The correlation of chemical structure, crystalline morphology, and space charge distribution under a dc electrical field was investigated with three kinds of poly(propylene) (PP) with a different chemical structure, that is, homogeneous PP and block copolymer and random copolymer of PP. The space charge distribution of the samples was prominently affected by their chemical sequence structure and crystalline microstructure. Among samples of different PPs, all isothermally crystallized at 140℃, the sample of random coPP represents the most well proportional space charge distribution and the smallest number of space charges. The effect of thermal history on the space charge distribution was also investigated by the samples of block coPP. The sample thermally treated at 50℃ clearly represents a better proportional distribution than that at higher temperature of 140 and 100℃. Subsequent experiments indicate that the better proportional distribution attributes to imperfect and fine sperulites with the fine distribution of the "amorphous" region. The imperfect and fine sperulites originate from the random incorporation of ethylene segments or units into PP chains or fromthe low annealing temperature, and play an important role in the formation of shallowtraps and transportation of space charges.

Anewmethod to synthesize polyimide (PI)/silica nanohybrids has been presented. It uses silicic acid oligomer as the silica precursor, which was obtained by extracting with tetrahydrofuran (THF) from PH-adjusted water glass. The films of PI/silica nanohybrids remained transparent even at high silica content due to the formation of nanometer-scaled SiO2 particles at the addition of γ-aminopropyltriethoxysilane (APTES). In comparison with pure PI, PI/silica hybrids showed improved thermal stability and mechanical properties, and lower linear coefficients of thermal expansion (CTEs). The glass transition temperatures of the hybrids were increased with increasing content of silica or APTES as a result of the increasing limitation to the movements of the PI backbone.

A novel process to prepare microporous hollow fiber membranes is proposed. Fibers of blends of isotactic polypropylene (i-PP) and atactic polypropylene (a-PP) spun under high take-up draw ratio are found to be elastic. Small angle X-ray scattering (SAXS) observation indicates that fibers have row-nucleated lamella structure normal to the fiber direction. Microporous polypropylene hollow fiber membranes were obtained from the fibers by extraction of atactic polypropylene and cool-stretching. The membranes have smaller pore size and higher permeability than those of traditional stretch method. The mechanism of micropore formation is discussed.