チグラー・ナッタ触媒の立体特異性とオレフィン共重合体の構造

概要

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Since heterogeneous Ziegler-Natta catalysts usually contain multiple active species with different chemical properties, it is difficult to control the composition and monomer sequence distribution of copolymers by using them as catalyst. In the present paper, therefore, we have prepared both heterogeneous and homogeneous model catalysts which completely differ in stereospecificity and regiospecificity and applied them for olefin copolymerizations to investigate the effect of catalyst stereo- and regiospecificity on copolymers. A detailed analysis of copolymers produced with isospecific and aspecific heterogeneous catalysts has led to the conclusion that isospecific sites give blocky copolymers with less contents of higher olefins while aspecific ones give random copolymers abundant in higher olefin contents. Homogeneous Kaminsky-Sinn type catalysts are known to produce random copolymers. It was found, however, the microstructure of copolymers is slightly dependent upon the stereospecificity, i.e., bulkiness or symmetry of ligand attached to the active site. On the other hand, the Al2O3 supported CpTiCl3 catalyst was found to give atactic polypropene with frequent chemical inversion as well as random olefin copolymers, which are very different from those obtained with ordinary Ti-based heterogeneous catalysts.
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