PARTIALLY MISCIBLE BLENDS OF EPOXY-RESIN AND EPOXIDIZED RUBBER - STRUCTURAL CHARACTERIZATION OF THE EPOXIDIZED RUBBER AND MECHANICAL-PROPERTIES OF THE BLENDS

The cure process and the mechanical properties of blends of diglycidyl ether of bisphenol-A-based epoxy resin and hydroxyl terminated, inter nally epoxidized polybutadiene rubber have been studied. Internal oxir ane groups are characterized by a main absorption at 885 cm-1 in the i nfrared spectrum while the terminal oxirane groups of the diepoxide mo nomer absorb at 913 cm-1. In the absence of prereaction of the rubber, gelation of the epoxy matrix occurs much faster than any reaction inv olving the internal oxirane groups or the terminal hydroxyl groups. Th erefore, only weak chemical bonding between the rubber particles and t he epoxy matrix exists and the fracture toughness of the blends does n ot show any significant improvement. Upon prereaction of the rubber wi th an excess diepoxide monomers, a 40% improvement in the value of the critical stress intensity factor is obtained. However, dynamic mechan ical spectra of these blends acquired in the rubbery plateau region un iquely demonstrate that this improvement is due to the incorporation o f the rubber into the epoxy network rather than to the presence of pha se-separated rubber particles. (C) 1994 John Wiley & Sons, Inc.