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With a view to improve the affinity of silica particles for the polymer matrix, a new type of polyimide/silica(PI/SiO2) hybrid composite films has been successfully prepared using the polymer-modified silica gels. First, poly(maleic anhydride-co-styrene)/silica[P(MA-ST)/SiO2], polymer-modified silica gels, were prepared by the condensation reaction of the surface hydroxyl group of silica gel with a polymeric coupling agent, P(MA-ST)–trimethoxysilane. Then, PI/SiO2 hybrid films of different silica contents were obtained by the blending of polymer-modified silica gels with poly(amic acid)(PAA) from pyromellitic dianhydride(PMDA) and 4,4′-diaminodiphenyl ether(ODA) in N-methyl-2-pyrrolidinone(NMP). The decomposition temperature at 5 wt% loss(Td5) of the hybrid films, as measured by thermogravimetric analyses(TGA), increased with the increasing P(MA-ST)/SiO2 content within the measured range. The PI/SiO2 hybrid films with ca. 5 wt% of modified-silica exhibited balanced mechanical properties, whereas the hybrid films with higher silica contents had reduced mechanical properties, as confirmed by the scanning electron micrographs(SEM) observation. [ABSTRACT FROM AUTHOR]

Thermoreversible gelation of poly(vinylidene fluoride) (PVDF) in propylene carbonate (PC) solutions at relatively low concentrations (0.5–3.5 wt.%) has been studied in terms of the gelation time (or rate) as a function of temperature and polymer concentration. A master curve could be made for the gelation time–temperature curves using the temperature shift based on the difference in the gel melting temperature (Tmg) at different PVDF concentrations. The apparent activation energy of gelation was estimated to be proportional to (Tmg − T)−1.8. The gel melting enthalpy (ΔHmg) determined from the modified Eldrige–Ferry equation was 18.67 kJ/mol. In dried gel films many spherulites connected by tie molecules were observed by scanning electron microscopy (SEM). From the wide angle x‐ray diffraction (WAXD) measurement, crystallites from PVDF gels were found to consist only of the γ‐type crystal with the TTTGTTTG¯ conformation, irrespective of the polymer concentration. As judged from the results obtained, the gelation of PVDF in PC seems to proceed mainly via liquid–liquid phase separation (even if followed by crystallization in the final stage) within the concentration range covered. #Dedicated to Prof. Won‐Jei Cho on the occasion of his retirement. [ABSTRACT FROM AUTHOR]