ISOTACTIC POLYSTYRENE POLY(VINYL METHYL-ETHER) BLENDS - MISCIBILITY, CRYSTALLIZATION AND PHASE-STRUCTURE

The dependence of the miscibility, melting behaviour, kinetics of crystallization and morphology in isotactic polystyrene/poly(vinyl methyl ether) (iPS/PVME) blends on temperature, thermal history and blend composition has been studied by using differential scanning calorimetry, scanning electron and optical microscopy and small-angle X-ray diffraction. For the blends obtained by casting, three glass transitions were detected, indicating that in the amorphous material three different phases were present: plain PVME, plain iPS and a homogeneous iPS/PVME mixture. This last phase seems to undergo phase separation by melting the sample at 270°C for 15 min. There is no detectable change in the melting behaviour of iPS in the blends with composition, indicating that the percentage of PVME in the iPS-rich phase is very small. The spherulite crystallization growth rate at a given temperature increases with increasing PVME content in the blend, whereas the overall crystallization rate is independent of composition. These results can be explained by considering the increase of the mobility of the crystallizable chains in the melt and the decrease of the nucleation rate due to the presence of PVME in the melt. It was found that during crystallization the iPS spherulites occluded droplet particles of PVME-rich phase in their intraspherulitic regions. © 1990.