Study of model systems as a powerful tool for producing reliable structure - Property relationships in epoxy networks

Series of epoxy-amine networks were designed to separate the effects on the properties of chain rigidity and of architectural characteristics, i.e., cross-link density and extender type. Glass transition temperature (T-g) was shown to increase with the increasing cross-link density and rigidity of the epoxide and amine residues, but these effects were not completely decoupled. In addition, inspection of non-stoichiometric systems revealed the occurrence of peculiar effects in the presence of unreacted epoxide moieties. A general correlation between the values of the rubbery modulus and T-g has been proposed. As regards the sub-T-g beta-transition, the onset of the process has been shown to occur at the same temperature irrespective of chain stiffness and cross-link density as a result of short-range cooperativity of the hydroxypropyl ether motions. As a consequence of practical interest, the higher cross-link densities lead to the lower Young moduli at room temperature.