Chemically recyclable polyhydroxyalkanoate

Abstract

Polyhydroxyalkanoates (PHA) are increasingly attracting attention as sustainable plastics due to their biodegradability and bioregenerability in the ambient environment. However, current semicrystalline PHAs face three long-standing challenges for widespread commercial introduction and application: lack of melt processability, mechanical brittleness, and unmet recyclability, the last of which is essential to achieve a circular plastic economy. Here, we report a synthetic PHA platform that addresses the origin of thermal instability by eliminating the α-hydrogen in the PHA repeating unit, thus preventing facile cis-elimination during pyrolysis. This simple α,α-disubstitution in PHA substantially enhances thermal stability, rendering the PHA melt processable. Synergistically, the structural modification also endows the PHA with mechanical toughness, intrinsic crystallinity, and closed-loop chemical recyclability.

Description

Technical Field

[0001] Related Applications This application claims priority to U.S. Provisional Patent Application No. 63 / 340,168, filed May 10, 2022, and 63 / 434,550, filed Dec. 22, 2022, under 35 U.S.C. § 119(e), the disclosures of which are incorporated herein by reference.

[0002] Government Support This invention was made with government support under grants DE-AC36-08GO28308 and DE-SC0022290 awarded by the Department of Energy. The government has certain rights in this invention.

Background Art

[0003] Polyhydroxyalkanoates (PHA) are a class of polyesters that are either naturally accumulated by living microorganisms or synthetically produced from a variety of chemical catalysts, particularly biorenewable resources. They have tunable thermomechanical properties and are biodegradable in ambient environments, thus providing a more sustainable alternative to petroleum-derived and / or non-degradable plastics. Over the past 60+ years, ring-opening polymerization (ROP) of 4-membered β-lactones, such as β-butyrolactone (β-BL), and their derivatives with different substituents at the α and β positions, has been widely studied to enable the chemical synthesis of PHA, particularly poly(3-hydroxybutyrate) (P3HB), with atactic, isotactic, syndiotactic, or syndiotactic stereomicrostructures (tacticities).

Numbers

[0004] However, before widespread commercial introduction and application can be realized, three long-standing challenges faced by PHA must be addressed: 1) thermal instability during melt processing, 2) mechanical performance to overcome brittleness, and 3) closed-loop chemical recyclability. Therefore, it is necessary to develop PHA that is thermally stable in the molten state, has excellent mechanical properties, and is chemically recyclable into monomers. SUMMARY OF THE INVENTION

[0005] This disclosure provides a class of novel semi-crystalline polyesters that have not only excellent thermal and mechanical properties required for a wider range of applications but also high chemical recyclability and provide their chemical recyclability. The geminal disubstituted polyesters disclosed herein at the α-position to the ester carbonyl are rationally designed to exhibit the following complex and advanced properties compared to current polyesters: (a) enhanced mechanical performance and higher melting temperature for a wider application window; (b) higher decomposition temperature for better high-temperature performance and melt processability; and (c) higher chemical recyclability to recover monomers in a pure state and in high yield, thus achieving chemical recyclability. The invention also provides a method for manufacturing and recycling such polyesters.

[0006] Accordingly, this disclosure provides a polymer comprising Formula I:

Chemical formula

[0007] This disclosure also provides a method for forming the above polymers, including ring-opening polymerization (ROP) of monomers of formula III or step-growth polycondensation (SGP) of monomers of formula IV:

Chemical formula

[0008] In addition, this disclosure provides a method for depolymerizing the above polymer, which involves contacting the polymer and a base, and the polymer is depolymerized to its constituent monomers, and the conversion to the constituent monomers is about 20 wt% or more.

[0009] The technology provides novel polymers or copolymers of formula I and formula II, intermediates for the synthesis of polymers or copolymers of formula I and formula II, and methods for preparing polymers or copolymers of formula I and II. The technology also provides polymers or copolymers of formula I and II that are useful as intermediates for the synthesis of other useful polymers or copolymers.

[0010] The following drawings form a part of the specification and are included to further illustrate certain embodiments or various aspects of the invention. In some cases, embodiments of the invention may be best understood by referring to the accompanying drawings in combination with the detailed description presented herein. The description and the accompanying drawings can highlight certain specific examples or certain aspects of the invention. However, those skilled in the art will understand that some of the examples or aspects can be used in combination with other examples or aspects of the invention.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

DETAILED DESCRIPTION OF THE INVENTION

[0012] The invention provides a technically important polyester having not only the physical and chemical properties required for practical applications but also high chemical recyclability that provides their chemical recyclability. These redesigned geminal disubstituted polyesters at the α-position (similarly the 2-position) relative to the ester carbonyl exhibit the following complex and advanced properties relative to current polyesters: (a) a higher T m value, thus resulting in enhanced mechanical performance and a wider application window; (b) a higher T d value (due to the absence of hydrogen), thus resulting in better high-temperature performance and melt processability; and (c) higher chemical recyclability, enabling clean monomer recovery and thus achieving chemical recyclability. The invention also provides a method for manufacturing such polyesters and for recycling them. In particular, the invention provides a class of high-performance, recyclable polyesters shown in Chart 1. Chart 1. α,α-Disubstituted polyesters having high-performance characteristics (high T m , T d ) and chemical recyclability for recycling

Chemical formula

[0013] The α,α-disubstituted polyesters are produced by the ROP of the corresponding lactones of various ring sizes from small 4-membered to large 16-membered macrolactones or by the polycondensation of the corresponding α,α-disubstituted ω-hydroxy acids. The polyester is a semi-crystalline material having T m ≥ 110 °C and T dExhibits a thermal stability of ≧250 °C, has high chemical recyclability, and has a pure monomer recovery of ≧75%. To optimize the performance characteristics, copolymers of different polyesters can also be formed by copolymerization between two or more different disubstituted lactones, or between one disubstituted lactone and another unsubstituted lactone.

[0014] Additional information and data supporting the invention can be found in the following publications by the inventors: Science 380, 64 - 69 (2023) and its supplementary materials (which are hereby incorporated by reference in their entirety).

[0015] Definitions. To provide a clear and consistent understanding of the specification and the claims, the following definitions are included. As used herein, the recited terms have the following meanings. All other terms and phrases used in this specification have their ordinary meanings as would be understood by one of ordinary skill in the art. Such ordinary meanings can be obtained by referring to a technical dictionary, such as Hawley’s Condensed Chemical Dictionary, 14th Edition, R.J. Lewis, John Wiley & Sons, New York, N.Y., 2001.

[0016] References in the specification to "one embodiment", "an embodiment", etc. indicate that the described embodiment can include a particular aspect, characteristic, structure, part, or feature, but not all embodiments necessarily include that aspect, characteristic, structure, part, or feature. Moreover, such phrases do not necessarily refer to the same embodiment mentioned elsewhere in the specification. Further, when a particular aspect, characteristic, structure, part, or feature is described in connection with one embodiment, it is within the knowledge of one of ordinary skill in the art to affect or associate such aspect, characteristic, structure, part, or feature with other embodiments, whether or not explicitly described.

[0017] The singular forms "a", "an", and "the" include plural references unless the context clearly dictates otherwise. Thus, for example, a reference to "a compound" includes a plurality of such compounds, so that a compound X includes a plurality of compound Xs. It should further be noted that the claims can be drafted to exclude any optional elements. As such, this statement is intended to function as a basis for the use of exclusive terms such as "only", "solely", etc. in relation to any element described herein, and / or for the use of a listing of claim elements or "negative" limitations.

[0018] The term "and / or" means any one of the items, any combination of the items, or all of the items to which this term is related. The phrases "one or more" and "at least one" are readily understood by those skilled in the art when read in the context of their use. For example, such phrases can mean 1, 2, 3, 4, 5, 6, 10, 100, or any upper limit approximately 10, 100, or 1000 times higher than the recited lower limit. For example, one or more substituents on a phenyl ring can represent 1-5, or 1-4 when the phenyl ring is disubstituted.

[0019] As will be understood by those skilled in the art, all numerical values representing properties such as material components, molecular weights, and amounts such as reaction conditions are approximate values and are understood to be optionally modified by the term "about" in all cases. These values can vary depending on the desired properties that the skilled person is trying to obtain using the teachings of the description herein. It is also understood that such values inherently include variability due to the standard deviation found in their individual test measurements. It will be understood that when a value is expressed as an approximate value by the use of the antecedent "about", a specific value without the modifier "about" also forms a further aspect.

[0020] The terms "about" and "approximately" are used interchangeably. Either term can indicate a variation of ±5%, ±10%, ±20%, or ±25% of a specified value. For example, "about 50" percent can, in some embodiments, have a variation of from 45 to 55 percent, or, alternatively, as defined by a particular claim. For integer ranges, the term "about" can include 1 or 2 integers greater than and / or less than the recited integer at each end of the range. Unless otherwise specified herein, the terms "about" and "approximately" are intended to include the nearest value to the recited range that is equivalent from a functional standpoint for an individual material component, composition, or embodiment, e.g., a weight percentage. The terms "about" and "approximately" can also modify the endpoints of the recited ranges described above in this paragraph.

[0021] As will be understood by those skilled in the art, for all purposes, particularly from the perspective of providing a written specification, all ranges recited herein also include any and all possible sub-ranges and combinations of those sub-ranges, as well as the individual values, particularly integer values, that make up those ranges. Thus, it is understood that each unit between two specific units is also disclosed. For example, if 10 - 15 is disclosed, 11, 12, 13, and 14 are also disclosed individually and as part of the range. The recited ranges (e.g., weight percentages or carbon groups) include each specific value, integer, fraction, or identity within that range. It can be readily recognized that all of the recited ranges are sufficiently described to be divisible into at least equal halves, thirds, fourths, fifths, tenths. By way of non-limiting example, each range described herein can be readily decomposed into a lower third, middle third, and upper third, etc. As will also be understood by those skilled in the art, all languages, e.g., "up to", "at least", "more", "less", "exceeding", "above", etc., include the recited numbers, and such terms indicate ranges that can thereafter be decomposed into the above-described sub-ranges. Similarly, all ratios recited herein also include all sub-ratios within the broader ratio. Thus, the specific values recited for radicals, substituents, and ranges are for illustrative purposes only; they do not exclude other defined values or other values within the defined ranges for the radicals and substituents. It will be further understood that each endpoint of a range is important in relation to, and independent of, the other endpoints.

[0022] This disclosure provides ranges, limits, and deviations of variables such as volume, mass, percentage, ratio, etc. It is understood by those skilled in the art that a range such as "number 1" to "number 2" means a continuous range of numbers including integers and fractions. For example, 1 to 10 means 1, 2, 3, 4, 5, … 9, 10. It also means 1.0, 1.1, 1.2, 1.3, …, 9.8, 9.9, 10.0, and also means 1.01, 1.02, 1.03, etc. If the disclosed variable is a number less than "number 10", it means a continuous range including integers and fractions less than number 10 as described above. Similarly, if the disclosed variable is a number greater than "number 10", it means a continuous range including integers and fractions greater than number 10. These ranges can be modified by the term "about", and its meaning is described above.

[0023] The enumeration of a), b), c), … or i), ii), iii), etc. in a list of components or steps does not give a particular order unless explicitly stated.

[0024] Those skilled in the art will also readily recognize that when members are grouped together in a common manner, for example, in a Markush group, the invention encompasses not only the entire group of enumerated groups as a whole, but also each member of the group individually and all possible subgroups of the main group. In addition, for all purposes, the invention encompasses not only the main group but also the main group without one or more group members. Therefore, the invention contemplates the express exclusion of any one or more members of the enumerated groups. Thus, a condition is applicable to any of the disclosed categories or embodiments, whereby any one or more of the enumerated elements, species, or embodiments can be excluded from such a category or embodiment, for example, for use in an express negative limitation.

[0025] The term "contact" refers to the act of touching, bringing into contact, or bringing close immediately or very closely, including at the cellular or molecular level, such that, for example, a physiological reaction, chemical reaction, or physical change is caused in, for example, a solution or a reaction mixture.

[0026] The term "substantially" is a broad term herein and is used in its ordinary meaning, without limitation but including that which is a majority, but not necessarily all, of that which is specified. For example, the term could indicate a numerical value that need not be 100% of a total value. The total value could be as little as about 1%, about 2%, about 3%, about 4%, about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 15%, or about 20% less.

[0027] When the term "comprising" is used herein, alternatives of using the terms "consisting of" or "consisting essentially of" are contemplated. As used herein, "comprising" is synonymous with "including", "containing", or "characterized by", is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. As used herein, "consisting of" excludes any element, step or ingredient not specified in the aspect elements. As used herein, "consisting essentially of" does not exclude materials or steps that do not substantially affect the basic and novel characteristics of the aspect. In each instance herein, any of the terms "comprising", "consisting essentially of", and "consisting of" may be replaced with either of the other two terms. The disclosure exemplified herein can be suitably practiced without any one or more elements, one or more limitations (not specifically disclosed herein).

[0028] This disclosure discloses methods for manufacturing the compounds and compositions of the present invention. The compounds and compositions can be prepared by optionally combining any of the applicable techniques described herein with standard techniques of organic synthesis. Many techniques, such as etherification and esterification, are well known in the art. However, many of these techniques are described in detail below: Compendium of Organic Synthetic Methods (John Wiley & Sons, New York), Vol. 1, Ian T. Harrison and Shuyen Harrison, 1971; Vol. 2, Ian T. Harrison and Shuyen Harrison, 1974; Vol. 3, Louis S. Hegedus and Leroy Wade, 1977; Vol. 4, Leroy G. Wade, Jr., 1980; Vol. 5, Leroy G. Wade, Jr., 1984; and Vol. 6; as well as standard organic reference texts, such as March’s Advanced Organic Chemistry: Reactions, Mechanisms, and Structure, 5th Edition, M. B. Smith and J. March (John Wiley & Sons, New York, 2001); Comprehensive Organic Synthesis. Selectivity, Strategy & Efficiency in Modern Organic Chemistry. In 9 Volumes, Barry M. Trost, editor-in-chief (Pergamon Press, New York, 1993 printing); Advanced Organic Chemistry, Part B: Reactions and Synthesis, 2nd Edition, Cary and Sundberg (1983); for heterocyclic synthesis, see Hermanson, Greg T., Bioconjugate Techniques, 3rd Edition, Academic Press, 2013.

[0029] The formulas and compounds described herein can be modified using protecting groups. Suitable amino and carboxy protecting groups are known to those skilled in the art (see, for example: Protecting Groups in Organic Synthesis, 2nd Edition, Greene, T. W., and Wutz, P. G. M., John Wiley & Sons, New York and the references cited therein; Philip J. Kocienski; Protecting Groups (Georg Thieme Verlag Stuttgart, New York, 1994), and the references cited therein); as well as, Comprehensive Organic Transformations, Larock, R. C., 2nd Edition, John Wiley & Sons, New York (1999), and the references cited therein).

