Copolymerization of glycolide and trimethylene carbonate

The bulk ring‐opening copolymerization of glycolide with trimethylene carbonate was performed under different conditions. The influence of the composition, temperature, reaction time, and catalyst on the chain microstructure was studied by means of ¹H and ¹³C NMR spectroscopy. The final microstructure was found to be highly dependent on the transesterification reactions. The thermal behavior was sensitive to the composition and to the length of the glycolyl microblocks. Differential scanning calorimetry and X‐ray diffraction demonstrated that glycolyl‐rich sequences could give rise to a single crystalline phase, whereas trimethylene carbonyl units were incorporated into the amorphous phase. The synthesis of copolymers from the melt‐state transesterification of polyglycolide and poly(trimethylene carbonate) homopolymer mixtures was also studied. The hydrolytic degradation rate of the copolymers was found to depend on the microstructure and in general was enhanced with the degree of randomness. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 993–1013, 2006     

Influence of degradation on the crystallization behaviour of a biodegradable segmented copolymer constituted by glycolide and trimethylene carbonate units

The influence of degradation on non-isothermal crystallization from the melt of a segmented copolymer constituted of glycolide and trimethylene carbonate units and used as a bioabsorbable surgical suture was studied by optical microscopy, differential scanning calorimetry and time-resolved X-ray diffraction. Fibrillar positive spherulites were obtained with slightly degraded samples but new axialitic morphologies were detected when samples had a molecular weight, M_w, lower than 29,000 g/mol and the crystallization started at a high temperature.Crystal growth kinetics of samples degraded under different conditions was evaluated over a wide temperature range by a non-isothermal method. Two crystallization regimes (I and II) were determined for the more degraded samples (i.e., those able to crystallize according to axialitic and spherulitic morphologies), whereas only regime II was found for samples of higher molecular weights. Primary nucleation density decreased with the extent of degradation provided no morphological changes occurred, and so did the regularity of lamellar stacking, as shown by synchrotron measurements, although the morphological parameters remained practically constant.     

Influence of chain microstructure on the hydrolytic degradation of copolymers from 1,3‐trimethylene carbonate and L‐lactide

Ring‐opening copolymerization of L ‐lactide (LLA) and 1,3‐trimethylene carbonate (TMC) blends with LLA/TMC feed ratios from 90/10 to 50/50 was realized at 110 or at 180 °C for various time periods, using low toxic zirconium (IV) acetylacetonate (Zr(Acac)₄) as initiator. The resulting copolymers exhibit different chain microstructures. Copolymers obtained at 110 °C exhibit a gradient chain structure with the presence of lactidyl sequences next to very short ones, and are semicrystalline. In contrast, copolymers obtained at 180 °C are amorphous because of a more random chain microstructure with the presence of larger amounts of medium sequences. Degradation of the copolymers was carried out in pH 7.4 phosphate buffer at 37 °C. Analytical techniques such as ¹H NMR, DSC, GPC, and XRD were used to monitor the degradation. Initially amorphous copolymers can remain amorphous during degradation because of the highly random unit's distribution, and equivalent LLA and TMC contents. However, initially amorphous copolymers containing larger amounts of lactidyl units are able to crystallize during degradation because of the presence of relatively long LLA blocks. Insofar, as initially semicrystalline copolymers are concerned, degradation occurs preferentially in the amorphous zones. Therefore, various degradation behaviors and degradation rates can be obtained by varying the chemical composition, chain microstructure, and morphology of PLLA‐PTMC copolymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3869–3879, 2009     

Influence of electron beam irradiation on physicochemical properties of poly(trimethylene carbonate)

Electron beam (EB) irradiation of poly(trimethylene carbonate) (PTMC), an amorphous, biodegradable polymer used in the field of biomaterials, results in predominant cross-linking and finally in the formation of gel fraction, thus enabling modification of physicochemical properties of this material without significant changes in its chemical structure. PTMC films (M_w: 167-553 kg mol⁻¹) were irradiated with different doses using an electron accelerator. Irradiation with a standard sterilization dose of 25 kGy caused neither significant changes in the chemical composition of the polymer nor significant deterioration of its mechanical properties. Changes in viscosity-, number-, weight-, and z-average molecular weights of PTMC for doses lower than the gelation dose (D_g) as well as gel-sol analysis and swelling tests for doses above D_g indicate domination of cross-linking over degradation. EB irradiation can be considered as an effective tool for increasing the average molecular weight of PTMC and sterilization of PTMC-based biomaterials.     

