In vitro Degradation of Poly[(L‐lactide)‐co‐(trimethylene carbonate)] Copolymers and a Composite with Poly[(L‐lactide)‐co‐glycolide] Fibers as Cardiovascular Stent Material

TMC/LLA copolymers with several TMC/LLA ratios are synthesized and a composite is obtained by reinforcing with short PLGA fibers. In vitro degradation is studied at 37 °C in pH = 7.4 buffer and compared with a PLLA homopolymer. The degradation of the copolymers appears slower than that of PLLA, showing that TMC units are more resistant to hydrolysis than LLA. Compositional changes indicate a preferential degradation of LLA units as compared to TMC ones. Morphological changes with crystallization of degradation by‐products are observed. The composite degrades much faster than the neat copolymer and PLLA because the faster degradation of PLGA fibers speeds up the degradation of the matrix. The composite appears promising for the fabrication of totally bioresorbable stents.

     

丙交酯合成条件的研究

丙交酯作为合成聚乳酸的重要中间体,它的制备是影响开环聚合高分子量PLA的关键因素。反应时间和反应温度是制备丙交酯的两个重要的工艺参数,直接影响丙交酯的产率。本文着重就反应时间对丙交酯产率的影响进行了初步研究,并提出了一种制备丙交酯的优化工艺。     

Solid‐state linear viscoelastic properties of intercalated poly(L‐lactide)/organo‐modified montmorillonite hybrids

Hybrids of poly(L ‐lactide)/organophilic clay (PLACHs) have been prepared by a melt‐compounding process using poly(L ‐lactide) (PLLA) and different contents of surface‐treated montmorillonite modified with a dimethyl dioctadecyl ammonium salt. The dispersion structures of clay particles in PLACHs were investigated using wide‐angle X‐ray diffraction and transmission electron microscopy. The solid‐state linear viscoelastic properties for these PLACHs were examined as functions of temperature and frequency. The incorporation of organo‐modified silicate into PLLA matrix enhanced significantly both storage moduli (E′) and loss moduli (E″). The strong enhancement observed in dynamic moduli of PLACHs could be attributed to uniformly dispersed state of the clay particles with high aspect ratio (= length/thickness of clay) and the intercalation of the PLLA chains between silicate layers. Copyright © 2006 Society of Chemical Industry     

Preparation of nano-HA/PLA composite by modified-PLA for controlling the growth of HA crystals

In order to control the growth of hydroxyapatite (HA) crystals and obtain nano-hydroxyapatite/poly(lactide) (n-HA/PLA) composite with interfacial interaction between the two phases, PLA surfaces were modified with poly(α-methacrylic acid) (PMAA) via photooxidization and UV induced polymerization. FTIR analysis showed that the PMAA was grafted onto the PLA surface and the grafting rate increased with the grafting time. The n-HA/PLA composites were synthesized by modified-PLA and characterized by FTIR, XRD and SEM. Several analyses suggested that the m-PLA could act as a template to manipulate the nucleation and growth of n-HA crystals, control the morphology and size of n-HA crystals as well as their distribution over the organic phase.     

聚乳酸纤维的制备及其染色性能分析

比较系统地介绍了聚乳酸纤维(PLA)的合成方法及其特性,并对PLA的染色性能进行了初步的探讨.     

超临界CO_2中左旋丙交酯的开环聚合反应

以辛酸亚锡为催化剂,用超临界CO2作溶剂,实现了左旋丙交酯的开环聚合,系统地研究了催化剂用量、单体浓度、聚合时间、聚合温度、CO2纯度和压力等因素对单体转化率、聚合产物相对分子质量及其分布的影响。研究结果表明,在超临界状态下聚合温度、催化剂用量和CO2纯度是影响聚合的几个最重要的因素。超临界状态下的丙交酯开环聚合与本体丙交酯开环聚合相似,聚合过程符合配位插入聚合反应的机理。     

Dramatic improvements in toughness in poly(lactide-co-glycolide) nanocomposites

Poly(lactide-co-glycolide) (PLG), a biocompatible and biodegradable polymer, is dramatically toughened by adding small amounts of surface modified clay nanoparticles. The elongation during tensile tests increases from 7% for the pure polymer to 210% for the nanocomposite, accompanied with a modest increase in modulus. In contrast, PLG nanocomposites based on fumed silica treated with hexamethyldisilazane show only modest improvements in toughness. Electron microscopy, X-ray scattering, rheometry, and dielectric relaxation spectroscopy are used to investigate the toughening mechanism. Multiple crazing occurs in the clay nanocomposite after yielding. Small angle X-ray scattering studies show significant orientation of the clay nanoparticles along the tensile stress direction during deformation. The clay nanocomposites show a new, slow relaxation mode, most likely due to interfacial adsorbption of PLG chains on the surface of the clay nanoparticles. The dramatic increase in toughness is attributed to physical crosslinks introduced by the clay nanoparticles, a mechanism absent in the PLG/silica nanocomposites. The physical crosslinks increase the brittle fracture strength of the polymer and, consequently, trigger a toughening mechanism via multiple crazing and shear yielding.     

Morphology and Properties of Poly(L‐Lactide) (PLLA) Filled with Hollow Glass Beads

The morphology, crystalline behavior, and mechanical and thermal properties of poly(L ‐lactide)/hollow glass beads (PLLA/HGBs) composites were investigated. The incorporation of HGBs enhanced the crystallization rate and crystallinity of PLLA, but slightly decreased its elongation at break. In addition, HGBs acted as stress concentration points inducing the plastic deformation of PLLA, leading to increased Izod impact strength. Differential scanning calorimetry results show that annealed PLLA eliminated cold crystallization phenomenon in the region of 100–140 °C and presented a double melting peak around 150 °C. Moreover, annealing was demonstrated to be effective for the improvement of tensile modulus, strength, Izod impact strength and heat distortion temperature of the composites due to the increased crystallinity and more perfect crystals. Silane coupling agents can enhance the interfacial adhesion of the composites, and lead to better mechanical properties. Compared to neat PLLA, the HGBs filled PLLA composites did not exhibit an obvious increase of the density.

     

Synthesis of branched poly(lactide) using polyglycidol and thermal, mechanical properties of its solution-cast film

Branched poly(lactide)(PLA)s with various lengths of graft chain were synthesized by ring-opening polymerization of l- or d-lactide (l- or d-LA) in bulk using polyglycidol as a macroinitiator. The properties of polymer films of branched PLLA or PDLA obtained and their stereocomplex were investigated through thermal analysis and tensile testing. The branched PLLA or PDLA film exhibited a lower glass transition temperature (T_g), melting temperature (T_m), crystallinity, Young's modulus and a higher strain at break than the corresponding linear PLLA or PDLA film. The branched PLLA/branched PDLA stereocomplex film showed a high maximum stress and a high Young's modulus keeping its high strain at break. Moreover, the usefulness of branched PLLA or PDLA as a plasticizer of linear PLLA was investigated with 1:9 blend or stereocomplex film prepared from the branched PLLA or branched PDLA and linear PLLA. The blend or linear PLLA/branched PDLA stereocomplex film showed a higher strain at break compared with linear PLLA film. The mechanical properties of the blend or linear PLLA/branched PDLA stereocomplex film could easily be controlled by changing the molecular weight of branched PLA.