Degradable polyesters with improved thermomechanical properties

Abstract

A polyester is provided comprising repeating units derived from cis-5-hydroxymethyl-2- tetrahydrofuroic acid and repeating units derived from at least one other hydroxy acid.

Description

DEGRADABLE POLYESTERS WITH IMPROVED THERMOMECHANICAL PROPERTIESGOVERNMENT RIGHTS

[0001] This invention was made with Government support under National Science Foundation contracts (CHE-2317582 and CHE-2403822). The Government has certain rights in the invention.CROSS-REFERENCE TO RELATED APPLICATION

[0002] This application claims the benefit of priority of U.S. Application No. 63 / 678,253, filed August 1, 2024, which is incorporated herein by reference for all purposes.BACKGROUND

[0003] The present disclosure relates to polyesters. The present disclosure more specifically relates to bio-derived and degradable polyester.SUMMARY

[0004] To achieve the foregoing and in accordance with the purpose of the present disclosure, a polyester is provided comprising repeating units derived from cis-5- hydroxymethyl-2-tetrahydrofuroic acid and repeating units derived from at least one other hydroxy acid.

[0005] These and other features of the present invention will be described in more detail below in the detailed description of the disclosure and in conjunction with the following figures.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 shows depictions of the molecular structures of representative polyesters that are embodiments of the present invention and examples of monomers that can be used to prepare polyesters of the present invention.

[0007] FIG. 2 shows a schematic depiction of a melt polymerization used to prepare a polyester comprising repeating units derived from cz.s'-5-hydroxymelhyl-2-letrahydrofuroic acid (HMTA) and repeating units derived from lactic acid.

[0008] Table 1 shows thermomechanical properties for a polyester without repeating units derived from HMTA and polyesters with different amounts of repeating units derived from HMTA.

[0009] FIG. 3 shows stress-strain curves for a sample of a polyester without repeating units derived from HMTA and samples of two polyesters with different amounts of repeating units derived from HMTA.DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

[0010] The present disclosure describes polyesters with enhanced properties that lead to improved performance. Polyesters are polymers wherein the repeating units are linked together by one or two ester linkages. The present disclosure concerns polyesters containing a repeating unit derived from cw-5-hydroxymethyl-2-tetrahydrofuroic acid (HMTA).

[0011] Thermoplastics are indispensable to modern society, yet concerns about waste accumulation, pollution, and the emissions footprint of conventional plastics have inspired searches for environmentally benign alternatives. While they are inexpensive to manufacture and have exceptional properties, conventional petroleum-based polymers are responsible for more than 2 billion metric tons of CO2 equivalent emissions and 300 million metric tons of waste generated annually. Bio-derived polyesters that can be recycled or degraded back to CO2 and H2O at end-of-life are attractive alternatives. Poly(lactic acid) (PLA) currently comprises more than 70% of global bio-based polyester production and is valued for its ability to be degraded under industrial composting conditions. However, while PLA has high modulus, strength and optical clarity, it suffers from brittleness - fracturing at elongations < 10%. Numerous strategies to improve the toughness of PLA have been reported, but these approaches have often suffered from an accompanying loss in thermal or mechanical performance. For bio-derived polyesters to replace petroleum-based plastics, advances are needed to achieve optimal thermomechanical properties without sacrificing other performance metrics.

[0012] FIG. 1 shows depictions of the molecular structures of representative polyesters that are embodiments of the present invention and examples of monomers that can be used to prepare polyesters of the present invention. It is understood by those skilled in the art that polyester samples are typically comprised of a mixture of polymer molecules with a distribution of different chain lengths and, if the polyester contains more than one repeating unit, a distribution of different sequences of repeating units.

[0013] In some embodiments, polyesters are prepared using the bicyclic lactone 2-oxo- 3,8-dioxabicyclo[3.2.1]octane (ODO) as a monomer in a polymerization reaction. ODO is the lactone derived from lactonization of HMTA. HMTA can be synthesized from bio-derived 5- hydroxymethyl furoic acid (HMFA). ODO can therefore be synthesized as a bio-derived monomer.

