Evolution of the rheological properties during the reactive processing of thermoplastic/thermoset epoxy

The melt state reaction, or fusion process of bisphenol-A and the diglycidyl ether of bisphenol-A can produce both linear phenoxy backbone chains and crosslinked network structures. The linear chains can be thought of as thermoplastic polymer, while the crosslinked molecular matrix is a thermoset; therefore, this resin system can be termed a thermoplastic/thermoset epoxy.Rheological analysis has been performed on this system to determine the occurrence of the crossover of the storage and loss moduli during the reaction using three techniques: isothermal cure, interval frequency sweep, and interval stress relaxation.Determination of the activation energy of the reaction by consideration of the conventional gel-point determination prove unsatisfactory as compared to that which is determined by FTIR. An alternative technique is presented which yields a value in good agreement with that obtained by following epoxide consumption. The thermoplastic/thermoset nature of this material leads to the deviation from traditional thermoset cure behavior.