A DIELECTRIC, MECHANICAL, RHEOLOGICAL, AND ELECTRON-MICROSCOPY STUDY OF CURE AND PROPERTIES OF A THERMOPLASTIC-MODIFIED EPOXY-RESIN

Dielectric, mechanical, thermal, rheological, and electron microscopy measurements are reported on the effect of varying the proportion of a blended thermoplastic, poly(ether sulfone), on the cure and properties of an epoxy resin system, an aromatic diamine cured trifunctional aromatic epoxide. Data presented cover both changes in physical properties during cure and final properties of the cured matrix. The initial mixture, prepared by solution casting, is homogeneous, but phase separation occurs rapidly in the initial stages of curing. Dielectric, thermal, and rheological measurements obtained during the curing process are consistent with phase separation occurring within the resin. Analysis of the dielectric data obtained from fully cured materials demonstrates the existence of a relaxation process which can be ascribed to polarization of a conducting occluded phase. Correlation of these data with those obtained from electron micrographs indicates that the type of phase structure changes with thermoplastic content. A number of the mechanical properties are observed to change at about 20-25 % (w/w) of incorporated thermoplastic, coincident with the occurrence of a cocontinuous phase. The effects of these changes in the morphology on the mechanical, dielectric, and thermal properties of this thermoplastic-modified thermoset are discussed.