Simultaneous reinforcement and toughness improvement in an aromatic epoxy network with an aliphatic hyperbranched epoxy modifier

Hyperbranched polymers have been shown to improve epoxy fracture toughness at the cost of other mechanical properties. In this study an aliphatic, epoxide-functional hyperbranched polymer was synthesized and incorporated at different concentrations into an aromatic epoxy-amine network without cure-induced phase separation. The resulting homogeneous network architecture and thermomechanical properties were studied using DSC, DMA and FTIR, while the mechanical properties were investigated using uniaxial compression and single edge notch beam 3-point bending. It was found that although the flexible hyperbranched structure decreased the glass transition temperature of the network, it also allowed for simultaneous enhancement in both fracture toughness and Young's modulus. These findings were attributed to relationships between chemical structure, crosslink density and non-bond interactions, and indicate the potential for further glassy network fracture toughness improvement without loss of critical mechanical properties by tailoring of the hyperbranched structure. (C) 2015 Elsevier Ltd. All rights reserved.