Binary Catalyst\nManipulating the Sequences of Poly(ester-carbonate)\nCopolymers in Metal-Free Terpolymerization of Epoxide, Anhydride,\nand CO<sub>2</sub>

The one-pot terpolymerization of epoxide (EP), anhydride\n(AH),\nand CO<sub>2</sub> to synthesize polyester-polycarbonate copolymers\nwith precise sequences remains a significant challenge in polymer\nchemistry. In this study, promising progress was achieved by utilizing\na cyclic trimeric phosphazene base (CTPB) and triethylboron (TEB)\nas a binary catalyst, enabling the synthesis of both well-defined\nblock and truly random poly(ester-carbonate) copolymers through the\none-pot terpolymerization of EP/AH/CO<sub>2</sub>. By adjusting the\nmolar ratio of CTPB/TEB to 1/0.5, remarkable chemoselectivity for\nring-opening alternating copolymerization (ROAC) of propylene oxide\n(PO) and phthalic anhydride (PA) was achieved, followed by the ROAC\nof PO/CO<sub>2</sub>. This sequential control allowed for the synthesis\nof well-defined block poly(ester-carbonate) copolymers, containing\nthree possible sequences, ester–ester sequence (EE)/ester-carbonate\nsequence (EC)/carbonate-carbonate sequence (CC) = 59/4/37, from a\nmixture of PO, PA, and CO<sub>2</sub>. Moreover, the versatility of\nthis CTPB/TEB catalyst in regulating chemoselectivity was demonstrated,\nwith a ratio of 1/3 facilitating the simultaneous ROAC of PO/PA and\nPO/CO<sub>2</sub> with compatible rates, resulting in the production\nof random poly(ester-carbonate) copolymers, in which three possible\nsequences (EE/EC/CC = 26/50/24) are very close to theoretical values.\nThis metal-free catalytic system and its flexible chemoselectivity\nregulation strategy proved to be applicable to a wide range of epoxides\n(PO, cyclohexene oxide (CHO)) and anhydrides (PA, diglycolic anhydride\n(DGA), and succinic anhydride (SA)), enabling the successful synthesis\nof poly(ester-carbonate) copolymers with diverse sequences and compositions.