Copolymers comprising thioester bonds

Abstract

The invention relates to a process for synthesizing a copolymer comprising the step of polymerizing a monomer mixture, comprising: a cyclic comonomer selected from the list comprising lactones, lactams, cyclic amines, cyclic esters or mixtures thereof; and, a compound according to Structure I: wherein R1 is an hydrogen or an alkyl having 1 to 6 carbon atoms; and, wherein R2 and R3 is each independently hydrogen or an alkyl, cycloalkyl, aralkyl, aryl, alkynyl, cycloalkenyl; or, wherein R2 and R3 together with the atom to which they are attached form a saturated or unsaturated 3-, 4-, 5-, 6-, or 7-membered ring, which may be substituted. The invention relates further to the copolymer obtained in the process and to the use of compound according to structure (I) to accelerate biodegradability.

Description

[0001] COPOLYMERS COMPRISING THIOESTER BONDS

[0002] FIELD OF THE INVENTION

[0003] The invention relates to the (bio-)degradable polymers and copolymers and methods for making them. More particularly, the invention relates to increasing the biodegradability of polymers, and preferably while remaining easy to produce. In particular embodiment, the invention may provide an indication of the state of biodegradability of polymers.

[0004] BACKGROUND OF THE INVENTION

[0005] Aliphatic polyesters (PEs) are an interesting group of chemically recyclable or non-persistent polymers. Some of them are bio-based and sometimes they even can be fully biodegradable due to the susceptibility of their ester linkages to chemical and / or enzymatic hydrolysis. One of the most prominent polyesters is poly(lactic acid) (PLA). Although PLA is thought of as biodegradable, its degradation is only sufficiently fast under industrial composting conditions. Commercial PLA is currently synthesized by ring-opening polymerization (ROP) of the dilactone, lactide (LD), which is made by backbiting depolymerization of polycondensed lactic acid (LA), a time- and energy intensive process.

[0006] While PLA and its degradation properties are widely studied, research on its sulphur containing counterpart, poly(thiolactic acid) (PTLA), is still in its infancy. Polythiolesters (PTEs) such as PTLA, are rather new in the polymer research field but are shown to be an interesting group of possibly sustainable materials with potential in the context of biodegradation and / or chemical recycling.

[0007] Similar to PLA, PTLA could be synthesized by either polycondensation of thiolactic acid (TLA) or via ROP of dithiolactide (DTL), the sulphur containing analogue of LD. However there have not yet been many synthesis routes for DTL found and the existing routes either require the pyrolysis of PTLA polymer or the use of an only recently disclosed synthesis route (Suzuki et al. 2021 and Wang et al. 2021) requiring complex and toxic reagents and waste products. As a result polymerization reactions with DTL or variants thereof have not been studied extensively.

[0008] It is accordingly one of the objects of the present invention to overcome or ameliorate one or more of the aforementioned disadvantages present in the market, or to meet any of the demands that are present in the market. Preferably the invention provides in solutions, that can be easily implemented in existing production plants and processes. SUMMARY OF THE INVENTION

[0009] The present inventors have now surprisingly found that thiodioxolanones can be used as a monomer in the copolymerization reaction with other cyclic monomers, preferably selected from the list comprising lactones, lactams, cyclic amines, cyclic esters or mixtures thereof. The obtained copolymers may biodegrade faster compared to the polymers made from only the other cyclic monomers.

[0010] The invention provides in a process for synthesizing a copolymer comprising the step of polymerizing via ring opening a monomer mixture, comprising: a cyclic comonomer selected from the list comprising lactones, lactams, cyclic amines, cyclic esters or mixtures thereof; and, a compound according to Structure I: wherein R1is a hydrogen or an alkyl having 1 to 6 carbon atoms, preferably R1is an alkyl having 1 to 6 carbon atoms; and, wherein R2and R3is each independently hydrogen or an alkyl, cycloalkyl, aralkyl, aryl, alkynyl, cycloalkenyl, having 1 to 8, preferably 1 to 6, carbon atoms and optionally a heteroatom; or, wherein R2and R3together with the atom to which they are attached form a saturated or unsaturated 3-, 4-, 5-, 6-, or 7-membered ring, which may be substituted, such that R2and R3together are having 3 to 12 carbon atoms and optionally a heteroatom.

[0011] In some embodiments, R1is a methyl or ethyl group, preferably wherein R1is a methyl group; and / or, wherein R2and R3together with the atom to which they are attached form a saturated or unsaturated 3-, 4-, 5-, 6-, or 7-membered ring, which may be substituted, such that R2and R3together are having 3 to 12 carbon atoms and optionally a heteroatom.

[0012] In some embodiments, the monomer mixture, comprises: at least 30.0 wt% to at most 99.5 wt% of a cyclic comonomer selected from the list comprising lactones, lactams, cyclic amines, cyclic esters or mixtures thereof, and, at least 0.50 wt% to at most 70.0 wt% of a compound according to Structure I.

[0013] In some embodiments, the monomer mixture, comprises: at least 30.0 wt% to at most 99.0 wt%, preferably at least 40.0 wt% to at most 98.0 wt%, preferably at least 45.0 wt% to at most 97.0 wt%, preferably at least 50.0 wt% to at most 95.0 wt%, preferably at least 60.0 wt% to at most 90.0 wt%, preferably at least 70.0 wt% to at most 85.0 wt%, of a cyclic comonomer selected from the list comprising lactones, lactams, cyclic amines, cyclic esters or mixtures thereof; and, at least 1.0 wt% to at most 70.0 wt%, preferably at least 2.0 wt% to at most 60.0 wt%, preferably at least 3.0 wt% to at most 55.0 wt%, preferably at least 5.0 wt% to at most 50.0 wt%, preferably at least 10.0 wt% to at most 40.0 wt%, preferably at least 15.0 wt% to at most 30.0 wt%, of a compound according to Structure I.

[0014] In some embodiments, the cyclic comonomer comprises a 5- to 7- membered heterocycle.

[0015] In some embodiments, the cyclic comonomer is a lactone or a lactam; preferably lactide, caprolactone or caprolactam.

[0016] In some embodiments, the monomer mixture is contacted with an initiator, and / or a catalyst.

