury catalyst (e.g. phenylmercuric acid), a ferric chelate catalyst (e.g. ferric acetylacetonate), a zirconium chelate catalyst (e.g. Zn(AcAc)4), a tertiary amine catalyst (e.g. triethylamine, DABCO (1,4-diazabicyclo[2.2.2]octane)), an amidine / amine catalyst (e.g. amino alcohols, 1,8-Diazabicyclo[5.4.0]undec-7-ene), an acid catalyst (e.g. Methanesulfonic Acid (MSA), Trifluoromethanesulfonic Acid (TFMSA), and Dimethyl Hydrogen Phosphate (DMHP)), and a base catalyst (e.g. potassium alkoxides, phenolates); the multiisocyanate compound is a diisocyanate compound (e.g. hexamethylene diisocyanate (HDI), L-lysine diisocyanate ethyl ester (LDI), trimethyl hexamethylene diisocyanate (TMDI)).64. The method of item 62 or item 63, wherein the reacting step and reactive blending step are performed simultaneously, or sequentially.65. The method of any one of items 59 to 64, wherein the at least one PHA polymer comprises at least one polymerised monomer selected from 3-hydroxybutyrate, 3-hydroxyvalerate, 4-hydroxybutyrate, and 3- hydroxyhexanoate.66. The method of any one of items 59 to 65, wherein the at least one PHA polymer comprises or is selected from poly(3-hydroxybutyrate), poly(3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).67. The method of any one of items 59 to 66, wherein the at least one PHA polymer comprises or is poly(3-hydroxybutyrate-co-3-hydroxyvalerate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate).68. The method of any one of items 59 to 67, wherein the at least one PHA polymer has an average molecular weight of about 80 kDa to about 10,000 kDa.69. The method of any one of items 59 to 68, wherein the at least one PHA polymer is provided in an amount of about 99.70 wt% to about 99.99 wt%, based on the total amount of the at least one PHA polymer and the initiator.70. The method of any one of items 59 to 69, wherein the initiator is selected from dicumyl peroxide, t- amyl-2-ethylhexyl peroxycarbonate, 1 , 1 -bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2, 5-d i methy I-2, 5-d i(t- butylperoxy) hexane, 2,5-dimethyl-2,5-di(t-amyl peroxy) hexane, 2,5-bis(t-butylperoxy)-2,5-dimethylhexane, 2,5- dimethyl-di(t-butylperoxy)hexyne-3, di-t-butyl peroxide, benzoyl peroxide, di-t-amyl peroxide, t-butyl cumyl peroxide, n-buty I-4, 4-bis(t-buty lperoxy)valerate, 1 , 1 -d i(t-buty lperoxy)-3, 3, 5-tri methy l-cyclohexane, 1 , 1 -di(t- butylperoxy)cyclohexane, 1 , 1 -di(t-amylperoxy)-cyclohexane, 2, 2-d i (t-buty lperoxy)butane, ethy I-3, 3-d i (t- butylperoxy)butyrate, 2,2-di(t-amylperoxy)propane, ethyl-3,3-di(t-amylperoxy)butyrate, t-butylperoxy-acetate, t-amylperoxyacetate, t-butylperoxybenzoate, t-amylperoxybenzoate, di-t-butyldiperoxyphthalate, and combinations thereof.71 . The method of any one of items 59 to 70, wherein the initiator is an organic peroxide.72. The method of any one of items 59 to 71 , wherein the initiator is dicumyl peroxide.73. The method of any one of items 59 to 72, wherein the initiator is provided in an amount of about 0.01 wt% to about 0.30 wt%, based on the total amount of the at least one PHA polymer and the initiator.74. The method of any one of items 59 to 73, wherein the initiator is provided in an amount of about 0.0032 mol% to about 0.096 mol%, based on the total amount of the at least one PHA polymer at the initiator.75. The method of any one of items 59 to 74, wherein the mono-reactive grafting agent comprises an unsaturated functional group as a reactive group.76. The method of item 75, wherein the unsaturated functional group is an alkene, preferably a terminal alkene.77. The method of item 75 or item 76, wherein the mono-reactive grafting agent comprises an Ce-Cis alkene, which may be optionally substituted.78. The method of any one of items 59 to 77, wherein the mono-reactive grafting agent is selected from undecanoic acid, dodecene and octeadecene.79. The method of any one of items 59 to 78, wherein the mono-reactive grafting agent is provided in an amount of about 0.1 wt% to about 5.0 wt%, based on the total amount of the at least one PHA polymer and the mono-reactive grafting agent.80. The method of any one of items 59 to 79, wherein the mono-reactive grafting agent is provided in an amount of about 0.0470 mol% to about 2.3500 mol%, based on the total amount of the at least one PHA polymer and the mono-reactive grafting agent.81 . The method of any one of items 59 to 80, wherein the mixture consists of the at least one PHA