[0014] In some embodiments, polyesters of the present invention contain repeating units derived from HMTA and repeating units derived from at least one other hydroxy acid, which is a molecule that contains both a carboxylic acid group and a hydroxyl group. Non- limiting examplesof the other hydroxy acid include any of a class of hydroxy acids known as hydroxyalkanoic acids, which consist of a saturated hydrocarbon chain with a terminal carboxylic acid group and a hydroxyl group attached at some position on the hydrocarbon chain. Examples include linear hydroxyalkanoic acids of general formula HOCH2(CH2)nCO2H where n is a natural number (0, 1, 2, 3...), such as glycolic acid (n=0), 3-hydroxypropionic acid (n=l), 4-hydroxybutanoic acid (n=2), etc. Other examples include hydroxyalkanoic acids wherein the OH is attached to a nonterminal carbon of the hydrocarbon chain, such as L-lactic acid, D-lactic acid, and 3- hydroxybutyric acid. In other embodiments, the other hydroxy acid contains an aromatic ring. In some embodiments, the other hydroxy acid contains a benzene ring. In other embodiments, the other hydroxy acid contains a furan ring. In some embodiments, the other hydroxy acid is 5- (hydroxymethyl)furan-2-carboxylic acid.

[0015] In some embodiments, polyesters of the present invention contain a minority of repeating units derived from HMTA and a majority of repeating units derived from one or more other hydroxy acids. For example, in some embodiments, the polyesters comprise from 0.1 mol% to 50 mol% repeating units derived from HMTA and from 50 mol% to 99.9 mol% repeating units derived from at least on of another hydroxy acids. In some embodiments, the polyesters comprise from 0.1 mol% to 10 mol% repeating units derived from HMTA and from 90 mol% to 99.9 mol% repeating units derived from at least one other hydroxy acid. In some embodiments, the polyesters comprise from 1 mol% to 15 mol% repeating units derived from HMTA and from 85 mol% to 99 mol% repeating units derived from at least one other hydroxy acid. In some embodiments, the repeating units derived from HMTA are distributed randomly throughout the polyester chains, in which case the polyester may be described as a statistical copolymer. In other embodiments, the repeating units derived from HMTA are distributed in blocks throughout the polyester chains, in which case the polyester may be described as a block copolymer. In some embodiments, the polyesters comprise repeating units from HMTA and at least two of another hydroxy acid.

[0016] In preferred embodiments, polyesters of the present invention contain repeating units derived from HMTA and lactic acid. In some embodiments, the repeating units derived from HMTA are distributed randomly throughout the polyester chains, forming a statistical copolyester. In some embodiments, polyesters of the present invention contain repeating units derived from HMTA and L-lactic acid. In some embodiments, polyesters of the present invention contain repeating units derived from HMTA and D-lactic acid. In some embodiments, polyesters of the present invention contain repeating units derived from HMTA and a mixture of L and D-lactic acid. In some embodiments, the polyesters containing repeating units derived from HMTA andlactic acid are prepared by polycondensation reactions of HMTA and lactic acid. In other embodiments, the polyesters containing repeating units derived from HMTA and lactic acid are prepared by ring-opening polymerization of ODO and lactide. Lactide is a cyclic bislactone derived from two molecules of lactic acid.

[0017] In some embodiments, the polyesters containing repeating units derived from HMTA and lactic acid contain at least 0.5 wt% a repeating unit derived from HMTA. In other embodiments, the polyesters contain at least 1 wt%, at least 2 wt%, at least 5 wt%, at least 10 wt%, or at least 20 wt% a repeating unit derived from HMTA.

