Evolution of Glass Transition Temperature as a Function of Cure in Epoxy Vinyl ester Resins

摘要

During the cure of thermosetting polymers, several properties evolve dramatically both in terms of speed and magnitude that essentially change the polymer’s ability to sustain load, temperature, environment and a host of other factors. Glass transition or T Tg is one such important transition that evolves during cure and has a profound effect. First and foremost T Tg sets the upper bound on the service temperature of the polymer. Other issues relate to the role that this transition plays in moving from kinetics to diffusion-controlled reaction kinetics, chemorheology of the thermoset and inception of internal stresses. Tg changes occur due to several reasons. To name a few, functionality, types and amount of resin and curing agent, catalyst type, stoichiometry and finally degree of conversion. Of these, the one that is common to all of them is degree of conversion and it is often times the most dramatic. Therefore several valuable attempts have been made to both characterize and model this behavior behavior1, 2, 3 and 4 1, 4. Much of the work historically has however been focused on Epoxy resins that are cured in a traditional way using step growth polymerization. . The present paper will discuss the challenges associated with translating this across to the chain growth polymerized systems such as epoxy vinyl esters and unsaturated polyesters. These challenges tend to primarily be on the experimental front where traditionally differential scanning calorimetry (DSC) has been used in the literature to measure T Tg and degree of conversion.