Ethoxy triethylene glycol monomethacrylate was synthesized and polymerized at 80 degrees C in dimethylformamide solution with AIBN as initiator. Both monomer and polymer were characterized by C-13 n.m.r. spectroscopy. The analysis of the microstructure of the poly(ethoxy triethylene glycol monomethacrylate), PTEG, revealed an isotacticity parameter of 0.24, rather similar to free-radical poly(methyl methacrylate) and other poly(alkyl methacrylate)s. Swelling behaviour of the polymer was studied by the immersion of films in water and in buffered solutions at various pH values from 1 to 10. The hydration process was followed gravimetrically and the diffusion of water was analysed on the basis of the stress relaxation model of polymer chains. The results obtained are in good agreement with a second-order diffusion kinetics. A sharp increase of the equilibrium hydration degree between pH 5.5 and 7.4 is observed. The pH-sensitive transition is reversible, as is shown by the dehydration of swollen gels when they are introduced into acidic solutions (pH 1-5) after swelling in alkaline media at pH 8-10.