Characterization of biodegradable polymers by inverse gas chromatography. III. Blends of amylopectin and poly(L‐lactide)

The morphology changes and surface thermodynamics of blends of amylopectin (AP)–poly(L ‐lactide) (PLA) were investigated over a wide range of temperatures and compositions using the inverse gas chromatography method. Twenty‐five solutes were selected such as alkanes, acetates, oxy, halogenated, and six‐member ring families. They provided a variety of specific interactions with the blends' surface. The morphology showed two regions, some others showed a de‐polymerization above 130°C. These zones enabled the estimation of T_g and T_m of AP, PLA, and the blends. Blending AP with PLA caused a decrease in AP's T_g value due to the reduction of the degree of crystallinity of the blend. Exothermic values of χ₂₃ were obtained indicating the compatibility of AP and PLA at all temperatures and weight fractions of AP–PLA. The miscibility was favored at 75%AP, only 25%AP–75%PLA composition influenced the degree of crystallinity. The dispersive component of the surface energy of the blends ranged from 16.09 mJ/m² for the pure AP as high as 58.36 mJ/m² at 110°C when AP was mixed with PLA in a 50–50% ratio. The surface energy was at its highest value when the composition was 75% of AP, in good agreement with χ₂₃ values. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

乳酸合成丙交酯的研究现状

聚乳酸是目前应用最为广泛的可降解材料之一,丙交酯是由乳酸制备聚乳酸的中间体,其产率偏低是制约聚乳酸大规模应用的关键。对乳酸合成丙交酯近20年来的现状作了比较全面的回顾,包括乳酸合成丙交酯的主要方法、工艺及影响丙交酯产率的主要因素。进而提出了提高丙交酯产率应采取的相应措施。     

聚乳酸合成研究进展

概述了聚乳酸的发展简史、聚乳酸材料的一些重要性质,介绍了聚乳酸一步法合成和两步法合成技术的研发现状。     

Study of the thermal stabilization mechanism of biodegradable poly(L‐lactide)/silica nanocomposites

Biodegradable poly(L ‐lactide) (PLA)/silica (SiO₂) nanocomposites were prepared by melt compounding to investigate the effect of spherical nanofillers on the thermal stability of PLA. The nanocomposites displayed improved thermal stability both under nitrogen and in air. The stabilization mechanism was attributed mainly to the barrier effect of the network formed, which was demonstrated by the improved barrier properties and rheological performance. The dispersion of nanofiller and matrix‐nanoparticle interactions were investigated to evaluate the dependence of the network on SiO₂ loadings. Fourier transform infrared spectroscopy and thermogravimetric analysis indicated that hydroxyl groups on SiO₂ surfaces and PLA chain‐ends reacted during melt processing. The resulting grafted SiO₂ and entangled PLA chains formed a dense network, which hindered the diffusion of oxygen and volatile decomposition products. Furthermore, the improvement in thermal stability resulted from the restraining effect on the mobility of active hydroxyl end‐groups, so that some related thermal decomposition reactions were inhibited, which was confirmed from gel permeation chromatography measurements. Copyright © 2010 Society of Chemical Industry     

3D polylactide-based scaffolds for studying human hepatocarcinoma processes in vitro

We evaluated the combination of leaching techniques and melt blending of polymers and particles for the preparation of highly interconnected three-dimensional polymeric porous scaffolds for in vitro studies of human hepatocarcinoma processes. More specifically, sodium chloride and poly(ethylene glycol) (PEG) were used as water-soluble porogens to form porous and solvent-free poly(L,D-lactide) (PLA)-based scaffolds. Several characterization techniques, including porosimetry, image analysis and thermogravimetry, were combined to improve the reliability of measurements and mapping of the size, distribution and microarchitecture of pores. We also investigated the effect of processing, in PLA-based blends, on the simultaneous bulk/surface modifications and pore architectures in the scaffolds, and assessed the effects on human hepatocarcinoma viability and cell adhesion. The influence of PEG molecular weight on the scaffold morphology and cell viability and adhesion were also investigated. Morphological studies indicated that it was possible to obtain scaffolds with well-interconnected pores of assorted sizes. The analysis confirmed that SK-Hep1 cells adhered well to the polymeric support and emitted surface protrusions necessary to grow and differentiate three-dimensional systems. PEGs with higher molecular weight showed the best results in terms of cell adhesion and viability.     

