Calcium-catalysed ring-opening copolymerisation of epoxides and cyclic anhydrides

Novel dinuclear calcium complexes have been employed as bifunctional catalysts for the ring-opening copolymerisation reaction of epoxides and cyclic anhydrides. The catalysts exhibited good performances and quantitative formation of ester linkages for the poly(CHO-alt-PA) production under mild reaction conditions and in the absence of a cocatalyst. Furthermore, these catalysts demonstrated tolerance to a variety of bio-sourced epoxides/phthalic anhydrides, providing access to a range of potentially functionalisable polyesters. On the other, polymerisation kinetic analyses revealed a half-order dependence on catalyst concentration and first-order dependence on cyclic anhydride concentration, whilst MALDI-ToF analyses supported an initiation step involving the ring-opening of the epoxide. Taken together, these findings underpin a mononuclear pathway, with the ring-opening of the cyclic anhydride identified as the rate-limiting step in the process.