Water diffusion in hydroxyethyl methacrylate (HEMA)-based hydrogels formedby gamma-radiolysis

Polymer hydrogels based upon methacrylates are used extensively in the phar maceutical industry, particularly as controlled release drug delivery syste ms. These materials are generally prepared by chemically initiated polymeri zation, but this can lead to the presence of unwanted initiator fragments i n the polymer matrix. In the present work, initiation of polymerization by gamma-irradiation of hydroxyethyl methacrylate, with and without added cros slinkers, has been investigated, and the diffusion coefficients for water i n the resulting polymers have been measured through mass uptake by the poly mers. The diffusion of water in poly(hydroxyethyl methacrylate) at 310 K wa s found to be Fickian, with a diffusion coefficient of 1.96 +/- 0.1 x 10(11 ) m(2) s(-1) and an equilibrium water content of 58%, NMR imaging analyses confirmed the adherance to a Fickian model of the diffusion of water into p olymer cylinders. The incorporation of small amounts (0.2-0.5 wt%) of added ethyleneglycol-dimethacrylate-based crosslinkers was found to have only a small effect on the diffusion coefficient and the equilibrium water content for the copolymers. (C) 1999 Society of Chemical Industry.