Terpolymerization of epoxide, oxetane, and CO2 for the synthesis of polycarbonates with high CO2 contents, physical tunability, and enzymatic degradability

Although poly(cyclohexene carbonate) (PCHC) synthesized by the copolymerization of cyclohexene oxide (CHO) and CO2 is a promising material, the physical properties of this material need to be altered and tuned for its wider applications. To this end, we employed a terpolymerization strategy increasing the CO2 content in the resulting polymers. Terpolymerization of CHO, oxetane, and CO2 using AlIII porphyrin catalysts with quaternary ammonium halides afforded polycarbonates with high CO2 contents, physical tunability, and enzymatic degradability. The counter anions of the catalysts were crucial factors in the formation of the poly(trimethylene carbonate) (PTMC) unit. 1a with bromide ions preferentially produced trimethylene carbonate (TMC) over PTMC, while 1d with chloride ions suppressed the formation of TMC and produced PCHC–PTMC directly. PCHC–PTMC showed glass transition temperatures (Tg) between 69 °C and −9 °C, depending on the PCHC/PTMC ratio. The tensile test revealed that the PTMC unit contributed to the softening of the film materials. For example, a film material with a CO2 content of 38 wt% showed 505% elongation at break with an elastic character, which contrasted starkly with the 1.3% elongation at break of PCHC with a CO2 content of 31 wt%. Moreover, the selective degradation of the PTMC unit in PCHC–PTMC was achieved with lipases, and a gradient character in the sequence structure was suggested. Overall, PCHC–PTMC is an environmentally benign and sustainable CO2-based polycarbonate.