RENEWABLY DERIVED POLYESTERS CONTAINING BRANCHED-CHAIN MONOMERS AND METHODS OF MAKING AND USING THE SAME

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application Serial No. 62/302,475 filed on March 2, 2016, the content of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The disclosure generally provides polyesters derived from renewable sources, such as certain natural oils. In some embodiments, the polyesters disclosed herein contain monomers that introduce branching into the backbone of the polymer. The disclosure also provides methods of making such polyesters. The disclosure also provides certain uses of such polyesters.

DESCRIPTION OF RELATED ART

Growing concerns over the environmental impacts of non-biodegradable plastic waste and the need for sustainability have stimulated research efforts on biodegradable polymers from renewable resources. Rising costs and dwindling petrochemical feedstocks also make renewable resource-based materials attractive alternatives to their petroleum-based counterparts. Many of these efforts have concerned ester containing polymers such as polyesters, polyester amides, and polyester urethanes, where the polar ester groups (-COO-) offer biodegradability through hydrolytic or enzymatic degradation, and hydrophobicity through the long aliphatic segments.

Linear aliphatic polyesters of the [-(CH ₂ ) _y -COO-] _z homologue series, synthesized from lactones or hydroxy 1 acid/ester monomers derived from renewable carbon sources, have gained considerable attention because of their potential suitability in biomedical applications. The medium chain homologue poly(nonane lactone) derived from natural oils has been shown to exhibit improved thermal properties compared to poly(s-caprolactone) (PCL) and has been suggested as potential replacement for petroleum derived PCL in drug delivery applications. Most of the earlier reported polyesters in this series, however, are short chain homologues, such as poly (glycolic acid), poly (3 -hydroxy propionic acid), poly(4-hydroxy butyrate) etc., which suffer from poor thermal stability, low melting points, and consequently, poor melt processibility. Long chain polyester homologues have recently attracted significant interest as potential new degradable analogues of linear polyethylene (PE). Linear PE is one of the best- known commodity polymers, but due to its hydrophobicity and molecular size, is nonbiodegradable. PE is used in large volumes for household products and packaging applications because of its adequate mechanical properties and its relatively lower cost compared to engineering polymers. Recent efforts have indicated that the PE-like properties of the long chain polyester homologues, along with biodegradability, present ecological advantages by offering alternative solutions to the PE commodity waste problem.

Therefore it would be desirable to develop suitable means of making renewably derived aliphatic polyesters, such as those of the [-(CH ₂ ) _y -COO-] _z homologue series, that have properties analogous to polyethylene, but without the corresponding commodity waste problem.

SUMMARY

Most of the research on renewable and biodegradable food packaging materials based on polyesters has concentrated on polylactic acid and short chain polyhydroxyalkanoates, with comparatively much less attention paid to mid-chain and long-chain polyhydroxyesters. One of the reasons has traditionally been the lack of efficient routes to obtain mid- and long- chain hydroxyl fatty acids.

U.S. Patent Application Publication No. 2015/0065682 describes the preparation of certain ω-hydroxyl fatty acids (e.g., with carbon number of 9, 13 and 18) by employing ozone to oxidize an unsaturated fatty acid, or by the cross-metathesis of fatty acids and fatty alcohols followed by hydrogenation in the presence of Ni catalyst and prepared their poly(o hydroxyl fatty acid)s by melt polycondensation. In some embodiments, these linear polyesters presented a high tensile strength but, in some cases, due to their high degree of crystallinity, the polyesters showed pronounced brittleness, thereby limiting their use in many applications, such as coatings.

In the present disclosure, this shortcoming is overcome by the introduction of branching in the polyesters. Branched monomers can be used in various systems, including phenol resins, epoxy resins, and natural rubber products. In the present disclosure, the introduction of branching was expanded to copolymer-like polyester based systems resembling linear low-density polyethylene (LLDPE). For example, co-polyesters with various degrees of branching prepared from castor oil and veronia oil platforms synthesized using acyclic diene metathesis (ADMET) copolymerization in bulk presented thermal- mechanical properties similar to LLDPE and very low-density polyethylene (VLDPE).

Furthermore, the melting points of the

co-polyesters were tunable between 50 °C and 90 °C, and considered as good sustainable alternatives to olefin-based elastomers, especially for specific applications which require degradability.

In certain aspects and embodiments, the present disclosure extends the property range of poly(o hydroxyl fatty acid)s, in which branching of the linear polyester structures is used as a tool to improve the thermoplastic properties, particularly the strain. The polyester elastomers disclosed herein are produced from bio-based ω-hydroxyl fatty acids, for example, methyl ω-hydroxynonanoate, methyl ω-hydroxytridecanoate and methyl ω- hydroxyoctadecanoate which were branched with 2-butyl-2-ethyl-l , 3-propanediol. Dimethyl diacid esters, namely dimethyl azelate, dimethyl adipate and dimethyl octadecanedioate were used to realize a stoichiometric balance between OH and COOH suitable for achieving high molecular weight polyesters. The effect of the number of branches, ω-hydroxyl fatty acid chain length and dimethyl diacid ester chain length on the thermal properties and mechanical properties was investigated.

In a first aspect, the disclosure provides polymer compositions, comprising one or more polyester polymers comprising constitutional units formed from a reaction mixture, the reaction mixture comprising: (a) one or more monomers of formula (I):

HO-(CH ₂ )p-C(0)0-R ¹ (I) wherein p is an integer from 8 to 17, and R ¹ is a hydrogen atom or Ci-6 alkyl; and (b) one or more monomers of formula (II):

HO-X^OH (II) wherein X ¹ is a branched-chain C _3-18 alkylene. In some embodiments, the reaction mixture further comprises constitutional units formed from aliphatic dibasic acids or esters thereof. In some embodiments, the reaction mixture further comprises one or more monomers of formula (III):

R ² -0-C(0)-(CH ₂ ) _q -C(0)-0-R ³

(III)

wherein q is an integer from 4 to 20, and R ² and R ³ are independently a hydrogen atom or Ci-6 alkyl.

