Bottlebrush polymeric catalyst: Boosting activity for CO2/epoxide copolymerization

Abstract

A dynamic multi-cooperative strategy of constructing bottlebrush catalysts for the ring-opening copolymerization of carbon dioxide and propylene epoxide was developed. Nine bottlebrush polymeric aluminum porphyrin catalysts (BPAPC) were prepared through regulation of both brush length and bristle length, affording enhanced catalytic performances. Among them, BPAPC 5 with optimized topology exhibited a high activity (turnover frequency = 8,110 h−1) for the copolymerization of carbon dioxide and propylene epoxide, while maintaining high polymer selectivity of 99% at 110 °C. Notably, BPAPC 5 even could achieve a high turnover number of 39,000 at a very low catalyst loading ([PO]/[Al] = 50,000), yielding the copolymer with a number-average molecular weight of 271 kg∙mol−1. Moreover, through customizable catalyst design by manipulating steric confinement and ligand chemistry environment, the carbonate unit content of resulting polymers can be adjusted in the range of 35%–75%. Furthermore, the established balloon chain model explained the structure–function relationships of BPAPCs. This study provides a general design guide for cooperative catalytic systems.