[0030] The term "halo" or "halide" refers to fluoro, chloro, bromo, or iodo. Similarly, the term "halogen" refers to fluorine, chlorine, bromine, and iodine.

[0031] The term "alkyl" refers to, for example, a branched or unbranched hydrocarbon having from 1 to 20 carbon atoms, often from 1 to 12, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms; or for example, having a range of from 1 to 20 carbon atoms, for example, from 2 to 6, 3 to 6, 2 to 8, or 3 to 8 carbon atoms. As used herein, the term "alkyl" also includes "cycloalkyl" as defined below. Examples include, but are not limited to: methyl, ethyl, 1-propyl, 2-propyl (isopropyl), 1-butyl, 2-methyl-1-propyl (isobutyl), 2-butyl (sec-butyl), 2-methyl-2-propyl (t-butyl), 1-pentyl, 2-pentyl, 3-pentyl, 2-methyl-2-butyl, 3-methyl-2-butyl, 3-methyl-1-butyl, 2-methyl-1-butyl, 1-hexyl, 2-hexyl, 3-hexyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl, 4-methyl-2-pentyl, 3-methyl-3-pentyl, 2-methyl-3-pentyl, 2,3-dimethyl-2-butyl, 3,3-dimethyl-2-butyl, hexyl, octyl, decyl, dodecyl, and the like. Alkyl can be unsubstituted or can be substituted with substituents as described below or otherwise described herein. Alkyl can also optionally be partially or completely unsaturated. As such, the listing of alkyl groups can include alkenyl or alkynyl groups. Alkyl can be the monovalent hydrocarbon radical as described and exemplified above, or it can be a divalent hydrocarbon radical (i.e., alkylene).

[0032] Alkylene is an alkyl group having two free valences at one carbon atom of the carbon chain or at two different carbon atoms. Similarly, alkenylene and alkynylene are an alkene and an alkyne having two free valences at two different carbon atoms, respectively, or alkenylene can have two free valences on the same carbon.

[0033] The term "cycloalkyl" refers to a cyclic alkyl group having a single ring or multiple fused rings, for example, a cyclic alkyl group of 3 to 10 carbon atoms. Examples of cycloalkyl groups include monocyclic structures such as cyclopropyl, cyclobutyl, cyclopentyl, cyclooctyl, etc., or polycyclic structures such as adamantyl, etc. Cycloalkyl can be unsubstituted or substituted. The cycloalkyl group can be monovalent or divalent and can be optionally substituted as described for alkyl groups. The cycloalkyl group can optionally contain one or more sites of unsaturation. For example, the cycloalkyl group can contain one or more carbon-carbon double bonds. For example, by way of example, 1-cyclopent-1-enyl, 1-cyclopent-2-enyl, 1-cyclopent-3-enyl, cyclohexyl, 1-cyclohex-1-enyl, 1-cyclohex-2-enyl, 1-cyclohex-3-enyl, etc.

[0034] The term "heteroatom" refers to any atom in the periodic table that is not carbon or hydrogen. Typically, heteroatoms are O, S, N, P. Heteroatoms can also be halogen, metal or metalloid.

[0035] The term "heterocycloalkyl" or "heterocyclyl" refers to a saturated or partially saturated monocyclic, bicyclic, or polycyclic ring containing at least one heteroatom selected from nitrogen, sulfur, oxygen, preferably 1 to 3 heteroatoms in at least one ring. Each ring is preferably 3 to 10 membered, more preferably 4 to 7 membered. Examples of suitable heterocycloalkyl substituents include the following: pyrrolidyl, tetrahydrofuryl, tetrahydrothiofuranyl, piperidyl, piperazyl, tetrahydropyranyl, morpholino, 1,3-diazepane, 1,4-diazepane, 1,4-oxazepane, and 1,4-oxathiapane. The group can be a terminal group or a bridging group.

[0036] The term "aryl" refers to an aromatic hydrocarbon group derived by removing at least one hydrogen atom from a single carbon atom of a parent aromatic ring system. The radical bond site can be a saturated or unsaturated carbon atom of the parent ring system. An aryl group can have 6 to 30 carbon atoms, for example, about 6 - 10 carbon atoms. An aryl group can have a monocyclic (e.g., phenyl) or multiple fused rings, where at least one ring is aromatic (e.g., naphthyl, dihydrophenanthrenyl, fluorenyl, or anthryl). Typical aryl groups include, but are not limited to, radicals derived from benzene, naphthalene, anthracene, biphenyl, etc. An aryl can be unsubstituted or, optionally, substituted with substituents described below. For example, the phenyl moiety or group can be substituted with one or more substituents R X where R X is in the ortho, meta, or para position and X is an integer variable from 1 to 5.

[0037] The term "heteroaryl" refers to a monocyclic, bicyclic, or tricyclic ring system containing 1, 2, or 3 aromatic rings and containing at least 1 nitrogen, oxygen, or sulfur atom within the aromatic ring. Heteroaryl can be unsubstituted or can be substituted with, for example, one or more, particularly 1 - 3, substituents as described in the definition of "substituted". Typical heteroaryl groups contain 2 - 20 carbon atoms in the ring backbone in addition to one or more heteroatoms, and the ring backbone includes a 5 - membered ring, 6 - membered ring, two 5 - membered rings, two 6 - membered rings, or a 5 - membered ring fused to a 6 - membered ring. Examples of heteroaryl groups include, but are not limited to: 2H - pyrrolyl, 3H - indolyl, 4H - quinolidinyl, acridinyl, benzo[b]thienyl, benzothiazolyl, β - carbolinyl, carbazolyl, chromenyl, cinnolinyl, dibenzo[b,d]furanyl, furazanyl, furyl, imidazolyl, imidizolyl, indazolyl, indolisinyl, indolyl, isobenzofuranyl, isoindolyl, isoquinolyl, isothiazolyl, isoxazolyl, naphthyridinyl, oxazolyl, perimidinyl, phenanthridinyl, phenanthrolinyl, phenarsazinyl, phenazinyl, phenothiazinyl, phenoxathiinyl, phenoxazinyl, phthalazinyl, pteridinyl, purinyl, pyranyl, pyrazinyl, pyrazolyl, pyridazinyl, pyridyl, pyrimidinyl, pyrrolyl, quinazolinyl, quinolyl, quinoxalinyl, thiadiazolyl, thianthrenyl, thiazolyl, thienyl, triazolyl, tetrazolyl, and xanthenyl. In one embodiment, the term "heteroaryl" refers to a monocyclic aromatic ring containing 5 or 6 ring atoms including carbon and 1, 2, 3, or 4 heteroatoms independently selected from non - peroxide oxygen, sulfur, and N(Z), where Z is absent or is H, O, alkyl, aryl, or (C1 - C6)alkylaryl.In some embodiments, the heteroaryl represents an ortho-fused bicyclic heterocycle of about 8 to 10 ring atoms derived therefrom, in particular, a benz derivative, or one derived by condensing a propylene, trimethylene, or tetramethylene diradical thereto.

[0038] As used herein, the terms "substituted" or "substituent" are intended to indicate that one or more (e.g., in various embodiments, 1-10; in other embodiments, 1-6; in some embodiments 1, 2, 3, 4, or 5; in certain embodiments, 1, 2, or 3; and in other embodiments, 1 or 2) of the hydrogens on the group indicated in an expression using "substituted" (or "substituent") are replaced with a selection from the indicated group(s) or with a suitable group known to those skilled in the art, provided that the normal valency of the indicated atoms is not exceeded and that a stable compound is obtained by the substitution. Suitable indicated groups include, for example: alkyl, alkenyl, alkynyl, alkoxy, haloalkyl, hydroxyalkyl, aryl, heteroaryl, heterocyclyl, cycloalkyl, alkanoyl, alkoxycarbonyl, amino, alkylamino, dialkylamino, carboxyalkyl, alkylthio, alkylsulfinyl, and alkylsulfonyl. The substituents of the indicated groups can be those listed in the specific list of substituents described herein, or can be one or more substituents selected from the following, as would be recognized by one skilled in the art: alkyl, alkenyl, alkynyl, alkoxy, halo, haloalkyl, hydroxy, hydroxyalkyl, aryl, heteroaryl, heterocycle, cycloalkyl, alkanoyl, alkoxycarbonyl, amino, alkylamino, dialkylamino, trifluoromethylthio, difluoromethyl, acylamino, nitro, trifluoromethyl, trifluoromethoxy, carboxy, carboxyalkyl, keto, thioxo, alkylthio, alkylsulfinyl, alkylsulfonyl, and cyano.Suitable substituents for the directing group can be attached to the carbon atom being substituted and include: F, Cl, Br, I, OR’, OC(O)N(R’)2, CN, CF3, OCF3, R’, O, S, C(O), S(O), methylenedioxy, ethylenedioxy, N(R’)2, SR’, SOR’, SO2R’, SO2N(R’)2, SO3R’, C(O)R’, C(O)C(O)R’, C(O)CH2C(O)R’, C(S)R’, C(O)OR’, OC(O)R’, C(O)N(R’)2, OC(O)N(R’)2, C(S)N(R’)2, (CH2). 0-2 NHC(O)R’, N(R’)N(R’)C(O)R’, N(R’)N(R’)C(O)OR’, N(R’)N(R’)CON(R’)2, N(R’)SO2R’, N(R’)SO2N(R’)2, N(R’)C(O)OR’, N(R’)C(O)R’, N(R’)C(S)R’, N(R’)C(O)N(R’)2, N(R’)C(S)N(R’)2, N(COR’)COR’, N(OR’)R’, C(=NH)N(R’)2, C(O)N(OR’)R’, or C(=NOR’)R’, where R’ can be hydrogen or a carbon-based moiety (e.g., (C1-C6)alkyl), and the carbon-based moiety can itself be further substituted. When the substituent is monovalent, e.g., for example, F or Cl, it is attached to the atom being substituted by a single bond. When the substituent is divalent, e.g., O, it is attached to the atom being substituted by a double bond; for example, a carbon atom substituted with O forms a carbonyl group, C=O.

[0039] The stereochemical definitions and conventions used herein generally follow S.P. Parker, Ed., McGraw-Hill Dictionary of Chemical Terms (1984) McGraw-Hill Book Company, New York; and Eliel, E. and Wilen, S., “Stereochemistry of Organic Compounds”, John Wiley & Sons, Inc., New York, 1994. The compounds of the invention may contain asymmetric or chiral centers and, therefore, may exist in different stereoisomeric forms. All stereoisomeric forms of the compounds of the invention, for example, but not limited to, diastereomers, enantiomers and atropisomers, as well as mixtures thereof, for example, racemic mixtures are intended to form part of the present invention. Many organic compounds exist in optically active forms, i.e., they have the ability to rotate the plane of plane-polarized light. When describing an optically active compound, the prefixes D and L, or R and S are used to indicate the absolute configuration about the chiral center(s) of the molecule. The prefixes d and l or (+) and (-) are used to specify the sign of rotation of plane-polarized light by the compound, where (-) or l means that the compound is levorotatory. A compound prefixed with (+) or d is dextrorotatory. For a given chemical structure, these stereoisomers are identical except that they are mirror images of each other. Certain stereoisomers are also sometimes called enantiomers, and mixtures of such isomers are often called racemic mixtures. A 50:50 mixture of enantiomers is called a racemic mixture or racemate (as defined below) and may occur when there is no stereoselectivity or stereospecificity in a chemical reaction or process.

[0040] The terms “racemic mixture” and “racemate” refer to an equimolar mixture of two enantiomeric species and are optically inactive.

[0041] The "solvent" described in this specification can include water or an organic solvent. Examples of organic solvents include the following: hydrocarbons such as toluene, xylene, hexane, and heptane; chlorinated solvents such as methylene chloride, chloroform, and dichloroethane; ethers such as diethyl ether, tetrahydrofuran, and dibutyl ether; ketones such as acetone and 2-butanone; esters such as ethyl acetate and butyl acetate; nitriles such as acetonitrile; alcohols such as methanol, ethanol, and tert-butanol; and aprotic polar solvents such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), and dimethyl sulfoxide (DMSO). The solvents can be used alone or mixed to provide a "solvent system" for use of two or more of them.

[0042] A nonpolar solvent is a liquid or solvent that has a low or no dipole moment and no partial positive or negative charges. Generally, there is a small difference in electronegativity between atoms in the solvent molecules and it has a low relative permittivity. Nonpolar solvents cannot effectively dissolve polar compounds. Examples of nonpolar solvents include alkanes, toluene, chloroform, and diethyl ether.

[0043] The terms "repeating unit", "iterative unit", or "block" as used in this specification refer to a portion of a polymer that repeats. A repeating unit can include one or more repeating units labeled, for example, as repeating unit A, repeating unit B, repeating unit C, etc. Repeating units A-C can be joined together, for example, by covalent bonds to form combined repeating units. Monomers or combinations of one or more different monomers can combine to form the (combined) repeating units of a polymer or copolymer.

[0044] The term "molecular weight" for the copolymers disclosed in this specification refers to the number average molecular weight (M n ). The corresponding weight average molecular weight (M w) can be determined by methods known to those skilled in the art (e.g., by calculation) from other disclosed parameters.

[0045] The copolymers disclosed herein can include random or block copolymers. In various embodiments, the ends of the polymer or copolymer (i.e., the initiator end or terminus) are low molecular weight moieties (e.g., less than 500 Da), such as H, OH, OOH, CH2OH, CN, NH2, or a hydrocarbon, such as an alkyl (e.g., the butyl or 2-cyanoprop-2-yl moieties at the initiator and terminus), an alkene or alkyne, or a moiety as a result of an elimination reaction at the first and / or last repeating unit in the copolymer.

[0046] Embodiments of the technology 1. A polymer comprising Formula I:

Chemical formula

[0047] 2. The polymer of Embodiment 1, wherein R 1 and R 2 are each independently methyl, ethyl, propyl, butyl, pentyl, hexyl, or heptyl, and R 3 is H, methyl, ethyl, propyl, or butyl, pentyl, hexyl, or heptyl. In some embodiments, propyl is n-propyl or isopropyl. In some embodiments, butyl is n-butyl, isobutyl, or tert-butyl. In some embodiments, pentyl is n-pentyl or isopentyl.

[0048] 3. The polymer of Embodiment 1 or 2, wherein p is 0, 1, or 2.

[0049] In various embodiments, the repeating unit (x unit) represented by x is at least 60% isotactic or at least 60% syndiotactic. In some embodiments, the % isotactic repeating x units are about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, about 95%, about 99%. In some embodiments, the % syndiotactic repeating x units are about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, about 95%, about 99%.

