Stereoregular Polyesters Research Articles

Thermal degradation and upcycling of stereoregular polyesters

In this study, the thermal degradation behavior and the decomposition products obtained during the pyrolysis of a new polyester, poly(HASA/CHO) (PHC), were investigated. Thermogravimetric (TG) and differential thermogravimetric (DTG) analyses indicated that the pyrolysis of PHC could be divided into three stages. The average activation energies for stages I and III were estimated using the Kissinger method. The pyrolytic processes were monitored using gel permeation chromatography (GPC), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), and ultraviolet-visible UV–vis spectroscopy. The effects of the PHC configuration on the thermal stability and evolution of the thermal process were explored. The results demonstrated that, compared to the cis-PHC, the trans-PHC is more likely to release anthracene via a retro-Diels-Alder reaction, and exhibits higher main chain stability. Interestingly, PHC could be reversibly recycled via the Diels-Alder reaction, leading to potential upcycling of the copolymer.

Ring-opening Polymerization of Enantiopure Bicyclic Ether-ester Monomers toward Closed-loop Recyclable and Crystalline Stereoregular Polyesters via Chemical Upcycling of Bioplastic.

Although great successes have been achieved, the preparation of closed-loop recyclable polyesters with high working temperatures still remains as a big challenge. Herein, we present the syntheses of a series of enantiopure bicyclic ether-ester monomers by upcycling of poly(3-hydroxybutyrate) bioplastic. The "living"/controlled ring-opening polymerizations of these enantiopure monomers to produce stereoregular polyesters with controlled molecular weights and well-defined chain ends were achieved. The effects of stereoconfiguration and substituent on polymerization kinetics and thermodynamics as well as the thermal properties of resultant polyesters were investigated. Of note, the stereoregular polyesters are semi-crystalline materials with melting temperatures up to 176 °C, even higher than the commodity polyolefin plastics. These polyesters can be depolymerized back to recover pristine monomers, thus successfully establishing a closed-loop life cycle.

Ring‐opening Polymerization of Enantiopure Bicyclic Ether‐ester Monomers toward Closed‐loop Recyclable and Crystalline Stereoregular Polyesters via Chemical Upcycling of Bioplastic

AbstractAlthough great successes have been achieved, the preparation of closed‐loop recyclable polyesters with high working temperatures still remains as a big challenge. Herein, we present the syntheses of a series of enantiopure bicyclic ether‐ester monomers by upcycling of poly(3‐hydroxybutyrate) bioplastic. The “living”/controlled ring‐opening polymerizations of these enantiopure monomers to produce stereoregular polyesters with controlled molecular weights and well‐defined chain ends were achieved. The effects of stereoconfiguration and substituent on polymerization kinetics and thermodynamics as well as the thermal properties of resultant polyesters were investigated. Of note, the stereoregular polyesters are semi‐crystalline materials with melting temperatures up to 176 °C, even higher than the commodity polyolefin plastics. These polyesters can be depolymerized back to recover pristine monomers, thus successfully establishing a closed‐loop life cycle.

Unimolecular Anion‐Binding Catalysts for Selective Ring‐Opening Polymerization of O‐carboxyanhydrides

AbstractAnion‐binding can regulate anion transport in chloride channels through dynamic non‐covalent interactions, which gives insights into the designing of new organocatalytic transformations but is surprisingly unexplored in polymerization catalysis. Herein, we describe an effective unimolecular anion‐binding organocatalysis where 4‐(dimethylamino)pyridine is anchored to a thiourea for ring‐opening polymerization of O‐carboxyanhydrides (OCAs) to furnish highly isotactic poly(phenyllactic acid) (Ph‐PLA) with molecular weight (MW) up to 150.0 kDa, which well addresses the formidable challenge of synthesizing high MW stereoregular polyesters. Calculations and experimental studies indicate a dynamic cooperative anion‐binding mechanism, where the dynamic anion‐binding interaction of thiourea moiety to propagating species facilitates efficient chain propagation and the synergetic decarboxylation retains high selectivity for OCA ring‐opening over side reactions (such as cyclization, epimerization, and transesterification).

