Siloxane-modified epoxy resins

Epoxy resins chemically modified with functionally terminated poly (dimethyl siloxane), poly(dimethyl-co-methyltrifluoropropyl siloxane), and poly(dimethyl-co-diphenyl siloxane) oligomers are described in terms of their synthesis, morphology, solid-state properties, and friction and wear properties. The compatibility between the epoxy resin and the siloxane modifiers can be enhanced by increasing the percentage of methyltrifluoropropyl (TFP) siloxane or diphenyl (DP) siloxane relative to dimethyl siloxane. The compatibility of the siloxane modifier with the epoxy resin subsequently controls the size and make-up of the phase-separated elastomeric domains. Fracture toughness of the epoxy resin can be improved by modification with siloxanes containing 40% or higher TFP content or 20 and 40% DP content. Both fracture toughness and modulus changes are given a morphological basis. Friction and wear properties in both fatigue and abrasive wear tests have been found to be related to changes in modulus, fracture toughness, and morphology in ways dependent on the particular modifier. The properties and morphology of epoxy resin modified with amine-terminated and carboxyl-terminated butadiene acrylonitrile elastomers prepared under similar curing conditions have been determined and compared to those of the siloxane-modified resins.