EFFECT OF CROSS-LINKER FUNCTIONALITY ON SWELLING AND NETWORK PARAMETERS OF COPOLYMERIC HYDROGELS

Crosslinked xerogels comprising N-vinyl-2-pyrrolidone (VP) and butyl a crylate (BA) with different weight fractions of BA ranging between 0.1 and 0.3 were prepared by gamma-ray initiation copolymerization using different concentrations of either hexa- or tetrafunctional crosslinki ng agents. Methylene bisacrylamide (MBA) was selected as tetrafunction al crosslinker, while 1,I,trimethylolpropane trimethacrylate (TPT) was used as a hexafunctional crosslinker. The concentration of both cross linkers ranged between 0.5% and 2%. Thin disks of the prepared copolym ers were swollen in deionized water at 294K. The final equilibrium wat er content, volume fraction of polymer and swelling capacity were dete rmined. The effective corsslinking density V-e the average molecular w eight between the crosslinks M-c and the polymer-water interaction par ameter were determined from stress-strain measurements. For different compositions of VP/BA, the linear relations between theoretical crossl inking densities V-t and V-e were established. The efficiencies of MBA and TPT crosslinking agents towards VP-BA copolymers were determined. (C) 1998 John Wiley & Sons, Ltd.