Synthesis of poly(glycolic acid) in ionic liquids

The synthesis of poly(glycolic acid) (PGA) by polyesterification of glycolic acid was studied using ionic liquids, mainly 1,3‐dialkylimidazolium salts, as reaction media. The ¹H NMR spectra of PGA oligomers were assigned and end‐group signals were used to follow the reaction. Low PGA yields were obtained by the direct polyesterification of glycolic acid at 200–240 °C, because of monomer evaporation during the reaction. On the other hand, PGAs of DP _n up to 45 were obtained by the postpolycondensation of a preformed oligomer in 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)amide (BMIm⁺Tf₂N^?). The precipitation of PGA in reaction medium at long reaction times limited the achievable molar mass. Rate constants were determined for catalyzed and noncatalyzed reactions, assuming a second‐order reaction mechanism. The efficiency of esterification catalysts such as Zn(OAc)₂ was low in these media, as only about twofold increases in reaction rate were observed. This was assigned to the preferential interaction of Zn²⁺ with ionic liquid anion instead of the polymer carboxylic acid end‐groups. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3025–3035, 2006     

Synthesis and rheology of biodegradable poly(glycolic acid) prepared by melt ring‐opening polymerization of glycolide

Ring‐opening polymerization (ROP) of glycolide was studied in melt conditions and in the presence of two different initiators: 1‐dodecanol and 1,4‐butanediol and tin(II) 2‐ethylhexanoate as catalyst. Its subsequent polymerization provided poly(glycolic acid) with controlled molar masses ranging from 2000 to 42,000 g/mol with well‐defined structures characterized by NMR. Their thermal properties were evaluated by DSC analysis, and a glass transition temperature at infinite molar mass (T_g∞) of 44.8 °C was thus calculated. From rheological data, the critical molar mass for entanglement, M_c, was estimated to be near 11,000 g/mol. Furthermore, in situ polymerizations were also performed between the plates of the rheometer within a same temperature range from 210 to 235 °C. The variation of the storage and loss moduli during the polymerization step have been monitored by time sweep oscillatory experiments under an angular frequency ω = 10 rad/s. Finally, the development of an inverse rheological method allowed to calculate the bulk polymerization kinetics in the temperature range 200–230 °C. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1440–1449, 2009     

XPS and wettability characterization of modified poly(lactic acid) and poly(lactic/glycolic acid) films

Poly(lactic acid) (PLA) and poly(lactic/glycolic acid) copolymers (PLGA) are biodegradable drug carriers of great importance, although successful pharmaceutical application requires adjustment of the surface properties of the polymeric drug delivery system to be compatible with the biological environment. For that reason, reduction of the original hydrophobicity of the PLA or PLGA surfaces was performed by applying a hydrophilic polymer poly(ethylene oxide) (PEO) with the aim to improve biocompatibility of the original polymer. PEO-containing surfaces were prepared by incorporation of block copolymeric surfactants, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (Pluronic), into the hydrophobic surface. Films of polymer blends from PLA or PLGA (with lactic/glycolic acid ratios of 75/25 and 50/50) and from Pluronics (PE6800, PE6400, and PE6100) were obtained by the solvent casting method, applying the Pluronics at different concentrations between 1 and 9.1% w/w. Wettability was measured to monitor the change in surface hydrophobicity, while X-ray photoelectron spectroscopy (XPS) was applied to determine the composition and chemical structure of the polymer surface and its change with surface modification. Substantial reduction of surface hydrophobicity was achieved on both the PLA homopolymer and the PLGA copolymers by applying the Pluronics at various concentrations. In accordance with the wettability changes the accumulation of Pluronics in the surface layer was greatly affected by the initial hydrophobicity of the polymer, namely, by the lactide content of the copolymer. The extent of surface modification was also found to be dependent on the type of blended Pluronics. Surface activity of the modifying Pluronic component was interpreted by using the solubility parameters.     

