Interrelation between Primary and Secondary Relaxations in Polymerizing Systems Based on Epoxy Resins

Abstract

There is a wealth of experimental data published on the change of molecular dynamics of epoxy resins during polymerization reaction. Common aspects are an increase of the primary α-relaxation time τα and a broadening of the α-relaxation process during the polymerization reaction. In this paper we discuss systematic changes in the two secondary relaxations β and γ on the way from a neat molecular glass-former to the fully polymerized state based on literature data and new dielectric results for diglycidyl ether of bisphenol A (DGEBA) cured with ethylenediamine (EDA). The discussion is focused on common trends in the relaxation time τβ which were not reported previously. It is shown that the relative changes of τα andτβ during the polymerization process are in accord with the predictions of the coupling model and that it is the β-relaxation which is the initiator of the α-relaxation of the epoxy resins in its neat state as well as the initiator of the local segmental relaxation of polymerized or cross-linked epoxy resins. In the terminology of small molecular glass-forming substances, the β-relaxation of the epoxy resins would be called the Johari−Goldstein process.