[0050] 4. The polymer of any one of Embodiments 1-3, wherein x is from about 20 to about 500,000. In some embodiments, x is 1-10, 10-100, about 100, about 1,000, about 10,000, about 50,000, about 100,000, about 200,000, about 300,000, about 400,000, about 500,000, about 600,000, about 700,000, about 800,000, about 900,000, or about 1,000,000.

[0051] 5. The polymer of any one of Embodiments 1-5, wherein the polymer is a copolymer comprising Formula II: [Chemical formula] In the formula, G 1 and G 2 are each independently O, S, or NR b where R b is H or -(C1-C 12 ) alkyl; R 4 and R 5 are each independently -(C1-C 12 ) alkyl, -(C2-C 12 ) alkenyl, -(C2-C 12 ) alkynyl, aryl or heteroaryl; or R 4 and R 5 together with the carbon atom to which they are attached form (C3-C 16 ) cycloalkyl; R 6 is H, -(C1-C 12 ) alkyl, -(C2-C 12 ) alkenyl, -(C2-C 12 ) alkynyl, aryl or heteroaryl; q is 0, 1, 2, 3, 4, or 5; y is 10 or more; and z is 1 or more; The structure of the repeating unit represented by x and y in Formula II is different (e.g., not the same), polymer. For example, G 2 , R 4 , R 5 , R 6 , and at least one variable of Formula II selected from q is different from the corresponding variable of Formula II (or Formula I) selected from G 1 , R 1 , R 2 , R 3 , and p, so that the structure of the monomer represented by y in Formula II is different from the structure of the monomer represented by x in Formula II (or Formula I).

[0052] 6. The copolymer of Embodiment 5, wherein R 4 and R 5 are methyl, ethyl, propyl, or butyl, pentyl, hexyl, or heptyl, and R 6 is hydrogen, methyl, ethyl, propyl, butyl, pentyl, hexyl, or heptyl. In some embodiments, propyl is n-propyl or isopropyl. In some embodiments, butyl is n-butyl, isobutyl, or tert-butyl. In some embodiments, pentyl is n-pentyl or isopentyl.

[0053] In various embodiments, the repeating unit (y unit) represented by y is at least 60% isotactic or at least 60% syndiotactic. In some embodiments, the % isotactic repeating y units are about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, about 95%, about 99%. In some embodiments, the % syndiotactic repeating y units are about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, about 95%, about 99%.

[0054] 7. The copolymer of Embodiment 5 or 6, wherein y is from about 20 to about 500,000 and z is from about 10 to about 100,000. In some embodiments, y is 1-10, 10-100, about 100, about 1,000, about 10,000, about 50,000, about 100,000, about 200,000, about 300,000, about 400,000, about 500,000, about 600,000, about 700,000, about 800,000, about 900,000, or about 1,000,000. In some embodiments, z is from about 1 to about 500,000. In some embodiments, z is about 10, about 100, about 1,000, about 10,000, about 50,000, about 100,000, about 200,000, about 300,000, about 400,000, or about 500,000.

[0055] 8. A method for forming a polymer of any one of Embodiments 1-7, comprising ring-opening polymerization (ROP) of a monomer of Formula III:

Chemical formula

[0056] 9. The method of Embodiment 8, wherein the catalyst is {1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)phosphoranylidene-amino]2λ 5 ,4λ 5 -cathenadi(phosphazene)}( t Bu-P4), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), titanium tert-butoxide, or a lanthanide.

[0057] In some embodiments, the initiator is an alcohol, aliphatic alcohol, aryl alcohol, diol, polyol, benzyl alcohol (BnOH), methanol, ethanol, propanol, isopropanol, butanol, amine, or thiol.

[0058] 10. A method for forming a polymer of any one of Embodiments 1-7, comprising step-growth polycondensation (SGP) of a monomer of Formula IV:

Chemical formula

[0059] 11. The method of embodiment 10, wherein the catalyst is a Lewis acid. In some embodiments, the Lewis acid is BF3·OEt2, B(C6F5)3, or Ti(O n Bu)4.

[0060] In various embodiments, the chemical reactions described herein include cooling or warming (heating) the reactants. In some embodiments, the reaction is hydrolysis, lactonization, ROP, or SGP, and the reaction is promoted.

[0061] In some embodiments, the warming or heating is carried out at a temperature lower than or higher than room temperature, such as about -80 °C, about -70 °C, about -60 °C, about -50 °C, about -40 °C, about -30 °C, about -20 °C, about -10 °C, about 0 °C, about 20 °C, about 30 °C, about 40 °C, about 50 °C, about 60 °C, about 70 °C, about 80 °C, about 90 °C, about 100 °C, about 125 °C, about 150 °C, about 175 °C, about 200 °C, about 210 °C, or about 250 °C.

[0062] 12. The method of any one of embodiments 8 - 11, wherein the monomer of formula III or formula IV is optically active. In some embodiments, the carbon atom bonded to R of formula III or formula IV has an (S)-configuration or an (R)-configuration. 3 has an (S)-configuration or an (R)-configuration.

[0063] 13. A method for depolymerizing a polymer or copolymer of any one of embodiments 1 - 9, comprising contacting the polymer with a base, and the polymer is depolymerized into its constituent monomers. In some embodiments, the conversion to the constituent monomers is about 20 wt% or more based on the initial weight of the polymer or copolymer. In some embodiments, the wt% conversion is about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, about 95%, or about 99%.

[0064] In some embodiments, the base is an aqueous base. In some embodiments, the base is an alkali base. In some embodiments, the base is sodium hydroxide or lithium hydroxide.

[0065] In some embodiments, the base is an inorganic base. In some embodiments, the inorganic base is an alkoxide such as sodium hydroxide, an oxide such as lithium oxide, a hydride such as potassium hydride, or a carbonate such as potassium carbonate. In some embodiments, the inorganic base can be replaced with a salt such as lithium chloride.

[0066] In some embodiments, depolymerizing includes heating to promote the depolymerization reaction. In some embodiments, the heating is carried out at a temperature higher than room temperature, about 50 °C, about 100 °C, about 150 °C, about 200 °C, about 210 °C, about 220 °C, about 230 °C, about 240 °C, about 250 °C, about 260 °C, about 280 °C, or about 300 °C.

[0067] 14. The method of embodiment 13, wherein the constituent monomer is represented by formula III:

Chemical formula

[0068] 15. The method of embodiment 13, wherein the constituent monomer is represented by formula IV:

Chemical formula

[0069] Embodiments of the polymerization process: ROP is typically carried out in the absence of a solvent (i.e., bulk polymerization) or in solution (e.g., in toluene, methylene chloride) at room temperature in the presence of a catalyst. Suitable ROP catalysts can also be grouped into four classes: lanthanides (also called rare earth metals), transition metals, main groups, and organic catalysts. They can be used alone or in combination with a protic initiator, such as an alcohol.

[0070] Examples of lanthanide (Ln) catalysts include: f-block metal homoleptic and heteroleptic amides, alkoxides, and alkyl complexes, such as Ln(NR2)3, Ln(OR)3, LnR3, Ln(NR2) x (OR) 3-x (x = 1, 2), or discrete LLn-X complexes [L = dianionic ligand, bridged or unbridged, polydentate organic ligand, such as tetradentate amino-alkoxy-bis(phenoxy); X = OR, NR2, SR, R, where R is alkyl, aryl, substituted alkyl, or substituted aryl]. Examples of transition metal catalysts include d-block metal discrete molecular complexes, L n M-X (X = OR, NR2, SR, R), where R is alkyl, aryl, substituted alkyl, or substituted aryl, and the complex can either directly initiate polymerization or react with an initiator to generate active species. The metal center is typically protected by one or more bulky monodentate or polydentate organic ligands, such as tetradentate amino-alkoxy-bis(phenoxy) ligands. Examples of main group catalysts include s and p-block metal (groups 1, 2, 12, and 13) metal homoleptic and heteroleptic complexes, such as RLi, MgR2, LM-X (M = Mg, Zn, X = R, OR, SR, NR2), Al(OR)3, and L2AlOR, where R is alkyl, aryl, substituted alkyl, or substituted aryl.

[0071] The organic catalyst is a strong organic base or nucleophile, such as 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), which can directly initiate polymerization or activate a protic initiator to promote polymerization. Basic catalysts can be grouped into two general classes: strong organic bases and inorganic bases. They can be used alone, but are often used in combination with protic initiators. Examples of organic catalysts include: strong organic bases, especially polyaminophosphazene superbase, such as TBD, 1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)-phosphoranylideneamino]-2λ 5 ,4λ 5 -cathenadi(phosphazene)( t Bu-P4); guanidine, such as proazaphosphatrane (cyclic azaphosphine), and cyclopropenimine superbase, such as the following catalysts. Anionic versions of organic catalyst / initiators, such as urea or thiourea anions, can also be used.

[0072] Examples of inorganic bases include strong bases of alkali and alkaline earth compounds, such as ROM (R = Me, Et, i Pr, n Bu, t Bu; M = K, Na, Li), (RO)2M (R = Me, Et, i Pr, n Bu, t Bu; M = Mg or Ca), MH (M = K, Na, Li), MOH (M = K, Na, Li), and R2NM (R = alkyl; M = K, Na, Li), where R is alkyl, aryl, substituted alkyl, or substituted aryl.

[0073] Typical initiators include: protic compounds, such as alcohols (ROH), diols (HO-R-OH), polyols (compounds containing more than two OH groups), or sugars; amines (RNH2, R2NH); thiols (RSH) (where R is alkyl, aryl, substituted alkyl, or substituted aryl), or deprotonated monomers.

[0074] The polycondensation reaction is typically carried out in the absence of solvent, at high temperature and under vacuum, optionally in one or more steps (gradually increasing the temperature and vacuum), in the presence of a catalyst. Typical catalysts are Sn(Oct)2, Ti(O n Bu)4, and the metal-based and organic catalysts outlined above.

[0075] Embodiments of the depolymerization process: The above catalysts and other compounds for polymerization can also be used as catalysts for depolymerization at high temperatures (typically 100 - 250 °C) at which the monomers are recovered by distillation, sublimation, etc. For example, the catalyst can be an inorganic base such as M I (OH) (M = Na, K) and M II (OH)2 (M = Mg, Ca), an inorganic Lewis acid such as ZnCl2, an organic acid such as para-toluenesulfonic acid (p-TsOH), camphorsulfonic acid (CSA), DOWEX 50W-X8 resin - hydrogen form, and an organic base / acid adduct (salt).

[0076] Results and Discussion Before achieving widespread commercial introduction and application, three long-standing challenges that PHA faces and that must be addressed are as described below. First, current PHAs are inherently thermally unstable and have a relatively low decomposition temperature (T d , temperature at 5% weight loss) of about 250 °C. Due to the presence of α-hydrogen, facile cis elimination is promoted via a six-membered transition state, forming internal alkenes and carboxylic acids (Chart 2), and causing a large continuous drop in shear viscosity under melt processing conditions (e.g., the shear viscosity (shear rate r n ) of it-P3HB (M . = 1 s -1 ) in the molten state at 180 °C showed a large continuous drop in viscosity over 30 minutes due to rapid decomposition). Second, the mechanical properties of PHA are generally inferior to those of commonly used plastics; for example, it-P3HB is very brittle and the elongation at break (e b ) is about 4%, which is that of it-PP (eb Much lower than >400%). Thirdly, synthetic PHAs lack the desired closed-loop chemical recyclability. For example, the acid-catalyzed depolymerization of P3HB leads to the formation of cyclic oligomers (which can only be repolymerized to oligomers of about 5 kDa), rather than its readily polymerizable monomer β-BL or 8DL Me instead of the formation of cyclic oligomers (which can only be repolymerized to oligomers of about 5 kDa), while in base-catalyzed depolymerization, crotonic acid is obtained. Biodegradability in the ambient environment is a clear advantage of PHAs for protecting our environment when they are placed there, but they should not be landfilled as deposits of degradation intermediates, as the final CO2 would cause unintended environmental and climate problems. In addition, the inability to recover PHA building blocks represents a significant loss of energy and resources still given in used PHAs. Therefore, it is important to endow biodegradable PHAs with chemical recyclability towards the ultimate goal of establishing a circular plastic economy. n Chart 2. Three problems faced by current PHAs (especially P3HB): (1) not melt-processable (T about 250 °C); (2) mechanically brittle (e in it-P3HB d about 4%); (3) not chemically recyclable (to monomers). b about 4%); (3) not chemically recyclable (to monomers). [Chemical formula]

[0077] Strategies for suppressing thermal decomposition and achieving melt processability. A straightforward strategy for suppressing thermal decomposition by cis elimination enabled by α-hydrogens in conventional PHAs is to replace both α-hydrogens with alkyl or aryl groups. Substituting only one of the α-hydrogens in parent P3HB with a methyl group results in the obtained poly(3-hydroxy-2-methylbutyrate), which actually shows improved thermal stability, but only by about 20 °C compared to the P3HB used in that study. However, when both α-hydrogens are substituted, poly(3-hydroxy-2,2-dimethylbutyrate) [P3H(Me)2B] is obtained, and its thermal and mechanical properties are significantly enhanced: P3H(Me)2B is semicrystalline and has a high T m in the range of 167 °C to 243 °C, and is also thermally stable and has a high T d in the range of 314 °C to 335 °C (i.e., an enhancement of 56 °C to 85 °C), is not only melt processable but also ductile and has an e b > 200% (Chart 3 and Figure 1). Moreover, P3H(Me)2B can be chemically recycled back to its starting monomer, α,α-dimethyl-β-butyrolactone [(Me)2BL] (used in chain-growth ROP), or 3-hydroxy-2,2-dimethylbutyric acid [3H(Me)2BA] (used in step-growth polycondensation (SGP)), thus achieving closed-loop chemical recyclability (Chart 3). Poly(3-hydroxy-2,2-dimethylpropionate), P3H(Me)2P (M n = 162 kDa, prepared from ROP of α,α-dimethyl-β-propionolactone, Table 1) also shows high T d (up to 373 °C) and T m (up to 232 °C) values, but it is very brittle and has an e b < 4%. The ROP of (Me)2BL (prepared from highly reactive dimethylketene and acetaldehyde) was attempted, but only oligomeric species (M n = 2.9 kDa) were obtained in a 35% yield after 10 days. The method reported herein enables the rapid synthesis of high molar mass P3H(Me)2B in quantitative yields, with M n up to 554 kDa and T mis up to a maximum of 243 °C, T d is up to a maximum of 335 °C. Overall, such thermal robustness of α,α-dimethylated PHA enables their melt processability, and such PHAs exhibit the desired chemical recyclability by closing the monomer-polymer-monomer loop. m Despite the further enhanced T **Table 1** Chart 3. The redesigned α,α-disubstituted PHA, P3H(R)2B lacks α-hydrogen and synergistically combines three desirable properties. Chemical recyclability was achieved by closing both the hydroxy acid SGP, base-catalyzed hydrolysis and lactone ROP, and base-catalyzed chain dissociation loop for P3H(Me)2B. **[Chemical Structure]** (R = Me); melt processable (T d up to a maximum of 335 °C); crystalline but ductile (e b > 200%); recyclable (to monomer)

[0078] Double closed loops for achieving chemical recyclability. α,α-Dimethylated PHAs can be synthesized either via the SGP of hydroxy acid (HA) 3H(Me)2BA or the ROP of lactone (Me)2BL (Chart 3). HA, 3H(Me)2BA is obtained in 88% yield in one step from acetaldehyde (produced on an industrial large scale or can be of biological origin) and isobutyric acid, a commercially available chemical (biologically obtainable from glucose) (see materials and methods for its synthesis on a 362 g scale from methyl isobutyrate), while lactone (Me)2BL was prepared via one-step lactonization of HA [e.g., 232 g of (Me)2BL was prepared in 93% yield]. The diethyl derivative (Et)2BL was synthesized using the same lactonization method. In particular, HA and lactone monomers can be prepared or recovered in good to quantitative yields from the selective depolymerization of PHAs (see below).

