Properties’ improvement of epoxy resin using prepolymers prepared from diisocyanates and 3,9-dihydroxyethyl-3′,9′-dibenzyl-1,5,7,11-tetraoxaspiro(5,5)undecane

The prepolymers were prepared by the reaction of 3,9-dihydroxyethyl-3′,9′-dibenzyltetraoxaspiro(5,5)undecane (2) with 4,4′-diphenylenemethane diisocyanate (MDI) or hexamethylene diisocyanate (HDI) for improving the properties of the epoxy resin. The volume changes of the curing system was measured. The effects of the prepolymers on the conversion of epoxy group and thermal stability of the epoxy resin were studied. Glass transition temperature (Tg) of the modified matrix slightly decreased as the content of the prepolymers in the resin system increased. Two peaks appeared on derivative thermal gravimetry (DTG) curves of the modified epoxy resin. The one at the lower temperature was due to the decomposition of the polymeric linkages produced from the prepolymers, the other belonged to the decomposition of epoxy resin. The thermal stability of the modified matrix decreased because of the prepolymers as modifiers. However, the residual carbon of the modified matrix had an increasing tendency with quantity of prepolymer added. The strength of the modified matrix slightly decreased, but the elongation increased. When the mixture of E-51, prepolymers and BF3-H2NEt were used as adhesives, the tensile strength and shear strength were improved. The factors influencing the adhesive strength were investigated