[0017] In some embodiments, wherein the process comprises a step of subjecting the formed copolymer to a reduced pressure treatment.

[0018] The invention further provides in a copolymer formed by ring opening polymerization of a monomer mixture, comprising: a cyclic comonomer selected from the list comprising lactones, lactams, cyclic amines, cyclic esters or mixtures thereof; and, a compound according to Structure I:

[0019] (I), wherein R1is a hydrogen or an alkyl having 1 to 6 carbon atoms; and, wherein R2and R3is each independently hydrogen or an alkyl, cycloalkyl, aralkyl, aryl, alkynyl, cycloalkenyl, having 1 to 8, preferably 1 to 6 carbon atoms and optionally a heteroatom; or, wherein R2and R3together with the atom to which they are attached form a saturated or unsaturated 3-, 4-, 5-, 6-, or 7-membered ring, which may be substituted, such that R2and R3together are having 3 to 12 carbon atoms and optionally a heteroatom.

[0020] Preferably, the copolymer is obtained or obtainable by means of the synthesis process as described herein. In some embodiments, the copolymer is a linear, cyclic or a branched copolymer, preferably wherein the linear copolymer is chosen from an alternating copolymer, a random copolymer, a statistical copolymer, or a block or segmented copolymer, or preferably wherein the cyclic copolymer is chosen from an alternating cyclic copolymer, a random cyclic copolymer, a statistical cyclic copolymer, or a block or segmented cyclic copolymer, or preferably wherein the branched copolymer is chosen from a graft copolymer, a star copolymer or a branched copolymer with a different architecture.

[0021] In some embodiments, the copolymer has a melting peak at 60.0 °C or higher as measured by differential scanning calorimetry (DSC), in particular a melting peak ranging between 60.0 to 240.0 °C, in particular from 100.0 to 200.0 °C, and more in particular from 120.0 to 160.0 °C.

[0022] In some embodiments, the copolymer has a weight-average molecular weight (Mw) from 1000 to 500000 g / mol as measured by gel permeation chromatography (GPC).

[0023] In some embodiments, the copolymer has a number-average molecular weight (Mn) from 1000 to 500000 g / mol as measured by gel permeation chromatography (GPC).

[0024] In some embodiments, the copolymer has a weight-average molecular weight (Mw) from 1000 to 500000 g / mol and / or a number-average molecular weight (Mn) from 1000 to 500000 g / mol as measured by gel permeation chromatography (GPC).

[0025] In some embodiments, the copolymer has a crystallinity between 5% and 50%.

[0026] The invention provides further in the use of a compound according to Structure (I);

[0027] (I), wherein R1is a hydrogen or an alkyl having 1 to 6 carbon atoms, preferably R1is an alkyl having 1 to 6 carbon atoms; and, wherein R2and R3is each independently hydrogen or an alkyl, cycloalkyl, aralkyl, aryl, alkynyl, cycloalkenyl, having 1 to 8, preferably 1 to 6, carbon atoms and optionally a heteroatom; or, wherein R2and R3together with the atom to which they are attached form a saturated or unsaturated 3-, 4-, 5-, 6-, or 7-membered ring, which may be substituted, such that R2and R3together are having 3 to 12 carbon atoms and optionally a heteroatom; as a biodegrading accelerator or an olfactory indicator of biodegradation in a polycondensate, preferably in ester- or amide- containing polycondensates, preferably in a polylactic acid, a polycaprolactone or a polycaprolactam. The invention provides further in an article comprising the copolymer according to an embodiment described herein, or a copolymer produced by a process according to an embodiment described herein.

[0028] The invention provides further in a compound according to Structure (I), wherein R1is a hydrogen or an alkyl having 1 to 6 carbon atoms, preferably R1is an alkyl having 1 to 6 carbon atoms; and, wherein R2and R3is each independently hydrogen or an alkyl, cycloalkyl, aralkyl, aryl, alkynyl, cycloalkenyl, having 1 to 8, preferably 1 to 6, carbon atoms and optionally a heteroatom; or, wherein R2and R3together with the atom to which they are attached form a saturated or unsaturated 3-, 4-, 5-, 6-, or 7-membered ring, which may be substituted, such that R2and R3together are having 3 to 12 carbon atoms and optionally a heteroatom.

[0029] Preferred embodiments of the invention are disclosed in the detailed description and appended claims. In the following passages different aspects of the invention are defined in more detail. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous. (Preferred) embodiments of one aspect of the invention are also (preferred) embodiments of all other aspects of the invention.

[0030] DETAILED DESCRIPTION OF THE INVENTION

[0031] When describing the invention, the terms used are to be construed in accordance with the following definitions, unless a context dictates otherwise.

[0032] Unless otherwise defined, all terms used in disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, term definitions are included to better appreciate the teaching of the present invention.

[0033] In the following passages, different aspects of the invention are defined in more detail. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

[0034] Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments. Furthermore, while some embodiments described herein include some, but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims and statements, any one of the embodiments can be used in any combination.

[0035] The terms "comprising", "comprises" and "comprised of" as used herein are synonymous with "including", "includes" or "containing", "contains", and are inclusive or open-ended and do not exclude additional, non-recited members, elements, or method steps. It will be appreciated that the terms "comprising", "comprises" and "comprised of" as used herein comprise the terms "consisting of", "consists" and "consists of".

[0036] As used in the specification and the appended claims, the singular forms "a", "an," and "the" include plural referents unless the context clearly dictates otherwise. By way of example, "a step" means one step or more than one step.

[0037] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art.

[0038] The recitation of numerical ranges by endpoints includes all integer numbers and, where appropriate, fractions subsumed within that range (e.g., 1 to 5 can include 1, 2, 3, 4 when referring to, for example, a number of elements, and can also include 1.5, 2, 2.75 and 3.80, when referring to, for example, measurements). The recitation of endpoints also includes the end point values themselves (e.g., from 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all subranges subsumed therein.

[0039] The term "about" as used herein when referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of + / -10% or less, preferably + / -5% or less, more preferably + / -!% or less, of and from the specified value, insofar such variations are appropriate to perform in the disclosed invention. It is to be understood that the value to which the modifier "about" refers is itself also specifically, and preferably, disclosed.

