Effect of crosslink density on the molecular relaxations in diepoxide‐diamine network polymers. Part 1. The glassy region

Abstract The effects of systematically varying the crosslink density on the mechanical relaxations in the glassy region of typical highly crosslinked diepoxide‐diamine polymers are reported. Activation enthalpies and intensities for the β relaxation have been measured using a torsion pendulum at 1 Hz. The glyceryl groups, which are thought to be responsible for this process, are divided into a number of categories defined by the structure of the surrounding matrix. Concentrations of these units are calculated using probability theory, and a correlation is obtained with three measures of the relaxation Intensity, In the case of non‐stoichiometric networks, variations in the intensity of the β relaxation are interpreted in terms of the simultaneous motion of each class of glyceryl group. The manner in which these processes combine to produce a composite peak appears to be unimportant. For the γ relaxation (−140°C), it is shown that at least four methylene units are needed in the diamine component before the process is observable, whereas only two consecutive methylene units in the center of the diepoxide molecule produce the relaxation.