A series of branched poly (ω-hydroxyl fatty acid) polyesters have been prepared from methyl ω-hydroxyl fatty acid esters including methyl ω-hydroxynonanoate, methyl ω-hydroxytridecanoate and methyl ω-hydroxyoctadecanoate using a green melt poly condensation route. In some embodiments, the branches were implanted by random polymerization of the methyl ω-hydroxyl fatty acid esters and 2-butyl-2-ethyl-l,3- propanediol. To achieve high molecular weight polyesters, a diacid methyl ester including dimethyl azelate, dimethyl adipate or dimethyl octadecanedioate, was used in amounts to make the ratio of OH and COOH unity. The reaction was conducted under vacuum (initially at 300 mbar, and then at 20 mbar) at a gradually increasing temperature (from 80 °C to 200 °C) to avoid the evaporation of the monomers. The structure of polyesters and their branches have been confirmed by ^-NMR. The ratio of the branched structures to the ω-hydroxyl fatty acid structures (simply ratio of branches) in the polyesters was also determined by 1H- NMR.

The thermal degradation and thermal transition properties of the polyesters were investigated with TGA and DSC, respectively, and their mechanical properties were determined using a texture analyzer. The polyesters were found to be thermally stable at as high temperatures as 300 °C, a favorable property for the thermal processing of the polyesters. The melting point, melting enthalpy, glass transition temperature, young's modulus, stress at break and strain of the polyesters were directly correlated to the ω- hydroxyl fatty acid chain length, diacid dimethyl ester chain length and number of branches. Furthermore, predictive relationships between melting enthalpy and the mechanical properties of the polyesters were confirmed. In some embodiments, a branched polyester elastomer with strain at break of 285%, young's modulus of 115 MPa and stress of 5.32 MPa was produced from methyl ω-hydroxytridecanoate, 2-butyl-2-ethyl-l,3-propanediol and dimethyl adipate. In further embodiments, the elastomers of the present work was achieved using milder reaction conditions, such as temperature and pressure, compared to the reaction conditions used previously to prepare elastomeric materials with similar strain properties, the previously reported work also reporting vastly limited elongations at break.

Further aspects and embodiments are disclosed in the Detailed Description.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are provided for purposes of illustrating various embodiments of the compounds, compositions, and methods disclosed herein. The drawings are provided for illustrative purposes only, and are not intended to describe any preferred compounds, preferred compositions, or preferred methods, or to serve as a source of any limitations on the scope of the claimed inventions. Figure 1 shows a reaction scheme for the synthesis of aliphatic polyesters of certain embodiments disclosed herein.

Figure 2 shows the ^-NMR spectrum for the PEn _-2 m ₂ polyester.

Figure 3 shows the ^-NMR spectrum for the PEn _-2 m ₅ polyester.

Figure 4 shows the ^-NMR spectrum for the PEn _-2 mi ₄ polyester.

Figure 5 shows the ^-NMR spectrum for the PEn ₇ m ₂ -0.1 polyester.

Figure 6 shows the ^-NMR spectrum for the PEn ₇ m ₂ -0.2 polyester.

Figure 7 shows the ^-NMR spectrum for the PEn ₇ m ₅ -0.2 polyester.

Figure 8 shows the ^-NMR spectrum for the PEn ₇ mi ₄ -0.2 polyester.

Figure 9 shows the ^-NMR spectrum for the PEnnm ₂ -0.1 polyester.

Figure 10 shows the H-NMR spectrum for the PEnnm ₂ -0.2 A polyester.

Figure 11 shows the H-NMR spectrum for the PEnnm ₂ -0.2 B polyester.

Figure 12 shows the ^-NMR spectrum for the PEnnm ₂ -0.3 polyester.

Figure 13 shows the ^-NMR spectrum for the PEnnm ₅ -0.1 polyester.

Figure 14 shows the H-NMR spectrum for the PEnnm ₅ -0.2 polyester.

Figure 15 shows the H-NMR spectrum for the PEnnm ₅ -0.3 polyester.

Figure 16 shows the H-NMR spectrum for the PEnnm ₅ -0.1 polyester.

Figure 17 shows the H-NMR spectrum for the PEnnmi ₄ -0.2 polyester.

Figure 18 shows the ^X H-NMR spectrum for the PEnnmi ₄ -0.3 polyester.

Figure 19 shows the ^X H-NMR spectrum for the PEni ₆ m ₂ -0.2 polyester.

Figure 20 shows the DTG curves for certain PEn _z m _x -y polyesters.

Figure 21 shows the DTG curves for PEn _-2 m ₅ and PEnnm ₅ -0.2 polyesters.

Figure 22 shows heating thermograms (2 ^nd cycle) of certain PEn _-2 m _x polyesters, where x=2, 5 and 14.

Figure 23 shows: (a) DSC heating thermograms of PEnnm ₂ -y polyesters, where y=0.1, 0.2 and 0.3 and corresponding; (b) melting (·, T _m ) and glass transition ( ^A , T ) temperatures as a function of ratio of branches; (c) melting enthalpy as a function of ratio of branches. Dashed lines in (b) and (c) are guides for the eye.

Figure 24 shows: (a) DSC heating thermograms of PEn _z m ₂ -0.2 polyesters, where z=7, 11 and 14; and corresponding; (b) melting point (·, T _m ) and glass transition temperature ( ^A ,

T ) as a function of ω-hydroxyl fatty acid chain length (n); (c) melting enthalpy as a function of n. Dashed lines in (b) and (c) are guides for the eye. Figure 25 shows: (a) DSC heating thermograms of PEnnm _x -0.2 polyesters, where x=2, 5 and 14; and corresponding; (b) melting (·, T _m ) and glass transition ( ^A , T ) temperatures as a function of diacid methyl ester chain length (m); (c) melting enthalpy as a function of m. Dashed lines in (b) and (c) are guides for the eye.

