Effect of curing agent on the phase behaviour of epoxy resin/phenoxy blends

Abstract

The poly(hydroxyether of bisphenol A) (phenoxy) was found to be miscible with uncured bisphenol-A-type epoxy resin, i.e. the diglycidyl ether of bisphenol A (DGEBA), as shown by the existence of a single glass transition temperature ( T g) over the whole composition range. However, dynamic mechanical analysis (d.m.a.) and scanning electron microscopy (SEM) studies revealed that the phenoxy exhibits different miscibilities with five cured epoxy resins (ERs). The miscibility and phase behaviour, as well as the resulting morphology of the cured blends, are dependent on the choice of cure agent. For the blends cured with 4,4′-diaminodiphenylmethane (DDM) and aliphatic anhydrides, i.e. maleic anhydride (MA) and hexahydrophthalic anhydride (HHPA), no phase separation, as indicated by both d.m.a. or SEM. However, for the blends cured with 4,4′-diaminodiphenyl sulfone (DDS) and phthalic anhydride (PA), both d.m.a. and SEM studies clearly show evidence of phase separation. The SEM study shows that two phases interact well in the PA-cured blends while the interface bonding between the two phases is relatively poor in the DDS-cured blends. The phenomena have been discussed from the points of view of both thermodynamics and kinetics.