Effective crosslinking densities and elastic moduli of some physically crosslinked hydrogels

Abstract

Samples of poly( N-vinyl-2-pyrrolidone (VP)- co-methyl methacrylate (MMA)), containing 41–76.5 wt% MMA, have been prepared by a controlled, semicontinuous copolymerization procedure and swollen to equilibrium in water at various temperatures T (283–343 K) to yield hydrogels in which the network structure is maintained by physical crosslinking involving sequences of MMA units. The effective crosslinking densities ( v e) and Young's moduli ( E) were determined by compression—strain measurements. Values of v e and E decreased with decreasing content of MMA in copolymer, this effect being more pronounced the lower the temperature. For a particular composition, v e and E decreased with increasing T to an extent which was greater the higher the MMA content of copolymer. The findings are compared with the behaviour of corresponding chemically crosslinked hydrogels of poly(VP- co-MMA).