Highly active aggregate catalysts for the synthesis of high-molecular-weight polyesters via copolymerization of epoxides and cyclic anhydrides

Abstract

Although the ring-opening copolymerization (ROCOP) of epoxides and cyclic anhydrides is a promising route to polyesters, the efficient production of high molecular weight (M_n) polyesters remains a great challenge. Herein, we constructed aggregate catalysts by polymerizing multiple mononuclear aluminum porphyrin catalysts using the aggregation-enhanced synergy strategy for the ROCOP of epoxides and cyclic anhydrides, facilitating the production of high M_n polyesters. It was shown that the aggregate catalysts could significantly increase the reaction activity and effectively suppress the transesterification side reactions. For example, for the ROCOP of 1-butene oxide (BO) with phthalic anhydride (PA), the aggregate catalyst PAPC-Cl give the alternating polyesters a high M_n of 125.6 kg mol⁻¹ with a high turnover frequency (TOF) of 3600 h⁻¹ under a very low catalyst loading ([PA]/[Al] = 20 000/1) at 125 °C. Remarkably, the PAPC-Cl can maintain a TOF of 4500 h⁻¹ under an ultra-low catalyst loading ([BO]/[PA]/[Al] = 150 000/30 000/1). Moreover, the aggregate catalysts displayed exceptional thermal stability even up to 150 °C, achieving a TOF of 8200 h⁻¹. The resultant high molecular weight polyesters exhibited initial decomposition temperatures of up to 300 °C and stress of up to 34.2 MPa with an elongation at break of up to 12%. In conclusion, our strategy of designing aggregate catalysts provides a new perspective to develop catalysts with high activity and low concentration tolerance, especially the capability of producing high molecular weight polyesters.