Effect of gamma-irradiation on the structure of poly(ethyl acrylate-co-hydroxyethyl methacrylate) copolymer networks for biomedical applications.

The effect of the sterilization process by gamma-irradiation on the structure of poly(ethyl acrylate-co-hydroxyethyl methacrylate) copolymer networks, P(EA-co-HEMA) is studied for a broad dose range (7, 15, 25 and 50 kGy) and copolymer composition interval (0, 0.3, 0.5, 0.7 and 1 weight fraction of HEMA in the copolymer). gamma-irradiation promotes chain scission in PHEMA homopolymer but induces new crosslinking points in PEA homopolymer. Both effects are present in the copolymers, with a net result that depends on composition. For copolymers with high HEMA fractions chain scission predominates, while, as the amount of EA in the copolymer increases, the situation changes and the net effect turns out to be an increase in the number of elastically active chains. Further, gamma-irradiation strengthens the gamma relaxation in PHEMA homopolymer, what suggest that the number of interchain hydrogen bonds decreases. FTIR spectroscopy reveals no oxidation as a consequence of the sterilization process.