Morphological characteristics and electrical conduction in syndiotactic polypropylene

Molecular structure, morphological characteristics and electrical conduction in syndiotactic polypropylene (sPP) are studied, sPP is found to be highly resistant to thermal oxidation. The crystallinity measured by the x-ray diffraction meter is very low and shows no significant change with annealing, compared with that in isotactic polypropylene (iPP). The development of spherulites occurs at a lower temperature than in iPP and the size of spherulites is much smaller than that in iPP, even though the number of spherulites increases drastically. The influence of the morphological change on electrical conduction in sPP is negligibly small, in contrast to iPP, where the breakdown strength decreases markedly due to spherulite growth upon heat treatment. In electrical conduction in the high field region above 10(7) V m(-1). the predominant conduction mechanism is interpreted to be the Schottky effect in the low temperature region below 70 degrees C. But in the high temperature region above 70 degrees C, the conduction is considered to be ionic conduction, with the jump distance estimated to be 3.3 nm smaller than that in IPP. These results are discussed in terms of the molecular structure differences between sPP and iPP. (Some figures in this article appear in colour in the electronic version; see www.iop.org).