Observations on the swelling behaviour of copolymeric hydrogels containing N‐vinyl‐2‐pyrrolidone

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 ther 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.