Flexible epoxy resins formed by blending with the diblock copolymer PEO-b-PCL and using a hydrogen-bonding benzoxazine as the curing agent

Abstract

In this study, we enhanced the toughness of epoxy resin by blending it with the diblock copolymer poly(ethylene oxide-b-"-caprolactone) (PEO-b-PCL) with a benzoxazine monomer (PA-OH) as the thermal curing agent. After thermal curing, Fourier transform infrared spectroscopy revealed that intermolecular hydrogen bonding existed between the OH units of the epoxy-benzoxazine copolymer and the C-O-C (C=O) units of the PEO (PCL) segment. Differential scanning calorimetry and dynamicmechanical analysis revealed that the glass transition temperature and storagemodulus of the epoxy-benzoxazine matrix decreased significantly upon increasing the concentration of PEO-b-PCL. The Kwei equation predicted a positive value of q, consistent with intermolecular hydrogen bonding in this epoxy-benzoxazine/PEO-b-PCL blend system. Scanning electron microscopy revealed a wormlike structure with a high aspect ratio for PEO-b-PCL as the dispersed phase in the epoxy-benzoxazine matrix; this structure was responsible for the improved toughness.