Figure 26 shows the stress-strain curves for (a) PEnnm ₂ -y (y=0.1 , 0.2 and 0.3); and

(b) PEnnm ₅ -y (y=0.1, 0.2 and 0.3).

Figure 27 shows the mechanical properties of PEnnm _x -y (x=2 and 5, y=0.1 , 0.2 and 0.3) as a function of the ratio of branches, (a) Young's modulus; (b) Stress at break; and (c) strain. Dashed lines are guides for the eye.

Figure 28 shows the mechanical properties of branched polyesters as a function of the enthalpy of melting, (a) Young's modulus; (b) Stress at break; (c) strain. Dashed lines are guides for the eye.

Figure 29 shows the strain - stress curve of the PEnnm ₂ -0.2 B polyester.

DETAILED DESCRIPTION

The following description recites various aspects and embodiments of the inventions disclosed herein. No particular embodiment is intended to define the scope of the invention. Rather, the embodiments provide non-limiting examples of various compositions, and methods that are included within the scope of the claimed inventions. The description is to be read from the perspective of one of ordinary skill in the art. Therefore, information that is well known to the ordinarily skilled artisan is not necessarily included.

Definitions

The following terms and phrases have the meanings indicated below, unless otherwise provided herein. This disclosure may employ other terms and phrases not expressly defined herein. Such other terms and phrases shall have the meanings that they would possess within the context of this disclosure to those of ordinary skill in the art. In some instances, a term or phrase may be defined in the singular or plural. In such instances, it is understood that any term in the singular may include its plural counterpart and vice versa, unless expressly indicated to the contrary.

As used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. For example, reference to "a substituent" encompasses a single substituent as well as two or more substituents, and the like. As used herein, "for example," "for instance," "such as," or "including" are meant to introduce examples that further clarify more general subject matter. Unless otherwise expressly indicated, such examples are provided only as an aid for understanding

embodiments illustrated in the present disclosure, and are not meant to be limiting in any fashion. Nor do these phrases indicate any kind of preference for the disclosed embodiment.

As used herein, "reaction" and "reacting" refer to the conversion of a substance into a product, irrespective of reagents or mechanisms involved.

As used herein, "polymer" refers to a substance having a chemical structure that includes the multiple repetition of constitutional units formed from substances of

comparatively low relative molecular mass relative to the molecular mass of the polymer. The term "polymer" includes soluble and/or fusible molecules having chains of repeat units, and also includes insoluble and infusible networks.

As used herein, "monomer" refers to a substance that can undergo a polymerization reaction to contribute constitutional units to the chemical structure of a polymer.

As used herein, "polyester" refers to a polymer comprising two or more ester linkages. Other types of linkages can be included, however. In some embodiments, at least 80%, or at least 90%, or at least 95% of the linkages in the polyester are ester linkages. The term can refer to an entire polymer molecule, or can also refer to a particular polymer sequence, such as a block within a block copolymer. The term "dihydroxyl polyester" refers to a polyester having two or more free hydroxyl groups, e.g., at the terminal (e.g., reacting) ends of the polymer (i.e., a "dihydroxyl-terminated polyester"). In some embodiments, such polyesters have exactly two free hydroxyl groups.

As used herein, "alcohol" or "alcohols" refer to compounds having the general formula: R-OH, wherein R denotes any organic moiety (such as alkyl, aryl, or silyl groups), including those bearing heteroatom-containing substituent groups. In certain embodiments, R denotes alkyl, alkenyl, aryl, or alcohol groups. In certain embodiments, the term "alcohol" or "alcohols" may refer to a group of compounds with the general formula described above, wherein the compounds have different carbon lengths. The term "hydroxyl" refers to a -OH moiety. In some cases, an alcohol can have more than two or more hydroxyl groups. As used herein, "diol" and "polyol" refer to alcohols having two or more hydroxyl groups.

As used herein, "carboxylic acid" or "carboxylic acids" refer to compounds having the general formula: R-C0 ₂ H, wherein R denotes any organic moiety (such as alkyl, aryl, or silyl groups), including those bearing heteroatom-containing substituent groups. In certain embodiments, R denotes alkyl, alkenyl, aryl, or alcohol groups. In certain embodiments, the term "carboxylic acid" or "carboxylic acids" may refer to a group of compounds with the general formula described above, wherein the compounds have different carbon lengths. The term "carboxyl" refers to a -C0 ₂ H moiety. In some cases, an isocyanate can have more than two or more carboxy groups. As used herein, "dicarboxylic acid" and "poly carboxylic acid" refer to carboxylic acids having two or more carboxyl groups.

The terms "group" or "moiety" refers to a linked collection of atoms or a single atom within a molecular entity, where a molecular entity is any constitutionally or isotopically distinct atom, molecule, ion, ion pair, radical, radical ion, complex, conformer etc., identifiable as a separately distinguishable entity.

As used herein, "mix" or "mixed" or "mixture" refers broadly to any combining of two or more compositions. The two or more compositions need not have the same physical state; thus, solids can be "mixed" with liquids, e.g., to form a slurry, suspension, or solution. Further, these terms do not require any degree of homogeneity or uniformity of composition. This, such "mixtures" can be homogeneous or heterogeneous, or can be uniform or non- uniform. Further, the terms do not require the use of any particular equipment to carry out the mixing, such as an industrial mixer.

As used herein, the term "natural oil" or "lipid" refers to oils derived from various plants or animal sources. These terms include natural oil derivatives, unless otherwise indicated. The terms also include modified plant or animal sources (e.g., genetically modified plant or animal sources), unless indicated otherwise. Examples of natural oils include, but are not limited to, vegetable oils, algae oils, fish oils, animal fats, tall oils, derivatives of these oils, combinations of any of these oils, and the like. Representative non- limiting examples of vegetable oils include rapeseed oil (canola oil), coconut oil, com oil, cottonseed oil, olive oil, palm oil, peanut oil, safflower oil, sesame oil, soybean oil, sunflower oil, linseed oil, palm kernel oil, rung oil, jatropha oil, mustard seed oil, penny cress oil, camelina oil, hempseed oil, and castor oil. Representative non-limiting examples of animal fats include lard, tallow, poultry fat, yellow grease, and fish oil. Tall oils are by-products of wood pulp manufacture. In some embodiments, the natural oil or natural oil feedstock comprises one or more unsaturated glycerides (e.g., unsaturated triglycerides).

