Elastomers FormedIn-Situin Epoxy Resins: Chemistry and Toughening

Abstract

Abstract The chemistry of the in-situ formation of elastomer particles in epoxy resins is described. Under normal synthetic conditions, if one polymerizes an acrylic monomer in an epoxy resin, the resulting polymer is soluble in the epoxy resin or it grossly phase separates, depending upon the solubility parameter difference between the acrylic polymer and the epoxy resin. This work shows that with the use of a specifically tailored material (which we believe operates as a “polymeric surfactant”) in the reaction mixture, a free-flowing, stable suspension of acrylic elastomer particles in epoxy resin can be obtained. Thus, the reaction product of isocyanatoethylmethacrylate and EPONTM 1009 can be used as the polymeric surfactant in a reaction mixture containing hexyl acrylate, azo-bis(isobutyronitrile) and the diglycidyl ether of bisphenol A. The resulting dispersion is stable to settling even after exposure to 150°C. When properly formulated, the resulting modified epoxy resins are improved in their fracture resistance after cure over a similar resin without the elastomeric particles. The effect of the following parameters on the fracture resistance of the cured epoxy resin are discussed: chemistry of the polymeric surfactant, chain extension in the cure of the epoxy resin, type of acrylic monomer and the level of the elastomer. The physical properties of several adhesive formulations based upon these modified epoxy resins are also discussed.