Sustainable polyesters via ROCOP of bio-based epoxides with cyclic anhydrides catalyzed by [OSSO]-type chromium(iii) and iron(iii) complexes

The ring-opening copolymerization (ROCOP) of various epoxides with cyclic anhydrides derived from β-myrcene and isoprene, named MDA and IDA respectively, was achieved using [OSSO]-type iron(III) (1) or chromium(III) (2) catalysts in combination with bis(triphenylphosphine)iminium chloride (PPNCl). In all binary ROCOP reactions, polyesters with anhydride conversion > 99% and tunable glass-transition temperatures ( T g = from − 2 to 98 °C) were obtained. The Cr(III) catalyst increased polymerization rates, while Fe(III) delivered comparable polymer properties, supporting iron as a more sustainable catalyst platform. Sequential ROCOP using two cyclic anhydrides, for example MDA followed by phthalic anhydride (PA), afforded multiblock copolymers with > 95% overall conversion. Extending this chemistry to one-pot epoxide/anhydride/CO 2 terpolymerizations enabled a switch from polyester to polycarbonate formation, with up to 82% of the consumed epoxide incorporated as carbonate linkages at low catalyst loading (0.10 mol%). Nuclear Magnetic Resonance (NMR) spectroscopy analyses indicated minimal polyether formation and controlled block architectures, highlighting the Fe(III) catalyst as a selective and versatile system for sustainable, renewable polymers.