Acrylonitrile was polymerized using a redox system. The polyacrylonitrile was modified by heating with aqueous 50% H2SO4 or with aqueous 50% NaOH. Acrylonitrile was also copolymerized with acrylic acid or acrylamide or methylenebisacrylamide using a redox system. The sorption abilities of the modified acrylics and copolymers were determined from aqueous solutions of two dyes, namely methylene blue and alizarin yellow R. The porous structure of the polymers was determined by using mercury porosimetry. The experimental results of the dye uptake were theoretically treated by using a diffusion-limited adsorption method. The equation was applied for short reaction times and the parameters were graphically determined from log-log plots : the specific rate constant k’ from the intercept A and the parameter n (0 < n < 1) from the slope. The diffusion coefficient D was calculated from Fick’s equation. The results were discussed taking into consideration the pore structure of the polymers as well as the ’pore model’ and the ’free volume model’ of the diffusion process. The electron donor-acceptor interactions between the functional groups of the polymers and the functional groups of the dyes strongly influence the sorption process.