As used herein, "natural oil derivatives" refers to the compounds or mixtures of compounds derived from a natural oil using any one or combination of methods known in the art. Such methods include but are not limited to saponification, fat splitting,

transesterification, esterification, hydrogenation (partial, selective, or full), isomerization, oxidation, and reduction. Representative non-limiting examples of natural oil derivatives include gums, phospholipids, soapstock, acidulated soapstock, distillate or distillate sludge, fatty acids and fatty acid alkyl ester (e.g. non-limiting examples such as 2-ethylhexyl ester), hydroxy substituted variations thereof of the natural oil. For example, the natural oil derivative may be a fatty acid methyl ester ("FAME") derived from the glyceride of the natural oil.

As used herein, "alkyl" refers to a straight or branched chain saturated hydrocarbon having 1 to 30 carbon atoms, which may be optionally substituted, as herein further described, with multiple degrees of substitution being allowed. Examples of "alkyl," as used herein, include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, isobutyl, n-butyl, sec-butyl, tert-butyl, isopentyl, n-pentyl, neopentyl, n-hexyl, and 2-ethylhexyl. In some cases, the "alkyl" group can be bivalent, in which case, the group can be described as an "alkylene" group.

For any compound, group, or moiety, the number carbon atoms in that compound, group, or moiety is represented by the phrase "C _x-y " which refers to an such a compound, group, or moiety, as defined, containing from x to y, inclusive, carbon atoms. Thus, "Ci_6 alkyl" refers to an alkyl chain having from 1 to 6 carbon atoms.

As used herein, "comprise" or "comprises" or "comprising" or "comprised of refer to groups that are open, meaning that the group can include additional members in addition to those expressly recited. For example, the phrase, "comprises A" means that A must be present, but that other members can be present too. The terms "include," "have," and

"composed of and their grammatical variants have the same meaning. In contrast, "consist of or "consists of or "consisting of refer to groups that are closed. For example, the phrase "consists of A" means that A and only A is present.

As used herein, "or" is to be given its broadest reasonable interpretation, and is not to be limited to an either/or construction. Thus, the phrase "comprising A or B" means that A can be present and not B, or that B is present and not A, or that A and B are both present. Further, if A, for example, defines a class that can have multiple members, e.g., Al and A2, then one or more members of the class can be present concurrently.

As used herein, the various functional groups represented will be understood to have a point of attachment at the functional group having the hyphen or dash (-) or an asterisk (*). In other words, in the case of -CH ₂ CH ₂ CH ₃ , it will be understood that the point of attachment is the CH ₂ group at the far left. If a group is recited without an asterisk or a dash, then the attachment point is indicated by the plain and ordinary meaning of the recited group. In some instances herein, organic compounds are described using the "line structure" methodology, where chemical bonds are indicated by a line, where the carbon atoms are not expressly labeled, and where the hydrogen atoms covalently bound to carbon (or the C-H bonds) are not shown at all. For example, by that convention, the formula represents n-propane.

As used herein, multi-atom bivalent species are to be read from left to right. For example, if the specification or claims recite A-D-E and D is defined as -OC(O)-, the resulting group with D replaced is: A-OC(0)-E and not A-C(0)0-E.

Unless a chemical structure expressly describes a carbon atom as having a particular stereochemical configuration, the structure is intended to cover compounds where such a stereocenter has an R or an S configuration.

Other terms are defined in other portions of this description, even though not included in this subsection.

Polyester Compositions

In certain aspects, the disclosure provides polymer compositions, comprising one or more polyester polymers comprising constitutional units formed from a reaction mixture, the reaction mixture comprising (a) one or more monomers of formula (I):

HO-CCHz CCO -R ¹ (I) wherein p is an integer from 8 to 17, and R ¹ is a hydrogen atom or Ci-6 alkyl; and (b) one or more monomers of formula (II):

HO-X^OH (II) wherein X ¹ is a branched-chain C _3-18 alkylene. In some embodiments, the reaction mixture further comprises constitutional units formed from aliphatic dibasic acids or esters thereof.

Any suitable monomers of formula (I) or combination of monomers of formula (I) can be used. Compounds, such as those of formula (I) can be referred to as "ω-hydroxy aliphatic acids" or "ω-hydroxy aliphatic esters," depending on whether the a-end of the compound is a carboxylic acid group or an acid or ester group, respectively. In some embodiments, the monomers of formula (I) are acids, such that R ¹ is a hydrogen atom. In some other embodiments, the monomers of formula (I) are esters, for example, if R ¹ is Ci_6 alkyl, such as methyl or ethyl. In some embodiments, R ¹ is methyl.

The monomers of formula (I) can be present in the reaction mixture in any suitable combination. For example, in some embodiments, the reaction mixture comprises monomers of formula (I) where p is 8, monomers of formula (I) where p is 12, monomers of formula (I) where p is 17, or any combination thereof. In some such embodiments, the reaction mixture comprises monomers of formula (I) where p is 8. In some such embodiments, the reaction mixture comprises monomers of formula (I) where p is 12. In some such embodiments, the reaction mixture comprises monomers of formula (I) where p is 17. In some such

embodiments, the reaction mixture comprises monomers of formula (I) where p is 8 and monomers of formula (I) where p is 12. In some such embodiments, the reaction mixture comprises monomers of formula (I) where p is 8 and monomers of formula (I) where p is 17. In some such embodiments, the reaction mixture comprises monomers of formula (I) where p is 12 and monomers of formula (I) where p is 17. In some such embodiments, the reaction mixture comprises monomers of formula (I) where p is 8, monomers of formula (I) where p is 12, and monomers of formula (I) where p is 18.