[0079] First, the ROP of (Me)2BL (as a racemate) was investigated by using different organic base catalysts and reaction conditions, and the ROP was optimized at 70 °C in tetrahydrofuran (THF) using the superbase catalyst t Bu-P4 {1-tert-butyl-4,4,4-tris(dimethyl-amino)-2,2-bis[tris(dimethylamino)phosphoranylidene-amino]2λ 5 ,4λ 5 -cathenadi(phosphazene)} (Table 1). Thus, in THF, t in the ROP using Bu-P4 as a catalyst and benzyl alcohol (BnOH) as an initiator,

Number

[0080]

Number

[0081] We envisioned another synergistic benefit of α,α-disubstitution that enables chemical recyclability to α,α-dialkylated PHA by direct depolymerization to its monomers via the gem-dialkylated soap-Ingold effect that promotes ring-closing and stabilization of the strain ring. First, the depolymerization of ROP-derived P3H(Me)2B samples was screened using different base catalysts under vacuum at temperatures below 240 °C (Table 2), and (Me)2BL and the byproduct 2-methyl-2-butene were obtained in different ratios. For example, when the sample was heated with NaOH (5 wt%) at 210 °C under vacuum, the pure (Me)2BL monomer was recovered in 60% isolated yield after the rapid evolution of 2-methyl-2-butene as a gas (which was also recovered and could be reused) (Figure 2B). Next, through consecutive polymerization-depolymerization cycles, we achieved a cyclic monomer-polymer-monomer loop. A second route for establishing closed-loop chemical recycling is via the hydrolytic depolymerization of PHA to HA. For example, the hydrolysis of P3H(Me)2B with aqueous LiOH (Table 3) enabled its depolymerization, and pure 3H(Me)2BA was formed in quantitative yield (Figure 2B). The recovered HA can be converted to (Me)2BL via one-step lactonization (Chart 3). (Me)2BL can also be obtained by the NaOH (2 wt%)-catalyzed depolymerization of oligomeric P3H(Me)2B prepared by the SGP of 3H(Me)2BA catalyzed by BF3·OEt2 (Chart 3). These results show that using the SGP of HA, oligomers or polymers with low to medium molar masses can be obtained, which are effectively depolymerized to form lactones for the rapid ROP to high molar mass PHA.

[0082] (Intrinsic) crystallinity independent of thermal properties and tacticity. Isotactic (R)-P3H(Me)2B shows a particularly high T m of 243 °C (Figure 3A), which is 68 °C higher than (R)-P3HB (T m = 175 °C). Moreover, tThe atactic at-P3H(Me)2B produced by the ROP of rac-(Me)2BL catalyzed by the Bu-P4 achiral organocatalyst is also semicrystalline, with T m Thus, P3H(Me)2B represents a rare example of a polymer that exhibits tacticity-independent crystallinity - the absolute T m It is a class of polymers that are essentially semicrystalline in nature, with T values ​​varying but similar crystallinity regardless of backbone tacticity. To explore the possibility of stereocomplexation, we prepared 1:1 physical blends of enantiomeric it-polymers derived from the enantiomeric monomers, (R)-(Me)2BL and (S)-(Me)2BL, and found that the resulting blends exhibited the same thermal properties as the homochiral polymers, suggesting the absence of stereocomplexation. Furthermore, the iso-rich P3H(Me)2B derived from (Me)2BL with a 70 / 30 (S) / (R) ratio exhibited T values ​​of 189 °C and 204 °C. m values, which lie between those of the it- and at-P3H(Me)2B samples (Figure 3A). [Table 2] [Table 3]

[0083] The two melting peaks observed in all melt-crystallized P3H(Me)2B samples present in the second heating scan (but not in the first) on the differential scanning calorimetry (DSC) thermograms (Figure 3A), which become more pronounced as tacticity decreases, could be due to melting of two different polymorphic forms that crystallized upon cooling from the melt; transformation between two different crystalline forms; or simply melting and recrystallization into the same crystalline form. To clarify this point, three DSC experiments with a second heating scan were performed at different heating rates (2.5, 10, and 20 °C / min). The higher T with increasing heating rate was observed. m Reduced peak area and lower T mThe simultaneous increase in the areas of the peaks suggests that the two peaks are not due to the melting of two different crystalline phases formed by cooling from the melt. Rather, it is shown that melting and recrystallization phenomena occur during heating. To further test this hypothesis, we also collected wide-angle X-ray scattering (WAXS) profiles at different temperatures during heating of the melt-crystallized samples and showed identical profiles between those collected at room temperature before the first heating scan and after crystallization from the melt. From these results, it was confirmed that there are no two different polymorphic forms, and the two melting peaks are suggested to be due to the rapid recrystallization of the melt, involving the melting of the same crystalline form at approximately 167 °C - 169 °C and the formation of more regularly thick crystals melting at a higher temperature of 177 °C - 181 °C. The result that the temperatures of both melting peaks increase with a decrease in the heating rate is further evidence for the occurrence of recrystallization during heating.

[0084] As-synthesized at-P3H(Me)2B(M n = 554 kDa) shows three main diffraction peaks centered at 2θ ≈ 13.1°, 15.7°, and 17.6°, and other small diffraction peaks of much lower intensity at higher 2θ values (Figure 3B), and the calculated crystallinity (χ c ) is 67%. Comparing the as-synthesized it- and at-P3H(Me)2B materials, they show essentially the same main diffraction peaks and have slightly different intensities in the higher 2θ region (Figure 3B); indeed, the crystallinity of at-P3H(Me)2B (χ c = 67%) is higher than that of it-P3H(Me)2B (χ cIt was found to be even higher than that of (58%). To understand the origin of the crystallinity observed in at-P3H(Me)2B, we first performed conformational analysis on chain models of it-P3H(Me)2B with opposite chirality, namely, (R)-P3H(Me)2B and (S)-P3H(Me)2B, and then extended it to a chain model of at-P3H(Me)2B characterized by random sequences of R and S units along the chain. Oriented fibers of at-P3H(Me)2B were obtained by stretching compression-molded samples at about 150 °C and annealing the fibers under tension at 143 °C for 35 minutes. The two-dimensional X-ray fiber diffraction pattern of at-P3H(Me)2B reveals three of the strongest reflections centered at the same 2θ positions polarized at the equator and observed in the powder profile (Figure 3B). These results indicate that the fibers crystallize in the same crystal form as the as-prepared, melt-crystallized samples and that no polymorphic transformation occurs upon stretching. Other reflections are polarized on the first layer line, and even weaker reflections are polarized on the second layer line. From the separation between different layer lines observed in the fiber pattern, a value of 4.66 Å for the chain axis c was determined. This value is consistent with the trans-planar conformation corresponding to one of the energy minima found by conformational analysis. Overall, this study shows that the shape of the at-P3H(Me)2B chains and the protrusions perpendicular to the chain axis are very similar to the ordered model of the R-enantiomer, which explains the fact that, despite the conformational disorder, the at-P3H(Me)2B chains can crystallize and that at-P3H(Me)2B exhibits a WAXS profile similar to that of the pure enantiomer (R)-P3H(Me)2B. In fact, they probably crystallize in the same crystal form (Figure 3B).

[0085] The thermal stability of the PHA samples was analyzed and compared by thermogravimetric analysis (TGA). Despite the significantly different T m values between the it- and at-P3H(Me)2B materials, they each showed similarly high T d values of 322 °C and 335 °C, respectively (Figure 3C). These values are those of it-P3HB dMuch higher than the value (about 250 °C). The molar mass has a substantial effect on T d but has little effect on T m . For example, the T d of P3H(Me)2B increases from 314 °C to 335 °C as M n increases from 179 to 554 kDa, while the T m remains the same.

[0086] Mechanical and rheological properties. Compared with it-P3HB (e b ≈ 4%), the semi-crystalline at-P3H(Me)2B (M n = 554 kDa) shows significantly enhanced ductility (e b = 228 ± 24.6%), a higher elastic modulus (E = 2.94 ± 0.40 GPa), and a higher stress (σ = 31.6 ± 1.8 MPa), and the α,α-dimethyl substitution is also shown to overcome the brittleness of it-P3HB (Figure 4A, Table 4). By introducing the more flexible diethyl group, P3H(Et)2B achieved further enhanced ductility, with e b = 501 ± 36%, while maintaining a high modulus of E = 1.22 ± 0.27 GPa (Figure 4A, Table 5). The Me / Et random copolymer P3H(Me / Et)2B synthesized by copolymerizing (Me)2BL and (Et)2BL shows even higher fracture strain (e b = 517 ± 35%) and stress (σ = 34.1 ± 2.1 MPa) than P3H(Et)2B, which was superior to both high-density PE (HDPE) and it-PP (Figure 4A, Table 6). Also, the mechanical properties of the P3H(Me)2B material (M n = 332 kDa) prepared from a large-scale (115 g) run were further improved compared to the polymer prepared on a 5 g scale, showing a higher elastic modulus (E = 3.08 ± 0.18 GPa), stress (σ = 33.9 ± 2.1 MPa), and ductility (e b = 252 ± 30.1%) (Figure 4B, Table 7). These results further demonstrate the scalability of the polymerization for producing high-performance P3H(Me)2B.

Table 4

Table 5

Table 6

Table 7

[0087] The third synergistic effect, which removes two cis-eliminable α-protons by α,α-dialkyl substitution and enhances the thermal stability of PHA in the solid state, is the realization of melt processability. To test the possibility of melt processing, we monitored the shear viscosity change over time for P3H(Me)2B at temperatures above T m in continuous flow mode at a shear rate of 1 s -1 . For reference, it-P3HB (M n = 111 kDa, T m = 170 °C) was also subjected to the same shear viscosity test in the molten state (180 °C). The shear viscosity for P3H(Me)B (M = 79 kDa) remained constant, showing no significant decrease over a 30-minute time frame at temperatures up to 210 °C (well above the corresponding melting temperature) (Figure 4C). Furthermore, P3H(Me)2B samples with a wide molar mass range, M n = 79 - 554 kDa, behaved similarly over the same period at 190 °C, showing stable shear viscosity (Figure 1), further demonstrating the melt processability. In contrast, it-P3HB, known for its rapid decomposition in the molten state, showed a substantial attenuation of its shear viscosity from 17 to 4 Pa·s (76%) after 30 minutes at 180 °C (Figure 4C). P3H(Me)2B (M n = 79 kDa) showed a small but significant decrease in its shear viscosity at 220 °C, indicating its upper limit melting processing temperature (Figure 4C). Overall, the shear viscosity studies presented here solidify the effectiveness of the strategy of removing α-protons in PHA repeat units to enhance their thermal stability and enable their melt processability.

[0088] Many studies have focused on the fine-tuning of the thermal and mechanical properties of PHAs by varying the backbone composition and stereochemistry, as well as the β-pendant group chain length and functionality, and notable success has been achieved in addressing some aspects of the long-standing challenges of PHAs, but the inherent problems of thermal stability and chemical recyclability remain unresolved. The α,α-dialkylated PHA platform described in this study is designed to address the root cause of PHA thermal instability - the facile cis-elimination process during thermal decomposition involving the α-hydrogen in the repeating unit - by replacing both α-hydrogens with alkyl groups. This simple α,α-dialkyl substitution substantially enhances thermal stability, making the PHA melt-processable and, moreover, synergistically confers upon the PHA high ductility and toughness comparable to, or exceeding, that of it-PP and HDPE. Furthermore, this platform offers ease of synthesis, since, in contrast to the parent P3HB, α,α-dimethylated P3H(Me)2B is always semicrystalline regardless of its tacticity due to its intrinsic crystallinity that is independent of its tacticity, thereby enabling the synthesis of semicrystalline high-performance PHAs without the need to control the polymerization stereochemistry, which often requires specifically designed chiral catalysts. Notably, this design achieves chemical recyclability by closing both the ROP and SGP loops in PHA production and chemical recycling to monomers, thereby solving the three challenges currently faced by current PHAs.

[0089] The following examples are intended to illustrate the above invention and should not be construed as limiting its scope. Those skilled in the art will readily recognize that the examples suggest many other ways in which the invention could be practiced. It is to be understood that many changes and modifications can be made within the scope of the invention.

[0090] Examples Example 1. Materials and Methods All syntheses and manipulations of air- and moisture-sensitive materials were carried out in a dual manifold Schlenk line on a flame-dried Schlenk-type glassware product, on a high-vacuum line, or in an inert gas (Ar or N2)-filled glove box. HPLC grade organic solvents were first sparged extensively with nitrogen during the filling of a 20 L solvent reservoir, then passed through activated alumina (for tetrahydrofuran (THF) and dichloromethane (DCM)), and subsequently dried by passing through a Q-5 supported copper catalyst (for toluene and hexane) stainless steel column. For THF used in the polymerization reaction, HPLC grade THF was degassed and dried over sodium and benzophenone for 12 h, followed by vacuum distillation.

