Flexible Epoxy Resins Formed by Blending with the Diblock Copolymer PEO--PCL and Using a Hydrogen-Bonding Benzoxazine as the Curing Agent.

In this study, we enhanced the toughness of epoxy resin by blending it with the diblock copolymer poly(ethylene oxide⁻⁻ε-caprolactone) (PEO--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 dynamic mechanical analysis revealed that the glass transition temperature and storage modulus of the epoxy⁻benzoxazine matrix decreased significantly upon increasing the concentration of PEO--PCL. The Kwei equation predicted a positive value of , consistent with intermolecular hydrogen bonding in this epoxy⁻benzoxazine/PEO--PCL blend system. Scanning electron microscopy revealed a wormlike structure with a high aspect ratio for PEO--PCL as the dispersed phase in the epoxy⁻benzoxazine matrix; this structure was responsible for the improved toughness.