In some embodiments, ω-hydroxy aliphatic acids/esters besides those of formula (I) can be present. Even so, in some such embodiments, the monomers of formula (I) (according to any of the aforementioned embodiments) make up at least 50 percent by weight, or at least 60% by weight, or at least 70% by weight, or at least 80% by weight, or at least 90% by weight, or at least 95% by weight, or at least 97% by weight, or at least 99% by weight, of the ω-hydroxy aliphatic acids/esters present in the reaction mixture, based on the total weight of ω-hydroxy aliphatic acids/esters present in the reaction mixture.

Any suitable monomers, or combination of monomers, of formula (II) can be used. In some embodiments, X ¹ is a branched-chain Cs _-14 alkylene, or a branched-chain C _7-12 alkylene. The monomers of formula (II) can have any suitable degree of branching (i.e., the number of carbon atoms covalently bound to three or four other carbon atoms. In some embodiments, X ¹ comprises one branching point. In some such embodiments, the carbon atom at that branching point is covalently bound to four other carbon atoms. In some embodiments, X ¹ is represented by the following formula:

G ⁵

^* — G ¹ — C— G ² — G ³ — G ⁴ — ^*

I

G ⁶

wherein G ¹ is -CH ₂ -; G ² is a direct bond or is -CH ₂ -, -CH ₂ -CH ₂ -, or -CH ₂ -CH ₂ -CH ₂ -; G ³ is a direct bond or -C(G ⁷ )(G ⁸ )-; G ⁴ is a direct bond or is -CH ₂ -, -CH ₂ -CH ₂ -, or -CH ₂ -CH ₂ -CH ₂ -; G and G are independently a hydrogen atom or Ci-6 alkyl, wherein at least one of G ⁵ and G ⁶ is not a hydrogen atom; and G ⁷ and G ⁸ are independently a hydrogen atom or Ci-6 alkyl, wherein at least one of G ⁷ and G ⁸ is not a hydrogen atom. In some such embodiments, G ² is a direct bond. In some such embodiments, G ² is -CH ₂ -. In some such embodiments of any of the aforementioned embodiments, G ³ is a direct bond. In some such embodiments of any of the aforementioned embodiments, G is or -C(G ⁷ )(G ⁸ )-. In some such embodiments, G is a hydrogen atom. In some other such embodiments, G ⁷ is methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, isobutyl, pentyl, or isobutyl. In some such embodiments of any of the aforementioned embodiments, G ⁸ is a hydrogen atom. In some other such embodiments of any of the aforementioned embodiments, G ⁸ is methyl, ethyl, propyl, isopropyl, butyl, sec- butyl, isobutyl, pentyl, or isobutyl. In some embodiments of any of the aforementioned embodiments, G ⁴ is a direct bond. In some other such embodiments of any of the aforementioned embodiments, G ⁴ is -CH ₂ -. In some other such embodiments of any of the aforementioned embodiments, G ⁴ is

-CH2-CH2-. In some embodiments of any of the aforementioned embodiments, G ⁵ is a hydrogen atom. In some other such embodiments of any of the aforementioned

embodiments, G ⁵ is methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, isobutyl, pentyl, or isobutyl. In some further such embodiments, G ⁵ is methyl, ethyl, propyl, or butyl. In some embodiments of any of the aforementioned embodiments, G ⁶ is a hydrogen atom. In some other such embodiments of any of the aforementioned embodiments, G ⁶ is methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, isobutyl, pentyl, or isobutyl. In some further such embodiments, G ⁶ is methyl, ethyl, propyl, or butyl. In some embodiments, G ⁵ is ethyl and G ^{ is butyl.

In some embodiments of any of the aforementioned embodiments, the monomer of formula (II) is 2-butyl-2-ethyl-l,3-propanediol.

In some embodiments, the polyesters comprise constitutional units formed from a reaction mixture that further comprises a C6-22 aliphatic dibasic acid or ester thereof. For example, in some embodiments, the reaction mixture further comprising one or more monomers of formula (III):

R ² -0-C(0)-(CH ₂ ) _q -C(0)-0-R ³

(III)

wherein q is an integer from 4 to 20, and R ² and R ³ are independently a hydrogen atom or Ci-6 alkyl.

The reaction mixture can contain any combination of monomers of formula (III). In some embodiments, the reaction mixture comprises monomers of formula (III) where q is 4, monomers of formula (III) where q is 7, monomers of formula (III) where q is 10, monomers of formula (III) where q is 16, or any combinations thereof. In some embodiments, the reaction mixture comprises monomers of formula (III) where q is 4. In some embodiments, the reaction mixture comprises monomers of formula (III) where q is 7. In some

embodiments, the reaction mixture comprises monomers of formula (III) where q is 10. In some embodiments, the reaction mixture comprises monomers of formula (III) where q is 16.

The monomers of formula (III) can exist either as free acids or as esters. Thus, in some embodiments of any of the aforementioned embodiments, R ² and R ³ are a hydrogen atom. In some other embodiments of any of the aforementioned embodiments, R ² and R ³ are Ci-6 alkyl, such as methyl.

Any suitable amount of monomers of formula (III) can be included in the reaction mixture. In some embodiments, the molar ratio of monomers of formula (II) to monomers of formula (III) ranges from 1 :3 to 3: 1, or from 1 :2 to 2: 1, or from 1.5 : 1 to 1 : 1.5, or from 1.2: 1 to 1 : 1.2.

Further, the monomers of formula (I) can have any suitable ratio to the monomers of formula (II) and the monomers of formula (III). In some embodiments, the molar ratio of monomers of formula (I) to monomers of formula (II) ranges from 1 : 1 to 25: 1, or from 2: 1 to 20: 1 , or from 3: 1 to 15: 1, or from 4: 1 to 12: 1. In some embodiments, the molar ratio of (a) monomers of formula (I) to (b) the sum of monomers of formula (II) and monomers of formula (III), ranges from 1 : 1 to 20: 1, or from 1 : 1 to 15: 1, or from 2: 1 to 10: 1.

