DYNAMIC MECHANICAL-PROPERTIES OF CYCLOALIPHATIC EPOXY-RESINS CURED BY ULTRA-VIOLET-INITIATED AND HEAT-INITIATED CATIONIC POLYMERIZATIONS

The dynamic mechanical properties and impact resistance of cycloaliphatic epoxy resins cured by ultra-violet- and heat-induced sulphonium salt initiators were found to depend on the type and concentration of initiator. The glass transition temperatures of both u.v.- and heat-cured samples decrease with increase in initiator concentration owing to the plasticization effect of initiator fragments remaining in the samples. The beta-relaxation, observed in all samples around -80-degrees-C at 1 Hz. was found to be due to molecular motions of the cyclohexyl rings. Slight suppression of this relaxation was observed only in the u.v.-cured system consisting of 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexene carboxylate (ECC) and triphenylsulphonium hexafluoroantimonate (TPSHA), and was attributed to antiplasticization due to the decomposed TPSHA. The above findings lead to the conclusion that the u.v.-cured ECC system is more brittle than the heat-cured ECC system.