Stereoelective polymerization of racemic α-olefins: Influence of conversion and of nature of catalyst components

The dependence of stereoelectivity on conversion has been investigated by polymerizing racemic 4-methyl-1-hexene (I) and 3,7-dimethyl-1-octene (II) in the presence of catalysts prepared from TiCl₄ and bis[(S)-2-methylbutyl]-zinc(III) or tris [(S)-2-methylbutyl]aluminum (IV). The influence of the nature of transition metal halide has also been examined by polymerization of racemic I and II with catalysts obtained from III and transition metal halides as well as from TiCl₄ and optically active organometallic compounds containing phenyl groups. Stereoelectivity remains practically constant or increases slightly with increasing conversion, but it is affected by the nature of transition metal halide. Moreover a detectable variation of stereoelectivity was observed by changing the chemical structure of the alkyl group in the optically active organometallic component of the catalyst. In any case, however, stereoelectivity is not higher than 5–10%. Evidence in favor of asymmetric induction by the catalytic complex is reported and discussed.