Unimolecular Anion‐Binding Catalysts for Selective Ring‐Opening Polymerization of O‐carboxyanhydrides

AbstractAnion‐binding can regulate anion transport in chloride channels through dynamic non‐covalent interactions, which gives insights into the designing of new organocatalytic transformations but is surprisingly unexplored in polymerization catalysis. Herein, we describe an effective unimolecular anion‐binding organocatalysis where 4‐(dimethylamino)pyridine is anchored to a thiourea for ring‐opening polymerization of O‐carboxyanhydrides (OCAs) to furnish highly isotactic poly(phenyllactic acid) (Ph‐PLA) with molecular weight (MW) up to 150.0 kDa, which well addresses the formidable challenge of synthesizing high MW stereoregular polyesters. Calculations and experimental studies indicate a dynamic cooperative anion‐binding mechanism, where the dynamic anion‐binding interaction of thiourea moiety to propagating species facilitates efficient chain propagation and the synergetic decarboxylation retains high selectivity for OCA ring‐opening over side reactions (such as cyclization, epimerization, and transesterification).

Enantioselective Resolution Copolymerization of Racemic Epoxides and Anhydrides: Efficient Approach for Stereoregular Polyesters and Chiral Epoxides.

Herein we report an efficient strategy for preparing isotactic polyesters and chiral epoxides via enantioselective resolution copolymerization of racemic terminal epoxides with anhydrides, mediated by enantiopure bimetallic complexes in conjunction with a nucleophilic cocatalyst. The chirality of both the axial linker and the diamine backbones of the ligand are responsible for the chiral induction of this kinetic resolution copolymerization process. The catalyst systems exhibit exceptional levels of enantioselectivity with a kinetic resolution coefficient exceeding 300 for various racemic epoxides, affording highly isotactic copolymers (selectivity factors of more than 300) with a completely alternating structure and low polydispersity index. Most of the produced isotactic polyesters are typical semicrystalline materials with melting temperatures in the range from 77 to 160 °C.

CO2-Tuned Sequential Synthesis of Stereoblock Copolymers Comprising a Stereoregularity-Adjustable Polyester Block and an Atactic CO2-Based Polycarbonate Block

Stereoblock copolymers composed of atactic CO2-based polycarbonate and various stereoregular polyester blocks with cis-2,3-(exo, exo), cis-2,3-(endo, endo), or partly trans-2,3-(exo, endo) repeating units were successfully synthesized via sequential ring-opening copolymerization (ROCOP) of cyclohexene oxide (CHO) with norbornene anhydride (NA) and then ROCOP of CHO with CO2 using a salcyCrCl/PPNCl binary catalyst. The structure of the block copolymers was confirmed by NMR and GPC. Incorporation of carboxyl groups by the thiol–ene reaction of the pendant norbornenyl groups further confirmed the polymer structures. The geometric structure of polyester units in the block copolymers is tailored simply by varying the NA isomer and the monomer feed ratio of CHO to NA. Notably, CO2 suppressing the configuration transformation from cis-(exo, exo) to trans-(exo, endo) of polyester block has been revealed in the sequential ROCOP. Using this strategy, the stereospecific polyester with an dominant cis-2,3-(exo, exo)-...

Asymmetric Alternating Copolymerization of Meso-epoxides and Cyclic Anhydrides: Efficient Access to Enantiopure Polyesters.

Synthesis of stereoregular polyesters with main-chain chirality was achieved for the first time by the asymmetric copolymerization of meso-epoxides and cyclic anhydrides using catalyst systems based on enantiopure bimetallic complexes. The combination of the biphenol-linked dinuclear aluminum complex with tert-butyl groups in the phenolate ortho-positions and a nucleophilic co-catalyst was found to be more efficient in catalyzing this asymmetric copolymerization, affording enantiomerically enriched polyesters (up to 91% ee) with completely alternating structure and narrow molecular weight distribution. It was discovered that the isotactic-enriched poly(cyclopentene phthalate) is a typical semicrystalline material with a melting endothermic peak at 221 °C. This study is expected to provide a promising route to prepare various stereoregular polyesters having a wide variety of physical properties and degradability.

Controllable Synthesis of Stereoregular Polyesters by Organocatalytic Alternating Copolymerizations of Cyclohexene Oxide and Norbornene Anhydrides

A facile strategy has been demonstrated for the selective synthesis of highly stereoregular polyesters with cis-2,3-(exo, exo) or trans-2,3-(exo, endo) repeating units by the organocatalysts mediated alternating copolymerization of cyclohexene oxide and norbornene anhydride (NA) stereoisomers. The geometrical structure of polyester can be tuned simply by modulating the type of NA isomers (endo- or exo-NA), monomer feed ratio, and reaction temperature. The cis- (>99%) and trans-polyesters (>99%) exhibit high glass transition temperature up to 129.8 and 115.9 °C, respectively. The resulting polyesters provide a versatile platform to incorporate various functional groups through the robust thiol–ene reaction of the pendant norbornenyl groups.

