A facile route to realize the copolymerization of L-lactic acid and ε-caprolactone: sulfonic acid-functionalized Brønsted acidic ionic liquids as both solvents and catalysts

Biodegradable copolymers of L-lactic acid and ε-caprolactone [P(LLA-CL)s] were prepared in sulfonic acid-functionalized Brønsted acidic ionic liquids (SFBAILs) with very different anions and cations. SFBAILs work as both solvents and catalysts. The copolymerization process was proved to be a combination of polycondensation and simultaneous transesterification after a fast ring-opening polymerization of ε-caprolactone through a kinetic study. Copolymers with different monomer ratios were obtained. We found that the anions rather than the cations of SFBAILs have a great impact on the polymerizations. In addition, SFBAILs can be simply recovered by phase separation and recycled without decreasing the efficiency.