One‐pot regioselective and stereoselective terpolymerization of rac‐lactide,CO2 and rac‐propylene oxide with TPPMCl (M = Cr,Co, Al)/PPNCl binary catalyst

Tetraphenyl porphyrin metal compound (TPPMCl) (where the TPPMCl was TPPCrCl, TPPCoCl, TPPAlCl), in combination with cocatalyst PPNCl (bis(triphenylphosphine)iminium chloride, the molar ratio of TPPMCl to PPNCl was 1:0.5), was used to catalyze the polymerization of racemic lactide (rac‐LA) in racemic propylene oxide (rac‐PO) medium and the terpolymerization of rac‐LA, CO₂ and rac‐PO. It was found that these TPPMCl/PPNCl binary catalysts could initiate the stereoselective polymerization of rac‐LA in rac‐PO medium to form enriched isotactic polylactide (PLA) (P_i ≥ 68.0%) and terpolymerization of CO₂, rac‐LA, rac‐PO to form PPC‐PLA‐PPO (PPC, poly(propylene carbonate); PPO, poly(propylene oxide)) multiblock copolymer. In particular the PPC‐PLA‐PPO multiblock copolymer thus formed displayed high regioregularity and stereoregularity, and has high head‐to‐tail structure content in the PPC block (H‐T% ≥ 63.6%) and high isotacticity in the PLA block (P_i ≥ 64.0%). The influence of catalyst formula, the monomer feeding ratio, reaction temperature, carbon dioxide pressure and reaction time on the terpolymerization was investigated by ¹H NMR, ¹³C NMR, gel permeation chromatography, DSC and TGA. © 2018 Society of Chemical Industry     

乳酸合成丙交酯的催化剂回收的研究

丙交酯的合成是乳酸间接法合成聚乳酸的关键步骤,该过程产生的反应底物经水解后,残余物主要有催化剂、乳酸氧化产物和高温炭化物。采用了焚烧-沉淀的方法,回收其中催化剂并对废弃物进行有效处理。利用差热/热重分析仪（DTA/TG）和X射线衍射仪（XRD）分别对热分解过程、前驱物及产物进行了表征分析。试验结果表明,该方法催化剂的回收率为98%,其方法具有工艺简单、能耗小等优点。     

Morphology,crystallization and enzymatic hydrolysis of poly(L‐lactide) nucleated using layered metal phosphonates

Poly(L ‐lactide) (PLLA) was prepared via melt blending and nucleated using three layered metal phosphonates, i.e. zinc phenylphosphonate (PPZn), calcium phenylphosphonate (PPCa) and barium phenylphosphonate (PPBa). The morphology, crystallization and enzymatic hydrolysis of PLLA nucleated using PPZn, PPCa and PPBa were investigated. The results of both wide‐angle X‐ray diffraction and transmission electron microscopy observations show that the layers of PPZn, PPCa or PPBa are barely exfoliated or intercalated by PLLA chains in the melt‐blending process. PPZn, PPCa and PPBa serve as effective nucleating agents, accelerating both non‐isothermal and isothermal crystallization and enzymatic hydrolysis of PLLA. An interesting aspect is that the nucleating ability of PLLA incorporating PPZn, PPCa and PPBa decreases in the order PPZn > PPCa > PPBa, whereas the enzymatic hydrolysis of PLLA incorporating PPZn, PPCa and PPBa decreases in the reverse order, which is due to the different dispersion and interfacial interactions of PPZn, PPCa and PPBa throughout the PLLA matrix. Copyright © 2010 Society of Chemical Industry     

丙交酯开环聚合催化体系的研究进展

介绍了丙交酯开环聚合的三种反应机理:阴离子型开环聚合、阳离子型开环聚合和配位-插入开环聚合。根据其反应机理,催化剂可分为:质子酸型催化体系、路易斯酸型催化体系、碱金属催化体系、金属有机化合物催化体系、氧化物催化体系、稀土化合物催化体系及其他催化体系。此文阐述了这7种催化体系的不同特点,对其催化性能进行了比较。