[0040] The terms "wt%", "vol%", or "mol%" refers to a weight percentage of a component, a volume percentage of a component, or molar percentage of a component, respectively, based on the total weight, the total volume of material, or total moles, that includes the component.

[0041] When describing the present invention, the terms used are to be construed in accordance with the following definitions, unless a context dictates otherwise.

[0042] The invention provides in a process for synthesizing a copolymer, comprising the step of polymerizing, preferably via ring opening, a monomer mixture, comprising: a compound according to Structure I: wherein R1is a hydrogen or an alkyl having 1 to 6 carbon atoms, preferably R1is an alkyl having 1 to 6 carbon atoms; and, wherein R2and R3is each independently hydrogen or an alkyl, cycloalkyl, aralkyl, aryl, alkynyl, cycloalkenyl, having 1 to 8, preferably 1 to 6, carbon atoms and optionally a heteroatom; or, wherein R2and R3together with the atom to which they are attached form a saturated or unsaturated 3-, 4-, 5, 6, or 7 membered ring, which may be substituted, such that R2and R3together are having 3 to 12 carbon atoms and optionally a heteroatom; and, a cyclic comonomer selected from the list comprising lactones, lactams, cyclic amines, cyclic esters or mixtures thereof.

[0043] As used herein, the term "thiodioxolanones" refers to a compound according to Structure (I), regardless of the definition R1, R2and R3. In other words, it may refer to the five membered lactone with a sulphur atom in the beta position, wherein the alpha and / or the gamma carbon atom may be independently substituted.

[0044] In some embodiments, R1is a hydrogen, methyl or ethyl group, preferably wherein R1is a hydrogen or methyl group, preferably wherein R1is a methyl group.

[0045] In some embodiments, R2and R3is each independently an alkyl, cycloalkyl, aralkyl, aryl, alkynyl, cycloalkenyl, having 1 to 8, preferably 1 to 6, carbon atoms and optionally a heteroatom; or, wherein R2and R3together with the atom to which they are attached form a saturated or unsaturated 3-, 4-, 5-, 6-, or 7-membered ring, which may be substituted, such that R2and R3together are having 3 to 12 carbon atoms and optionally a heteroatom. Such structures may provide thioketal like properties.

[0046] In some embodiments, R2and R3are each independently an alkyl, having 1 to 8, preferably 1 to 6, carbon atoms and optionally a heteroatom; or, wherein R2and R3together with the atom to which they are attached form a saturated or unsaturated 3-, 4-, 5-, 6-, or 7-membered ring, which may be substituted, such that R2and R3together are having 3 to 12 carbon atoms and optionally a heteroatom. In some embodiments, R2and R3is each independently an alkyl, having 1 to 8, preferably 1 to 6, carbon atoms. In some embodiments, R2and R3are identical.

[0047] In some embodiments, R2and R3together with the atom to which they are attached form a saturated or unsaturated 3-, 4-, 5-, 6-, or 7-membered ring, which may be substituted, such that R2and R3together are having 3 to 12 carbon atoms and optionally a heteroatom. In some embodiments, R2and R3together with the atom to which they are attached form a saturated 3-, 4-, 5-, 6-, or 7-membered ring, which may be substituted, such that R2and R3together are having 3 to 12 carbon atoms and optionally a heteroatom. In some embodiments, R2and R3together with the atom to which they are attached form a saturated 5-, 6-, or 7-membered ring, which may be substituted, such that R2and R3together are having 3 to 12 carbon atoms and optionally a heteroatom. In some embodiments, R2and R3together with the atom to which they are attached form a saturated 5-, 6-, or 7-membered ring, such that R2and R3together are having 4 to 6 carbon atoms. The selection of R1, R2and R3may have an influence on the crystallinity of the obtained copolymer, the speed of the polymerisation reaction, the hydrophobicity of the obtained copolymer, the speed of biodegradation of the obtained copolymer, or the architecture of the obtained copolymer.

[0048] Is some embodiments, the compound according to Structure (I) may be the condensation product of a thiol-acid compound according to structure (II) and an aldehyde or a ketone according to Structure (III), wherein R1, R2and R3are as defined herein.

[0049] (ID (HI) (I) Preferably, the condensation reaction to form the compound according to Structure (I) is acid catalysed, preferably by an organic acid, preferably by a sulphonic acid, such as p-toluenesulphonic acid.

[0050] Preferably, the condensation reaction to form the compound according to Structure (I) is carried out in a Dean-Stark trap, preferably in a water immiscible solvent, such as toluene.

[0051] In some embodiments, the compound according to structure (II) is thiolactic acid or 2-mercaptobutyric acid, preferably thiolactic acid. These compounds may have the advantage that in the final copolymer, the side chains may not disturb the crystallinity too much, to achieve certain properties, such as glass transition temperature (Tg), transparency, melting point and the like.

[0052] In some embodiments, the aldehyde according to Structure (III) is selected from the list comprising acetaldehyde, propionaldehyde, butyraldehyde, valeraldehyde, isovaleraldehyde, hexaldehyde, octaldehyde, benzaldehyde, and furfural.

[0053] In some embodiments, the ketone according to Structure (III) is selected from the list comprising acetone, methyl ethyl ketone, 3-pentanone, hexanone, cyclopropanone, cyclobutanone, cyclopentanone, cyclohexanone, and isophorone.

[0054] In some embodiments, the monomer mixture, comprises at least 1.0 wt%, preferably at least 2.0 wt%, preferably at least 5.0 wt%, preferably at least 10.0 wt%, preferably at least 15.0 wt%, preferably at least 20.0 wt%, preferably at least 25.0 wt%, of a compound according to Structure I.

[0055] In some embodiments, the monomer mixture, comprises: at least 30.0 wt% to at most 99.5 wt%, or at least 30.0 wt% to at most 99.0 wt%, preferably at least 40.0 wt% to at most 98.0 wt%, preferably at least 45.0 wt% to at most 97.0 wt%, preferably at least 50.0 wt% to at most 95.0 wt%, preferably at least 60.0 wt% to at most 90.0 wt%, preferably at least 70.0 wt% to at most 85.0 wt%, of a cyclic comonomer selected from the list comprising lactones, lactams, cyclic amines, cyclic esters or mixtures thereof; and, at least 0.50 wt% to at most 70.0 wt%, or at least 1.0 wt% to at most 70.0 wt%, preferably at least 2.0 wt% to at most 60.0 wt%, preferably at least 3.0 wt% to at most 55.0 wt%, preferably at least 5.0 wt% to at most 50.0 wt%, preferably at least 10.0 wt% to at most 40.0 wt%, preferably at least 15.0 wt% to at most 30.0 wt%, of a compound according to Structure I.