In some embodiments, the polyester consists entirely or almost entirely of monomers of formula (I) and monomers of formula (II). Thus, in some embodiments, the reaction mixture consists essentially of monomers of formula (I) and monomers of formula (II). In some embodiments, the polyester consists entirely or almost entirely of monomers of formula (I), monomers of formula (II), and monomers of formula (III). Thus, in some embodiments, the reaction mixture consists essentially of monomers of formula (I), monomers of formula (II), and monomers of formula (III).

The resulting polyesters can have certain desirable physical properties. In some embodiments, the one or more polyesters lose no more than 5 percent of their weight upon heating to a temperature of at least 300 °C, or to a temperature of at least 320 °C, or to a temperature of at least 340 °C. In some embodiments, the one or more polyesters have a Young's modulus of at least 200 MPa, or at least 250 MPa, or at least 300 MPa, or at least 350 MPa, or at least 400 MPa. In some embodiments, the one or more polyesters have a strain at break of at least 10%, or at least 20%, or at least 50%, or at least 100%, or at least 150%, or at least 200%, or at least 250%. The polyesters disclosed herein can be synthesized by any suitable means, although some means may be more desirable than others. Suitable synthetic methodologies are disclosed in the Examples, below. The claims to the compounds, or to compositions including the compounds, are not limited in any way by the synthetic method used to make the compounds.

EXAMPLES

The following examples are provided to illustrate one or more preferred embodiments of the invention. Numerous variations can be made to the following examples that lie within the scope of the claimed inventions.

Materials and Methods

Materials

Erucic acid (90% purity), methyl oleate (70% purity), oleyl alcohol (85% purity), Raney nickel 2800 (slurry in water), Ti(IV) isopropoxide [Ti(OiPr) ₄ ] (99.99% purity), Grubbs 2nd generation catalyst, 2-butyl-2-ethyl-l,3-propanediol (99% purity), dimethyl azelate and dimethyl adipate were purchased from Sigma-Aldrich. Methyl ω- hydroxynonanoate and methyl

ω-hydroxytridecanoate were prepared from methyl oleate and methyl erucate by ozonolysis followed by hydrogenation with Raney-Ni as catalyst. Methyl ω-hydroxyoctadecanoate was prepared using the cross-metathesis of methyl oleate and oleyl alcohol in the presence of Grubbs 2nd generation catalyst according to the methods disclosed in Jose et al, Polymer Int'l, vol. 63, pp. 1902-1911 (2014) and Jose et al, Polymer Chem, vol. 5, pp. 3203-3213 (2014). Dimethyl octadecanedioate was prepared from methyl oleate by self-metathesis in the presence of Grubbs 2nd generation catalyst as reported in Hojabri et al,

Biomacromolecules, vol. 11, pp. 911-918 (2010).

Methods

Chemistry Characterization

^-NMR spectra were recorded in CDC1 ₃ on a Varian Unity-INOVA at 499.695 MHz. All spectra were obtained using an 8.6 pulse with 4 transients collected in 16,202 points. Datasets were zero-filled to 64 000 points, and a line broadening of 0.4 Hz was applied prior to Fourier transformation. The spectra were processed using ACD Labs NMR Processor, version 12.01. H chemical shifts are internally referenced to CDCI ₃ (7.26 ppm). Physical Characterization

TGA was carried out on a TGA Q500 (TA Instruments, DE, USA) equipped with a TGA heat exchanger (P/N 953160.901). Approximately 8.0-15.0 mg of sample was loaded in the open TGA platinum pan. The sample was heated from 25 °C to 600 °C under dry nitrogen at a constant rate of 10 °C/min.

DSC analysis was carried out under a dry nitrogen atmosphere on a Q200

(TA Instruments, Newcastle, DE, USA) following the ASTM D3418 standard procedure. The sample (5.0-6.0 mg) was first equilibrated at 0 °C and heated to 130 °C at 3.0 °Cmin ^_1 (first heating cycle). The sample was held at that temperature for 10 min to erase the thermal history, then cooled to -90 °C at 3 °Cmin ^_1 and subsequently reheated to 130 °C at the same rate (second heating cycle). During the heating process, measurements were performed with a modulation amplitude of ± 1°C every 60 s.

The static mechanical properties of the polymer films were determined at room temperature using a Texture Analyzer (TA HD, Texture Technologies Corp., Robbinsville, NJ, USA) equipped with a 2-kg load cell. The measurements were performed following the ASTM D882 standard procedure. The sample was stretched at a rate of 5 mm min ¹ from a gauge of 35 mm.

Polymerization of Branched Polyesters

The branched polyesters were prepared from methyl ω-hydroxyl fatty acids, 2-butyl- 2-ethyl-l,3-propanediol by a polycondensation reaction, as shown in Figure 1. The recipe for the polymerizations is provided in Table 1. The amount of dimethyl diacid ester was adjusted to realize an equal ratio of OH:COOH suitable for achieving high molecular weight. The procedure follows: A+B+C (from Figure 1) was heated to 80 °C and catalyst (Ti(OiPr) ₄ ) with a concentration 5.1 μ1/2 g monomers was added under stirring at 1000 rpm. The reaction was continued for 1 h at 80 °C, then 1 h at 100 °C, 2h at 120 °C, 2 h at 140 °C, and overnight at 160 °C with a vacuum of 300 mbar, and then 2 h at 180 °C, and 4 to 6 h at 200 °C with a vacuum of 20 mbar. For effective stirring, the nominal stirring speed was adjusted gradually during the reaction from 1000 rpm at the start of the reaction to 300 rpm depending on the viscosity of the reaction system. The reaction was terminated at the last step of

polymerization, i.e., at 200 °C, when the magnetic stir, nominally at 300 rpm, stopped. This ensured that a polyester with a high molecular weight was achieved. The polymerization of PEnnm ₂ -0.2 was duplicated with 4 h longer at 200 °C and 20 mbar. The polyesters of these two experiments are labeled PEnnm ₂ -0.2 A and PEnnm ₂ -0.2 B in Table 1. Table 1. Recipes for the preparation of the branched polyesters.

