Tuning the crystallinity and degradability of PCL by organocatalytic copolymerization with δ-hexalactone

The copolymerization of ε -caprolactone (CL) with its structural isomer , δ -hexalactone (HL), or trimethylene carbonate (TMC) catalysed by diphenyl phosphate was investigated. Copolymers with molar fraction of CL units ranging from 54% to 95% were obtained. Molecular characterization exhibited random distribution of the two monomeric units (CL/HL or CL/TMC), owing to the extensive occurrence of transesterification scrambling reactions at high temperature. Compared with poly( ε -caprolactone) (PCL), the copolymers showed reduced crystallinity and enhanced enzymatic degradability as revealed by the analysis with differential scanning calorimetry and quartz crystal microbalance with dissipation, respectively. Interestingly, the incorporation of HL units showed a more profound impact than TMC. It is therefore considered that organocatalytic copolymerization with HL, a bio-renewable lactone, can serve as an effective method to regulate the properties of PCL.