Thermoreversible behaviour in water of chemically crosslinked poly(2-methoxyethylacrylate-co-N,N-dimethylacrylamide)

Abstract

Hydrogels of poly(N,N-dimethylacrylamide-co-2-methoxyethyl-acrylate) have been synthesized by crosslinking copolymerization, and the dimensions of swollen films at swelling equilibrium in water have been measured over a range of temperature (T). At 4°C, transparency and maximum water content are exhibited. On heating, deswelling occurs and loss of transparency develops at 35°C, opacity and deswelling being complete at 50°C. The process is reversible and the lower critical swelling temperature (Tc) is found to be 38±2°C. Although water content at any temperature increases with decreasing content of crosslinker, the latter has no discernible influence on Tc. Microgels of the same copolymer have also been prepared by dispersion polymerization in 2-propanol. After dialysis in water, the diameters (D) of the microbeads in dilute aqueous suspension were measured by dynamic light scattering. D decreased from 2·3μm at 10°C to 0·2μm at T≥50°C, and Tc was located at 36±2°C. Optical microscopy revealed the spherical nature and polydispersity of the beads, the dimensions of which lay in the range 7μm>D>0·8μm. These copolymers were sticky in both the dry and the swollen states, which may be advantageous for coating to an inert substrate for application as a possible separation device based on thermoreversible swelling. ©1997 SCI