[0018] In some embodiments, polyesters of the present invention contain repeating units derived from HMTA and glycolic acid. In some embodiments, the polyesters containing repeating units derived from HMTA and glycolic acid are prepared by polycondensation reactions of HMTA and glycolic acid. In other embodiments, the polyesters containing repeating units derived from HMTA and glycolic acid are prepared by ring-opening polymerization of ODO and 1,4-dioxane- 2, 5-dione.

[0019] In some embodiments, the polyesters containing repeating units derived from HMTA and glycolic acid contain at least 0.5 wt% a repeating unit derived from HMTA. In other embodiments, the polyesters contain at least 1 wt%, at least 2 wt%, at least 5 wt%, at least 10 wt%, or at least 20 wt% a repeating unit derived from HMTA.

[0020] In some embodiments, the polyesters containing repeating units derived from HMTA and at least one other hydroxy acid contain at least 0.5 wt% a repeating unit derived from HMTA. In other embodiments, the polyesters contain at least 1 wt%, at least 2 wt%, at least 5 wt%, at least 10 wt%, or at least 20 wt% a repeating unit derived from HMTA. For example, in some embodiments, the polyesters contain in the range from 0.01 wt% to 20 wt% of repeating units derived from HMTA and from 80 wt% to 99.99 wt% of repeating units derived from at least one other hydroxy acid.

[0021] In some embodiments, the incorporation of a repeating unit derived from HMTA into a polyester improves the mechanical properties compared to the polyester without a repeating unit derived from HMTA. In some embodiments, the incorporation of a repeating unit derived from HMTA improves the toughness of the polyester such that it is less likely to break upon impact. In some embodiments, the incorporation of a repeating unit derived from HMTA increases the elongation at break. In some embodiments, the incorporation of a repeating unit derived from HMTA increases the elongation at break by at least 10 percentage points (10%). For example, if a polyester without repeating units derived from HMTA has an elongation at break of 9%,incorporation repeating units derived from HMTA into the same polyester results in a polyester that has an elongation at break of at least 19%. In some embodiments, the incorporation of a repeating unit derived from HMTA increases the elongation at break by at least 20 percentage points (20%), by at least 30 percentage points (30%), by at least 40 percentage points (40%), by at least 50 percentage points (50%), by at least 60 percentage points (60%), by at least 70 percentage points (70%), by at least 80 percentage points (80%), by at least 90 percentage points (90%), or by at least 100 percentage points (100%).

[0022] The improvements to toughness and / or elongation at break by incorporation of a repeating unit derived from HMTA can be achieved without compromising other thermomechanical properties of the polyester. In some embodiments, the incorporation of a monomer derived from HMTA improves the elongation at break while changing the Young’s modulus by less than 1 gigapascal (GPa). In some embodiments, the incorporation of a monomer derived from HMTA improves the elongation at break while changing the Young’s modulus by less than 0.8 GPa, by less than 0.6 GPa, by less than 0.4 GPa, or by less than 0.2 GPa. In some embodiments, the incorporation of a monomer derived from HMTA improves the elongation at break while changing the glass transition temperature by less than 20 °C. In some embodiments, the incorporation of a monomer derived from HMTA improves the elongation at break while changing the glass transition temperature by less than 15 °C, by less than 10 °C, by less than 5 °C, by less than 2 °C, or by less than 1 °C.

[0023] In some embodiments, polyesters of the present invention are prepared by a melt copolymerization. In some embodiments, the melt copolymerization comprises combining ODO and one or more other lactones and heating to a temperature to form a melt and induce ringopening polymerization. A catalyst is often added to catalyze melt copolymerizations. In some embodiments, a Lewis acid catalyst is used. Examples of Lewis acid catalysts include SnO, Sn(Oct)2, SnCh, SnBn, SnO2, SnCLi, SnBn, Zn(OAc)2, ZnO, ZnCh, Ti(O / Bu)4. In some embodiments, an initiator is added to the melt copolymerization reaction. Examples of initiators include alcohols such as methanol, ethanol, propanol, butanol, and benzyl alcohol.