Bacterial Polyesters: Biosynthesis, Biodegradable Plastics and Biotechnology

The discovery and chemical identification, in the 1920s, of the aliphatic polyester: poly(3-hydroxybutyrate), PHB, as a granular component in bacterial cells proceeded without any of the controversies which marked the recognition of macromolecules by Staudinger. Some thirty years after its discovery, PHB was recognized as the prototypical biodegradable thermoplastic to solve the waste disposal challenge. The development effort led by Imperial Chemical Industries Ltd., encouraged interdisciplinary research from genetic engineering and biotechnology to the study of enzymes involved in biosynthesis and biodegradation. From the simple PHB homopolyester discovered by Maurice Lemoigne in the mid-twenties, a family of over 100 different aliphatic polyesters of the same general structure has been discovered. Depending on bacterial species and substrates, these high molecular weight stereoregular polyesters have emerged as a new family of natural polymers ranking with nucleic acids, polyamides, polyisoprenoids, polyphenols, polyphosphates, and polysaccharides. In this historical review, the chemical, biochemical and microbial highlights are linked to personalities and locations involved with the events covering a discovery timespan of 75 years.

Synthesis and rheological study of some maleic acid and fumaric acid stereoregular polyesters, 10. Synthesis and characterization of ,-dihydroxyoligo(alkylene maleate)s

Synthesis and rheological study of some maleic acid and fumaric acid stereoregular polyesters, 10. Synthesis and characterization of ,-dihydroxyoligo(alkylene maleate)s

Synthesis and rheological study of some maleic acid and fumaric acid stereoregular polyesters, 10. Synthesis and characterization ofα,ω-dihydroxyoligo(alkylene maleate)s

α,ω-Dihydroxyoligo(alkylene maleate)s with molecular weights ranging from 1 500 to 4 000 were prepared by polycondensation, in 1-methyl-2-pyrrolidone at 105°C, of potassium maleate and 1,4-dibromobutane, 1,6-dibromohexane or 1,8-dibromooctane in the presence of 2-bromoethanol. The structure of oligomers was checked by 1H and 13C NMR spectroscopy. In most cases the mean functionality of oligomers is reasonably close to two.

Synthesis and rheological study of some maleic acid and fumaric acid stereoregular polyesters, 10. Synthesis and characterization of α,ω-dihydroxyoligo(alkylene maleate)s

Synthesis and rheological study of some maleic acid and fumaric acid stereoregular polyesters, 10. Synthesis and characterization of α,ω-dihydroxyoligo(alkylene maleate)s

Synthesis and rheological study of some maleic acid and fumaric acid stereoregular polyesters, 10. Synthesis and characterization of ,-dihydroxyoligo(alkylene maleate)s

Synthesis and rheological study of some maleic acid and fumaric acid stereoregular polyesters, 10. Synthesis and characterization of ,-dihydroxyoligo(alkylene maleate)s

Biocatalytic Synthesis of Polyesters Using Enzymes

Plants and animals have been exploited as sources of materials for centuries but, as our ability to analyze and fractionate them has progressed, the extraordinary range of properties available from materials produced by living systems has continued to grow. Doi, in another article in this issue of theMRS Bulletin, presents a discussion of a group of naturally occurring polyesters related to poly(beta-hydroxybutyrate). These polyesters are formedin vivoby several microorganisms as part of an energy storage scheme. Research on these systems has allowed growth conditions to be found that can lead, in a controlled fashion, to a number of copolymers. Useful materials based on these bacterial polyesters appear to be at hand.Thein-vivoformation of polyesters in microorganisms also illustrates several of the important reasons for examining biocatalytic polymer synthesis. First, unlike most industrial syntheses of polyesters, the poly(beta-hydroxybutyrate) biosynthesis occurs at a near-ambient temperature using a carbohydrate feedstock. Second, and perhaps most importantly, the stored polyesters are readily biodegraded by the bacteria that manufacture them, so materials based on these polyesters should also be biodegradable. Third, although there are side chains along the polymer backbone, they are introduced in a highly stereo-specific fashion duringin-vivosynthesis, leading to an entirely stereoregular polyester. However, along with these advantages, there are also significant limitations to bacterial polyester synthesis. First, there are some substrates that are not incorporated into the polyester by the bacteria. Second, normal metabolism leads to the polyester, always incorporating a fraction of hydroxybutyrate monomers. Third, the backbone is always comprised of four-atom, A-B type 3-hydroxy acid repeat units with variations appearing in the side chain at carbon-3.

