Thermally reprocessable chemically cross-linked shape memory PCL network based on the dynamic exchange of disulfide bonds

Abstract

In this study, branched polycaprolactone polyol containing disulfide bond (PCL-DS) was synthesized by in-situ ring-opening polymerization of ε-caprolactone in the presence of 2-hydroxyethyl disulfide (HEDS) as an initiator. And, PCL-DS/HEDS mixture with different HEDS content was reacted with hexamethylene diisocyanate to produce networks containing various amounts of disulfide bonds. Structure of the PCL-DS and PCL/HEDS networks was characterized by Fourier-transform infrared (FT-IR), Nuclear magnetic resonance (NMR), Raman spectroscopies, and gel permeation chromatography (GPC). Thermomechanical properties of the PCL/HEDS networks were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and tensile test. DSC and DMA results revealed that crosslink density of the network are varied with HEDS content, and melting temperature of PCL of the network decreased with increasing crosslink density. All network samples exhibit typical ductile deformation accompanied with yieding. Further, the PCL/HEDS networks exhibit excellent thermal reprocessability when there contains sufficient amount of disufide bonds. Further, all PCL/HEDS networks demonstrated excellent thermally-triggered shape memory effect with full shape recovery and fixing ratios.