[0024] In some embodiments, polyesters of the present inventions are prepared by polycondensation reactions. In some embodiments, the polycondensation comprises of combining HMTA and one or more other hydroxy acid and heating the reaction under reduced pressure or in the presence of a high boiling solvent (>80 °C). Suitable solvents include toluene, benzene, xylene, mesitylene and other hydrocarbon solvents. In embodiments where the invention is prepared by polycondensation under vacuum, aliphatic esters of HMTA and other hydroxy esters are alsosuitable precursors. In some embodiments, the polyester copolymer is prepared by condensing a mixture of HMTA and another hydroxy acid. In some embodiments, the polyester copolymer is prepared by condensing two or more polyester homopolymers, one comprised of repeating units derived from HMTA and others with repeating units derived from other hydroxy acids. In some embodiments, the polyester copolymer is prepared by condensing one polyester homopolymer containing repeating units derived from HMTA or repeating units derived from another hydroxy acid with another hydroxy acid or HMTA, respectively. In some embodiments, partial epimerization of cA-5-hydroxymethyl-2-tetrahydrofuroic acid to frans-5-hydroxymethyl-2- tetrahydrofuroic acid occur. Preferred catalysts for this transformation are similar to aforementioned melt polymerization catalysts such as SnO, Sn(Oct)2, and etc.

[0025] In some embodiments, polyesters of the present invention are prepared by ringopening polymerization (ROP) of ODO and at least one other lactone monomer performed in a solvent. Examples of solvents that are suitable for ROP include tetrahydrofuran (THF). In some embodiments, polyesters of the present invention are prepared by ROP catalyzed by an organic catalyst, which is referred to as organocatalytic ring opening polymerization (OROP). Organocatalysts for OROP that can be used to make polyesters of the present invention include urea catalysts such as l,3-bis(3,5-bis(trifhroromethyl)phenyl)urea (Schreiner’s urea catalyst, SU), which is typically used in combination with a base such as l,8-diazabicyclo[5.4.0]undec-7-ene (DBU). In some embodiments, OROP is performed in the presence of an initiator. Examples of initiators include alcohols such as benzyl alcohol.EXAMPLESExample 1: ODO Synthesis

[0026] 5-hydroxymethyl-2-furoic acid, HMFA (15.466 g, 109 mmol), RI1 / AI2O3 or Rh / C (0.2046 g, 5 wt% Rh), and water (70 mL) were combined in a pressure reactor. The reactor was purged with inert gas before being pressurized with H2 to 10 bar. The reactor was left stirring for 1-3 days, or until H2 pressure stabilized. Upon completion, the reactor was depressurized and flushed with inert gas. The catalyst was removed by centrifugation and filtration before the solution was dried via rotary evaporation. The resulting oil comprising 5-hydroxymethyl-2- tetrahydrofuroic acid (HMTA) was used without further purification (93% yield).1H NMR (D2O, 5): 4.56 (1H, m), 4.22 (1H, m), 3.72 (1H, dd), 3.66 (1H, dd), 2.36 (1H, m), 2.09 (2H, m), 1.76 (1H, m).

[0027] HMTA (14.7555 g) was condensed at 120°C under reduced pressure (-200 mbar) in the presence of SnO (0.2681 g, 2 wt%) for 8 hours to generate oligomeric poly(oxo-3,8- dioxabicyclo[3.2.1]octane) (o-PODO). After condensation, glycerol ethoxylate (GEO, 0.2662 g, 2 wt%) was added to o-PODO and the mixture was heated to 180 °C under stronger reduced pressure (< 10 mbar) to distill off crude ODO. The ODO was distilled into a vessel containing a desiccant such as CafL or 3 A or 4 A molecular sieves (81% yield relative to HMTA and 76% yield relative to HMFA). The crude ODO is then separated from the desiccant via filtration before being purified by recrystallized in toluene, 1:1 toluene:hexanes or 2: 1 THF:hexanes (67% yield relative to crude ODO). Precipitated ODO crystals are then washed with hexanes before being sublimed under vacuum (mbar) at 35-40 °C (80% relative to recrystallized ODO).1H NMR (CDCh, 5): 4.61 (3H, m), 4.13 (1H, d), 2.22 (3H, m), 2.01 (1H, m).13C NMR (CDCh, 5): 169.0, 75.7, 74.2, 71.2, 30.5, 26.5. LC-MS (positive ESI) m / z calcd for C6H8O3 [M + H]+ : 129.1; found: 129.1.Example 2: Polymerization of ODO to form poly(oxo-3,8-dioxabicyclo[3.2.1]octane) PODO

