Viscoelasticity of crosslinked epoxy polymer in the transition region

Abstract

AbstractThe dynamic mechanical properties of highly crosslinked epoxyamine polymer networks with nonrandomly distributed crosslinks were investigated. The transition temperatures of these polymers can be correlated with the number of CH2 groups between crosslink junctions in the aliphatic amine portions of the network. The steepness of the modulus‐temperature curve is also a function of crosslink density. This is in contrast with the case of natural rubber crosslinked by sulfur or by electron irradiation, where the modulus‐temperature curves have similar shapes although the glass transition temperature increases with the degree of crosslinking. An empirical distribution function, similar to the one used by Tobolsky for stress relaxation distributions, was used to describe the temperature dispersion of the dynamic moduli. Two parameters, hg and hr, are used to characterize the steepness of the dispersion curve below and above the transition temperature, respectively. It is tentatively concluded that hg correlates with the length of the CH2 sequences in the amine portion of the polymer. The quantity hr may be related perhaps to the motion involving the trifunctional nitrogen junction.