Metal-free controlled ring-opening polymerization of ε-caprolactone in bulk using tris(pentafluorophenyl)borane as a catalyst

Abstract

Narrowly distributed poly(ε-caprolactone) (PCL) was synthesized by the ring-opening polymerization (ROP) of ε-caprolactone (CL) using tris(pentafluorophenyl)borane (B(C₆F₅)₃) as an acidic catalyst and benzyl alcohol (BnOH) as the initiator in bulk at 80 °C. 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. ¹H NMR, SEC and MALDI-TOF MS measurements clearly indicate the presence of an initiator residue at the chain end of the obtained PCL homopolymers. The study on polymerization kinetics confirms the controlled/living nature of the B(C₆F₅)₃-catalyzed ROP of CL. Accordingly, the block copolymerization of CL with δ-valerolactone (VL) and trimethylene carbonate (TMC) successfully proceeded to give PCL-b-PVL and PCL-b-PTMC copolymers. Macrocyclic PCL was also prepared by the intramolecular click reaction of the heterotelechelic α-azido,ω-ethynyl-PCL.