In vitro degradation behaviour of non-porous ultra-fine poly(glycolic acid)/poly(l-lactic acid) fibres and porous ultra-fine poly(glycolic acid) fibres

The in vitro degradation behaviour of non-porous ultra-fine poly(glycolic acid)/poly(l-lactic acid) (PGA/PLA) fibres and porous ultra-fine PGA fibres was investigated. The non-porous ultra-fine PGA/PLA fibres were prepared by electrospinning of a PGA/PLA solution in 1,1,1,3,3,3-hexafluoro-2-propanol and the porous ultra-fine PGA fibres were obtained from them via selective removal of PLA with chloroform. Since PLA has a lower degradation rate than PGA, the degradation rates of the ultra-fine PGA/PLA fibres decreased with increasing content of PLA. The porous ultra-fine PGA fibres were degraded in vitro in the order of non-porous PGA > P-PGA/PLA(90/10) > P-PGA/PLA(70/30) > P-PGA/PLA(50/50) > P-PGA/PLA(30/70) due to autocatalytic hydrolysis.     

紫外光交联可降解聚对二氧环己酮/聚乙二醇薄膜制备与表征

以2,2-二甲氧基-2-苯基苯乙酮(DMPA)为引发剂,将四臂端丙烯酸酯聚对二氧环己酮(PPDO-4AC)和聚乙二醇双丙烯酸酯(PEG-DA)经紫外光照射制得PPDO/PEG交联薄膜.研究了光照时间和DMPA用量对PPDO/PEG交联薄膜凝胶含量的影响.DSC研究表明共聚物中两组分的相容性较好,Tg随着共聚物中PEG链...     

Conjugation of bioactive groups to poly(lactic acid) and poly[(lactic acid)-co-(glycolic acid)] films

A novel PLA-based polymer containing reactive pendent ketone or hydroxyl groups was synthesized by the copolymerization of L-lactide with epsilon-caprolactone-based monomers. The polymer was activated with NPC, resulting in an amine-reactive polymer which was then cast into thin polymeric films, either alone or as part of a blend with PLGA, before immersion into a solution of the cell adhesion peptide GRGDS in PBS buffer allowed for conjugation of GRGDS to the film surfaces. Subsequent 3T3 fibroblast cell adhesion studies demonstrated an increase in cellular adhesion and spreading over films cast from unmodified PLGA. Hence the new polymer can be used to obtain covalent linkage of amine-containing molecules to polymer surfaces.     

Crystallization kinetics of poly(glycolic acid-alt-6-aminohexanoic acid)

The crystallization behavior of a new regular poly(ester amide) constituted by glycolic acid and 6-aminohexanoic acid units under both isothermal and non-isothermal conditions is studied. Differential scanning calorimetry (DSC) is used to monitor bulk crystallization, and subsequently Avrami and Ozawa analyses are applied. A three-dimensional spherulitic growth from heterogeneous nuclei is deduced for isothermal crystallization, whereas higher exponents are obtained for non-isothermal crystallization when an Avrami equation is applied. However, modifications of the Ozawa methodology indicate a crystallization mechanism similar to that of the isothermal process.The maximum crystallization rate is deduced to take place at a temperature close to 91 °C by considering experimental data and theoretical equations with adjusted parameters. The equilibrium melting temperature is determined to be 168 °C by the characteristic Hoffman-Weeks plot. One crystallization regime is detected by using the Lauritzen-Hoffman kinetic theory for isothermal crystallization and also with an isoconversional method applied for non-isothermal crystallization. Activation energy of molecular transport and nucleation constant are close to 1500 cal/mol and 1.81 × 10⁵ K², respectively. Crystal morphology, nucleation, and spherulitic growth rates are also investigated with hot-stage optical microscopy (HSOM).     

Micropatterned self-assembled film based on temperature-responsive poly(N-isopropylacrylamide-co-acrylic acid)

Micropatterned cross-linked film making up a temperature-responsive component has been fabricated through the following two steps: layer-by-layer electrostatic assembly of photosensitive nitrodiazoresin (NDR) and a thermosensitive copolymer of poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPA-AA)), and subsequent selective exposure to UV light through a photomask followed with development in sodium dodecyl sulfate (SDS) aqueous solution. The irradiated regions of the film are retained due to the formed covalently linked structure, whereas the unirradiated parts of the film are removed fully from the substrate in SDS solution. The well-defined micropatterns were characterized with field-emission scanning electron spectroscopy (FE-SEM) and atomic force microscopy (AFM).     