[0091] 1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD) was purchased from TCI Chemical Co., t Bu-P4 (0.8 M hexane solution) was purchased from Sigma-Aldrich Chemical Co.; both catalysts were used as received. 3-Hydroxy-2,2-dimethylpropionic acid [3H(Me)2PA] purchased from Oakwood Chemical Co. was purified by sublimation. Sodium hydroxide purchased from Fisher Scientific Co. and boron trifluoride diethyl etherate purchased from TCI Chemical Co. were used directly in the glove box. Benzyl alcohol (BnOH) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) were purchased from Fisher Scientific Co. and Sigma-Aldrich Chemical Co., respectively, purified by distillation over CaH2, and stored over activated Davison 4 Å molecular sieves. Isotactic polypropylene (it-PP, 5 mm gran., M n= 97.0 kDa) and high-density polyethylene (HDPE, 2 - 4 mm gran., MFI = 7.6) were purchased from Sigma-Aldrich and Goodfellow, respectively. All other chemicals were purchased from their respective commercial sources (isobutyric acid, 2-ethylbutyric acid, 3-chloropivalic acid were purchased from TCI Chemical Co.; (R) / (S)-methyl 3-hydroxybutanoate was purchased from AmBeed Co.; methyl isobutyrate, n-butyllithium (1.6 M), diisopropylamine, benzenesulfonyl chloride, triethylamine, iodomethane, paraformaldehyde were purchased from Oakwood Chemical Co.; acetaldehyde was purchased from Acros Organics Co.) and used as received.

[0092] General polymerization procedure For P3H(Me)2P. The ROP reaction was carried out in a 10 mL Schlenk flask in an inert glove box at ambient temperature (ca. 23 °C). The mixture of base catalyst and alcohol initiator shown in the polymerization table was stirred at ambient temperature for 10 min and then the predetermined amount of lactone monomer (Me)2PL was added. The sealed reactor was taken out of the glove box and stirred at 70 °C. After the desired period, the mixture turned solid, a sample was taken out from the reaction mixture, 1 prepared for 1H NMR analysis and percent monomer conversion data were obtained. The polymerization was then quenched by the addition of CHCl3 (5 mg / mL) containing benzoic acid, dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), and subsequently precipitated 2 - 3 times in methanol. After filtration, the white polymer solid was dried in vacuo at 60 °C until a constant weight was achieved.

[0093] For P3H(R)2B where R = Me, Et. The ROP reaction was carried out in a 10 mL Schlenk flask in an inert glove box or in a 5.5 mL glass reactor at ambient temperature (about 23 °C). A mixture of THF containing the catalyst and initiator (shown in Polymerization Table 1) was stirred at ambient temperature for 10 minutes and then a predetermined amount of lactone monomer (R)2BL was added. The sealed reactor was taken out of the glove box and stirred at 70 °C. After the desired period, the mixture became sticky, an aliquot was taken out from the reaction mixture, 1 prepared for 1H NMR analysis and percent monomer conversion data was obtained. The polymerization was quenched by the addition of chloroform (5 mg / mL) containing benzoic acid, dissolved in DCM [or HFIP for isotactic (S)-P3H(Me)2B], and then precipitated 2 - 3 times in methanol. After filtration, the white polymer solid was vacuum dried at 60 °C until a constant weight was achieved.

[0094] The polycondensation reaction was carried out in a sealed Schlenk flask containing 3H(Me)2BA (660 mg, 5 mmol) and BF3.OEt2 (62 μL, 0.5 mmol). The flask was stirred at 160 °C for 22 hours and then a vacuum of 200 mTorr was applied to the polycondensation setup for an additional 2 hours. After cooling to room temperature, the mixture became sticky and an aliquot was 1 taken out from the reaction mixture for 1H NMR analysis. The dark brown mixture was dissolved in DCM / water and extracted with DCM (10 mL × 3). The organic layers were combined, washed with brine, dried over Na2SO4, and then evaporated in vacuo. The resulting oligomer P3H(Me)2B (353 mg, 62% yield) was used directly for the depolymerization to (Me)2BL.

[0095] Chemical recycling of the lactone monomer (Me)2BL. In a separate depolymerization experiment, NaOH or another catalyst shown in Table 2 (5.7 mg, 5 wt%), and P3H(Me)2B obtained by ROP of (Me)2BL (0.114 g, 1 mmol) were added to a 5.5 mL glass reactor equipped with a stir bar. The mixture was heated at 210 °C (oil bath) and distilled using a receiving flask cooled under vacuum and liquid nitrogen. After the powder disappeared, two methods were applied to analyze the depolymerization product. In the first method, when the temperature of the receiving flask was still low, CDCl3 was added from the distilled head to the receiving flask, and then the ratio of the recycled monomer (Me)2PL and 2-methyl-2-butene was 1 analyzed by 1H NMR. In the second method, the vacuum was stopped and the cold bath was removed. As the flask was warmed to room temperature, a colorless liquid was received (2-methyl-2-butene became a gas), which was 1 confirmed by 1H NMR analysis to be the recycled pure monomer (Me)2BL (60% isolated yield). When the oligomer P3H(Me)2B obtained from polycondensation was used for depolymerization, the recycled monomer (Me)2BL (48% yield) was obtained by reaction with NaOH (2 wt%) at 190 °C.

[0096] Chemical recycling of the HA monomer 3H(Me)2BA. In a separate depolymerization experiment, a solution of P3H(Me)2B (100 mg) and aqueous LiOH (384 mg, 4 mL H2O) in THF / MeOH (4 / 0.5 mL) was reacted in a Schlenk flask at 100 °C for 72 h as shown in Table 3. Aqueous HCl solution (2 N) was added to adjust the pH value to 1, followed by extraction with EtOAc (15 mL × 3). The organic phase was washed with brine, dried over Na2SO4, and then evaporated in vacuo to obtain the recycled, pure 3H(Me)2BA in 99% isolated yield.

[0097] Equipment and characterization Nuclear magnetic resonance (NMR) analysis. NMR spectra were recorded at 298 K on a Varian Inova or Bruker AV-III 400 MHz spectrometer (400 MHz, 1 H; 100 MHz, 13 C). Chemical shifts (δ) are reported in ppm and solvent resonances are used as internal standards (chloroform-d1, 1 7.26 ppm for 1H-NMR and 13 77.0 ppm for 13C-NMR; hexafluoroisopropanol (HFIP)-d2, 1 4.41, 4.86 ppm for 1H-NMR and ppm 13 68.07, 120.66 for 13C-NMR). Signals are reported as integral, multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet or unresolved, br = broad signal), coupling constant(s) in Hz (multiple possible), and assignment.

[0098]

Number

Number

[0099] Wide-angle X-ray scattering (WAXS). The WAXS profiles of the as-synthesized samples were collected using Ni-filtered Cu Kα radiation (λ = 1.5418 Å) with a Bruker D8 Discover DaVinci diffractometer for measurements at room temperature and an Empyrean diffractometer by Malvern Panalytical for measurements at elevated temperatures. Both were operated in reflection mode with a continuous scan of the 2θ angle and a scan rate of 0.02° / s. The degree of crystallinity (χ c ) was determined from the WAXS profiles as the ratio between the crystalline diffraction area (Ac) and the area of the total diffraction profile (A t = A c + A am ). Here, Aam is the amorphous scattering area, and χ c = (Ac / At) × 100. The area of the crystalline phase A c was evaluated by subtracting the background baseline and the scattering halo of the amorphous phase (A am ) from the total diffraction profile. The diffraction profile of the amorphous phase was obtained from the diffraction profile of the melt collected after heating the sample above its melting temperature.

[0100] The two-dimensional WAXS patterns of the fibers of at-P3H(Me)2B were recorded using Ni-filtered Cu Kα radiation (λ = 1.5418 Å) on a BAS-MS imaging plate (FUJIFILM) using a cylindrical camera and processed using a digital imaging reader, a Perkin Elmer Cyclone Plus (storage phosphor system).

[0101] Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The melting transition (T m ) and glass transition (T g ) temperatures were measured by DSC on an Auto Q20, TA Instrument. All T m and T g values were obtained from the second scan unless otherwise noted. The heating and cooling rates were 10 °C / min unless otherwise noted. The decomposition temperature (T d ) and the maximum rate decomposition temperature (Tmax ) was measured by TGA on a Q50 TGA analyzer, TA Instruments. The polymer sample was heated from ambient temperature to 700 °C at a heating rate of 10 °C / min. T max values were obtained from the derivative (wt% / °C) versus temperature (°C) plot.

[0102] Mechanical analysis. Tensile stress / strain tests were performed on dog-bone shaped test specimens (ASTM D638 standard; type V) prepared by compression molding using an Instron 5966 universal test system (10 kN load cell) and, unless otherwise noted, a Carver Bench Top Laboratory Press (model 4386) equipped with a two-column hydraulic unit (Carver, model 3912, maximum force 24000 psi). The isolated polymer material was loaded between anti-adhesion Teflon paper sheets into a stainless steel mold with in-house made insert dimensions 30×73.5×0.38 mm and compressed between two 6’’×6’’ electrically heated steel platens at a clamping force of 5000 psi and a temperature 10 °C higher than the individual T of each material. Analytical samples were prepared by compression molding and cut to standard dimensions using an ASTM D638-5-IMP cutting die (Qualitest). The mechanical behavior was averaged for all samples measured for each individual species investigated. The thickness (0.38 ± 0.01 mm), width (3.18 mm), and grip length (26.4 ± 0.2 mm) of the measured dog-bone samples were measured by Bluehill measurement software (Instron) for data normalization. The test specimens were fixed in a screw-clamp type grip frame. Tensile stress and strain were measured at a grip elongation rate of 5.0 mm min m at ambient conditions up to the material break point. -1

[0103] Rheology analysis. Shear viscosity measurements were carried out on a Discovery Series HR-2 hybrid rheometer (TA Instruments) under a nitrogen gas flow (30 psi). The specimen was loaded between two 8 mm steel electrically heated platens (EHP) loading disks. The specimens were trimmed at a predetermined temperature above the Tm of the individual polymers. The measurements were carried out at a gap length of approximately 800 μm and an experimental axial force of approximately 0.2 N. The time-dependent shear viscosity (in the molten state) experiment was carried out in a flow mode with shear rates

Number

[0104] Example 2. Lactone monomer synthesis

Chemistry

[0105] In a different method, 3-hydroxy-2,2-dimethylpropionic acid [3H(Me)2PA] (3.54 g, 30 mmol) was dissolved in dry DCM (300 mL), and then triethylamine (20.8 mL, 150 mmol) was added at -20 °C. After stirring for 15 minutes, benzenesulfonyl chloride (7.7 mL, 60 mmol) was added dropwise at this temperature. The reaction mixture was stirred at -20 °C for 16 hours. Then, the mixture was quenched with ice water and extracted with DCM (150 mL × 3). The combined organic layers were washed with saturated NaHCO3 and brine, dried over Na2SO4, and then evaporated in vacuo (35 °C, vacuum higher than 280 mbar, due to the low b.p. of the product). The crude product was purified by flash column chromatography on silica gel (pentane / acetone = 30:1) and concentrated in vacuo (35 °C, vacuum higher than 280 mbar). After vacuum distillation (about 200 mTorr, 30 - 40 °C), the monomer (Me)2PL (1.9 g, 63% yield) was obtained as a colorless oil. 1 1H NMR (400 MHz, CDCl3): δ 4.06 (s, 2H), 1.39 (s, 6H); 13 13C NMR (101 MHz, CDCl3): δ 175.3, 73.2, 53.2, 20.9.

[0106] [Chemical formula] Synthesis of α,α-dimethyl-β-butyrolactone [(Me)2BL]: To a solution of THF (150 mL) containing diisopropylamine (63 mL, 450 mmol), nn-BuLi (281 mL, 450 mmol, 1.6 M) was added dropwise at 0 °C. After stirring for 1 h, the reaction mixture was cooled to -78 °C and THF (60 mL) containing isobutyric acid (13.9 mL, 150 mmol) was added dropwise. After 0.5 h, the solution was heated at 55 °C for 4 h, and then THF (60 mL) containing acetaldehyde (9.2 mL, 165 mmol) was added at -78 °C. The solution was then warmed gradually to up to room temperature and stirred for 12 h. The mixture was quenched with H2O, aqueous HCl (4 N) was added to adjust the pH value to 1. After extraction with EtOAc (150 mL × 3), the organic phase was washed with brine, dried over Na2SO4, then evaporated in vacuo, and 3-hydroxy-2,2-dimethyl-β-butyric acid [3H(Me)2BA] (17.4 g, 88%) was obtained by simple vacuum distillation (ca. 200 mTorr, 200 - 220 °C). 1 1H NMR (400 MHz, CDCl3): δ 3.91 (q, J = 6.4 Hz, 1H), 1.24 (s, 3H), 1.22 - 1.20 (m, 6H); 13 13C NMR (101 MHz, CDCl3): δ 182.9, 72.4, 46.9, 22.4, 19.4, 17.5.

[0107] The distilled 3H(Me)2BA (13.2 g, 100 mmol) was dissolved in dry DCM (900 mL), and then triethylamine (69.4 mL, 500 mmol) was added at 0 °C. After stirring for 15 min, benzenesulfonyl chloride (25.5 mL, 200 mmol) was added dropwise. The reaction was stirred at 0 °C for 16 h, then the mixture was quenched with ice water and extracted with DCM (150 mL × 3). The combined organic layers were washed with saturated NaHCO3, brine, dried over Na2SO4, then evaporated in vacuo (35 °C, vacuum higher than 280 mbar, due to the low b.p. of the product). After flash column chromatography on silica gel (pentane / acetone = 30:1) and removal of the solvent in vacuo (35 °C, vacuum higher than 280 mbar), the obtained residue was further purified by vacuum distillation (ca. 200 mTorr, 50 - 60 °C) to give the monomer (Me)2BL (10.5 g, 92%) as a colorless oil. 11H NMR (400 MHz, CDCl3): δ 4.40 (q, J = 6.4 Hz, 1H), 1.42 (d, J = 6.4 Hz, 3H), 1.38 (s, 3H), 1.22 (s, 3H); 13 13C NMR (101 MHz, CDCl3): δ 175.4, 79.4, 53.4, 22.2, 16.3, 15.7. [Chemical formula]

[0108] Synthesis of (R)-α,α-dimethyl-β-butyrolactone [(R)-(Me)2BL]: To a solution of THF (120 mL) containing diisopropylamine (28.6 mL, 204.4 mmol), n BuLi (128 mL, 204.4 mmol, 1.6 M) was added dropwise at 0 °C. After 1 hour, the reaction mixture was cooled to -78 °C, and THF (20 mL) containing methyl (2S,3S)-3-hydroxy-2-methylbutanoate (8.2 g, 61.9 mmol) was added dropwise. After 0.5 hour, the solution was warmed and stirred at -20 °C for 1 hour. Subsequently, THF (20 mL) containing iodomethane (38.6 mL, 619 mmol) was added at -78 °C. Then, the solution was stirred at -20 °C until all the substrates were consumed. It was quenched with saturated NH4Cl and extracted with ether (60 mL × 3). The organic phase was washed with brine, dried over Na2SO4, then evaporated in vacuo, and subsequently, methyl (S)-3-hydroxy-2,2-dimethylbutanoate (6.4 g, 71%) was obtained by flash column chromatography (to remove the monosubstituted product). 1 1H NMR (400 MHz, CDCl3): δ 3.84 (q, J = 6.8 Hz, 1H), 3.68 (s, 3H), 2.70 (s, 1H), 1.15 - 1.14 (m, 6H), 1.11 (d, J = 6.4 Hz, 3H); 13 13C NMR (101 MHz, CDCl3): δ 178.2, 72.4, 51.8, 47.1, 22.2, 19.7, 17.6.