Synthesis and characterization of a novel terpolymer based on L‐lactide,glycolide, and trimethylene carbonate for specific medical applications

The bioresorbable new terpolymers of L ‐lactide, glycolide, and trimethylene carbonate were synthesized via ring‐opening polymerization reaction of the cyclic monomers using Stannous octoate as initiator. Glycolide and L ‐lactide were prepared from their parent acids and then purified by multiple re‐crystallization from ethyl acetate. The thermal and mechanical properties of this polymer were characterized by means of thermogravimetry, differential scanning calorimetry, stress–strain measurements, and dynamic mechanical analysis. The glass transition temperature of the terpolymers changed from 33 to 51°C with composition in a predictable manner. The rheological properties of copolymers and molecular weight of each copolymer were determined showing good processability for making fibers. Using a mini‐extruder, it was possible to produce some filaments. The filaments produced at 140°C had appropriate ductility. The in vitro measurements, specifying the biological properties were also carried out. The sample with monomer composition LLA:GA:TMC = 60:34:6 showed a slower degradation rate than the one with LLA:GA:TMC = 54:34:12. The low‐toxicity bioresorbable terpolymers with good rheological and in vitro properties are the promising new materials for biomedical applications specially a new suture formulation. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis of biodegradable copolymers with low‐toxicity zirconium compounds. IV. Copolymerization of glycolide with trimethylene carbonate and 2,2‐dimethyltrimethylene carbonate: Microstructure analysis of copolymer chains by high‐resolution nuclear magnetic resonance spectroscopy

The results of the copolymerization of glycolide with cyclic trimethylene carbonate and 2,2‐dimethyltrimethylene carbonate are described. The copolymerization was conducted in the presence of low‐toxicity zirconium(IV) acetylacetonate as an initiator. With this kind of initiator, the composition of the comonomer units in the copolymer chains was assumed to be obtained with high efficiency. Despite significant differences in the comonomer reactivity, in copolymers containing comparable amounts of glycolidyl and carbonate sequences, highly randomized chain structures were observed. This effect resulted from strong intermolecular transesterification that proceeded during the studied copolymerization and caused glycolidyl microblock randomization. The assignment of the spectral NMR lines to appropriate comonomer sequences of polymeric chains was performed in the region of methylene protons of glycolidyl units in ¹H NMR spectra of the copolymers and in the carbonyl region of carbon spectra. The equations were formulated for a detailed characterization of the obtained copolymer chains, the average lengths of the blocks, and the transesterification and randomization coefficients. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 98–114, 2006     

Synthesis of poly(ester carbonate) copolymers

The synthesis of poly(ester carbonate) copolymers based on bisphenol A, terephthalic acid, and phosgene is reviewed, and a new synthetic route is described leading to polymers which are different from those obtained by methods described in the literature. The most important features of the new method are quantitative incorporation of the dicarboxylic acid into the polymer and absence of undersirable side reactions. Synthesis of the random copolymer in which the dicarboxylic acid and carbonic acid groups are present in about equal molar amounts is discussed. Solution properties, effects of M?_n and copolymer composition on T_g, sequence length distribution, the effect of ester interchange reactions on molecular weight distribution, and effects of monofunctional chain termination on molecular weight of the final product are also discussed.     

Influence of microstructure on the tensile behavior of acrylic copolymers

Uniaxial tensile properties were determined for two series of copolymers: ethyl acrylate–acrylic acid and butyl acrylate–acrylic acid. The comonomer ratio was varied from 85/15 to 95/5 and various molar ratios of a difunctional carboxylate epoxy crosslinker were used. The master modulus curves indicated that increasing the amount of crosslinker and/or increasing the number of crosslink sites per chain caused both the equilibrium modulus and the transition temperature to increase while increasing the bulk of the side groups decreased both the modulus and transition temperature. All the master ultimate strain curves exhibited a maximum value corresponding to some value of reduced time τ_c and exhibited a shape analogous to a lognormal distribution function with nonzero asymptotes. The maximum ultimate strains were found to be a nonlinear function of the crosslink density and to occur at higher values of temperature and/or lower values of strain rate when either the amount of crosslinker or the relative frequency of the crosslink sites increased. Replacing the pendant ethyl group with a butyl group caused the maximum ultimate strains to occur at temperatures about 60°F lower than the corresponding ethyl acrylate copolymer. This replacement also decreased the magnitudes of the maximum ultimate strains associated with the same crosslink density. It was concluded that the chemical efficiency of the crosslink sites decreases with decreasing relative frequency of the crosslink sites along the prepolymer. Furthermore, the crosslink efficiency decreased as the length and flexibility of the nonreactive side groups increased. The dependency of the actual crosslink density was found to be critically influenced by the chemical crosslink efficiency. A molecular model involving both chain entanglements and chemical corsslinks is postulated which explains qualitatively the observed behavior of the master ultimate strain data.     

