Synthesis and curing behaviour of urethane‐modified epoxy resin having hydroxymethyl group

Abstract

AbstractSynthesis and curing behaviour of urethane‐modified epoxy resins were studied. The epoxy resins were synthesized by the reaction of 4‐cresol‐type epoxy resin having hydroxymethyl group (EPCDA) with isocyanates. First, as a model compound, EPCDAPI was synthesized by the reaction of EPCDA with phenyl isocyanate (PI). EPCDAPI was heated at 180°C and the reaction products were identified and the reaction mechanism was studied. The following reactions occurred: regeneration of hydroxymethyl group and PI by thermal dissociation of urethane linkage; reaction of epoxide ring and urethane linkage; reaction of epoxide ring and regenerated PI. Urethane‐modified epoxy resin having hydroxymethyl group and urethane linkage (EPCDAMDI) was synthesized by the reaction of EPCDA with 4,4′‐diphenylmethane diisocynate (MDI). The structure was identified by IR, 1H NMR and 13C NMR. The epoxy resin was cured with a mixture of 4,4′‐diaminodiphenylmethane and 1.3‐phenylenediamine (molar ratio 6:4) as a hardener. Curing behaviour of the epoxy resin with hardener was examined by differential scanning calorimetry (DSC). It was found that onset and peak temperatures of the exothermic cure reaction of the EPCDAMDI system were lower than those of the 2‐cresol novolac‐type epoxy resin (EOCN) system, and the rate constant (k) of the cure reaction at 100° C of the former system was about six times larger than that of the latter system and was the same as that of 2‐cresol resol‐type epoxy resin (EOCDA). Viscoelastic properties of the cured resin were studied by dynamic mechanical analysis. It was found that the tan δ of the EPCDAMDI system had two peaks and the lower temperature peak disappeared after further curing over 200° C.