Phase structure control of epoxy/polysulfone blends - effects of molecular weight of epoxy resins

Phase separation during the curing reaction in blends of diglycidyl ether of bisphenol A (E56, E51, E42, E39, E31, respectively), polysulfone (PSF) and diaminodiphenylsulfone (DDS, curing agent) was studied. Effects of epoxy resins with different molecular weight on phase structure of the blends were investigated. The relation between the degree of conversion and reaction time revealed that vitrification and gelation greatly affected the formation of phase structure in the low molecular weight epoxy systems. When Tg of the epoxy-rich phase went up to the reaction temperature, both reaction and phase separation were suppressed. While in the high molecular weight epoxy systems, the viscosity increasing of epoxy resins played an important role. Although the degree of conversion of the epoxy-rich phase did not reach the gel point after 24-h precure, phase separation was suppressed due to the high viscosity of the systems. SEM results showed that the desired phase structure could be achieved by using epoxy resins of different molecular weight. (C) 2000 Elsevier Science Ltd. All rights reserved.