Copolymerization of tricyclopentadiene and ethylene catalyzed by thiophene-fused-heterocyclic cyclopentadienyl scandium complexes

Abstract

Cyclic olefin copolymers (COCs) are excellent optical materials, and are of fundamental interest and practical importance. Bulky cyclic olefin based COCs possess higher glass-transition temperature at similar cyclo-olefin contents in copolymers. Tricyclopentadiene (TCPD) is a useful bulkier cyclo-olefin, and is easily accessible from cheap dicyclopentadiene. However, the copolymerization of TCPD and ethylene (E) is a challenge because of a lack of suitable catalysts. Herein, we report the synthesis of a series of TCPD/E copolymers with various TCPD contents (13.0% to 43.8%) and T_g (50 to 252 °C) by changing the catalyst structure and polymerization conditions. The polymerization activities are high, up to 5.38 × 10⁶ g mol_Sc⁻¹ h⁻¹. More importantly, we found that the glass-transition temperature (T_g) values of the TCPD/E copolymers are not only affected by the cyclo-olefin incorporation, but also by the TCPD distribution on the polymer chain for the first time. Higher alternating unit {–(TCPD)–E–} ratios led to higher T_g when the TCPD incorporation was similar. Hydrogenation of the TCPD/E copolymers is easily achieved via Ni(acac)₂ catalyzed reactions of the copolymers and hydrogen gas. The TCPD/E copolymers and their corresponding hydrogenated polymers possess high transparency at more than 89% in the visible range.