Diffusional effects in reactions involving macromolecular substrates and reactants in heterogeneous media lead to unique features. We report investigations on the hydrolysis of 2-hydroxy ethyl methacrylate copolymers catalyzed by imidazole and poly (W-vinyl imidazole) selected as an enzyme mimicing polymer. This process has been mathematically modelled, and the predictions compared with experimental findings. The model framework is general for diffusion-reaction problems of this class. The work has also pragmatic relevance in the design of drug delivery systems, since the reaction takes place in pH ranges of physiological significance.