[0028] Melt polymerization of ODO was conducted by combining oxo-3,8- dioxabicyclo[3.2.1]octane (570 mg, 4.5 mmol) and a 0.05 M solution of Sn(Oct)2 in THF (15 pL, 0.00075 mmol, 0.02 mol%) under an inert atmosphere. The reaction vessel was sealed or kept under inert atmosphere before being heated at 90 °C for 24 h. The resulting crude polymer was then dissolved in minimum amount of methylene chloride and precipitated in methanol. The precipitated polymer was washed with methanol three times before drying under high vacuum overnight to yield a soft colorless polymer, poly(oxo-3,8-dioxabicyclo[3.2.1]octane) (PODO) (78% yield).Example 3: Synthesis and thermomechanical testing of PLA-. / a / -PODO

[0029] Melt copolymerization was conducted by combining L-lactide and ODO and a Sn(Oct)2 catalyst in THF under inert atmosphere and heating to 100 °C. The ratio of lactide to ODO was varied to give a desired composition. As a specific example, L-lactide (790 mg, 5.5 mmol), ODO (70 mg, 0.5 mmol, 10 mol%), and a 0.05 M solution of Sn(Oct)2 in THF (25 pL, 0.0013 mmol, 0.02 mol%) were combined under an inert atmosphere. The reaction vessel was sealed or kept under inert atmosphere before being heated to 100 °C for 24 h. The resulting crudepolymer was then dissolved in minimum amount of methylene chloride and precipitated in methanol. Precipitated polymer was washed with methanol three times before drying under high vacuum overnight to yield a white polymer, poly(L-lactide-5tat-oxo-3,8- dioxabicyclo[3.2.1]octane) (PLA-sw-PODO, 10: 1 PLA / PODO) (90% yield).

[0030] Melt copolymerization used to produce high molecular weight copolymers. The reaction is illustrated in FIG. 2. Copolymerization of 0-19% ODO with lactide under these conditions resulted in high molecular weight (Mn> 20 kDa), semicrystalline copolymers with melting temperatures between 124-153 °C and glass transition temperatures between 54-60 °C. The % of repeating units derived from HMTA in the copolymer was determined by1H NMR analysis.

[0031] To prepare melt-pressed films, the purified polymer was dried in a vacuum oven overnight at 80 °C to remove residual solvent and ensure polymer was free of moisture. The polymer was then hollow pressed at 180 °C for 2 minutes under 3000 psi. After pressing, the sample was allowed to cool at ambient temperature. Polymer films were cut into tensile bars and aged overnight at ambient temperature. Tensile properties were investigated using a Linkam Mechanical Tester with an extension rate of 10 pm / s and gauge length of 15 mm using a 200 N load cell. Copolymer films were optically clear and did not exhibit discoloration. Each film was then cut into at least three dogbones for replicate measurements. PLA-stat-PODO copolymers had an average elongation at break (Eb) greater than 12x that of native PLA, with 10: 1 PLA-.v / o / -PC)DO able to elongate up to 144%. In addition, only a modest change in Young’s modulus and yield strength was observed for any of the copolymers, as shown in FIG. 3.