Synthesis and rheological study of some maleic acid and fumaric acid stereoregular polyesters, 7. Rheological study of copolymerization reaction of configurationally pure unsaturated copolyesters and styrene

AbstractThe crosslinking copolymerization of styrene and configurationally pure unsaturated copolyesters, containing phthalic acid and maleic or fumaric acid residues, was carried out in a dynamic shear field at a frequency of 6,28 rad · s−1 and ambient temperature. It was found that a clear distinction can be made between gelation and postgelation crosslinking. The former takes place between the onset at G′ ≈︁ G″ (G′, G″: storage and loss shear moduli) and the practical end point at (δG′/δt)max = k0, while the latter represents a first‐order process which is characterized by its rate constant, k1, and the corresponding crosslinking half‐time. The relationship between k0 and k1 was established. It appears that the reaction of the fumarate residues with styrene is much faster than that of the maleate residues. At the same degree of unsaturation of 50 mol‐%, k0 was about seven times higher for the reaction of fumarate copolyester than for the reaction of the maleates.

Synthesis and rheological study of some maleic acid and fumaric acid stereoregular polyesters

First unsaturated polyester fibers were prepared starting from stereoregular, macromolecular poly(octamethylene fumarate). Fibers obtained from octamethylene copolyesters of fumaric and terephthalic acids manifested improved mechanical properties and higher melting points. All unsaturated polyester fibers prepared in the study, based on the homopolymer and on copolymers of fumaric acid, even those containing as low as 10% of fumaric acid residues, are able to be covalently bonded to an unsaturated polyester matrix.

Synthesis and rheological study of some maleic acid and fumaric acid stereoregular polyesters, 6. Influence of some parameters on the polycondensation reaction of potassium maleate and 1,4‐dihalogenobutanes

AbstractThe influence of several parameters on the polycondensation reaction of potassium maleate and 1,4‐dihalogenobutanes has been studied in 1‐methyl‐2‐pyrrolidone at moderate temperature. The yield and molecular weight of the obtained polyesters as well as the extent of trans isomerization and the nature of chain end‐groups depend strongly on the mole ratio of reagents, the nature of halogen in the 1,4‐dihalogenobutanes and on the presence of small amounts of water in the reaction mixture. In particular, it has been observed that water increases the consumption rate constant of 1,4‐dibromobutane but at the same time acts as a terminating agent.

Synthesis and rheological study of some maleic acid and fumaric acid stereoregular polyesters, 5. Structural study by 1H and 13C NMR of random, multi‐block and alternating unsaturated copolyesters from fumaric, maleic and phthalic acid potassium salts and 1,4‐dibromobutane

AbstractThe sequence distribution in random, multi‐block and alternating copolyesters based on the reaction of fumaric, maleic and phthalic acid potassium salts with 1,4‐dibromobutane were examined by 1H and 13C NMR spectra. Quantitative sequence distibution results were obtained from the analysis of 13C NMR spectra. The different structures of synthesized copolyesters, expected from the experimental procedures used, were confirmed. In addition, it can be concluded that the esterification route used is irreversible and that no appreciable transesterification reaction between two different ester groups occurs in the course of the synthesis.

Synthesis and rheological study of some maleic acid and fumaric acid stereoregular polyesters, 4. Synthesis of random, multi‐block and alternating unsaturated copolyesters from fumaric, maleic and phthalic acid potassium salts and 1,4‐dibromobutane

AbstractThe reaction of dicarboxylic acid potassium salts with dibromo derivatives in 1‐methyl‐2‐pyrrolidone at moderate temperature was applied to the synthesis of high‐molecular‐weight co‐ and terpolyesters containing fumaric, maleic, phthalic and succinic ester residues and tetramethylene groups. Co‐ and terpolyesters with a random structure were obtained from the reaction of binary or ternary mixtures of salts with 1,4‐dibromobutane. While the composition in ester residues of the organic phase varies continuously during the first 6 h of the polycondensation reaction, that of the copolyesters obtained after 24 h is determined by the composition of the initial mixture of salts. The relative amounts of cyclic n‐mers produced in the course of the reaction and those of the different possible dimers were evaluated from GPC analyses of the reaction products. Multi‐block copolyesters were prepared either by the reaction of a potassium salt with a mixture of 1,4‐dibromobutane and a low‐molecular‐weight α‐ω‐dibromopolyester or by the coupling reaction of two low‐molecular‐weight α,ω‐dibromopolyesters with succinic acid potassium salt. The reaction of bis(4‐bromobutyl) phthalate and fumaric or maleic acid potassium salt produced the corresponding alternating copolyesters. Physico‐chemical and compositional data of the prepared unsaturated copolyesters are given.