polymer, the initiator and optionally the mono-reactive grafting agent.82. The method of any one of items 59 to 81 , wherein the mixture does not comprise one or more additives selected from: a chain extender, a plasticiser, a clarifier, a nucleating agent, a thermal stabiliser, an oxidative stabiliser, an inorganic filler, an anti-slip agent, a compatabiliser, and a blocking agent.83. The method of any one of items 59 to 82, wherein the mixture does not comprise a solvent.84. The method of any one of items 59 to 83, wherein the reactive blending is performed using a melt mixer.85. The method of any one of items 59 to 84, wherein the reactive blending is performed via melt mixing.86. The method of any one of items 59 to 83, wherein the reactive blending is performed using a twin screw extruder.87. The method of any one of items 59 to 83 and 86, wherein the reactive blending is performed via reactive extrusion.88. The method of any one of items 59 to 87, wherein the reactive blending is performed for a duration of about 1 to about 12 minutes.89. The method of any one of items 59 to 88, wherein the reactive blending is performed at a temperature of about 160 to about 190 °C.90. The method of any one of items 59 to 89, wherein the reactive blending is performed using a screw speed of about 20 to about 160 rpm, preferably about 20 to about 60 rpm.91 . A PHA polymer composition comprising a crosslinked and optionally grafted PHA polymer produced by, or obtained by, the method defined in any one of items 59 to 90.92. The PHA polymer composition of item 91, or produced by, or obtained by, the method of any one of items 59 to 90, wherein the produced crosslinked and optionally grafted PHA polymer exhibits a gel content of no more than about 5 wt%.93. The PHA polymer composition of item 91 or item 92, or produced by, or obtained by, the method of any one of items 59 to 90, wherein the PHA polymer composition exhibits strain hardening in a measurement of extensional viscosity at a temperature within the range of from about 150 °C to about 210 °C and a strain rate of 0.1 s-1.94. A film composition comprising the PHA polymer composition according to any one of items 26 to 58, 92 and 93, or produced by, or obtained by, the method according to any one of items 59 to 90.95. Use of the PHA polymer composition according to any one of items 26 to 58, 92 and 93, or produced by, or obtained by, the method according to any one of items 59 to 90, in a film or coating composition.95. Use of the PHA polymer composition according to any one of items 26 to 58, 92 and 93, or produced by, or obtained by, the method according to any one of items 59 to 90, or the film composition according to item 94, for producing a film or coating.96. A film comprising the PHA polymer composition according to any one of items 26 to 58, 92 and 93, or produced by, or obtained by, the method according to any one of items 59 to 90.97. The use of item 95 or the film of item 96, wherein the film is produced by extrusion, injection moulding or film blowing.98. The use or the film of any one of items 95 to 97, wherein the film is produced by film blowing.99. The use or the film of any one of items 95 to 98, wherein the film blowing is performed at a temperature at which the PHA polymer composition exhibits strain hardening when measured at a strain rate of 0.1 s-1.100. A film composition comprising: a polyhydroxyalkanoate block copolymer according to any one of items 1 to 9 or 22, or produced by, or obtained by, the method according to any one of items 10 to 21; and a PHA polymer composition according to any one of items 26 to 58, 92 and 93, or produced by, or obtained by, the method according to any one of items 59 to 90.101 . Use of the film composition of item 100 for producing a film.102. A film comprising: a polyhydroxyalkanoate block copolymer according to any one of items 1 to 9 or 22, or produced by, or obtained by, the method according to any one of items 10 to 21; anda PHA polymer composition according to any one of items 26 to 58, 92 and 93, or produced by, or obtained by, the method according to any one of items 59 to 90.103. The use of item 101 or the film of item 102, wherein the film is produced by film blowing.104. The use or the film of any one of items 101 to 103, wherein the film blowing is performed at a temperature at which the PHA polymer composition exhibits strain hardening when measured at a strain rate of 0.1 s-1.

