Enzymatic polyester synthesis in ionic liquids

The enzymatic synthesis of polyesters by ring-opening polymerization (ROP) and polycondensation in three ionic liquids, i.e., [bmim][Tf2N], [bmim][PF6] and [bmim][BF4] was investigated. For the enzymatic ROP of ε-caprolactone it was found that [bmim][PF6] and [bmim][BF4] result in an inhomogeneous reaction mixture upon polymerization, causing polymerization characteristics similar to bulk polymerization. In contrast, for [bmim][Tf2N] characteristics similar to toluene were observed. Molecular weights of 7000–9500 g/mol were obtained. In the polycondensation of dimethyl adipate and dimethyl sebacate, respectively, with 1,4-butanol the low volatility of ionic liquids was successfully utilized to perform the reactions in an open vessel at temperatures close to the boiling point of the condensation by-product. Molecular weights up to 5400 g/mol were obtained. This, in combination with the tunable solvent hydrophilicity of ionic liquids could offer an advantage in the polymerization of highly polar monomers with low solubility in organic solvents.