Acrylate-based liquid rubber as impact modifier for epoxy resin

Carboxyl-terminated poly(2-ethyl hexyl acrylate) (CTPEHA) having various molecular weights were synthesized by bulk polymerization in the form of liquid rubber. The liquid rubbers (LR-1 to LR-4) were characterized by C-13-NMR spectroscopic analysis, nonaqueous titration, and vapor-pressure osmometry (VPO). The liquid rubber having the lowest molecular weight (M-n = 3600) was prereacted with the epoxy resin and the modified epoxy networks were made by curing with an ambient temperature curing agent. The modified epoxy networks containing different concentrations of CTPEHA were evaluated with respect to their thermal and impact properties. The optimum properties were obtained at about 10-15 phr of CTPEHA concentration (phr stands for parts per hundred parts of epoxy resin). Fracture surface analysis by scanning electron microscopy (SEM) indicated the presence of a two-phase microstructure. (C) 2001 John Wiley & Sons, Inc.