Morphology and degradation of biodegradable poly(L-lactide-co-β-malic acid)

Poly(L -lactide-co-β-malic acid) was obtained after the hydrogenolysis of the copolymer of L -lactide (L-LA) and β-benzyl malate (MA). ¹H-NMR demonstrated that the composition of the copolymer was identical to the feeding dose. Thermal property study revealed the morphology of the copolymer could be changed from semi-crystalline to amorphous with increasing hydrophilic β-malic acid content. The copolymers with 8 and 13 mol% β-malic acid content possessed enough mechanical property for fabricating cell scaffold. Degradation result demonstrated that most of the hydrophilic β-malic acid units broke down from the copolymer within 1 week and the ester bond between L -lactide and β-malic acid hydrolyzed prior to the inner ester bond of poly(L -lactide) (PLLA). Copyright © 2003 John Wiley & Sons, Ltd.     

Design, synthesis and characterization of novel biodegradable macrodiols based on poly（DL-lactic acid） and poly（p-dioxanone）

Integrating poly(lactic acid)(PLA),glycolic acid(GA) and ethylene glycol(EG) will hopefully result in a novel copolymer that combines such advantages as fastened and controllable release rate and improved flexibility together with good biocompatibility.In this study,p-dioxanone(PDO) was employed to copolymerize with DL-lactide(LA) via ring-opening melt polymerization using Sn(Oct)_2 as an initiator and ethylene glycol as a co-initiator.The obtained degradable macrodiols(HO-P(LA-co-PDO)-OH) were just such...     

Synthesis and characterization of potentially biodegradable thermotropic polyesters based on p-hydroxybenzoic acid and glycolic acid

The synthesis of novel thermotropic liquid crystalline copolyesters derived from aliphatic hydroxy acid (glycolic acid, GA) and aromatic hydroxy acid (p-hydroxybenzoic acid, PHBA) via a melt-copolycondensation process in the presence of various catalysts was explored. The following three possible routes were checked: PHBA and GA in different feed ratios with or without a catalyst; PHBA and GA in different feed ratios with or without a catalyst in the presence of acetic anhydride as a condensation agent; and different PHBA derivatives were used to examine the reactivity of aromatic hydroxy acid. The copolycondensability, chemical structure, liquid crystallinity, textures and morphology, phase transition behaviors and thermal stability, and solubility were investigated by FTIR, NMR, DSC, TGA, and polarized-light microscope. It has been found that only the 60–70 mol % PHBA-containing copolyesters could exhibit a nematic liquid crystallinity. The as-prepared polymers were brittle due to relatively lower molecular weights. © 1994 John Wiley & Sons, Inc.     

(2‐Hydroxy isobutyric) acid containing poly(glycolic acid): Structure–properties relationship

Poly(glycolic acid) (PGA) and a series of novel random copolymers of PGA containing 2‐hydroxyisobutyrric acid (PGAPHIB) (HIB unit content from 1.5 to 7.4 mol %) were synthesized and characterized in terms of chemical structure and molecular weight. Afterward, the polyesters were examined by thermogravimetric analysis, differential scanning calorimetry, and X‐ray diffraction techniques. The copolymers, which displayed a better thermal stability than PGA, at room temperature appeared as semicrystalline materials: the main effect of copolymerization was a lowering in the amount of crystallinity and a decrease of the melting temperature with respect to homopolymer PGA. Baur's equation described well the T_m‐composition data. X‐ray diffraction measurements allowed the identification of the PGA crystalline structure in all cases. After melt quenching, semicrystalline samples were obtained with the exception of PGAPHIB7.4 copolymer. The introduction of HIB units decreased the crystallization rate compared with pure PGA. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1901–1910, 2010     

Micellization phenomena of biodegradable amphiphilic triblock copolymers consisting of poly(beta-hydroxyalkanoic acid) and poly(ethylene oxide)