[0056] In some embodiments, the monomer mixture, comprises: at least 30.0 wt%, preferably at least 40.0 wt%, preferably at least 45.0 wt%, preferably at least 50.0 wt%, preferably at least 60.0 wt%, preferably at least 70.0 wt%, preferably at least 75.0 wt% of a cyclic comonomer selected from the list comprising lactones, lactams, cyclic amines, cyclic esters or mixtures thereof; and, at least 0.50 wt%, or at least 1.0 wt%, preferably at least 2.0 wt%, preferably at least 3.0 wt%, preferably at least 5.0 wt%, preferably at least 10.0 wt%, preferably at least 15.0 wt%, preferably at least 20.0 wt%, preferably at least 25.0 wt%, of a compound according to Structure I.

[0057] In some embodiments, the monomer mixture, comprises: at least 70.0 wt% to at most 99.5 wt%, or at least 70.0 wt% to at most 99.0 wt% of a cyclic comonomer selected from the list comprising lactones, lactams, cyclic amines, cyclic esters or mixtures thereof; and, at least 0.50 wt% to at most 30.0wt%, or at least 1.0 wt% to at most 30.0 wt% of a compound according to Structure I.

[0058] In some embodiments, the monomer mixture, comprises: at least 0.50 wt% to at most 30.0wt%, or at least 1.0 wt% to at most 30.0 wt%, preferably at least 1.5 wt% to at most 20.0 wt%, preferably at least 2.0 wt% to at most 10.0 wt%, preferably at least 2.5 wt% to at most 7.5 wt%, preferably at least 3.0 wt% to at most 5.0 wt%, of a compound according to Structure I; and, preferably, wherein the rest of the monomer mixture is a cyclic comonomer selected from the list comprising lactones, lactams, cyclic amines, cyclic esters or mixtures thereof.

[0059] In some embodiments, the monomer mixture, comprises: or at least 0.50 wt%, at least 1.0 wt%, preferably at least 1.5 wt%, preferably at least 2.0 wt%, preferably at least 2.5 wt%, preferably at least 3.0 wt%, of a compound according to Structure I; and, preferably, wherein the rest of the monomer mixture is a cyclic comonomer selected from the list comprising lactones, lactams, cyclic amines, cyclic esters or mixtures thereof.

[0060] In some embodiments, the cyclic comonomer comprises a 5- to 7- membered heterocycle.

[0061] In some embodiments, the cyclic comonomer is a lactone or a lactam; preferably lactide, caprolactone or caprolactam. In some embodiments, the polymerization process as disclosed herein is a ring-opening polymerization process. As used herein "ring-opening polymerization" or "ROP" refers to a form of chain-growth polymerization, in which the terminus of a polymer chain attacks cyclic monomers to form a longer polymer. ROP is a versatile method commonly used for the synthesis of biopolymers.

[0062] In some embodiments, the monomer mixture is contacted with an initiator, and / or a catalyst.

[0063] In some embodiments, the process as disclosed herein provides that it takes place in the presence of a catalyst, preferably selected from: a Brpnsted acid, such as triflic acid or phosphoric acid derivatives; an organic base, such as 4-(dimethylamino)pyridine or l,5,7-triazabicyclo[4.4.0]dec-5- ene (TBD), triethylamine (TEA); diphenyl phosphate (DPP), a N-heterocyclic carbenes; or, a Sn(ll) species, such as stannous octoate.

[0064] In some embodiments, the process as disclosed herein provides that it takes place in the presence of an initiator of formula R-OH or R-SH; wherein R is selected from the group consisting of Cg-soarylCi. 2oalkyl, Ci-zoalkyl, Cs-iocycloalkyl, Cg-soaryl, Cs-sheteroaryl and Cs-sheterocyclyl, optionally substituted by one or more substituents selected from the group consisting of halogen, hydroxyl, and Ci.galkyl; preferably the initiator is benzyl alcohol (BnOH) or benzyl mercaptan (BnSH).

[0065] In some embodiments, the process as disclosed herein provides that the process is performed in the absence of a solvent. In some embodiments, the polymerization in the process is melt polymerization.

[0066] In some embodiments, the polymerizing is performed at a reduced pressure.

[0067] In some embodiments, the process comprises a step of subjecting the formed copolymer to a reduced pressure treatment. The reduced pressure may remove unreacted monomer and / or the ketone (R2- CO-R3) or aldehyde released during the polymerisation reaction. Preferably, the reduced pressure is a pressure of at most 1000 mbar, preferably of at most 750 mbar, preferably of at most 500 mbar, preferably of at most 250 mbar, preferably of at most 100 mbar, preferably of at most 50 mbar, preferably of at most 20 mbar.

[0068] In some embodiments, the process as disclosed herein provides that the copolymerization is performed at a temperature of at least 100.0°C to at most 220.0°C, preferably at least 120.0°C to at most 200.0°C, preferably at least 140.0°C to at most 180.0°C. In some embodiments, the process as disclosed herein provides that the process occurs in a solvent such as dichloromethane (DCM), chloroform, tetrahydrofuran (THF) or toluene. It is expected that the use of solvent will lower the required temperature at which the polymerization reaction occurs, even driving the temperature down to room temperature conditions.

[0069] The invention further provides in a copolymer formed by ring opening polymerization of a monomer mixture, comprising: a cyclic comonomer selected from the list comprising lactones, lactams, cyclic amines, cyclic esters or mixtures thereof; and, a compound according to Structure I:

[0070] (I), wherein R1is a hydrogen or an alkyl having 1 to 6 carbon atoms, preferably R1is an alkyl having 1 to 6 carbon atoms; and, wherein R2and R3is each independently hydrogen or an alkyl, cycloalkyl, aralkyl, aryl, alkynyl, cycloalkenyl, having 1 to 8, preferably 1 to 6, carbon atoms and optionally a heteroatom; or, wherein R2and R3together with the atom to which they are attached form a saturated or unsaturated 3-, 4-, 5-, 6-, or 7-membered ring, which may be substituted, such that R2and R3together are having 3 to 12 carbon atoms and optionally a heteroatom.

