17O NMR investigation of radiolytic hydrolysis in polysiloxane composites

The gamma -irradiated hydrolysis of polysiloxane composites was investigated as a function of gamma -irradiation dose using O-17 nuclear magnetic resonance (NMR) spectroscopy. It is demonstrated that by using O-17 labeled water during the high humidity exposure of the siloxane copolymer, details about the radiolytic hydrolysis degradation mechanism can be obtained directly from analysis of the O-17 NMR spectra. The formation of O-17 labeled silanols and Si-O-Si linkages occurs during the radiolytic hydrolysis, with the silanol species being the dominant non-volatile degradation product observed. For the polysiloxane composite investigated the distribution of hydrolysis species shows little variation at high total irradiation doses. In addition, the silica filler does have an effect on the distribution of the hydrolysis species within the copolymer at lower gamma -irradiation doses. The ability of O-17 NMR to isolate the hydrolysis species from other degradation processes within the polysiloxane composites demonstrates the applicability of this technique to address hydrolytic aging in other materials. (C) 2001 Elsevier Science Ltd. All rights reserved.