This paper reports the studies on micelle formation of new biodegradable amphiphilic poly(ethylene oxide)-poly[(R)-3-hydroxybutyrate]-poly(ethylene oxide) (PEO-PHB-PEO) triblock copolymer with various PHB and PEO block lengths in aqueous solution. Transmission electron microscopy showed that the micelles took an approximately spherical shape with the surrounding diffuse outer shell formed by hydrophilic PEO blocks. The size distribution of the micelles formed by one triblock copolymer was demonstrated by dynamic light scattering technique. The critical micellization phenomena of the copolymers were extensively studied using the pyrene fluorescence dye absorption technique, and the (0,0) band changes of pyrene excitation spectra were used as a probe for the studies. For the copolymers studied in this report, the critical micelle concentrations ranged from 1.3 x 10(-5) to 1.1 x 10(-3) g/mL. For the same PEO block length of 5000, the critical micelle concentrations decreased with an increase in PHB block length, and the change was more significant in the short PHB range. It was found that the micelle formation of the biodegradable amphiphilic triblock copolymers consisting of poly(beta-hydroxyalkanoic acid) and PEO was relatively temperature-insensitive, which is quite different from their counterparts consisting of poly(alpha-hydroxyalkanoic acid) and PEO.     

Crystallization kinetics and morphology of biodegradable poly(lactic acid) with a hydrazide nucleating agent

The effect of tetramethylenedicarboxylic dibenzoylhydrazide (designated here as TMC) on the nonisothermal and isothermal crystallization behavior of PLA was investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and wide angle X-ray diffraction (WAXD). TMC shows excellent nucleating effect on PLA. With the addition of 0.05 wt% TMC, the crystallization half-time of PLA decreases from 26.06 to 6.13 min at 130 °C. The isothermal crystallization data were further analyzed by the Avrami model. The values of the Avrami exponent of the blends are comparable to that of neat PLA, indicating that the presence of TMC does not change the crystallization mechanism of the matrix. The observation from POM and WAXD measurements showed that the presence of TMC increases significantly the nuclei density of PLA but has no discernible effect on its crystalline structure.     

Preparation and microstructural analysis of poly(lactic‐alt‐glycolic acid)

Alternating copolymers of glycolic (G) and lactic (L) acid were prepared by the condensation of the preformed dimers: L_LG and L_racG. By size exclusion chromatography (THF, PS standards), poly(L_LG) exhibited a molecular weight (M_n) of 15.6 kg mol^?1, with a weight average molecular weight (M_w) of 26.9 kg mol^?1 and a PDI of 1.72. The M_n for poly(L_racG) was 9.2 kg mol^?1, with a M_w of 12.9 kg mol^?1 and a PDI of 1.40. The NMR spectra of poly(L_LG) were consistent with an isotactic microstructure. NMR spectra of the racemic poly(L_racG) were consistent with an atactic structure. The methylene region of the ¹H NMR spectrum showed a tetrad level of resolution of the nearby stereochemical relationships, for example, iii. Resonances for other groups in both the ¹H and ¹³C NMR spectra gave only a triad level of resolution. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4704–4711, 2008     

Influence of the solvent on the spreading of poly[(D,L-lactic acid)-co-(glycolic acid)] monolayers

 The properties of mono layers of poly[(D,L-lactic acid)-co-(glycolic acid)] (PLA/GA) are strongly conditioned by the nature of the solvent from which they are spread. In this work, we studied the properties of PLA/GA films deposited on water from acetonitrile (a poor spreading solvent) and chloroform (a good one), observing marked differences with regard to the influence of the pH, temperature and ionic strength of the subphase. These differences were attributed to the structure of PLA/GA at the air/water interface, being pre-determined by its structure in the bulk spreading solvent (closely coiled in acetonitrile, unfolded in chloroform). Viscosity measurements on acetonitrile and chloroform solutions of PLA/GA, and the calculation of the corresponding intermolecular expansion factor, α, confirmed that PLA/GA was better solvated by chloroform than by acetonitrile, in which intramolecular interactions between polymer segments, and thus coiling, will therefore have predominated over polymer–solvent interactions. Received: 14 October 1996 Accepted: 7 January 1997