Synthesis and properties of polystyrene/polydimethylsiloxane graft copolymers

Polystyrene-graft-polydimethylsiloxane (PS-g-PDMS) copolymers with different PDMS content were synthesized by the radical bulk copolymerization of PDMS macromonomer and styrene. The copolymers were characterized by Fourier transform infrared (FT-IR), ¹H-nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), transmission electron microscopy (TEM) and the mechanical properties of the copolymers were also carried out. It was indicated that the notched impact strength and elongation at break of the polymers increased with the increase of PDMS content. The thermal stability of PS-g-PDMS is better than that of PS. __________ Translated from Journal of East China University of Science and Technology 2005, 31(2) (in Chinese)     

Chitosan-dextran branched copolymers: Synthesis and properties

Chitosan-dextran branched copolymers have been synthesized, and the rheological properties of their aqueous acetic acid solutions have been studied. On the basis of the data of FTIR spectroscopy, the formation of chemical bonds between chitosan and dextran at the nitrogen atom has been confirmed. With the use of dynamic mechanical analysis and differential scanning calorimetry, the temperatures of relaxation transitions in the resulting branched copolymers have been determined. It is shown that, along with the formation of a branched copolymer, the chemical crosslinking of chitosan macrochains can occur. Mechanical properties of films formed from solutions of the obtained polymers have been studied.     

聚三亚甲基碳酸酯的生物相容性研究

以实验室自制的聚三亚甲基碳酸酯(PTMC)为研究对象,通过测定聚三亚甲基碳酸酯在体外酶解过程中降解液pH变化,考察其在降解过程中是否产生酸性降解产物;通过MTS法考察聚三亚甲基碳酸酯的体外细胞毒性;通过HE染色的方法考察聚三亚甲基碳酸酯在大鼠体内埋植部位的皮肤刺激性,进而考察聚三亚甲基碳酸酯的生物相容性。结果表明:PTMC在降解过程中不产生酸性降解产物,可避免埋植部位无菌炎症的产生。同时不同分子量的PTMC可以存在于皮下组织而不会造成伤害,因此聚三亚甲基碳酸酯具有良好的生物相容性,可安全植入体内。     

Influence of melt behaviour on the flame retardant properties of ethylene copolymers modified with calcium carbonate and silicone elastomer

This work describes a halogen-free flame retardant material consisting of a polar ethylene copolymer, calcium carbonate and silicone elastomer. The flame retardant properties when using poly(ethylene-co-methacrylic acid) (EMAA) and poly(ethylene-co-butyl acrylate) (EBA) as the copolymer have been compared. Rheological measurements showed an increase in complex viscosity above 250 °C due to ionomer formation between acidic groups in the polymer and calcium ions. The increase in viscosity occurs at lower temperatures with the EMAA material and the increase is stronger. This has great impact on the fire performance, as shown with cone calorimetry and dripping test. In order to further elucidate the flame retardant mechanism in detail, thermogravimetric analysis and infrared spectroscopy have been used. The influence of the amount of comonomer and melt flow ratio of the polymer is also commented.     

Sequence analysis of glycolide and p‐dioxanone copolymers

Low and medium molecular weight copolymers constituted by glycolide and p‐dioxanone units have been synthesized by a ring‐opening polymerization. The p‐dioxanone monomer was obtained from (2‐hydroxyethoxy)acetate or by thermal depolymerization of poly(p‐dioxanone). ¹H and ¹³C NMR spectra were highly sensitive to the chemical sequences, which were effectively assigned by considering the data from samples with different compositions, and the acquisition of heteronuclear ¹H and ¹³C NMR‐correlated spectra. End groups were also identified, allowing methylene protons of sequences involving up to two glycolide units to be distinguished. These data seem basic to analyze degradation products or the influence of thermal treatments in chain microstructure. Glycolide/p‐dioxanone copolymers are an interesting system because changes on chemical sequences can easily occur due to a depolymerization reaction that eliminates p‐dioxanone residues. Furthermore, depending on the polymerization conditions, the occurrence of transesterification reactions may be highly significant. These reactions have a great impact in properties such as the melting temperature and can be easily quantified by NMR spectroscopy because of the occurrence of a new chemical sequence. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

