COMPARISON OF REACTION-MECHANISMS OF EPOXY-RESINS UNDERGOING THERMAL AND MICROWAVE CURE FROM INSITU MEASUREMENTS OF MICROWAVE DIELECTRIC-PROPERTIES AND INFRARED-SPECTROSCOPY

New methods have been developed which enable one to monitor in situ the changes in the dielectric and spectroscopic properties of epoxy materials as they undergo cure by microwave as well as by thermal energy. In situ measurements at 2.45 GHz of the complex dielectric constant and of the infrared spectra of a DGEBA/DDS system undergoing isothermal cure at a number of temperatures have been conducted. Results have shown that although microwave radiation accelerates the curing reaction during early stages of the process, the induced rapid cross-linking creates a molecular network which is rigid enough to trap unreacted functional groups, thus actually causing a lower degree of cure. The cross-linking in samples cured by microwave radiation is caused by an accelerated reaction of the secondary amine group whose reactivity becomes similar to that of the primary amine.