Oxidative degradation of Biomer fractions prepared by using preparative-scale gel permeation chromatography.

The possibility that some macromolecular chains within a chemically heterogeneous polyether-urethane (PEU) may be more susceptible to degradation than others has been investigated. Preparative scale gel permeation chromatography has been used to separate chemically different fractions of a sample of the commercial PEU, Biomer. The fractions were characterized and then tested for susceptibility to oxidative degradation by exposing them to hydrogen peroxide. After exposure to hydrogen peroxide, the samples were analyzed using high pressure gel permeation chromatography (HPGPC), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). By using these methods, we were able to identify chemical changes in some of the Biomer fractions but not in others. Clear differences in the chemistry and reactivity of the fractions were observed. Changes in the weight average molecular weight varied from a decrease of 55.8% to an increase of 3.9%. A decrease in hard segment content at the surface and in the bulk was observed in some samples, but opposite trends were observed in others. The evidence suggests that there may be a number of mechanisms by which hydrogen peroxide can react with PEUs. Some fractions separated from the Biomer were not significantly affected by concentrated hydrogen peroxide solutions. This suggests an intrinsic stability in some PEUs and points the way to the development of more degradation-resistant PEUs.