Temperature dependence of the relaxation time for a family of glass formers with systematically varying architecture

Using the mechanical and dielectric relaxation experiments, the linear relaxation behavior for series of diglycidyl ether of bisphenol-A (DGEBA) based polymers was investigated. The set of materials included: (i) the DGEBA monomer, (ii) a DGEBA based linear polymer (i.e. phenoxy) and (iii) a series of DGEBA based epoxy networks where various diamine cross-linking agents were used. For two of the diamine crosslinking agents the tightness of the network was systematically varied from loose to extremely tight. With the exception of loose networks and phenoxy, all systems exhibited just the α-relaxation process above Tg. In contrast, the loose networks and phenoxy exhibit the α-relaxation and a lower frequency α+-relaxation process that has a different temperature dependence than the main α-process. There are only two distinct loga_T vs T dependencies, which are both super-Arrhenian – branch A and branch B, where branch B has a stronger temperature dependence. The monomer and the linear polymer follow the A branch and all the tighter networks, despite their chemical variety, exhibit the same B branch temperature dependence when adjusted for Tg. Intriguingly, in case of the loose networks the α+-process follows the A branch and the α-process follows the B branch.