[0032] Table 1 shows the thermomechanical properties for PLA with no repeating units derived from HMTA (0%), PLA-.v / « / -PODO with 5 mol% repeating units derived from HMTA, and PLA-.S / <7 / -PODO with 9 mol% repeating units derived from HMTA. The mechanical properties (Young’s modulus, yield strength, and elongation at break) are reported as the average values + standard error of at least 3 independent measurements. Table 1 in entry 1 shows that for 0 mol% repeating units derived from HMTA (i.e., PLA), the polyester has a molecular weight determined by gel permeation chromatography of 349 kilodaltons (kDa), a polydispersity of 1.44, a glass transition temperature of 61°C, a melting temperature of 178°C, an enthalpy of fusion of 34.0 joules / gram (J / g), a Young’s modulus of 4.2+0.1 gigapascals (GPa), a yield strength of 43.6+0.9 megapascals (MPa), and an elongation at break of 7.4+0.6%. Entry 2 shows that for PLA-.s / a / -PODO with 5 mol% repeating units derived from HMTA, the polyester has a molecular weight 307 kDa, a poly dispersity of 1.17, a glass transition temperature of 60 °C, a meltingtemperature of 153°C, an enthalpy ef fusion of 6.0 J / g, a Young’s modulus of 3.8+0.1 GPa, a yield strength of 54.0+0.6 MPa, and an elonogation at break of 98.0+12.5%. Entry 3 shows that for PLA-.s / a / -PODO with 9 mol% repeating units derived from HMTA, the polyester has a molecular weight 134 kDa, a polydispersity of 1.38, a glass transition temperature of 56 °C, a melting temperature of 144 °C, an enthalpy of fusion of 0.9 J / g, a Young’s modulus of 3.5+0.1 GPa, a yield strength of 53.2+0.6 MPa, and an elongation at break of 96.7+19.6%.

[0033] FIG. 3 shows the stress-strain curve for one dogbone sample of each of the polymers with 0 mol%, 5 mol%, and 9 mol% repeating units derived from HMTA. For 0 mol% repeating units derived from HMTA (i.e., PLA), the elongation at break for this sample is about 10%; for PLA-.v / a / -PODO with 5 mol% repeating units derived from HMTA, the elongation at break for this sample is >80%, and for PLA-.w« / -PODO with 9 mol% repeating units derived from HMTA, the elongation at break for this sample is >110%.Example 4: Co-polymerization of glycolide and ODO to form PGA-.v / « / -PODO

[0034] Melt polymerization was conducted by combining glycolide (315 mg, 2.71 mmol), oxo-3,8-dioxabicyclo[3.2.1]octane (38.64 mg, 0.3 mmol, 10 mol%), and a 0.05 M solution of Sn(Oct)2 in THF (15 pL, 0.008 mmol, 0.02 mol%) under an inert atmosphere. The reaction vessel was sealed or kept under inert atmosphere before being heated to 100 °C for 24 h. The resulting crude polymer was then dissolved in minimum amount of 1,1, 1,3, 3, 3-Hexafluoro-2 -propanol and precipitated in methanol. Precipitated polymer was washed with methanol three times before drying under high vacuum overnight to yield a white polymer, poly(glycolide-.v / « / -oxo-3,8- dioxabicyclo[3.2.1]octane) (PGA-stat-PODO, 10: 1 PGA / PODO) (71% yield).

[0035] In some embodiments, for polyesters such as PLA, incorporation of repeating units derived from HMTA results in an elongation at break of at least 20%. In some embodiments, an elongation break of at least 50% is provided. In some embodiments, an elongation break of at least 70% is provided. In some embodiments, an elongation break of at least 100% is provided. In some embodiments, an elongation break of in the range of 70% to 200% is provided. In some embodiments with the above elongation at break ranges described above, a Young’s modulus of greater than 3.0 GPa is provided. In some embodiments with the above elongation at break ranges described above, a glass transition temperature in the range of 50 °C to 65 °C is provided. In some embodiments, the presence of repeating units derived from HTMA increases the elongation at break by at least 50 percentage points compared to the same polyester without repeating unitsderived from HTMA while changing the Young’s modulus by less than 0.5 GPa and the glass transition temperature by less than 10 °C. As a result, some embodiments, provide a significant increase in the elongation at break without significantly changing the Young’s modulus and the glass transition temperature.

