EPOXY-IMIDE RESINS BASED ON BIS(CARBOXYPHTHALIMIDE)S

Epoxy-imide resins have been obtained through the reaction of Araldite GY 250 (diglycidylether of bisphenol-A and epichlorohydrin; difunctional) and Araldite EPN 1138 (Novolac-epoxy resin; polyfunctional) with bis(carboxyphthalimide)s derived from 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 4,4'-diaminodiphenylether, and 4,4'-diaminodiphenylmethane and trimellitic anhydride. For each epoxy-imide resin system, epoxy equivalent to carboxy equivalent ratio has been optimised to obtain the maximum tensile lap shear adhesive strength on stainless steel substrates at room temperature. The lap shear strength at 100, 150, and 175-degrees-C has been determined for the optimum ratio. Araldite EPN-1138-based systems give the lap shear strength of 141-182 kg/cm2 at room temperature for the optimum compositions and retain about 84-100% of the lap shear strength at 150-degrees-C. Araldite GY-250-based systems have lap shear strength of 183-193 kg/cm2 and retain 76-84% of the lap shear strength at 150-degrees-C except for the one cured with bis(carboxyphthalimide) prepared from 4,4'-diaminodiphenylmethane, which retains only 17% of the lap shear strength. Among the systems studied, Araldite GY 250 cured with bis(carboxyphalimide) synthesized from 3,3'-diaminodiphenylsulfone appears to be the best, retaining 75% (138 kg/cm2) of the lap shear strength at 175-degrees-C.