Controlled Random Terpolymerization of β-Propiolactone,Epoxides,and CO_(2) via Regioselective Lactone Ring Opening

The random ring-opening terpolymerization of CO_(2),epoxides,and lactones remains challenging,mainly because CO_(2)/epoxide copolymerization and lactone ring-opening polymerization typically proceed at very different rates.Herein,we report the preparation of novel statistical terpolymers with random distributions of carbonate and ester units(up to 40%junction units)via the one-pot reaction ofβ-propiolactone(BPL),epoxides,and CO_(2) under mild conditions using a binary catalyst system consisting of SalcyCo(III)OTs(Salcy=N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-diaminocyclohexane;OTs=p-toluenesulfonate)and 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene.Since this catalytic system could yield similar reaction rates for alternating epoxide/CO_(2) copolymerization and BPL polymerization,terpolymers with nearly identical compositions were produced at various time points.CO_(2) played an important role in preventing intra-and/or intermolecular transesterification side reactions.Thereby,the terpolymerization proceeded in a controlled manner,allowing for the fine-tuning of molecular weight and composition.Two-dimensional nuclear magnetic resonance(NMR)analysis and density functional theory(DFT)calculations suggested that the nucleophilic attack of the coordinated BPL by carbonate ions cleaved the alkyl C–O bond predominantly rather than the acyl C(=O)–O bond,typically observable during the nucleophilic ring-opening polymerization of BPL.These findings have opened up a new avenue for preparing a broad family of biodegradable polymers with adjustable properties.