[0036] In some embodiments, incorporation of repeating units derived from HMTA increases the rate of degradation of a polyester compared to the polyester without repeating units derived from HMTA. Increasing the rate of degradation can be beneficial for the management of the material at the end of its intended use and the avoidance of accumulation of the material in the environment. Degradation of a polyester includes chemical processes such as hydrolysis of the ester linkages, which breaks the polymer chains into shorter chains and monomers, oxidation reactions, and photochemical transformations. In some embodiments, incorporation of repeating units derived from HMTA can increase the rate of degradation by reducing the amount or size of crystalline domains in the polymer. In some embodiments, incorporation of repeating units derived from HMTA can increase the rate of degradation by degradation of the tetrahydrofuranic functionality of the HMTA-derived repeating units. In some embodiments, incorporation of repeating units derived from HMTA increases the rate of degradation of the polyester under conditions used for industrial composting. In other embodiments, incorporation of repeating units derived from HMTA increases the rate of degradation of the polyester under conditions used for home composting. In other embodiments, incorporation of repeating units derived from HMTA increases the rate of degradation of the polyester under ambient conditions.

Claims

CLAIMSWhat is claimed:

1. A polyester comprising repeating units derived from HMTA and repeating units derived from at least one other hydroxy acid.

2. The polyester of claim 1, wherein the polyester comprises from 0.1 mol% to 50 mol% repeating units derived from HMTA and from 50 mol% to 99.9 mol% repeating units derived from the at least one other hydroxy acid.

3. The polyester of claim 1, wherein the polyester comprises from 0.1 wt% to 20 wt% of repeating units derived from HMTA and from 80 wt% to 99.9 wt% of repeating units derived from the at least one other hydroxy acid.

4. The polyester of claim 1, where the distribution of repeating units derived from HMTA and repeating units derived from the at least one other hydroxy acid form a statistical copolymer.

5. The polyester of claim 1 where the distribution of repeating units derived from HMTA and repeating units derived from the at least one other hydroxy acid form a block copolymer.

6. The polyester of claim 1, wherein the polyester is prepared by polycondensation of a mixture of HMTA and the at least one other hydroxy acid.

7. The polyester of claim 1, wherein the polyester is prepared by ring-opening polymerization of a mixture of 2-oxo-3,8-dioxabicyclo[3.2.1]octane (ODO) and at least one other lactone monomer.

8. The polyester of claim 1, wherein the at least one other hydroxy acid is at least one of lactic acid, glycolic acid, or another hydroxyalkanoic acid.

9. The polyester of claim 1, wherein the at least one other hydroxy acid comprises a lactic acid.

10. The polyester of claim 1, wherein the at least one other hydroxy acid is a glycolic acid.

11. The polyester of claim 1, with an elongation at break of at least 20%.

12. The polyester of claim 1, with an elongation at break of at least 70%.

13. The polyester of claim 12, with a Young’s modulus of greater than 3.0 GPa.

14. The polyester of claim 13, with a glass transition temperature in the range of 50°C to 65°C.

15. The polyester of claim 1, wherein the presence of repeating units derived from HTMA increases the elongation at break by at least 50 percentage points compared to a polyester without repeating units derived from HTMA while changing the Young’s modulus by less than 1 GPa and the glass transition temperature by less than 10°C.

16. The polyester of claim 1, wherein the presence of repeating units derived from HTMA increases the elongation at break by at least 70 percentage points compared to a polyester without repeating units derived from HTMA while changing the Young’s modulus by less than 1 GPa and the glass transition temperature by less than 10°C.

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