[0109] A solution of THF / MeOH (30 / 30 mL) containing methyl (S)-3-hydroxy-2,2-dimethylbutanoate (3.9 g, 26.7 mmol) was added to a solution of THF / MeOH / H₂O (40 / 40 / 30 mL) containing sodium hydroxide (5.3 g NaOH, 134 mmol). The mixture was stirred at 30 °C for 10 h and then evaporated in vacuo. Aqueous HCl solution (4N) was added to adjust the pH value to 1, followed by extraction with EtOAc (60 mL × 3). The organic phase was washed with brine, dried over Na₂SO₄, then evaporated in vacuo, and subsequently (S)-3-hydroxy-2,2-dimethyl-β-butyric acid [(S)-3H(Me)₂BA] was obtained by simple vacuum distillation (ca. 200 mTorr, 200 - 220 °C).

[0110] (S)-3H(Me)₂BA was dissolved in dry DCM (150 mL), then triethylamine (18.5 mL, 133.5 mmol) was added at 0 °C. After stirring for 15 min, benzenesulfonyl chloride (6.8 mL, 53.4 mmol) was added dropwise. After 16 h at 0 °C, the mixture was quenched with ice water and extracted with DCM (80 mL × 3). The combined organic layers were washed with saturated NaHCO₃, brine, dried over Na₂SO₄, then evaporated in vacuo (35 °C, above 280 mbar, due to the low b.p. of the product). After flash column chromatography on silica gel (pentane / acetone = 30:1) and removal of the solvent in vacuo (vacuum higher than 280 mbar at 35 °C), the obtained residue was purified by vacuum distillation (ca. 200 mTorr, 50 - 60 °C) to give the monomer (R)-(Me)₂BL as a colorless oil (2.2 g, 71% for 2 steps). [α] D 26.2 =-38.1 (c = 0.35, CHCl₃); 1 ¹H NMR (400 MHz, CDCl₃): δ 4.42 (q, J = 6.4 Hz, 1H), 1.44 (d, J = 6.4 Hz, 3H), 1.40 (s, 3H), 1.24 (s, 3H).

Chemical formula

[0111] (S)-α,α-dimethyl-β-butyrolactone [(S)-(Me)2BL] synthesis: To a solution of THF (200 mL) containing diisopropylamine (35 mL, 250 mmol), n BuLi (156 mL, 250 mmol, 1.6 M) was added dropwise at 0 °C. After 1 hour, the reaction mixture was cooled to -78 °C (dry ice / acetone), and THF (20 mL) containing methyl (2R,3R)-3-hydroxy-2-methylbutanoate (10 g, 75.8 mmol) was added dropwise. After 0.5 hour, the solution was warmed and stirred at -20 °C for 1 hour, and then THF (30 mL) containing iodomethane (47 mL, 758 mmol) was added at -78 °C. Thereafter, the solution was stirred at -20 °C until all the substrates disappeared. It was quenched with saturated NH4Cl and extracted with ether (60 mL × 3). The organic phase was washed with brine, dried over Na2SO4, then evaporated in vacuo, and subsequently, methyl (R)-3-hydroxy-2,2-dimethylbutanoate (6.2 g, 62%) was obtained by flash column chromatography (to remove the monosubstituted product).

[0112] To a solution of THF / MeOH (30 / 30 mL) containing methyl (R)-3-hydroxy-2,2-dimethylbutanoate (5.8 g, 40 mmol), a solution of THF / MeOH / H2O (40 / 40 / 30 mL) containing sodium hydroxide (8 g NaOH, 200 mmol) was added. The mixture was stirred at 30 °C for 10 hours and then evaporated in vacuo. Aqueous HCl solution (4 N) was added to adjust the pH value to 1, and then it was extracted with EtOAc (60 mL × 3). The organic phase was washed with brine, dried over Na2SO4, then evaporated in vacuo, and subsequently, crude (R)-3-hydroxy-2,2-dimethyl-β-butyric acid [(R)-3H(Me)2BA] was obtained by simple vacuum distillation (about 200 mTorr, 200 - 220 °C).

[0113] (R)-3H(Me)2BA was dissolved in dry DCM (200 mL), and then triethylamine (27.7 mL, 200 mmol) was added at 0 °C. After stirring for 15 minutes, benzenesulfonyl chloride (10.2 mL, 80 mmol) was added dropwise. The reaction mixture was stirred at 0 °C for 16 hours, then quenched with ice water and subsequently extracted with DCM (80 mL × 3). The combined organic layers were washed with saturated NaHCO3 and brine, dried over Na2SO4, and then evaporated in vacuo (35 °C, vacuum higher than 280 mbar, due to the low b.p. of the product). After flash column chromatography on silica gel (pentane / acetone = 30:1) and removal of the solvent in vacuo (35 °C, vacuum higher than 280 mbar), the resulting residue was further purified by vacuum distillation (about 200 mTorr, 50 - 60 °C) to give the monomer (S)-(Me)2BL (3.6 g, 78% for 2 steps) as a colorless oil. [α] D 26.2 = +40.9 (c = 0.40, CHCl3); 1 1H NMR (400 MHz, CDCl3): δ 4.42 (q, J = 6.4 Hz, 1H), 1.44 (d, J = 6.4 Hz, 3H), 1.41 (s, 3H), 1.24 (s, 3H).

Chemical Structure

[0114] Synthesis of α,α - diethyl - β - butyrolactone [(Et)2BL]: To a solution of THF (300 mL) containing diisopropylamine (84 mL, 600 mmol), nn-BuLi (375 mL, 600 mmol, 1.6 M) was added dropwise at 0 °C. After 1 hour, the reaction mixture was cooled to -78 °C, and THF (100 mL) containing 2-ethylbutyric acid (25.2 mL, 200 mmol) was added dropwise. After 0.5 hour, the solution was warmed to a maximum of 55 °C and stirred at this temperature for 4 hours. Subsequently, THF (100 mL) containing acetaldehyde (12.3 mL, 220 mmol) was added at -78 °C. The mixture was then stirred for 12 hours (gradually returning to room temperature) and then quenched with H2O. Aqueous HCl solution (4 N) was added to adjust the pH value to 1, and then extracted with EtOAc (150 mL × 3). The organic phase was washed with brine, dried over Na2SO4, and then evaporated in vacuo to obtain crude 3-hydroxy-2,2-diethyl-β-butyric acid [3H(Et)2BA], which was used directly without further purification in the next step.

[0115] The crude 3H(Et)2BA was dissolved in dry DCM (1.2 L), and then triethylamine (139 mL, 1000 mmol) was added at 0 °C. After stirring for 15 minutes, benzenesulfonyl chloride (51 mL, 400 mmol) was added dropwise. After stirring at 0 °C for 16 hours, the mixture was quenched with ice water and extracted with DCM (150 mL × 3). The combined organic layers were washed with saturated NaHCO3 and brine, dried over Na2SO4, and then evaporated in vacuo. After flash column chromatography on silica gel (pentane / acetone = 30:1) and removal of the solvent in vacuo, the resulting residue was further purified by vacuum distillation (about 200 mTorr, 65 - 80 °C) to obtain the monomer (Et)2BL (24.7 g, 87% for 2 steps) as a colorless oil. 1 1H NMR (400 MHz, CDCl3): δ 4.45 (q, J = 6.8 Hz, 1H), 1.87 - 1.73 (m, 3H), 1.69 - 1.60 (m, 1H), 1.45 (d, J = 6.4 Hz, 3H), 1.01 - 0.95 (m, 6H); 13 13C NMR (101 MHz, CDCl3): δ 174.3, 77.1, 60.9, 24.1, 20.0, 15.4, 7.9(2), 7.8(8). [Chemical formula]

[0116] (Me)2BL large-scale synthesis (>200 g). To a solution of THF (500 mL) containing diisopropylamine (515.2 g, 717.5 mL, 5.0 mol) n BuLi (3.18 L, 5.0 mol, 1.6 M) was added dropwise at 0 °C over a period of 6 hours using a cannula, and the mixture was stirred at this temperature for an additional 1 hour. The reaction mixture was then cooled to -78 °C for 15 minutes, and THF (200 mL) containing methyl isobutyrate (MIB, 400 g, 448.9 mL, 3.9 mol) was added dropwise at -78 °C. After stirring for 1 hour at the same temperature, THF (150 mL) containing acetaldehyde (189.7 g, 243.3 mL, 4.3 mmol) was added, and the reaction was stirred at -78 °C for 4 hours ( 1 monitored by 1H NMR). The reaction mixture was quenched with saturated aqueous NH4Cl and extracted with diethyl ether (500 mL × 3). The organic phase was washed with brine, dried over Na2SO4, and then evaporated on a rotary evaporator at 28 - 30 °C (low boiling point) to obtain a crude product (470 g), which was used directly for the hydrolysis step. Methyl-3-hydroxy-2,2-dimethylbutanoate was dissolved in THF / MeOH (100 / 100 mL). Then, THF / MeOH / H2O (200 / 200 / 800 mL) containing sodium hydroxide solution (385.7 g of NaOH, 9.6 mol) was added dropwise to the reaction mixture at 0 °C, and the mixture was stirred at 30 °C for 4 hours. After complete evaporation of the reaction solvents (methanol and THF) in vacuo, aqueous HCl (4 N) was added to adjust the pH value to 1. The reaction mixture was extracted with EtOAc (500 mL × 3), the organic phase was washed with brine, dried over Na2SO4, evaporated on a rotary evaporator, and then vacuum distilled (at about 200 mTorr, 180 - 200 °C) to obtain 3-hydroxy-2,2-dimethyl-β-butyric acid [3H(Me)2BA] as a yellow viscous liquid (362 g, 85%). 1 1H NMR (400 MHz, CDCl3): δ 3.91 (q, J = 6.4 Hz, 1H), 1.24 (s, 3H), 1.22 - 1.20 (m, 6H);13 13C NMR (101 MHz, CDCl3): δ 182.9, 72.4, 46.9, 22.4, 19.4, 17.5.

[0117] The distilled 3H(Me)2BA (2.2 mol, 320.2 g) was dissolved in dry DCM (4 L) using an overhead stirrer (500 rpm), and then triethylamine (1.5 L, 10.9 mol) was added at 0 °C. After stirring for 15 minutes, benzenesulfonyl chloride (561.5 mL, 4.3 mol) was added dropwise. The reaction mixture was stirred at 0 °C for 16 hours, then quenched with ice water and extracted with DCM (300 mL × 3). The combined organic layers were washed with saturated aqueous NaHCO3 and brine, dried over Na2SO4, and the solvent was evaporated on a rotary evaporator at 35 °C. To remove acid impurities, flash column chromatography was performed on silica gel (pentane / acetone = 30:1), and the resulting liquid residue was further purified by vacuum distillation (ca. 200 mTorr, 50 - 60 °C) to obtain the monomer (Me)2BL (232 g, 93%) as a colorless oil. 1 1H NMR (400 MHz, CDCl3): δ 4.40 (q, J = 6.4 Hz, 1H), 1.42 (d, J = 6.4 Hz, 3H), 1.38 (s, 3H), 1.22 (s, 3H); 13 13C NMR (101 MHz, CDCl3): δ 175.4, 79.4, 53.4, 22.2, 16.3, 15.7.

[0118] Example 3. Synthesis and Circular Recycling of Polymers and Copolymers Synthesis of poly(2,2-dimethyl-3-hydroxypropionate), P(2,2-Me2-3HP), from the ROP of pivalolactone. The polymerization of pivalolactone or α,α-dimethyl-β-propiolactone (prepared by either 3-hydroxy pivalic acid + PhSO2Cl + Et3N or 3-chloro pivalic acid + NaOH) was carried out at 70 °C in a 10 mL Schlenk flask using a monomer / catalyst (TBD) / BnOH (benzyl alcohol) ratio of 800 / 1 / 1. The catalyst (TBD, 0.0025 mmol) and initiator (BnOH, 0.0025 mmol) were stirred and mixed in a glove box supplied with an inert gas (N2 or Ar) for 10 minutes. Pivalolactone (2.0 mmol) was rapidly added to this flask via a syringe, and the mixture was stirred at 70 °C. After 15 minutes, the reaction was quenched by the addition of chloroform (5 mg / ml) containing 0.2 mL of benzoic acid, and the quenched polymer was dissolved in 2 mL of (CF3)2CHOH (1,1,1,3,3,3-hexafluoro-2-propanol). The solution was precipitated into 75 mL of cold methanol, filtered, washed with methanol to remove unreacted monomer and catalyst residues, and dried in a vacuum oven at 60 °C until a constant weight was achieved. The polyester obtained as a crystalline hard white solid is insoluble in common organic solvents except (CF3)2CHOH, but was analyzed by DSC (differential scanning calorimetry) to obtain a high T m , ΔH m = 138 J / g, and a T g of 91 °C, and by TGA (thermogravimetric analysis) to obtain a high T d (5% weight loss) of 321 °C. 1 H NMR ((CF3)2CDOD, 25 °C): δ 4.33 (s, 2H), 1.43 (s, 6H). 13 C NMR ((CF3)2CDOD, 25 °C): δ 177.7, 70.8, 43.0, 20.8. For comparison, the NMR data of the lactone monomer are also listed here: 1 H NMR (400 MHz, CDCl3): δ 4.09 (s, 2H), 1.43 (s, 6H).

[0119] Synthesis of poly(2,2-dimethyl-3-hydroxypropionate), P(2,2-Me2-3HP), from polycondensation of 3-hydroxypivalic acid. A flask was loaded with a stir bar, 5.9 g of 3-hydroxypivalic acid, and 170 mg of Ti(O n Bu)4 (1 mol%) and connected to a distillation unit. The flask was first heated at 170 °C for 4 h, then the temperature was increased to 230 °C for 4 h, and finally, the reaction was carried out at this temperature under vacuum for an additional 4 h. After cooling the reaction mixture to room temperature, the product was dissolved in 30 mL of (CF3)2CHOH. The solution was precipitated into 500 mL of cold methanol, filtered, and dried in a vacuum oven at 60 °C until a constant weight was obtained. The resulting hard pale yellow solid was analyzed by DSC and a high T m , ΔH m = 124 J / g, and T g of 96 °C were obtained.

