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Stereochemical regulation of polypropylenes prepared with various Ziegler-Natta catalysts
Authors:Katsuo Mitani  Toshimitsu Suzuki  Akihiro Matsuo  Yoshinobu Takegami
Abstract:The 220-MHz proton magnetic resonance and infrared spectra of stereoregular polypropylenes polymerized with a number of Ziegler-Natta catalysts and isotactic polymers of low molecular weight obtained by thermal degradation of a highly isotactic polypropylene were measured in an attempt to obtain some information on the local regularity. The fraction of thermally degraded polymer soluble in diethyl ether shows stereorandomness (tactie sequence length is quite short), and the portion soluble in n-pentane has stereoblock character. The results so obtained provide strong evidence that racemic dyads of whole polymer consist of two models of racemic dyad isolated and racemic dyads in groups. The polymers prepared with vanadium catalyst systems show stereorandom character and these polymers have documentclass{article}pagestyle{empty}begin{document}$hbox{-hskip-1pt-}hskip-4pt({rm CH}_2 rlap{--} )$end{document}equation image groups formed by two propylene units in a tail-to-tail linkage. Syndiotactic polypropylene has head-to-head and tail-to-tail arrangements of two propylene units and this is the origin of randomness of syndiotacticity.
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