[0071] In some embodiments, the copolymer is a linear, cyclic or a branched copolymer, preferably wherein the linear copolymer is chosen from an alternating copolymer, a random copolymer, a statistical copolymer, or a block or segmented copolymer, or preferably wherein the cyclic copolymer is chosen from an alternating cyclic copolymer, a random cyclic copolymer, a statistical cyclic copolymer, or a block or segmented cyclic copolymer, or preferably wherein the branched copolymer is chosen from a graft copolymer, a star copolymer or a branched copolymer with a different architecture.

[0072] In some embodiments, the copolymer has a melting peak at 60.0 °C or higher as measured by differential scanning calorimetry (DSC), in particular a melting peak ranging between 60.0 to 240.0 °C, in particular from 100.0 to 200.0 °C, and more in particular from 120.0 to 160.0 °C.

[0073] In some embodiments, the copolymer has a weight-average molecular weight (Mw) from 1000 to 500000 g / mol, preferably from 2000 to 400000 g / mol, preferably from 5000 to 300000 g / mol, preferably from 10000 to 200000 g / mol, preferably from 50000 to 100000 g / mol, as measured by gel permeation chromatography (GPC). Gel permeation chromatography (GPC) (also referred to size exclusion chromatography (SEC)) is typically calibrated with polystyrene standards. In some embodiments, the copolymer has a weight-average molecular weight (Mw) from at least 1000 g / mol, preferably from at least 5000 g / mol, preferably from at least 10000 g / mol, preferably from at least 50000 g / mol, preferably from at least 100000 g / mol, preferably from at least 200000 g / mol, as measured by gel permeation chromatography (GPC).

[0074] In some embodiments, the copolymer has a number-average molecular weight (Mn) from 1000 to 500000 g / mol, preferably from 2000 to 400000 g / mol, preferably from 5000 to 300000 g / mol, preferably from 10000 to 200000 g / mol, preferably from 50000 to 100000 g / mol, as measured by gel permeation chromatography (GPC). Gel permeation chromatography (GPC) (also referred to size exclusion chromatography (SEC)) is typically calibrated with polystyrene standards. In some embodiments, the copolymer has a number-average molecular weight (Mn) from at least 1000 g / mol, preferably from at least 5000 g / mol, preferably from at least 10000 g / mol, preferably from at least 50000 g / mol, preferably from at least 100000 g / mol, preferably from at least 200000 g / mol, as measured by gel permeation chromatography (GPC).

[0075] In some embodiments, the copolymer has a crystallinity at least 5.0 % to at most 50.0%, preferably at least 10.0% to at most 40.0%, preferably at least 15.0% to at most 30.0%. In an alternative embodiment copolymer as disclosed herein provides that it is characterized by being amorphous (crystallinity of 0%).

[0076] In some embodiments, the copolymer has a crystallinity at least 5.0 %, preferably at least 10.0%, preferably at least 15.0%, preferably at least 20.0%.

[0077] In some embodiments, the copolymer has a structure according to any of the structures (15), (17), or (19) (see example section), preferably wherein n is an integer of 0 to 10000, wherein m is an integer of 0 to 10000, wherein k is an integer of 0 to 10000, wherein p is an integer of 0 to 10000, wherein r is an integer of 0 to 10000 and wherein t is an integer of 0 to 10000.

[0078] In some embodiments, the copolymer is produced by a process according to an embodiments described herein.

[0079] The invention provides further in the use of a compound according to Structure (I); wherein R1is a hydrogen or an alkyl having 1 to 6 carbon atoms, preferably R1is an alkyl having 1 to 6 carbon atoms; and, wherein R2and R3is each independently hydrogen or an alkyl, cycloalkyl, aralkyl, aryl, alkynyl, cycloalkenyl, having 1 to 8, preferably 1 to 6, carbon atoms and optionally a heteroatom; or, wherein R2and R3together with the atom to which they are attached form a saturated or unsaturated 3-, 4-, 5-, 6-, or 7-membered ring, which may be substituted, such that R2and R3together are having 3 to 12 carbon atoms and optionally a heteroatom; as a biodegrading accelerator in a polycondensate, preferably in polyester or polyamide, preferably in ester- or amide- containing polycondensates, preferably in a polylactic acid, a polycaprolactone or a polycaprolactam. The rate of biodegradation can be influenced by the amount of compound according to Structure (I) used int eh polycondensate. This allows tuning of the biodegradability of a polycondensate according to certain applications or requirements.

[0080] The invention provides further in the use of a compound according to Structure (I); wherein R1is a hydrogen or an alkyl having 1 to 6 carbon atoms, preferably R1is an alkyl having 1 to 6 carbon atoms; and, wherein R2and R3is each independently hydrogen or an alkyl, cycloalkyl, aralkyl, aryl, alkynyl, cycloalkenyl, having 1 to 8, preferably 1 to 6, carbon atoms and optionally a heteroatom; or, wherein R2and R3together with the atom to which they are attached form a saturated or unsaturated 3-, 4-, 5-, 6-, or 7-membered ring, which may be substituted, such that R2and R3together are having 3 to 12 carbon atoms and optionally a heteroatom; as an olfactory indicator of biodegradation in a polycondensate, preferably in ester- or amide- containing polycondensates, preferably in polyester or polyamide, preferably in a polylactic acid, a polycaprolactone or a polycaprolactam. This use allows the detection of biodegradation of the polycondensate to occur by smell. This allows a consumer to judge the state of the polycondensate or an article made from the polycondensate by smelling it.

[0081] The invention provides further in an article comprising the copolymer according to an embodiment described herein, or a copolymer produced by a process according to an embodiment described herein. In particular said articles may be fabricated by 3D printing, casting, injection moulding, extrusion, and / or machining. For 3D printing filaments made from the copolymer as disclosed herein can be used.