[0120] Chemical recycling of P(2,2-Me2-3HP). This polymer can be recycled back to either pivalolactone monomer or 3-hydroxypivalic acid depending on the catalyst and conditions employed. A flask containing 3.4 g of purified P(2,2-Me2-3HP) and 462 mg of ZnCl2 (10 mol%) was heated at 250 °C in a vacuum distillation setup. The receiving flask was cooled in a -78 °C bath and the distilled monomer was collected. After 12 h of reaction, a colorless liquid was collected and 1 analysis by 1H NMR revealed it to be pure pivalolactone. The inorganic base Mg(OH)2 could also be used for this depolymerization to lactone.

[0121] A flask containing 100 mg of purified P(2,2-Me2-3HP) and THF / MeOH (30 / 0.5 mL) containing 2 mL of NaOH (4N) aq. was heated at 80 °C for 24 h. Then, aqueous HCl (2N) was added to adjust the pH value to 1.0. The mixture was extracted with EtOAc (200 mL × 3), the organic extract was washed with brine, and then dried over anhydrous Na2SO4. After filtering off the drying agent, the solution was evaporated in vacuo to obtain the product, which1 It was shown by 1H NMR analysis to be pure 3-hydroxypivalic acid quantitatively recovered, without column chromatography purification.

[0122] Synthesis of poly(2,2-dimethyl-3-hydroxybutyrate), P(2,2-Me2-3HB). Polymerization of rac-3,3,4-trimethyl-2-oxetanone or rac-α,α-dimethyl-β-butyrolactone [(prepared from (a) methyl isobutyrate, lithium diisopropylamide, acetaldehyde, (b) NaOH, and (c) PhSO2Cl, Et3N] was carried out in a 10 mL Schlenk flask using an organic base and BnOH. The base and BnOH were mixed by stirring for 10 minutes in the glove box, either solvent-free or in THF. The monomer was rapidly added to this flask via syringe, and the mixture was stirred at 70 °C. After a predetermined time, the reaction was quenched by the addition of chloroform (5 mg / ml) containing 0.2 mL of benzoic acid, and the quenched mixture was precipitated into 75 mL of cold methanol, filtered, washed with methanol to remove unreacted monomer and catalyst residues, and dried in a vacuum oven at 60 °C until a constant weight was achieved.

[0123]

Number

[0124] This polymer was recycled back to the lactone monomer. A flask containing 570 mg of purified P(2,2-Me2-3HB) and 29 mg of Mg(OH)2 (10 mol%) was heated at 250 °C in a vacuum distillation setup. The receiving flask was cooled in a -78 °C bath, 1 and the pure monomer rac-α,α-dimethyl-β-butyrolactone was collected as indicated by 1H NMR analysis. When ZnCl2 was used as a catalyst, the 2,2-dimethyl-3-butenoic acid by-product (42%) was obtained.

[0125] Synthesis of poly(2,2-dimethyl-3-thiopropionate), P(2,2-Me2-3TP) from the ROP of 2,2-dimethyl-3-propionthiola ctone. The ROP was carried out at ambient temperature in a 5 mL glass reactor inside a glove box. The DBU / BnOH mixture (0.0025 / 0.0025 mmol) was stirred in 0.2 mL of dichloromethane for 10 minutes. To this mixture, the monomer (400 equiv, 5.0 M) was rapidly added via pipette and the mixture was stirred for 12 h to achieve >99% conversion. The polymerization was quenched by the addition of 0.2 mL of chloroform (5 mg / ml) containing benzoic acid and the quenched solution was precipitated into 75 mL of cold methanol, filtered, washed with methanol to remove unreacted monomer and catalyst residues, and dried in a vacuum oven at 60 °C until a constant weight was obtained.

Number

[0126] Synthesis of poly(2,2-dimethyl-5-hydroxyvalerate), P(2,2-Me2-5HV) from the ROP of α,α-dimethyl-δ-valerolactone. The polymerization was carried out at ambient conditions (ca. 23 °C) in a 30 mL oven-dried glass reactor inside an inert (N2 or Ar supplied) glove box. The lactone monomer (200 equivalents to the catalyst) was first dissolved in toluene and the polymerization was initiated by the rapid addition of toluene containing the La[N(SiMe3)2]3 / 3BnOH mixture with vigorous stirring to the above solution. The initial monomer concentration was 1.0 M. After 5 min, the polymerization was immediately quenched by the addition of 0.5 mL of benzoic acid / CDCl3 (10 mg / mL), and later 1 analyzed by 1H NMR to afford 79% percent monomer conversion. The quenched mixture was then precipitated with stirring into 50 mL of cold methanol, filtered, washed with cold methanol to remove unreacted monomer, and dried in a vacuum oven at room temperature overnight to constant weight.

Number

[0127] Synthesis of poly(2,2-diethyl-5-hydroxyvalerate), P(2,2-Et2-5HV) from the ROP of α,α-diethyl-δ-valerolactone. The polymerization was carried out at ambient conditions (ca. 23 °C) in a 30 mL oven-dried glass reactor inside an inert (N2 or Ar supplied) glove box. The lactone monomer (200 equivalents to the catalyst) was first dissolved in toluene and the polymerization was initiated by the rapid addition of toluene containing the La[N(SiMe3)2]3 / 3BnOH mixture with vigorous stirring to the above solution. The initial monomer concentration was 2.0 M. After 30 min, the polymerization was immediately quenched by the addition of 0.5 mL of benzoic acid / CDCl3 (10 mg / mL), and later 1Analysis was performed by ¹H NMR to obtain percent monomer conversion data. The quenched mixture was then precipitated with stirring into 50 mL of cold methanol, filtered, washed with cold methanol to remove unreacted monomer, and dried in a vacuum oven at room temperature overnight to a constant weight.

Number

[0128]

Number

[0129] P(2,2- n Depolymerization of Pr2-5HV) to α,α-di(n-propyl)-δ-valerolactone. To a 10 mL round-bottom flask, P(2,2- n Pr2-5HV) (1.00 g) and catalyst ZnCl₂ (2 mol%, 14.8 mg) were added. The mixture was heated under vacuum to 150 °C in a distillation setup, with the receiver flask cooled in a liquid nitrogen / acetone bath to trap the condensed product. After 1 hour, the distillation was complete, and 0.98 g of pure monomer α,α-di(n-propyl)-δ-valerolactone was collected; yield, 98%.

[0130] Other P(2,2-R₂-5HV) materials were depolymerized similarly, and the corresponding monomers were recovered in pure form and in essentially quantitative yields.

[0131] Example 4. Additional Methods and Procedures Both α,α-dimethylated poly(3-hydroxy-2,2-dimethylpropionate) [P3H(Me)₂P] and P3H(Me)₂B can now be chemically recycled back to their starting monomers, α,α-dimethyl-β-propiolactone [(Me)₂PL] and α,α-dimethyl-β-butyrolactone [(Me)₂BL], respectively, achieving the first reported example of a PHA with closed-loop chemical recyclability.

[0132] α,α-Dialkylated PHAs can be synthesized via either the step-growth polycondensation reaction (SGP) of hydroxy acids (HAs), 3-hydroxy-2,2-dimethylpropionic acid [3H(Me)2PA] and 3-hydroxy-2,2-dimethylbutyric acid [3H(Me)2BA], or the ring-opening polymerization (ROP) of lactones, (Me)2PL and (Me)2BL. 3H(Me)2PA is commercially available, while the lactone (Me)2PL was prepared via one-step lactonization of HA. The other dialkyl-substituted lactones (R)2PL (R = Et, n Pr, n Bu) (Et)2BL were synthesized using the lactonization method. Importantly, the HA and lactone monomers can be prepared or recovered in good to quantitative yields since they do not depolymerize PHAs.

[0133] First, the ROP of (Me)2PL was investigated by using different organic base catalysts and reaction conditions (Table 1). Considering the insolubility of semicrystalline P3H(Me)2P in common organic solvents, the ROP was optimized at solvent-free and 70 °C using the superbase t Bu-P4 {1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)phosphoranylideneamino]2λ 5 ,4λ 5 -catena-di(phosphazene)}.

Number

[0134] The synergistic benefit of using α,α-dialkyl substitution to suppress cis-elimination to enhance PHA thermal stability is that it enables a simple SGP route to PHA. Thus, P3H(Me)2P can also be prepared using Ti(O nIt can be efficiently produced by the SGP of 3H(Me)2PA or its methyl ester, catalyzed by Bu)4 or B(C6F5)3. Since there is no α-hydrogen, the formation of crotonic acid end groups by transesterification and elimination / termination side reactions, which are important problems that interfere with the synthesis of PHA via SGP, is eliminated. In fact, the 1 1H NMR spectrum of P3H(Me)2P does not show alkene end groups, and furthermore, the effectiveness of the design using α,α-dialkyl substitution to suppress the cis elimination process is confirmed. It should be noted here that the thermal properties of P3H(Me)2P produced by the SGP and ROP pathways are similar.

[0135] The P3H(Me)2P sample prepared via the SGP of 3H(Me)2PA-methyl ester was depolymerized under vacuum at 230 °C and recycled to obtain pure (Me)2PL in 76% isolated yield (Figure 5A). These results indicate that SGP can be used to obtain oligomers or polymers with low to medium molecular weights, which can be effectively depolymerized to form lactones for the rapid ROP to high molecular weight PHA. The second route to establish closed-loop chemical recycling is by the hydrolytic depolymerization of PHA to HA. For example, pure 3H(Me)2PA was obtained in 99% isolated yield without chromatographic purification by hydrolysis of a P3H(Me)2P sample (M n = 20.7 kDa) in THF / MeOH containing aq.NaOH at 80 °C for 24 hours (Figure 5A). The same conditions are also efficient for the depolymerization of SGP-derived samples to pure 3H(Me)2PA in 99% yield. It should be noted here that the recycling of P3H(Me)2P via the HA-PHA loop is particularly beneficial due to the quantitative hydrolysis yield and the similar thermal properties between SGP- and ROP-produced P3H(Me)2P.

[0136] The introduction of α,α-dimethyl groups into poly(3-hydroxypropionate) (P3HP) results in, for P3H(Me)2P (M n = 162 kDa) obtained from ROP, T mincreased from 77 °C to 232 °C (ΔH f = 126 J / g) (Figure 5B). Interestingly, the T n of P3H(Me)2P produced by SGP, which has a much lower molecular weight (M m = 11.7 kDa), is similarly high, 220 °C, and a high ΔH f of 112 J / g for high crystallinity also accompanies it (Figure 5B). Thus, PCR provides a convenient alternative route to obtain P3H(Me)2P with corresponding thermal properties.

[0137] Increasing the chain length of the dialkyl group results in an increase in the T m of P3H(R)2P, and when forming from methyl to ethyl and finally to n-propyl, it leads to a maximum T m of 266 °C (Figure 5C). When the M n of P3H(Me)2P increases from 20.7 to 162 kDa, the T d is enhanced by only 51 °C from 322 to 373 °C, while the T m only changed slightly (by only 8 °C).

[0138] P3H(Me)2P (M n = 162 kDa) produced by ROP also showed three main WAXS diffractions centered at 2θ ≈ 11.7°, 15.6°, and 18.1°, and other diffractions with lower intensity at higher 2θ values. By the same analysis procedure, χ c = 76% was obtained for P3H(Me)2P. Interestingly, essentially identical WAXS profiles were observed for P3H(Me)2P samples produced from SGP and ROP (Figure 5D). Unexpectedly, the T n of P3H(Me)2P (M d reached 373 °C and the T max was 435 °C.

[0139] Due to their high crystallization rate and high crystallinity, P3H(Me)2P (M n = 162 kDa) and P3H(Et)2P (M nThe α,α-dialkylated derivatives of P3HP containing (Mw = 80 kDa) are very brittle and have low ε b values (Figure 5E). However, this mechanical brittleness can be overcome by forming the Me / Et random copolymer (M n = 79 kDa), P3H(Me / Et)2P. This semicrystalline copolymer is ductile and tough, with an ultimate tensile strength (σ) = 38 ± 2.0 MPa and ε b = 335 ± 8.0% (Figure 5E), which is comparable to it-PP and exceeds high-density polyethylene (HDPE). The shear viscosity for P3H(Me)2P remained constant over a period of 30 minutes at temperatures up to 240 °C (well above their corresponding melting temperatures), with no clear decrease.

[0140] P3H(R)2P, R = Me, Et, n Pr, n Bu. The ROP reaction was carried out at ambient temperature (about 23 °C) in a 10 mL Schlenk flask or a 5.5 mL glass reactor inside an inert glove box. The mixture of base catalyst and alcohol initiator, as shown in the polymerization table, was stirred at ambient temperature for 10 minutes, and then a predetermined amount of lactone monomer (R)2PL was added. The sealed reactor was taken out of the glove box and stirred at 70 °C. After the desired period, the mixture turned solid, and a sample was taken out of the reaction mixture 1 and prepared for 1H NMR analysis to obtain percent monomer conversion data. The polymerization was then quenched by the addition of CHCl3 (5 mg / mL) containing benzoic acid, dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), and subsequently precipitated 2 - 3 times in methanol. After filtration, the white polymer solid was vacuum dried at 60 °C until a constant weight was achieved.

[0141] The polycondensation reaction was carried out in a 100 mL three-necked round-bottom flask equipped with a magnetic stirrer. The HA monomer 3H(Me)2PA (3.54 g, 30 mmol) or 3H(Me)2PA-methyl ester (3.96 g, 30 mmol) was placed in the reaction flask inside the glove box. Then, the flask was sealed, taken out of the glove box, and heated at 160 °C in an oil bath with constant stirring. After observing the completion of the monomer melting, o-xylene (1 mL) containing the catalyst B(C6F5)3 or Ti(O n Bu)4 (1 mol% or 0.1 mol%) was added into the flask under a continuous flow of nitrogen gas. The polymer was stirred at 160 °C for 16 h, then the temperature was increased to 190 °C and stirred for another 16 h in a nitrogen atmosphere to confirm the complete conversion from monomer to oligomer. Then, a vacuum of 200 mTorr was applied to the polycondensation setup, and the reaction mixture was stirred at 190 °C for an additional 8 h. Finally, the temperature was gradually increased to 240 °C and reacted for another 3 h. After the completion of the polymerization, the reaction mixture was cooled to room temperature under a nitrogen atmosphere. The polymer was purified by dissolving it in HFIP, precipitated 2 - 3 times in methanol, and dried in vacuo at 60 °C until a constant weight was obtained to give an off-white polymer.

[0142] Chemical recycling to the lactone monomer (Me)2PL. NaOH (5.0 mg, 5 wt%) and P3H(Me)2P (0.10 g, 1 mmol) obtained by the polycondensation of 3H(Me)2PA-methyl ester were added to a 5.5 mL glass reactor equipped with a stir bar. The mixture was heated at 230 °C (oil bath) and distilled under vacuum with the receiving flask cooled in liquid nitrogen. After the powder disappeared, the vacuum was stopped and the cold bath was removed. As the flask warmed to room temperature, a colorless liquid was collected, which was 1 confirmed by 1H NMR analysis to be the recycled pure monomer (Me)2PL (76% isolated yield).

