Abstract
This chapter investigates time dependence of molecular weight in propylene bulk polymerization with MgCl 2 -supported Ziegler–Natta catalyst. Polymerizations were carried out in liquid propylene at 70°C at constant H 2 concentration with the catalyst of type MgCl 2 /TiCl 4 /diethyl phthalate. Dimethoxydialkoxysilane as an external donor reacts with A1Et 3 during polymerization and monomethoxysilane is formed. Thus part of type C site is transformed into another type C site. The polypropylene (PP) produced with the newly formed type C' site having the interaction with monoalkoxysilane is less isotactic and has lower M w than that of the original type C site probably because of flexible structure of type C' site and the less electron-donating effect of monoalkoxysilane. The obtained PP is fractionated by n -heptane at 95°C and the insoluble part is removed as a highly isotactic part. The soluble part is analyzed by CFC, 13 C-NMR, wide-angle X-ray scattering (WAXD), and small-angle X-ray scattering (SAXS). The elution peak by chlorofluorocarbon (CFC) was at 110°C and the isotactic pentad mmmm was 0.39. Besides mmmm , all other pentads were also observed. WAXD showed that the soluble part contained distinct crystallites but the crystallinity was fairly low. SAXS showed that there was no long-period structure.
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