Radiation‐grafted polymers for biomaterial applications. I. 2‐hydroxyethyl methacrylate: Ethyl methacrylate grafting onto low density polyethylene films

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Abstract
Studies were conducted on the radiation grafting of 2‐hydroxyethyl methacrylate (HEMA) and ethyl methacrylate (EMA) by the mutual irradiation technique onto low density polyethylene. Four different solution concentrations were used, and radiation doses ranged from 0.03 to 0.05 Mrad. Four copolymer compositions having different HEMA:EMA ratios were also studied using two total monomer concentrations. The kinetics of the grafting process demonstrated by the two monomers were basically different. While EMA showed a typical diffusion‐controlled kinetic pattern, HEMA exhibited a more complex behavior, the main features of which were an induction period, a slight autoacceleration and a significant drop in graft level after a maximum is reached. The difference in behavior was interpreted in terms of partitioning of monomers into the polyethylene substrate. The surface topography of the grafted films was studied by means of scanning electron microscopy. A mechanism based on osmotic cell formation was suggested for the HEMA graft system. The copolymer systems investigated showed that the graft reaction is faster in the initial stages for higher percentages of EMA in the monomer mixtures; as grafting proceeds the trend is reversed.