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Diffusion of water in epoxy–polyurethane (PU) interpenetrating networks was investigated using gravimetry, time‐resolved ATR‐FTIR, and 2D correlation analysis. In this study, the amount of PU component and the length of polyethylene oxide soft block in them were systematically varied to determine their influence on water uptake. The diffusion coefficients were calculated and anomalous water diffusion is well described by the Carter and Kibler model. Water molecules of four different states were identified in the network volume, and sequence of their formation was determined by 2D‐IR spectroscopy. One of them could be confined into free volume (microvoids) or molecularly dispersed with hydrogen‐bonding at cluster formation (bulk dissolved), while the others could be attributed to the bound water forming strong hydrogen bonds with hydrophilic entities of networks. These results were supported by solid‐state 2H NMR data. The influence of water uptake on thermomechanical behavior of epoxy/PU networks was determined. It was shown that the increase of PU content in composites leads to the changes of the effect of water uptake from plasticizing to the anti‐plasticizing as a result of the formation of new networks of interchain hydrogen bonds.
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Bratasyuk et al. (2022) studied this question.
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