[0143] Chemical recycling of HA monomer to 3H(Me)2PA. A solution of THF / MeOH (4 / 0.5 mL) containing P3H(Me)2P (100 mg) and aqueous NaOH (320 mg, 4 mL H2O) was reacted in a Schlenk flask at 80 °C for 24 h. Aqueous HCl solution (2 N) was added to adjust the pH value to 1, followed by extraction with EtOAc (15 mL×3). The organic phase was washed with brine, dried over Na2SO4, then evaporated in vacuo to obtain recycled, pure 3H(Me)2PA in 99% isolated yield. [Chemical formula]

[0144] Synthesis of α,α -diethyl-β -propiolactone [(Et)2PL]: To a solution of THF (250 mL) containing diisopropylamine (48 mL, 345 mmol), n BuLi (215 mL, 345 mmol, 1.6 M) was gradually added at 0 °C and the mixture was stirred at this temperature for 1 h. After 15 min, at -78 °C, THF (100 mL) containing 2-ethylbutyric acid (18.9 mL, 150 mmol) was added dropwise. The reaction mixture was stirred at -78 °C for 0.5 h, then at 55 °C for 4 h. Paraformaldehyde (9 g, 300 mmol) was added at -20 °C, followed by stirring for 0.5 h. Then the reaction mixture was brought to room temperature for about 12 h. After quenching with H2O, aqueous HCl solution (4 N) was added to adjust the pH value to 1. The solution was extracted with EtOAc (150 mL×3), the organic phases were combined, washed with brine, dried over Na2SO4, then evaporated in vacuo to obtain crude 3-hydroxy-2,2-diethylpropionic acid [3H(Et)2PA] by simple vacuum distillation (about 200 mTorr, 160 - 180 °C).

[0145] Triethylamine (104 mL, 750 mmol) was added dropwise at 0 °C to a stirred solution of dry DCM (900 mL) containing 3H(Et)2PA. After 15 minutes, benzenesulfonyl chloride (38 mL, 300 mmol) was added dropwise, and the mixture was then stirred at 0 °C for 16 h. The mixture was quenched with ice water and extracted with DCM (150 mL × 3). The combined organic layers were washed with saturated NaHCO3, brine, dried over Na2SO4, and then evaporated in vacuo. After flash column chromatography on silica gel (pentane / acetone = 30 / 1) and concentration in vacuo, the resulting residue was purified by vacuum distillation (ca. 200 mTorr, 70 - 80 °C) to afford the monomer (Et)2PL (9.8 g, 51% over 2 steps) as a colorless oil. 1 H NMR (400 MHz, CDCl3): δ 4.10 (s, 2H), 1.84 - 1.69 (m, 4H), 1.02 (t, J = 7.6 Hz, 6H); 13 C NMR (101 MHz, CDCl3): δ 174.3, 68.1, 62.6, 25.0, 8.6.

Chemical formula

[0146] Synthesis of α,α - di-(n - propyl)-β - propiolactone n [(Pr)2PL]: To a solution of THF (200 mL) containing diisopropylamine (34 mL, 242 mmol) at 0 °C, nn-BuLi (151 mL, 242 mmol, 1.6 M) was added dropwise. After 1 hour with stirring, the reaction mixture was cooled to -78 °C, and THF (80 mL) containing 2-propylpentanoic acid (16.8 mL, 105 mmol) was added dropwise. After 0.5 hour, the solution was heated at 55 °C for 4 hours, then paraformaldehyde (6.3 g, 210 mmol) was added at -20 °C, stirred for 0.5 hour, and heated at 0 °C for 2 hours. The mixture was then quenched with H2O, aqueous HCl (4 N) was added to adjust the pH to 1. After extraction with EtOAc (150 mL × 3), the organic phase was washed with brine, dried over Na2SO4, evaporated in vacuo to give crude 3-hydroxy-2,2-di-(n-propyl)-propionic acid n Pr)2PA], which was used directly without further purification in the next step.

[0147] 3H( n Pr)2PA was dissolved in dry DCM (600 mL), then triethylamine (71.4 mL, 515 mmol) was added at 0 °C. After stirring for 15 minutes, benzenesulfonyl chloride (26.8 mL, 210 mmol) was added dropwise. The reaction was stirred at 0 °C for 16 hours, then the mixture was quenched with ice water and extracted with DCM (150 mL × 3). The combined organic layers were washed with saturated NaHCO3, brine, dried over Na2SO4, and then evaporated in vacuo. The resulting residue was purified by flash column chromatography on silica gel (pentane / acetone = 30 / 1), concentrated in vacuo, and then chloroform (80 mL) and sodium hydroxide solution (6.7 g NaOH, 4 N) were added. After stirring at 50 °C for 6 hours, the mixture was extracted with DCM (60 mL × 3). The combined organic layers were washed with brine, dried over Na2SO4, and then evaporated in vacuo. The resulting residue was purified by vacuum distillation (ca. 200 mTorr, 105 - 115 °C) to give the monomer n Pr)2PL (7.7 g, 47% over 2 steps) as a colorless oil. 11H NMR (400 MHz, CDCl3): δ 4.10 (s, 2H), 1.72 - 1.65 (m, 4H), 1.57 - 1.44 (m, 2H), 1.41 - 1.30 (m, 2H), 0.96 (t, J = 7.2 Hz, 6H); 13 13C NMR (101 MHz, CDCl3): δ 174.4, 69.1, 61.4, 34.5, 17.6, 14.1.

Chemical formula

[0148] Synthesis of α,α - di-(n - butyl)-β - propiolactone [(( n To a solution of THF (250 mL) containing diisopropylamine (48 mL, 345 mmol), n BuLi (215 mL, 345 mmol, 1.6 M) was added dropwise at 0 °C. After stirring for 1 hour, the reaction mixture was cooled to -78 °C, and THF (100 mL) containing 2 - butylhexanoic acid (25.8 mL, 150 mmol) was added dropwise. After 0.5 hour, the solution was heated at 55 °C for 4 hours, followed by the addition of paraformaldehyde (9 g, 300 mmol) at -20 °C, and stirring at 0 °C for 2 hours. Then the mixture was quenched with H2O, aqueous HCl (4 N) was added to adjust the pH value to 1. After extraction with EtOAc (150 mL × 3), the organic phase was washed with brine, dried over Na2SO4, and then evaporated in vacuo to obtain crude 3 - hydroxy - 2,2 - di-(n - butyl)-propionic acid [3H( n Bu)2PA], which was used directly without further purification in the next step.

[0149] 3H( n(Bu)2PA was dissolved in dry DCM (900 mL), and then triethylamine (104 mL, 750 mmol) was added at 0 °C. After stirring for 15 minutes, benzenesulfonyl chloride (38 mL, 300 mmol) was added dropwise. The reaction mixture was stirred at 0 °C for 16 hours, then quenched with ice water and extracted with DCM (150 mL × 3). The combined organic layers were washed with saturated NaHCO3 and brine, dried over Na2SO4, and then evaporated in vacuo. The resulting residue was purified by flash column chromatography on silica gel (pentane / acetone = 30 / 1), concentrated in vacuo, and subsequently chloroform (80 mL) and sodium hydroxide solution (6.7 g NaOH, 4 N) were added. After stirring at 50 °C for 12 hours, the mixture was extracted with DCM (60 mL × 3). The combined organic layers were washed with brine, dried over Na2SO4, and then evaporated in vacuo. The resulting residue was purified by vacuum distillation (ca. 200 mTorr, 125 - 135 °C), and the monomer ( n (Bu)2PL (11.3 g, 41% for 2 steps) was obtained as a colorless oil. 1 1H NMR (400 MHz, CDCl3): δ 4.08 (s, 2H), 1.73 - 1.65 (m, 4H), 1.47 - 1.22 (m, 8H), 0.91 (t, J = 7.2 Hz, 6H); 13 13C NMR (101 MHz, CDCl3): δ 174.6, 69.1, 61.4, 32.2, 26.4, 22.8, 13.8.

Table 8

Table 9

Table 10

Table 11

[0150] Particular embodiments have been described above with reference to the disclosed embodiments and examples, but such embodiments are merely illustrative and not restrictive of the scope of the invention. Changes and modifications can be made in accordance with ordinary skill in the art without departing from the invention in its broader aspects as defined in the following claims.

[0151] Publications, patents, and patent documents are all incorporated herein by reference as if individually incorporated by reference. Limitations that are inconsistent with the present disclosure are not to be understood therefrom. The invention has been described with reference to various specific and preferred embodiments and techniques. However, it should be understood that many changes and modifications are possible while remaining within the spirit and scope of the invention.

Claims

**Claim 1** A polymer comprising Formula I: 【Chemical 1】 wherein G １ is O, S, or NR ａ wherein R ａ is H or -(C １ -C １２ ), alkyl; R １ and R ２ each independently is —(C １ —C １２ )alkyl, —(C ２ —C １２ )alkenyl, —(C ２ —C １２ )alkynyl, aryl or heteroaryl; or R １ and R ２ together with the carbon atoms to which they are attached form a (C ３ -C １６ ) cycloalkyl; R ３ is H, -(C １ -C １２ )alkyl, -(C ２ -C １２ )alkenyl, -(C ２ -C １２ )alkynyl, aryl or heteroaryl; p is from 0 to 5; and x is from 10 to about 500,000, the polymer. **Claim 2** R １ and R ２ is methyl, ethyl, propyl, or butyl, and R ３ is hydrogen, methyl, ethyl, propyl, or butyl, the polymer according to claim 1. **Claim 3** The polymer according to claim 1, wherein p is 0 or 2. **Claim 4** The polymer according to claim 1, wherein x is from about 20 to about 500,000. **Claim 5** The polymer according to any one of claims 1-4, wherein the polymer is a copolymer comprising Formula II: 【Chemical 2】 wherein G １ and G ２ are each independently O, S, or NR ｂ wherein, R ｂ is H or -(C １ -C １２ alkyl); R ４ and R ５ each independently is -(C １ -C １２ )alkyl, -(C ２ -C １２ )alkenyl, -(C ２ -C １２ )alkynyl, aryl or heteroaryl; or R ４ and R ５ together with the carbon atoms to which they are attached form a (C ３ -C １６ ) cycloalkyl; R ６ is H, -(C １ -C １２ )alkyl, -(C ２ -C １２ )alkenyl, -(C ２ -C １２ )alkynyl, aryl or heteroaryl; q is from 0 to 5; y is from 10 to about 500,000; and z is from 1 to about 100,000; the structure of the repeating units represented by x and y in Formula II is different, the polymer. **Claim 6** R ４ and R ５ is methyl, ethyl, propyl, or butyl, and R ６ is hydrogen, methyl, ethyl, propyl, or butyl, the copolymer according to claim 5. **Claim 7** The copolymer according to claim 5, wherein y is from about 20 to about 500,000 and z is from about 10 to about 100,000. **Claim 8** A method for forming the polymer according to claim 1, comprising ring-opening polymerization (ROP) of a monomer of Formula III: [Chemical 3] wherein G １ is O, S, or NR ａ where R ａ is H or -(C １ -C １２ ), an alkyl; R １ and R ２ are each independently, -(C １ -C １２ )alkyl, -(C ２ -C １２ )alkenyl, -(C ２ -C １２ )alkynyl, aryl or heteroaryl; or R １ and R ２ together with the carbon atoms to which they are attached form a (C ３ -C １６ ) cycloalkyl; R ３ is H, -(C １ -C １２ )alkyl, -(C ２ -C １２ )alkenyl, -(C ２ -C １２ )alkynyl, aryl or heteroaryl; and, p is from 0 to 5; ROP comprises contacting a monomer of Formula III, a catalyst, and an initiator; the polymer is thereby formed, the method. **Claim 9** The catalyst is {1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)phosphoranylidene-amino]2λ ５ ,4λ ５ -catenadi(phosphazene)}( ｔ Bu-P ４ ), and the initiator is an aliphatic alcohol or an aryl alcohol. The method according to claim 8. **Claim 10** A method for forming the polymer according to claim 1, comprising step-growth polycondensation (SGP) of a monomer of Formula IV: 【Chemical Formula 4】 wherein G ３ is OH, SH, or NHR ａ wherein R ａ is H or -(C １ -C １２ )alkyl; R １ and R ２ each independently is -(C １ -C １２ )alkyl, -(C ２ -C １２ )alkenyl, -(C ２ -C １２ )alkynyl, aryl or heteroaryl; or R １ and R ２ together with the carbon atoms to which they are attached form a (C ３ -C １６ ) cycloalkyl; R ３ is H, -(C １ -C １２ )alkyl, -(C ２ -C １２ )alkenyl, -(C ２ -C １２ )alkynyl, aryl or heteroaryl; and, p is from 0 to 5; SGP comprises contacting a monomer of Formula IV and a catalyst; the polymer is thereby formed, the method. **Claim 11** The method according to claim 10, wherein the catalyst is a Lewis acid. **Claim 12** The method according to claim 8 or 10, wherein the monomer is optically active. **Claim 13** A method for depolymerizing the polymer according to claim 1, comprising contacting the polymer and a base, wherein the polymer is depolymerized to its constituent monomers, and the conversion to the constituent monomers is at least about 20 wt%, the method. **Claim 14** The method according to claim 13, wherein the constituent monomer is represented by Formula III: [Chemical Formula 5] wherein G １ is O, S, or NR ａ where R ａ is H or -(C １ -C １２ )alkyl; R １ and R ２ are each independently, -(C １ -C １２ )alkyl, -(C ２ -C １２ )alkenyl, -(C ２ -C １２ )alkynyl, aryl or heteroaryl; or R １ and R ２ together with the carbon atoms to which they are attached form a (C ３ -C １６ ) cycloalkyl; R ３ is H, -(C １ -C １２ )alkyl, -(C ２ -C １２ )alkenyl, -(C ２ -C １２ )alkynyl, aryl or heteroaryl; and, p is from 0 to 5, the method. **Claim 15** The method according to claim 13, wherein the constituent monomer is represented by Formula IV: 【Chemical Formula 6】 wherein G ３ is OH, SH, or NHR ａ wherein R ａ is H or -(C １ -C １２ )alkyl; R １ and R ２ are each independently, -(C １ -C １２ )alkyl, -(C ２ -C １２ )alkenyl, -(C ２ -C １２ )alkynyl, aryl or heteroaryl; or R １ and R ２ together with the carbon atoms to which they are attached form a (C ３ -C １６ ) cycloalkyl; R ３ is H, -(C １ -C １２ )alkyl, -(C ２ -C １２ )alkenyl, -(C ２ -C １２ )alkynyl, aryl or heteroaryl; and, p is from 0 to 5, the method.

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