Claims

1. CLAIMS:1 . A polyhydroxyalkanoate (PHA) polymer composition comprising a crosslinked and optionally grafted PHA polymer, formed by reactive blending of a mixture comprising at least one PHA polymer, an initiator and optionally a mono-reactive grafting agent.

2. The PHA polymer composition of claim 1 , wherein the at least one PHA polymer is a single PHA polymer, a blend of two or more PHA polymers, or a PHA block-copolymer.

3. The PHA polymer composition of claim 1 or claim 2, wherein one or both of the following apply: the at least one PHA polymer comprises at least one polymerised monomer selected from 3- hydroxybutyrate, 3-hydroxyvalerate, 4-hydroxybutyrate, and 3-hydroxyhexanoate; the at least one PHA polymer comprises or is selected from poly(3-hydroxybutyrate), poly(3- hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

4. The PHA polymer composition of any one of the preceding claims, wherein the at least one PHA polymer is a PHA block copolymer, which is formed by reaction of one or more PHA polymers, a glycolytic agent, a glycolysis catalyst, and a multiisocyanate compound.

5. The PHA polymer composition of any one of the preceding claims, wherein the initiator is selected from dicumyl peroxide, t-amyl-2-ethylhexyl peroxycarbonate, 1 , 1 -bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy) hexane, 2,5-dimethyl-2,5-di(t-amyl peroxy) hexane, 2,5-bis(t-butylperoxy)-2,5- dimethylhexane, 2,5-dimethyl-di(t-butylperoxy)hexyne-3, di-t-butyl peroxide, benzoyl peroxide, di-t-amyl peroxide, t-butyl cumyl peroxide, n-butyl-4,4-bis(t-butylperoxy)valerate, 1 , 1 -di(t-butylperoxy)-3,3,5-trimethyl- cyclohexane, 1 , 1 -di(t-butylperoxy)cyclohexane, 1 , 1 -di(t-amylperoxy)-cyclohexane, 2,2-d i (t-buty lperoxy)butane, ethyl-3,3-di(t-butylperoxy)butyrate, 2,2-di(t-amylperoxy)propane, ethyl-3,3-di(t-amylperoxy)butyrate, t- butylperoxy-acetate, t-amylperoxyacetate, t-butylperoxybenzoate, t-amylperoxybenzoate, di-t- buty Idiperoxyphthalate, and combinations thereof.

6. The PHA polymer composition of any one of the preceding claims, wherein the initiator is provided in an amount of about 0.01 wt% to about 0.30 wt%, based on the total amount of the at least one PHA polymer and the initiator.

7. The PHA polymer composition of any one of the preceding claims, wherein the mixture consists of the at least one PHA polymer, the initiator and optionally the mono-reactive grafting agent.

8. The PHA polymer composition of any one of the preceding claims, wherein the mixture does not comprise one or more additives selected from: a chain extender, a plasticiser, a clarifier, a nucleating agent, a thermal stabiliser, an oxidative stabiliser, an inorganic filler, an anti-slip agent, a compatabiliser, and a blocking agent.

9. The PHA polymer composition of any one of the preceding claims, wherein the reactive blending is performed using a melt mixer or a twin screw extruder.

10. The PHA polymer composition of any one of the preceding claims, wherein the reactive blending is performed for a duration of about 1 minute to about 12 minutes.11 . The PHA polymer composition of any one of the preceding claims, wherein the reactive blending is performed at a temperature of about 160 °C to about 190 °C.

12. The PHA polymer composition of any one of the preceding claims, wherein the crosslinked and optionally grafted PHA polymer exhibits a gel content of no more than about 5 wt%.

13. The PHA polymer composition of any one of the preceding claims, wherein the PHA polymer composition exhibits strain hardening in a measurement of extensional viscosity at a temperature within the range of from about 150 °C to about 210 °C and a strain rate of 0.1 s-1.

14. A method of producing a PHA polymer composition comprising a crosslinked and optionally grafted PHA polymer, the method comprising: reactive blending of a mixture comprising at least one PHA polymer, an initiator and optionally a mono-reactive grafting agent to thereby provide the PHA polymer composition.

15. The method of claim 14, wherein the PHA polymer composition is a PHA block copolymer composition comprising a crosslinked and optionally grated PHA block copolymer, and the method comprises: reacting one or more PHA polymers, a glycolytic agent, a glycolysis catalyst, and a multiisocyanate compound to thereby provide a PHA block copolymer; and reactive blending of a mixture comprising the PHA block polymer, an initiator and optionally a mono- reactive grafting agent to thereby provide the PHA block copolymer composition.

16. The method according to claim 15, wherein the reacting step and reactive blending step are performed simultaneously.

17. Use of the PHA polymer composition according to any one of claims 1 to 13, or produced by, or obtained by, the method of any one of claims 14 to 16, in a film.

18. A film comprising the PHA polymer composition according to any one of claims 1 to 13, or produced by, or obtained by, the method of any one of claims 14 to 16.

19. The use of claim 17 or the film of claim 18, wherein the film is produced by extrusion, injection moulding or film blowing.

20. A polyhydroxyalkanoate block copolymer comprising a first block, a second block and optionally one or more further blocks, wherein each of the blocks have a number average molecular weight (Mn) of at least about 20 kDa, and wherein the first block and the second block are not the same.

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