Network and swelling parameters of chemically crosslinked thermoreversible hydrogels

Abstract

Two series of hydrogels of poly( N-isopropylacrylamide- co-acrylic acid) have been prepared by copolymerisation in solution using tetrafunctional N, N′-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 ( ν e) is reported and discussed. Both series exhibit low crosslinking efficiencies expressed as ν 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.