Polyepoxide-water interactions: Influence of the chemical structure of the network

We have investigated the influence of the chemical structure of polyepoxide networks on the sorption behaviour and water-induced changes of viscoelastic and mechanical properties. The β relaxation was found to be unaffected by the presence of adsorbed water for an anhydride and an aromatic amine based polyepoxide. The anhydride based network shows better behaviour in a water environment than the aromatic amine based network in terms of plasticisation, reversibility of the degradation and loss of mechanical properties. This has been attributed to (i) a smaller crosslinking density, leading to a smaller specific volume in the glassy state and thus a smaller water uptake and (ii) a strong interaction between water and tertiary amines in epoxide-aromatic amine networks. This interaction, probably of electrostatic nature, would result from the delocalization of the doublet of the nitrogen atom. The results are critically compared to the literature on aliphatic amine based polyepoxides, where the dependence of the β relaxation on the water content is proposed to be related to the electron-donating ability of the aliphatic chain.