Results and Discussion

Chemical Characterization

The general structure of the branched polyesters as shown in Figure 1 was confirmed by ^-NMR. The ^-NMR spectra for each of the above recipes are shown in Figures 2-19. The ^-NMR data of the polyesters of the present work are provided in Table 2.

Table 2. ^-NMR data of the branched polyester. A: integrated area of NMR peaks; a: peak at chemical shift 5=4.10-4.00 ppm, related to proton of -CH^O- of ω-hydroxyl fatty acids; b: peak at chemical shift 5=3.95-3.85ppm, related to proton of -CH^O- of 2-butyl-2-ethyl-l 3- propanediol; c: peak at chemical shift 5=3.70-3.50 ppm, related to proton of OH of 2-butyl-2- ethyl-1 3-propanediol and ω-hydroxyl fatty acids, or -OCH ₃ of methyl hydroxyl fatty acid esters or diacid methyl esters; d: peak at chemical shift 5=2.40-2.20 ppm, related to proton of -CHCOO- of ω-hydroxyl fatty acids, diacid methyl esters; e: peak at chemical shift 5=1.70- 1.50 ppm, related to proton of -CH ₂ CHCOO- or -CH ₂ CH ₂ 0- of ω-hydroxyl fatty acids, diacid methyl esters; f: peak at chemical shift δ= 1.40-1.20 ppm, related to proton of -CH ₂ -; g: peak at chemical shift 5=1.00-0.80 ppm, related to proton of -CH ₃ .

Generally, the peak at chemical shift δ= 4.07-4.04 ppm corresponds to-CH ₂ 0-, the protons from the methylene group of ω-hydroxyl fatty acids attached to the ester linkage; and the peak at δ= 3.92 ppm to -CH ₂ 0- of 2-butyl-2-ethyl-l,3-propanediol. The peak at δ= 3.50 ppm to 3.70 ppm corresponds to the unreacted methyl group-OCH ₃ , the hydrogen from the hydroxyl group (OH) and the -CH^OH of both ω-hydroxyl fatty acids and 2-butyl-2-ethyl- 1,3-propanediol and therefore cannot be used to accurately estimate the molecular weight of the polyesters. The relative number of the branches can be estimated by the ratio of -CH ₂ 0- at 4.07 ppm to the

-CH ₂ CH ₃ from 2-butyl-2-ethyl-l,3-propanediol at δ= 0.92-0.88 ppm and 0.85-0.81 ppm. As seen in Table 3, the experimental ratio of branches is generally higher than its related theoretical value, suggesting that part of 2-butyl-2-ethyl-l,3-propanediol evaporated during the polymerization. One can notice however, that with the increase of ω-hydroxyl fatty acid chain length (n) and diacid methyl ester chain length (m), the difference between the theoretical and experimental values becomes smaller. This is attributable to the increasing viscosity of the reaction mixture which limits the evaporation of the monomer.

Table 3. Number of branches from 2-butyl-2-ethyl-l,3-propanediol as estimated by the ratio of the integral of the ¹ H-NMR-CH ₂ 0-/-CH ₂ CH ₃ peaks. NB _exp : experimental value and

NB _theo : theoretical value based on the recipe of Table 1.

Effect of Molecular Parameters and Structure on Physical Properties

Thermal Stability

The thermal stability of the achieved branched polyesters was determined by thermal gravimetric analysis (TGA). The derivative of the TGA (DTG) curves of branched polyesters of the present work are provided in Figure 20. The DTG curves of PEn _-2 m ₅ and PEnnm ₅ -0.2 which exemplify the thermal degradation behavior of all these polyesters are shown in Fig. 2.

The TGA data (T _5¾ : temperature at 5% weight loss, T° _n : extrapolated onset of degradation temperature, T _{m 2} : peak temperatures of the DTG, TR: thermal degradation temperature range and Ash: ash content (%) after thermal degradation) of all the polyesters of the present work are provided in Table 4. The onset temperature of degradation or T _5% in Table 2) was higher than 300 °C for all the branched polyesters. This is a high enough temperature for the safe thermal processing of these materials. As exemplified in Fig. 21 with the DTG curve of PEn _-2 m ₂ , the PEn _-2 m _x (x=2 and 5) polyesters presented a one-step degradation with a DTG peak at 358 °C and 449 °C, respectively. The other polyesters (PEn _-2 mi ₄ and PEn _z m _x -y (z=7, 11 or 16; x=2, 5 and 14; y=0.1, 0.2 and 0.3) presented degradations in two-steps: the first at -300 °C to 440 °C with a weight loss of more than 85%, attributable to the ester linkage degradation. It should be noticed that some of polyesters showed two steps in this temperature range due to the different ester linkages formed from hydroxyl group from ω- hydroxyl fatty acids or from 2-butyl-2-ethyl-l,3-propanediol. The second step occurred at -440 °C to 480 °C, with a weight loss of less than 15%, related to the clearance of the carbon-carbon bonds. Most of the samples contained less than 2 % ash after the thermal degradation was complete.

