Mechanical and thermodynamic properties of butyl acrylate-N-vinylpyrrolidone hydrogels

Abstract

Copolymerization to almost 100% conversion has been effected by the γ-irradiation of mixtures of n-butyl acrylate (BA) and N-vinyl-2-pyrrolidone (VP) in the presence of a crosslinking agent, 1,1,1-trimethylolpropane trimethacrylate (TPT). Swelling in water at 294 K yielded hydrogels having equilibrium water contents in the range 1–89%, the corresponding extension ratios and volume fractions of water being obtained from dimensional changes on swelling. Stress(compression)-strain measurements yielded the compression and Young's moduli, the effective crosslinking density ( v e) and the copolymer-water interaction parameters (χ). From the linear dependence of v e on the theoretical value based on the concentration of TPT, the efficiency of crosslinking was found to increase with increasing BA content; a finite v e was also interpolated to exist even in the absence of added TPT. Increasing the VP content of xerogels produced a corresponding increase and decrease in the fractional contents of water and BA respectively within the hydrogels, whereas the fractional content of VP displayed an increase followed by a decrease. This latter behaviour mirrors that exhibited by v e and the elastic moduli. Possible explanations are proposed.