[0082] In some embodiments, the copolymers as disclosed herein can be used in a large variety of consumer products such as disposable tableware, cutlery, housings for kitchen appliances and electronics such as laptops and handheld devices, and microwavable trays. It can be used for compost bags, food packaging and loose-fill packaging material that is cast, injection moulded, or spun. In the form of fibres, it is used for monofilament fishing line and netting. In the form of nonwoven fabrics, it is used for upholstery, disposable garments, awnings, feminine hygiene products, and diapers.

[0083] In some embodiments, the copolymers as disclosed herein have applications in engineering plastics, where it may be blended with other polymers.

[0084] In some embodiments, the copolymers as disclosed herein may be used for automotive parts such as floor mats, panels, and covers.

[0085] In the form of fibres, the copolymers as disclosed herein may be used for monofilament fishing line and netting for vegetation and weed prevention, for sandbags, planting pots, binding tape and ropes.

[0086] The invention provides further in a compound according to Structure (I),

[0087] (I), wherein R1is a hydrogen or an alkyl having 1 to 6 carbon atoms, preferably R1is an alkyl having 1 to 6 carbon atoms; and, wherein R2and R3is each independently hydrogen or an alkyl, cycloalkyl, aralkyl, aryl, alkynyl, cycloalkenyl, having 1 to 8, preferably 1 to 6, carbon atoms and optionally a heteroatom; or, wherein R2and R3together with the atom to which they are attached form a saturated or unsaturated 3-, 4-, 5-, 6-, or 7-membered ring, which may be substituted, such that R2and R3together are having 3 to 12 carbon atoms and optionally a heteroatom.

[0088] The invention will be more readily understood by reference to the following examples, which are included merely for purpose of illustration of certain aspects and embodiments of the present invention and are not intended to limit the invention.

[0089] EXAMPLES Method section

[0090] Gel permeation chromatography (GPC)

[0091] The molecular weight (Mn(number average molecular weight), Mw(weight average molecular weight) and Disperity (Mw / Mn) were determined by Size Exclusion Chromatography (SEC) and in particular by IR-detected Gel Permeation Chromatography (GPC). Briefly, 5 mg / mL of polymer sample was dissolved in HFIP. About 1 pl of sample was injected in a PL HFIPgel column.

[0092] Calibration: narrow standards of polystyrene (PS) (commercially available) were used for calibration. Calculation of molecular weight Mi of each fraction i of eluted polymer is based on the Mark-Houwink relation.

[0093] The molecular weight averages used in establishing molecular weight / property relationships are the number average (Mn), weight average (Mw) and z average (Mz) molecular weight. These averages are defined by the following expressions and are determined from the calculated Mi:

[0094] Here Ni and Wi are the number and weight, respectively, of molecules having molecular weight Mi. The third representation in each case (farthest right) defines how one obtains these averages from SEC chromatograms, hi is the height (from baseline) of the SEC curve at the ith elution fraction and Mi is the molecular weight of species eluting at this increment.

[0095] In some cases, the elution curve can present two or more peaks from which different number average (Mn), weight average (Mw) and z average (Mz) molecular weights can be determined. For instance, a first peak may be labelled as Mniand a second peak may be labelled as Mn?.

[0096] Differential Scanning Calorimetry (DSC)

[0097] The glass transition temperature (Tg), crystallisation temperature (Tc), and melting temperature (Tm) were determined via Differential Scanning Calorimetry (DSC) on a DSC 214 polyma by Netzsch, calibrated with indium and using T zero mode. To erase any prior thermal and crystallization history the samples were first heated to 240°C at a heating rate of 10 °C / min and kept at 240°C for 10 minutes. The polymer was then cooled with a constant cooling rate of 10 °C / min up to -40°C and kept isothermal at -40°C for 10 minutes. The crystallization temperature was determined during this cooling step. The polymer was then heated to 240°C at a constant heating rate of 10 °C / min. The glass transition temperature and melting temperature were determined during this heating step. In some cases, the thermogram can present two or more glass transition temperatures, crystallization temperatures, and / or melting peaks. For instance, a first extremum may be labelled as Tmiand a second extremum may be labelled as Tm2-

[0098] Example 1

[0099] Preparation of compound according to Structure I:

[0100] A mixture of thiolactic acid (11) (106.14 g, 1 mol), and methyl ethyl ketone (12) (72.11 g, 1 mol), and p-toluenesulphonic acid (p-TSA) (1.72 g, 0.01 mol) in toluene (1 L), were vigorously stirred (250 rpm) and refluxed under a nitrogen atmosphere (220°C).

[0101] The water generated during the reaction was removed using a Dean-Stark trap with a reflux condenser through an azeotrope formation. After 1 hour, the reaction was quenched by adding NaCOs and washed with a saturated NaCI solution. Following the wash step, the organic layer was dried with magnesium sulphate, and the dried and filtered solution could be completed by solvent removal. Compound (13), a thiodioxolanone, was obtained as a liquid with a yield of about 90%.

[0102] Copolymerization of a lactide and a compound according to Structure I

[0103] 10 g of compound (13) and 10 g of lactide (14) were placed in a 100 ml round-bottom flask and dried for 1 hour at 80°C in an oil bath. Subsequently, 4 ml of a 0.5% solution of tin octoate (Sn(Oct)z) in toluene was added, and the mixture in the flask was further dried for 30 min to remove toluene. The reaction mixture was flushed with nitrogen multiple times, and the flask was sealed in the presence of nitrogen. The initiator for the polymerisation was the left over water present in the mixture. The temperature of the reaction mixture was then gradually increased with magnetic stirring to 180°C, and melt polymerization was allowed to proceed for 6 hours at 180°C, followed by 2 hours at 200°C. The reaction was halted by deactivating the catalyst with tartaric acid. The unreacted monomers were then removed through vacuum distillation, resulting in a viscous polymer (15).

[0104] Example 2

[0105] 0.3 g compound (13) and 9.7 g caprolactone (16) were placed in a 100 ml round-bottom flask and dried for 1 hour at 80°C in an oil bath. Subsequently, 4 ml of a 0.5% solution of tin octoate (Sn(Oct)z) in toluene was added, and the mixture in the flask was further dried for 30 min to remove toluene. The reaction mixture was flushed with nitrogen multiple times, and the flask was sealed in the presence of nitrogen. The initiator for the polymerisation was the left over water present in the mixture. The temperature of the reaction mixture was then gradually increased with magnetic stirring to 180°C, and melt polymerization was allowed to proceed for 6 hours at 180°C, followed by 2 hours at 200°C. The reaction was halted by deactivating the catalyst with tartaric acid. The unreacted monomers were then removed through vacuum distillation, resulting in a viscous polymer (17).

