Compressibility and compactibility of powdered polymers: poly(vinyl chloride) powders

The present investigation is concerned with the possible effects of material-related properties (molecular mass, glass transition and melting temperatures, crystallinity, tacticity) and particle-related properties (shape, size, specific surface area) on the compression characteristics of the chosen model polymer powder: poly(vinyl chloride) (PVC). Four grades were selected known in literature for providing compacts of varied mechanical strength. The compression characteristics were determined using an instrumented single-punch tableting machine. The differences in tableting characteristics could not be ascribed to any of the material-related properties, but a direct relationship was observed between the compact strength and the specific surface area of the particles, as measured by nitrogen adsorption. The compact hardness was thus only dependent on the inter- and the intraparticulate contact area, which in turn is dictated by the very peculiar morphology of the grains of the PVC powders, whether prepared by emulsion or suspension polymerization.     

Theory for water management in membranes for polymer electrolyte fuel cells: Part 2. The effect of impurity ions at the cathode side on the membrane performances

Performance degradation in membranes for polymer electrolyte fuel cells was discussed theoretically for the case where the membrane is contaminated with foreign impurity cations at the cathode side. Water transport in a two-cation system membrane was considered by assuming an ‘infected zone’ of finite thickness. Four kinds of boundary value problems were solved, and analytical formulae derived for the water concentration profile across the membrane. The water content in the membrane, the net water flux and the membrane resistance overvoltage were calculated systematically as functions of several relevant parameters in fuel cell operations. Localized contamination at the cathode ∣ membrane interface turned out to be even more serious than the uniform contamination of the membrane or localized contamination at the anode side. It is noted that special caution should be directed in order to avoid the membrane contamination, especially at the cathode side, because contaminant will easily enter from the air stream through the cathode compartment of a fuel cell.     

Low-density poly( -lactide-co-glycolide) foams for prolonged release of isoniazid

Incorporation of the antitubercular drug isoniazid, INH, into low density poly( -lactide-co-glycolide), PLGA, foams of high interstitial void volume prior to high pressure extrusion is shown to prolong the in vitro release of INH. In vitro studies indicate that the duration of INH release can be significantly increased, the early burst dramatically reduced, and variation in replicate samples reduced. Control of the specific gravity and interstitial void volume of the foam is achieved by lyophilization of frozen polymer solutions of specified concentration. The morphology of foams prepared by lyophilization of glacial acetic acid solutions of the polymers produces leaflet or platelet structures. Matrices were prepared by (1) extruding INH impregnated foams previously compacted and ground to 125–180 microns, (2) directly extruding impregnated foams without prior compaction and grinding, and (3) extruding mechanically mixed micronized INH and ground PLGA which had not been prepared as foam. INH release kinetics, analyzed in terms of the Roseman-Higuchi model, confirms that release is diffusion controlled. Diffusion constants for the three methods are 1.2( ±0.1) × 10⁻⁴, 2.1(±0.3) × 10⁻⁴, and 3.2(± 1.6) × 10⁻⁴ cm²/day.     

硫醚型芳香族二胺单体的合成及应用

以对氨基硫酸及４，４＇－二氯基二苯砜为原料合成了含硫醚键芳香族二胺单体：，用它制备的聚酰亚胺显示了良好的耐热性能。     

光折变聚合物材料研究进展

综述近年来光折变聚合物的材料的研究现状，着重介绍光折变聚合物材料的化学结构，组成及光折变性能。简单分析当前研究工作所面临的问题。     

HIPS的官能化及HIPS/PBT共混体系的研究

以过氧化二异丙苯（DCP）为引发剂，甲基丙烯酸缩水甘油酯（GMA）为活性单体，高抗冲苯乙烯（HIPS）通过熔融接枝制得了动能化的高抗冲聚苯乙烯接枝物（HIPS－g-GMA)。用红外光谱和电子能谱对其结构进行了表征。HIPS－g-GMA的红外谱图，证明GMA已经接枝到HIPS上。电子能谱分析也提供了相似的结论。研究了单体浓度和DCP用量对产物接枝率的影响，并用化学滴定方法测定了接枝物的接枝率。用DSC、SEM、WAXD、DMA等研究了PBT／HIPS和PBT、HIPS－g-GMA的结晶、形态结构、动态力学性能及力学性能随组成的变化。SEM及DMA分析表明增容后体系的相容性得到改善，力学性能有较大提高。     

Controlled release of nerve growth factor from a polymeric implant

Recent studies suggest that neurotrophic factors applied directly to brain tissue may enhance regeneration in the central nervous system. Biocompatible polymeric implants providing a controlled release of nerve growth factor (NGF) for over one month were developed. The released nerve growth factor stimulated neurite sprouting in cultured PC12 cells. While a model polymer with demonstrated biocompatibility was used for the present study, the methods can be extended to other polymer systems. Controlled release implants may be useful in the treatment of Alzheimer's disease.     

Crystallization and Morphological Features of Syndiotactic/Atactic Polystyrene Blends at High Temperatures

Crystalline/amorphous binary mixtures of polystyrene with different tacticities, syndiotactic/atactic isomers (sPS/aPS), have been systematically studied to reveal the composition dependence of the blend morphologies, i.e., sPS lamellar structure and aPS diluent segregation, developed after isothermal crystallization. To reveal the molecular weight effect of the aPS diluents, four different of aPS were used to prepare blends with various compositions. After being melt crystallized isothermally at 250 °C, all blends were investigated by means of POM, WAXS, and SAXS as well as SEM and TEM to reveal the spherulitic and lamellar morphologies developed.

     

Structure Formation of Binary Blends of Amphiphilic Block Copolymers in Solution and in Bulk

The self‐assembly and structure formation in binary blends of asymmetric polystyrene‐block‐poly(4‐vinylpyridine) diblock copolymers in different solvent systems and the bulk morphology of the blend films are studied by using dynamic light scattering, small‐angle X‐ray scattering, and transmission electron microscopy. In dilute solutions, the chains of pure diblock copolymers or binary blends of diblock copolymers having similar or different molecular weights remain as unimers, form common micelles in selective solvents or form unimers in coexistence with micelles in slightly selective solvents or solvent mixtures. The blends show mixing of the chemically similar blocks in the blend films and solutions at high concentrations. A single‐phase with common spherical morphology is formed in the blend films similar with the morphology of the individual components in the pure state. The characteristic length scale of the blends depends on the number average molecular weight following the typical scaling behavior of a strongly segregated block copolymer.

     

分子印迹聚合物及其应用

综述了分子印迹原理、分子印迹聚合物的制备和特性，以及分子印迹聚合物在对映体拆分、人工抗体、模拟酶、以及分子器件方面的应用。