Dielectric relaxation of heterocyclic polymer networks: Effect of the ratio and nature of the heterocyclic rings

Heterocyclic Polymer Networks (HPN) prepared by trimerization of 1,6-hexame thylene diisocyanate (HMDI) in presence of diglycidyl ether of bisphenol A (DGEBA) and triethylene diamine in two different regimes were characterized by dielectric spectroscopy in the 10(-1)-10(5) Hz frequency range and in t he 123 K-423 K temperature interval. The dielectric experiments reveal the existence of multiple composition dependent relaxation processes. The gamma process, appearing at low temperatures only in partially cured systems is related to the presence of free DGEBA. The beta process is associated to lo cal motions of the carbonyl groups present in the isocyanurate and oxazolid one cycles. The alpha relaxation, which has its origin in the segmental mot ions above the glass transition temperature, tends to appear at higher temp eratures with increasing network junction density and with the degree of cu ring. The fragility and cooperativity of the alpha relaxation is discussed in terms of recent relaxation approaches. (C) 2000 Kluwer Academic Publishe rs.