[0106] Example 3

[0107] 0.5 g compound (13) and 9.5 g caprolactam (18) g were placed in a 100 ml round-bottom flask and dried for 1 hour at 80°C in an oil bath. Subsequently, 4 ml of a 0.5% solution of tin octoate (Sn(Oct)z) in toluene was added, and the mixture in the flask was further dried for 30 min to remove toluene. The reaction mixture was flushed with nitrogen multiple times, and the flask was sealed in the presence of nitrogen. The initiator for the polymerisation was the left over water present in the mixture. The temperature of the reaction mixture was then gradually increased with magnetic stirring to 180°C, and melt polymerization was allowed to proceed for 6 hours at 180°C, followed by 2 hours at 200°C. The reaction was halted by deactivating the catalyst with tartaric acid. The unreacted monomers were then removed through vacuum distillation, resulting in a viscous polymer (19).

[0108] Example 4

[0109] 0.05 g compound (13) and 9.95 g Lactide (14) were placed in a 100 ml round-bottom flask and dried for 1 hour at 80°C in an oil bath. Subsequently, 4 ml of a 0.5% solution of tin octoate (Sn(Oct)z) in toluene was added, and the mixture in the flask was further dried for 30 min to remove toluene. The reaction mixture was flushed with nitrogen multiple times, and the flask was sealed in the presence of nitrogen. The initiator for the polymerisation was the left-over water present in the mixture. The temperature of the reaction mixture was then gradually increased with magnetic stirring to 180°C, and melt polymerization was allowed to proceed for 6 hours at 180°C, followed by 2 hours at 200°C. The reaction was halted by deactivating the catalyst with tartaric acid. The unreacted monomers were then removed through vacuum distillation, resulting in a viscous polymer (15).

[0110] Example 5

[0111] 0.10 g compound (13) and 9.90 g Lactide (14) were placed in a 100 ml round-bottom flask and dried for 1 hour at 80°C in an oil bath. Subsequently, 4 ml of a 0.5% solution of tin octoate (Sn(Oct)z) in toluene was added, and the mixture in the flask was further dried for 30 min to remove toluene. The reaction mixture was flushed with nitrogen multiple times, and the flask was sealed in the presence of nitrogen. The initiator for the polymerisation was the left-over water present in the mixture. The temperature of the reaction mixture was then gradually increased with magnetic stirring to 180°C, and melt polymerization was allowed to proceed for 6 hours at 180°C, followed by 2 hours at 200°C. The reaction was halted by deactivating the catalyst with tartaric acid. The unreacted monomers were then removed through vacuum distillation, resulting in a viscous polymer (15).

[0112] Example 6

[0113] 0.20 g compound (13) and 9.80 g Lactide (14) were placed in a 100 ml round-bottom flask and dried for 1 hour at 80°C in an oil bath. Subsequently, 4 ml of a 0.5% solution of tin octoate (Sn(Oct)z) in toluene was added, and the mixture in the flask was further dried for 30 min to remove toluene. The reaction mixture was flushed with nitrogen multiple times, and the flask was sealed in the presence of nitrogen. The initiator for the polymerisation was the left-over water present in the mixture. The temperature of the reaction mixture was then gradually increased with magnetic stirring to 180°C, and melt polymerization was allowed to proceed for 6 hours at 180°C, followed by 2 hours at 200°C. The reaction was halted by deactivating the catalyst with tartaric acid. The unreacted monomers were then removed through vacuum distillation, resulting in a viscous polymer (15).

[0114] Example 7

[0115] 0.50 g compound (13) and 9.50 g Lactide (14) were placed in a 100 ml round-bottom flask and dried for 1 hour at 80°C in an oil bath. Subsequently, 4 ml of a 0.5% solution of tin octoate (Sn(Oct)z) in toluene was added, and the mixture in the flask was further dried for 30 min to remove toluene. The reaction mixture was flushed with nitrogen multiple times, and the flask was sealed in the presence of nitrogen. The initiator for the polymerisation was the left-over water present in the mixture. The temperature of the reaction mixture was then gradually increased with magnetic stirring to 180°C, and melt polymerization was allowed to proceed for 6 hours at 180°C, followed by 2 hours at 200°C. The reaction was halted by deactivating the catalyst with tartaric acid. The unreacted monomers were then removed through vacuum distillation, resulting in a viscous polymer (15).

[0116] Example 8

[0117] Analysis of copolymers of a lactide and a compound according to Structure I (Examples 4-7)

[0118] The structural and thermal properties of the copolymers (15) prepared in Examples 4-7 were analyzed using Gel Permeation Chromatography (GPC) and Differential Scanning Calorimetry (DSC), as detailed in the methodology section. The resulting properties are summarized in Table 1 and Table 2 below. Without wishing to be bound by theory it is believed that the inclusion of a thiodioxolanone compound in the polymerization mixture may provide differences in reactivity which may result in distinct peaks in number average molecular weight (Mn) and molecular weight distribution. In addition, the resulting co-polymer may comprise heterogeneous domains, resulting in distinct thermal transitions including glass transition temperatures (Tg) and melting temperatures (Tm).

[0119] Table 1.

[0120] *Not applicable.

[0121] Table 2.

[0122] *Not applicable.

[0123] The present data demonstrates that copolymers with tuneable compositions and thermal properties can advantageously be obtained.

[0124] It is to be understood that although preferred embodiments and / or materials have been discussed for providing embodiments according to the present invention, various modifications or changes may be made without departing from the scope and spirit of this invention.

