Xerogels comprising n-butyl acrylate and jV-vinyl-2-pyrrolidone (30/70 wt/wt) and varying small amounts of a hexafunctional cross-linking agent have been prepared by y-ray-initiated copolymerization to complete conversion and then swollen in water to equilibrium at several different temperatures (T) within the range 284-349 K. Photographic determination of the sample dimensions afforded the volume fractions of polymer ( 2) and water within the resultant hydrogels, and the effective cross-linking densities (i

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Polymer-water interaction parameters, sequence length distributions and contents of total, freezing and non-freezing water have been discussed for a family of hydrogels. The. xerogel precursors contained N-vinyl-2-pyrrolidone (VP) with several co-monomers of different levels of hydrophobicity present in the xerogel over a wide range of composition. Common trends in the behaviour of these systems have been noted and rationalised. In particular the findings indicate that (i) in the poly-VP hydrogel there are ca. 8-10 molecules of non-freezing water per VP unit and (ii) in the copolymeric hydrogels the maximum occurring in the variation of mole fraction of VP versus mole fraction of water is due substantially to the sharp increase in uptake of freezing (or bulk) water by copolymers rich in VP.

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