Synthesis of polyisobutylene-polycaprolactone block copolymers using enzyme catalysis

Abstract

The synthesis of poly(isobutylene-b-e-caprolactone) diblock and poly(e-caprolactone-b-isobutylene-b-e-capro- lactone) triblock copolymers was accomplished using a combination of living carbocationic polymerization of isobutylene (IB) with the ring-opening polymerization (ROP) of e-caprolactone (e-CL). OH-PIB-allyl was prepared by living carboca- tionic polymerization of IB initiated with 1,2-propylene oxide/TiCl4 followed by termination with allyltrimethylsilane. Hy- droxyl telechelic HO-PIB-OH was obtained by living IB polymerization initiated by 2,4,4,6-tetramethyl-heptane-2,6- diol/TiCl4, termination with allyltrimethylsilane and subsequent thiol-ene click reaction with mercaptoethanol. The structure of the hydroxyl PIBs was confirmed by 1 H NMR (proton Nuclear Magnetic Resonance spectroscopy). OH-PIB-allyl and HO-PIB-OH were then successfully used as macroinitiators for the polymerization of e-CL catalyzed by Candida antarctica Lipase B (CALB), yielding poly(e-caprolactone-b-isobutylene) diblock and poly(e-caprolactone-b-isobutylene-b-e-capro- lactone) triblock copolymers, respectively. Differential Scanning Calorimetry (DSC), Transition Electron Microscopy (TEM) and Atomic Force Microscopy (AFM) demonstrated that the amorphous PIB and the semicrystalline PCL block segments phase separated, creating nanostructured phase morphology.