Network and swelling parameters of chemically crosslinked thermoreversible hydrogels

Two series of hydrogels of poly(N-isopropyiacrylamide-co-acrylic acid) have been prepared by copolymerisation in solution using tetrafunctional N,N-1-methylene bis-acrylamide and a novel octafunctional crosslinker glyoxal bis(dially acetal) (GLY) as crosslinker. These thermoreversible hydrogels were swollen to equilibrium in water at 301 K and examined by gravimetric, dimensional and compression-strain measurements. The influence of nature and content of crosslinker on swelling ratio, polymer-water interaction parameter, elastic moduli and effective crosslinking density (nu (e)) is reported and discussed. Both series exhibit low crosslinking efficiencies expressed as nu (e)/(theoretical crosslinking density calculated from feed composition). The extremely low efficiencies for the GLY-crosslinked gels is responsible, at least in part, for the ultra-high swellability of these hydrogels. (C) 2001 Elsevier Science Ltd. All rights reserved.