Claims

CLAIMS1. A process for synthesizing a copolymer comprising the step of polymerizing via ring opening a monomer mixture, comprising: a cyclic comonomer selected from the list comprising lactones, lactams, cyclic amines, cyclic esters or mixtures thereof; at least 70.0 wt% to at most 99.0 wt% of and, a compound according to Structure I at least 1.0 wt% to at most 30.0 wt% of:(I), wherein R1is a hydrogen or an alkyl having 1 to 6 carbon atoms; and, wherein R2and R3is each independently hydrogen or an alkyl, cycloalkyl, aralkyl, aryl, alkynyl, cycloalkenyl, having 1 to 8 carbon atoms and optionally a heteroatom; or, wherein R2and R3together with the atom to which they are attached form a saturated or unsaturated 3-, 4-, 5-, 6-, or 7-membered ring, which may be substituted, such that R2and R3together are having 3 to 12 carbon atoms and optionally a heteroatom.

2. The process according to claim 1, wherein R1is a methyl or ethyl group, preferably wherein R1is a methyl group; and / or, wherein R2and R3together with the atom to which they are attached form a saturated or unsaturated 3-, 4-, 5-, 6-, or 7-membered ring, which may be substituted, such that R2and R3together are having 3 to 12 carbon atoms and optionally a heteroatom.

3. The process according to claim 1 or 2, wherein the monomer mixture, comprises: at least 30.0 wt% to at most 99.5 wt%, or at least 30.0 wt% to at most 99.0 wt%, preferably at least 40.0 wt% to at most 98.0 wt%, preferably at least 45.0 wt% to at most 97.0 wt%, preferably at least 50.0 wt% to at most 95.0 wt%, preferably at least 60.0 wt% to at most 90.0 wt%, preferably at least 70.0 wt% to at most 85.0 wt%, of a cyclic comonomer selected from the list comprising lactones, lactams, cyclic amines, cyclic esters or mixtures thereof; and, at least 0.50 wt% to at most 70.0 wt%, or at least 1.0 wt% to at most 70.0 wt%, preferably at least 2.0 wt% to at most 60.0 wt%, preferably at least 3.0 wt% to at most 55.0 wt%, preferably at least 5.0 wt% to at most 50.0 wt%, preferably at least 10.0 wt% to at most40.0 wt%, preferably at least 15.0 wt% to at most 30.0 wt%, of a compound according toStructure I.

4. The process according to any one of the previous claims, wherein the cyclic comonomer comprises a 5- to 7- membered heterocycle.

5. The process according to any one of the previous claims, wherein the cyclic comonomer is a lactone or a lactam; preferably lactide, caprolactone or caprolactam.

6. The process according to any one of the previous claims, wherein the monomer mixture is contacted with an initiator, and / or a catalyst.

7. The process according to any one of the previous claims, wherein the process comprises a step of subjecting the formed copolymer to a reduced pressure treatment.

8. A copolymer formed by ring opening polymerization of a monomer mixture, preferably produced by a process according to any one of claims 1 to 7, the copolymer comprising: at least 70.0 wt% to at most 99.5 wt%, or at least 30.0 wt% to at most 99.0 wt% of a cyclic comonomer selected from the list comprising lactones, lactams, cyclic amines, cyclic esters or mixtures thereof; and, at least 0.50 wt% to at most 30.0 wt%, or at least 1.0 wt% to at most 30.0 wt% of a compound according to Structure I:(I), wherein R1is a hydrogen or an alkyl having 1 to 6 carbon atoms; and, wherein R2and R3is each independently hydrogen or an alkyl, cycloalkyl, aralkyl, aryl, alkynyl, cycloalkenyl, having 1 to 8 carbon atoms and optionally a heteroatom; or, wherein R2and R3together with the atom to which they are attached form a saturated or unsaturated 3-, 4-, 5-, 6-, or 7-membered ring, which may be substituted, such that R2and R3together are having 3 to 12 carbon atoms and optionally a heteroatom.

9. The copolymer according to claim 8, wherein the copolymer is a linear, cyclic or a branched copolymer, preferably wherein the linear copolymer is chosen from an alternating copolymer, a random copolymer, a statistical copolymer, or a block or segmented copolymer, or preferably wherein the cyclic copolymer is chosen from an alternating cyclic copolymer, a random cyclic copolymer, a statistical cyclic copolymer, or a block or segmented cyclic copolymer, or preferably wherein the branched copolymer is chosen from a graft copolymer, a star copolymer or a branched copolymer with a different architecture.

10. The copolymer according to any one of claims 8 to 9, having a melting peak at 60.0 °C or higher as measured by differential scanning calorimetry (DSC), in particular a melting peak ranging between 60.0 to 240.0 °C, in particular from 100.0 to 200.0 °C, and more in particular from 120.0 to 160.0 °C.

11. The copolymer according to any one of claims 8 to 10, having a weight-average molecular weight (Mw) from 1000 to 500000 g / mol and / or a number-average molecular weight (Mn) from 1000 to 500000 g / mol as measured by gel permeation chromatography (GPC).

12. The copolymer according to any one of claims 8 to 11, wherein the copolymer has a crystallinity between 5% and 50%.

13. Use of a compound according to Structure (I);wherein R1is a hydrogen or an alkyl having 1 to 6 carbon atoms; and, wherein R2and R3is each independently hydrogen or an alkyl, cycloalkyl, aralkyl, aryl, alkynyl, cycloalkenyl, having 1 to 8 carbon atoms and optionally a heteroatom; or, wherein R2and R3together with the atom to which they are attached form a saturated or unsaturated 3-, 4-, 5-, 6-, or 7-membered ring, which may be substituted, such that R2and R3together are having 3 to 12 carbon atoms and optionally a heteroatom; as a biodegrading accelerator or an olfactory indicator of biodegradation in a polycondensate, preferably in ester- or amide- containing polycondensates, preferably in a polylactic acid, a polycaprolactone or a polycaprolactam.

14. An article comprising the copolymer according to any one of claims 8 to 12, or a copolymer produced by a process according to any one of claims 1 to 7.

15. A compound according to Structure (I),wherein R1is a hydrogen or an alkyl having 1 to 6 carbon atoms; and, wherein R2and R3is each independently hydrogen or an alkyl, cycloalkyl, aralkyl, aryl, alkynyl, cycloalkenyl, having 1 to 8 carbon atoms and optionally a heteroatom; or, wherein R2and R3together with the atom to which they are attached form a saturated or unsaturated 3-, 4-, 5-, 6-, or 7-membered ring, which may be substituted, such that R2and R3together are having 3 to 12 carbon atoms and optionally a heteroatom.

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