Organo-catalyzed synthesis of aliphatic polycarbonates in solvent-free conditions

A new efficient and expeditious route to the synthesis of aliphatic polycarbonates, in solvent-free conditions and using 1-n-butyl-3-methylimidazolium-2-carboxylate (BMIM-2-CO2) as a catalyst precursor, is described. The protocol consists of a two-step polymerization process involving the transesterification of dimethyl carbonate (DMC) with linear alkane diols and leading to high molecular weight homopolymers. The reaction went to completion quantitatively with the liberation of methanol as the only by-product. The in situ formation of N-heterocyclic carbene species resulting from BMIM-2-CO2 decarboxylation is suggested to be a key feature of the condensation process. The protocol was then applied to the copolymerization of diverse diols leading to the synthesis of polycarbonates with average segment lengths and random sequences.