Binary Catalyst Manipulating the Sequences of Poly(ester-carbonate) Copolymers in Metal-Free Terpolymerization of Epoxide, Anhydride, and CO2.

Abstract

The one-pot terpolymerization of epoxide (EP), anhydride (AH), and CO₂ to synthesize polyester-polycarbonate copolymers with precise sequences remains a significant challenge in polymer chemistry. In this study, promising progress was achieved by utilizing a cyclic trimeric phosphazene base (CTPB) and triethylboron (TEB) as a binary catalyst, enabling the synthesis of both well-defined block and truly random poly(ester-carbonate) copolymers through the one-pot terpolymerization of EP/AH/CO₂. By adjusting the molar ratio of CTPB/TEB to 1/0.5, remarkable chemoselectivity for ring-opening alternating copolymerization (ROAC) of propylene oxide (PO) and phthalic anhydride (PA) was achieved, followed by the ROAC of PO/CO₂. This sequential control allowed for the synthesis of well-defined block poly(ester-carbonate) copolymers, containing three possible sequences, ester-ester sequence (EE)/ester-carbonate sequence (EC)/carbonate-carbonate sequence (CC) = 59/4/37, from a mixture of PO, PA, and CO₂. Moreover, the versatility of this CTPB/TEB catalyst in regulating chemoselectivity was demonstrated, with a ratio of 1/3 facilitating the simultaneous ROAC of PO/PA and PO/CO₂ with compatible rates, resulting in the production of random poly(ester-carbonate) copolymers, in which three possible sequences (EE/EC/CC = 26/50/24) are very close to theoretical values. This metal-free catalytic system and its flexible chemoselectivity regulation strategy proved to be applicable to a wide range of epoxides (PO, cyclohexene oxide (CHO)) and anhydrides (PA, diglycolic anhydride (DGA), and succinic anhydride (SA)), enabling the successful synthesis of poly(ester-carbonate) copolymers with diverse sequences and compositions.