C1-symmetric tert-butyl substituted pyridylamido hafnium complex for ethylene, α-olefin, and styrene polymerizations

Abstract

As a particularly promising new class of catalysts, pyridylamido hafnium catalysts show outstanding polymerization performance and the bridgehead substituents are located at a strategic place to control the macromolecular architecture. However, modifications of the catalysts from the alkyl bridgehead substituents are relatively unexplored. In this paper, a C1-symmetric tert-butyl substituted pyridylamido hafnium catalyst was designed and synthesized for homo- and copolymerizations of ethylene, α-olefin, and styrene. tert-Butyl pyridylamido hafnium showed intriguing polymerization performance because the bulky tert-butyl substituent on bridgehead created the Thorpe-Ingold-like “buttressing effect”. This catalyst afforded narrowly dispersed polymers for olefin homopolymerizations and showed high isoselectivity for α-olefin polymerizations ([mmmm] > 99%), but was inactive for styrene polymerization because of 2,1-insertion of styrene. Copolymerizations of ethylene and α-olefins produced bimodal-distribution copolymers, while copolymerizations of ethylene and styrene were realized to produce monomodal-distribution copolymers with ultrahigh molecular weight.