Homogeneous Metallic Oligomer Catalyst with Multisite Intramolecular Cooperativity for the Synthesis of CO2 -Based Polymers

Cooperative catalysis is a powerful strategy in the catalytic ring-opening copolymerization of epoxides and CO2, especially for breaking through the dependence of the polymer selectivity on the temperature and the restriction of the activity by catalyst concentration. In this work, to realize multisite cooperativity in a homogeneous catalysis, a series of oligomer catalysts flexibly bearing aluminum(III) porphyrin complexes in the side chains were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. The catalytic performance distinctly outperformed that of the previous molecular metal catalyst under identical conditions: (1) a 3-5-fold increase in activity was observed as approximately four to seven Al centers were anchored in one catalyst chain; (2) the required use of a cocatalyst was reduced by 50-75% (3) 99% polymer selectivity was achieved even at 90 degrees C; (4) the activity was maintained at a very low catalyst loading ([Al]/PO = 1/100 000), with the number-average molecular weight of the resulting copolymer above 200 kg/mol.