Cyclopolymerization of Si-Containing α,ω-Diolefins by a Pyridylamidohafnium Catalyst with High Cyclization Selectivity and Stereoselectivity

Abstract

Cyclopolymerization of unsymmetric and symmetric Si-containing α,ω-diolefins by dimethylpyridylamidohafnium/organoboron catalytic system with high cyclization selectivity and stereoselectivity was first reported here. Compared with the constrained geometry catalyst [Me2Si(η5-Me4C5)(NtBu)]TiCl2 and the typical metallocene catalyst rac-Et(Ind)2ZrCl2, the Hf complex has proved to be one more promising catalyst for the cyclopolymerization of unsymmetric 3,3-dimethyl-3-sila-1,5-hexadiene (DMSHD). The poly(DMSHD) with high molecular weight (up to 953 kg/mol), high cyclization selectivity (100%), high cis selectivity (>90%), and high isotactic selectivity (>90%) could be easily obtained by the Hf catalyst under mild conditions. Moreover, the poly(DMSHD) also possessed a high glass transition temperature (up to 99.8 °C) and high melting temperature (Tm >200 °C). The insertion reaction of the vinyl group into Hf–CAr bond was further investigated, and a possible cyclization mechanism of DMSHD was proposed according...