Reinvestigation of the Ring-Opening Polymerization of ε-Caprolactone with 1,8-Diazacyclo[5.4.0]undec-7-ene Organocatalyst in Bulk

Abstract 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) was used as organocatalyst to reinvestigate the ring-opening polymerization (ROP) of e-caprolactone (CL) with benzyl alcohol (BnOH) initiator in bulk at 90 °C considering the unsuccessful ROP of CL at RT in previously reported publications. Kinetic study indicates that the PCLs could be well-designed with a controlled/living character of polymerization. The use of functional initiators, such as 2-hydroxyethyl methacrylate (HEMA), propargyl alcohol (PGA), 6-azido-1-hexanol (AHA) and methoxy poly(ethylene glycol) (mPEG) leads to end-functionalized PCLs. Accordingly, the block copolymerization of CL with δ-valerolactone (VL), trimethylene carbonate (TMC) and lactide (LA) successfully proceeded to give PCL-b-PVL, PCL-b-PTMC and PCL-b-PLA copolymers. Finally, the reaction mechanism was studied with DFT calculations and NMR measurements.