VISCOELASTIC BEHAVIOR OF EPOXY-RESINS MODIFIED WITH POLY(METHYL METHACRYLATE)

The viscoelastic behaviour of a stoichiometric diglycidyl ether of bis phenol-A, (DGEBA), 4,4'-diaminodiphenylmethanes (DDM)s epoxy matrix mo dified with several amounts of poly(methyl methacrylate) (PMMA) has be en studied by dynamic-mechanical analysis. Mixtures pre-cured at 80 de grees C ranged from transparency to opacity as thermoplastic content c hanged from 5 to 15wt%. These changes have been attributed to variatio ns in the ratio between polymerization rate and phase separation rate when PMMA content increased in the mixtures. When PMMA segregated from the epoxy matrix during curing, it had no influence on the crosslinki ng density of the epoxy phase. The clear decrease of temperature and a ctivation energy of the beta relaxation with respect to those values f or the neat matrix, observed for the 5wt% PMMA-containing mixture but not for the 15wt% PMMA-containing one, are proposed to be a consequenc e of physical interactions between the PMMA chains and some epoxy olig omers. The dissimilar variation of the height of the omega relaxation with frequency when compared to that for the other relaxations studied , outlines the significance of physical factors influencing this relax ation. (C) 1998 Society of Chemical Industry.