Investigation of viscoelastic and thermal properties of cyclic carbonate bearing copolymers

In this paper, one-pot reaction of radical copolymerization of glycidyl methacrylate with methyl methacrylate, n-butyl acrylate and styrene under carbon dioxide atmosphere (1 atm) was employed to synthesize cyclic carbonate bearing copolymers. Obtained copolymers were characterized using ¹H NMR and FTIR spectroscopy. The viscoelastic and thermal properties of the resulted copolymers were investigated using dynamic mechanical thermal analysis and thermogravimetric analysis. Copolymer composition and monomer type had a significant effect on the properties of the copolymers. An increase in cyclic carbonate (2-oxo-1,3-dioxolane-4-yl-methyl methacrylate) content in the copolymer composition led to an increase in glass transition temperature, storage modulus and loss tangent as well as the thermal stability of the copolymers.     

Gradient copolymers: Synthesis,structure, and properties

Conditions of formation of gradient copolymers characterized by a continuous change in composition along each chain and methods of their synthesis by living ionic and pseudoliving radical polymerizations are considered. Characteristics, structure, and physicochemical properties of gradient copolymers are discussed.     

Novel synthesis method of ester free trimethylene carbonate derivatives

Ester free poly(trimethylene carbonate) (PTMC) derivatives show biocompatibility and biodegradability and do not generate any acidic compounds after decomposition. Their syntheses methods are limited however, hampering their material application. Herein, we established a novel synthesis route of ester free trimethylene carbonate (TMC) derivatives. The novel synthesis route was described using six aldehydes and one ketone as starting compounds. The key reaction is the selective deprotection from two protected hydroxyl groups in the cyclic acetal structure by diisobutylaluminium hydride. This novel synthesis route means that it is possible to convert aldehyde group to ether groups in the side chain of TMC. Conventionally, only a substituent derived from a primary alcohol was introduced into the side chain. We therefore succeeded in decreasing the number of reaction steps from five to three, compared with the conventional route. Furthermore, the development of a novel synthesis route enabled the introduction of substituents derived from secondary alcohols, anticipating the creation of further types of ester free TMC derivatives.     

Synthesis and properties of fullerene-containing N-vinylpyrrolidone copolymers

Branched copolymers containing covalently bonded fullerene C₆₀ were synthesized by cross-linking radical copolymerization of N-vinylpyrrolidone with triethylene glycol dimethacrylate in toluene saturated with fullerene. Their composition was studied by elemental analysis and IR and electronic absorption spectroscopy. The concentration of double bonds, characteristic viscosity, and glass-transition temperature of the fullerene-containing copolymers were determined by ozonoliysis, viscosimetry, and differential scanning calorimetry. The parameters and thermal stability of the fullerene-containing copolymers were compared with those of their non-functionalized analogs.     

Polymerization of trimethylene carbonate in aqueous solutions: Reaction mechanism and characterization

Polymerization of a trimethylene carbonate (TMC) in an aqueous solution was investigated by gel permeation chromatography, Fourier transform infrared spectroscopy, and nuclear magnetic resonance. The polymerization reaction proceeded rapidly in the aqueous solution and high conversion was achieved in a relatively short time. 1,3‐Propanediol (PPD) formed by hydrolysis of TMC was used as the initiator. The TMC oligomer obtained by ring‐opening polymerization had a TMC unit backbone with terminal 3‐hydroxypropyl groups at both chain ends. The oligomer underwent transesterification reaction with elimination of PPD, resulting in a gradual increase in the molecular weight of the product. The molecular weight was affected by the concentration of TMC. The thermal properties of the polymers were investigated by differential scanning calorimetry. Polymers within the molecular weight (M_n) range from 6.0 × 10³ to 2.3 × 10⁴ g/mol crystallized, and endothermic peaks corresponding to the melting temperature were observed. The glass transition temperature increased with the molecular weight of the polymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1485–1492, 2010