Table 4. Thermal gravimetric analysis of the branched polyesters. (°C): extrapolated onset of degradation temperature; T _5% (°C): the temperature at 5% weight loss; T _m (°C): peak temperatures at the DTG curve; Step I and II: step I and II of the thermal degradation; TR (°C): thermal degradation temperature range; WL (%): weight Loss; Ash: ash content (%) after thermal degradation

PEn _n mi ₄ -0.2 363 378 414 ~ 447 363-442 78 442-474 19 3

PEn _n mi ₄ -0.3 370 385 416 ~ 449 370-437 66 437-472 32 2

PEni ₆ m ₂ -0.2 345 384 415 ~ 458 345-453 88 453-473 10 2

Thermal Properties

The thermal properties were determined by DSC. The DSC data are provided in Table 5. The data of Fig. 22 showing the heating DSC thermograms (2 ^nd cycle) of the polyesters with C6, C9 and C18 diacid methyl ester, namely PEn _-2 m ₂ , PEn _-2 m ₅ and PEn _-2 mi ₄ and reveal the effect of the 2-butyl-2-ethyl-l,3-propanediol branches on the crystallinity of the diacid fatty acid chain. As can be seen in Fig. 22, 2-butyl-2-ethyl-l,3-propanediol has totally suppressed the crystallization of PEn _-2 m ₂ and PEn _-2 m ₅ (the diacid methyl ester chains from C6 and C9) but not the crystallization of PEn _-2 mi ₄ , (the diacid methyl ester chain from CI 8). These data suggest that the C6 and C9 diacid methyl esters are good candidates for the preparation of low crystallinity polyesters and therefore elastomeric polymers.

The effect on the melting behavior, including melting point (T _m ), melting enthalpy and glass transition temperature (T ) of the degree of branching, ω-hydroxyl fatty acid chain length (n) and diacid methyl ester chain length (m) is shown in Figs. 23-25, respectively.

Table 5. DSC results of the achieved polyesters. Τ _Λ and T _c2 ; high and low crystallization peak temperatures; T _m : melting temperature; T : glass transition temperature.

Cooling Heating (2 ¹

T T Enthalpy T Enthalpy

m T _g

PEn ₂ m ₂ -- — ~ -- ~ -48.2

PEn_ ₂ m ₅ -- ~ -- ~ -51.4

PEn_ ₂ iiii4 16.01 77.25 19.51 80.18 -22.9

PEn ₇ m ₂ -0.1 44.43 87.15 53.80 95.65 -56.8

PEn ₇ m ₂ -0.2 38.79 26.18 70.53 47.91 74.97 -57.7

PEn ₇ m ₅ -0.2 37.46 -23.27 77.68 45.24 85.61 -60.9

PEn ₇ mi4-0.2 37.01 -9.38 85.27 46.90 97.61 -53.8

PEniim ₂ -0.1 65.20 18.49 84.23 74.32 104.7 -22.5

PEniim ₂ -0.2 A 56.83 11.92 94.79 64.84 93.34 -41.2

PEniim ₂ -0.2 B 53.51 10.48 103.8 63.05 106.9 -45.7 PEniim ₂ -0.3 50.4 5.7 73.67 60.1 82.37 -42.2

PEniims-O.l 64.56 14.45 129.2 72.72 152.1 -40.1

PEniims-0.2 53.2 43.32 81.4 55.9 99.97 -43.7

PEniims-0.3 49.89 -4.26 75.32 56.87 92.13 -50.3

PEnnm ₁₄ -0.1 65.93 20.04 119.1 75.34 122.88 -21.8

PEnnmi ₄ -0.2 53.25 11.92 126.0 61.23 118.5 -26.9

PEnnmi ₄ -0.3 50.54 10.30 124.9 58.76 117.1 -39.1

PEni ₆ m ₂ -0.2 66.84 29.07 125.6 76.69 124.5 -25.5

Effect of branching

As shown in the panels of Fig. 23 representing the melting behavior of the PEnnm ₂ -y (y=0.1, 0.2 and 0.3) branched polyesters, with increased branching, the melting point and glass transition temperature (Fig. 23b), and enthalpy (Fig. 23c) decreased.

Effect of ω-hydroxyl fatty acid chain length

As shown in the panels of Fig. 24 representing the melting behavior of the PEn _z m ₂ - 0.2 (z=7, 11 and 16) branched polyesters, the melting point and glass transition temperature (Fig. 24b), and enthalpy (Fig. 24c) increase with increasing ω-hydroxyl fatty acid chain length.

Effect of diacid methyl ester chain length

As shown in the panels of Fig. 25 representing the melting behavior the PEnnm _x -0.2 (x=2, 5 and 14) branched polyesters, with the increase of diacid methyl ester chain length (m), the melting point (circles in Fig. 25b) decreases; whereas, the glass transition temperature (triangles in Fig. 25b) and enthalpy (Fig. 25c) increases.

Mechanical Properties

Only the polyesters of the PEnnm _x -y series were suitable for testing of the mechanical properties. The other polyesters were either too brittle or too soft to be tested. The static mechanical properties of the PEnnm _x -y polyesters are provided in Table 6. The strain versus stress curves of the PEnnm ₂ -y and PEnnm ₅ -y (y= 0.1, 0.2 and 0.3) are shown in Fig. 26a and 26b, respectively. The effect of the degree of branching on the Young's modulus, stress at break and strain is presented in Figs. 27a-c, respectively. As shown in Figs. 27a-c, Young's modulus and stress at break decrease, but the strain increases with the increase of the ratio of branches. The effect of the melting enthalpy on the mechanical properties is presented in Figs. 28a-c. As shown in Figs. 28a-b, Young's modulus and stress at break increase, whereas the strain decreases with increasing melting Enthalpy. The results are in the agreement with what was found in a previous study of linear poly (ω- hydroxyl fatty acid)s. These findings can be used to custom design polyesters from ω- hydroxyl fatty acids with optimized mechanical properties by varying the crystallinity of the polyesters.

Table 6. Mechanical properties of the obtained polyesters

The best elastomeric property was presented by PEnnm ₂ -0.2 B (Fig. 29), the sample prepared with an extended reaction time, suggesting that much higher molecular weight can be achieved with extended polymerization time. It showed a strain of 285 %, which is -17 times the strain achieved by PEnnm ₂ -0.2 A, the sample prepared with a similar recipe but with 4 hours shorter polymerization. These data suggest that very good elastomeric polyesters can be prepared by carefully controlling the reaction conditions, such as initial reaction temperature, vacuum and reaction time. Note that the viscosity of the reaction system is directly related to molecular weight, and can therefore be used as a very good indicator to determine the point at which the polymerization reaction can be terminated to achieve high molecular weight polymers and improved elastomeric properties. References

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