Water absorption characteristics of diglycidylether of butane diol-3,5-diethyl-2,4-diaminotoluene networks

The water absorption characteristics of various networks based on diglycidylether of butane diol (DGEBD) and 3,5-diethyl-2,4-diaminotoluene with amine/epoxide functional ratio ranging from 0.7 to 1.3 and T-g values ranging from 36 to 91 degrees C were studied in the 20-100 degrees C temperature range. The equilibrium concentrations of water are of the order of 6-7% by weight with slight tendency to decrease with temperature, which can be attributed to the relatively high (negative) value of the heat of dissolution (H-s approximate to -46 +/- 1 kJ mol(-1)). Plasticization effects can be predicted from a simplified version of the free volume theory showing that the Tg depletion is an increasing function of the initial T-g value. There is no significant discontinuity at T-g of the temperature variations of the solubility and diffusivity, showing that the behaviour is controlled by the presence of strong hydrogen bonds between water molecules and the polar groups (essentially hydroxyls) of the polymer. The comparison of various epoxide-amine networks shows that the molar contribution of a given hydroxyl group is an increasing function of the hydroxyl concentration, which suggests that close hydroxyls could play a concerted role in water absorption. For the samples having an epoxide excess, the gravimetric curves of water absorption display two steps, the first one being due to the physical sorption and the second one to the epoxide hydrolysis. The main characteristic features of this latter process are analysed. In the conditions under study (temperature, sample thickness), it is not diffusion controlled. (C) 2000 Elsevier Science Ltd. All rights reserved.