SECONDARY RETARDATION MODES IN DIGLYCIDYL ETHER OF BISPHENOL-A - DIAMINO DIPHENYL METHANE NETWORKS

Thermally stimulated creep (TSCr) has been used to follow the viscoelastic behavior of some amine-cured epoxy networks below the glass transition. The investigation of the -180/+40-degrees-C temperature range has revealed two essential retardation modes characterizing localized motion of chain segments: the gamma mode centered at -155-degrees-C in all samples, and the well-known beta mode observed around -40-degrees-C in the stoichiometric network. The magnitude of the beta mode was seen to decrease unexpectedly with the cross-link density, whereas its peak temperature and glass transition temperature both decreased. This evolution was confirmed by thermally stimulated currents (TSC) measurements and discussed on the basis of the antiplasticization concept. Water desorption under vacuum yielded additional information on the nature of the beta mode and TSCr fractional loading experiments brought evidence that two types of relaxing units participate in beta motions and furnished activation enthalpy data. (C) 1994 John Wiley & Sons, Inc.