Self-switchable terpolymerization of cyclic anhydrides, epoxides and lactide catalyzed by C2v-symmetric cobaltoporphyrins

Abstract

The urgency for biodegradable plastics free from crude oil-based chemicals is currently paramount. These materials should be easily recyclable and capable of undergoing degradation at the end of their useful life. Herein, a series of C2v-symmetric cobaltoporphyrins featuring different substituents were synthesized, and evaluated for their catalytic performance in the self-switchable terpolymerization of epoxides, cyclic anhydrides and lactide in coordination with a co-catalyst bis(triphenylphosphoranylidene) ammonium chloride (PPNCl), under initiator-free conditions. These cobaltoporphyrin homogeneous catalysts exhibit promising chemical selectivity in the multicomponent copolymerization, resulting in kinetic differentiation between the ring-opening copolymerization of epoxides with cyclic anhydrides and the ring-opening polymerization of lactide. Lactide only participates in polymerization after complete conversion of cyclic anhydrides, leading to sequence-regulated block copolyesters. The substituents on the porphyrin ligand have significant influence on its catalytic activity. Among all catalysts tested, DOMePP-CoCl exhibited the most outstanding reactivity under optimal conditions. Furthermore, by utilizing different cyclic anhydrides and epoxide monomers, the DOMePP-CoCl/PPNCl catalytic system still exhibited excellent reaction activity, allowing for the high-yielding and high-selectivity transformation into corresponding multiblock copolyesters.