Supercritical RROP: Exploring the radical ring-opening polymerisation of 2-methylene-1,3,6-trioxocane in supercritical CO2 as a green solvent

Radical ring opening polymerisation (RROP) of cyclic ketene acetals (CKAs) is an attractive technique to synthesize branched, (bio)degradable polyesters. However, CKAs as monomers of RROP suffer from hydrolysis lability, making aqueous heterogeneous precipitation polymerisations challenging. In order to explore the precipitation polymerisation of 2-methylene-1,3,6-trioxocane (MTC) and avoid the hydrolysis of monomer, kinetic studies in supercritical CO2 (scCO2) were performed. Tuning the reaction pressure and temperature allowed for synthesis in varying viscosity domains. Importantly, we describe the precipitation polymerisation of low Tg PMTC (−65 °C) in scCO2. In contrast to literature, where a particle-driven polymerisation mechanism has been described for high Tg polymers, a slurry-like precipitation polymerisation was observed for PMTC. Depending on the reaction temperature, polymers with either (i) a defined density of branches (DB) and a scattering of molar mass values, or (ii) a scattering of DB values and relatively defined molar mass were prepared. [Display omitted] •First comprehensive study of RROP in scCO2.•Polymerisation in scCO2 leads to precipitation polymerisation.•Molar mass can be regulated by the reaction temperature.•Dispersity and branching largely independent of reaction pressure.•Use of scCO2 green solvent enhances RROP as sustainable polymerisation.