Relationship between magnetic alignment and the crystallization condition of isotactic polystyrene

The relationship between a magnetic alignment and crystallization conditions of isotactic polystyrene (iPS) was studied by means of DSC, POM, WAXD, FT-IR, and birefringence measurements. The onset temperature for crystallization during the cooling process was found to depend on the melting temperature. From observations using a polarized optical microscope, the proportion of spherulite decreased in cases where melting occurred at greater than 265 °C. These results suggest that melting at less than 265 °C causes self-seeding, which is known as the 'melt memory effect' in iPS, leading to a high nucleation density. The maximum intensity of transmitted light that could be observed by birefringence measurements was also dependent on the melting temperature. The high nucleation density that was obtained by melting at less than 265 °C was suitable for achieving higher orientations. In situ infrared measurements in a magnetic field were carried out in a home-built apparatus into which an autorotation polarizer unit had been installed. This allowed us to automatically acquire simultaneous polarized infrared spectra both parallel and perpendicular to the magnetic field. Orientation was confirmed for the crystalline band, while no orientation was observed for the amorphous band. The dichroic difference increased during isothermal crystallization with increasing crystallinity. No orientation effects were observed in the melted state in the present study.