Mössbauer, NMR and ATR-FTIR spectroscopic investigation of degradation in RTV siloxane foams

The combination of experimental techniques allowed for a comprehensive study of aging processes occurring in RTV siloxane foams. 119Sn Mössbauer spectroscopy demonstrated that tin residues are composed of Sn(II) and Sn(IV) species. The 27-year-old foams showed only Sn(IV) species with a quadrupole-splitting parameter larger than that observed for SnO2. Solid-state 29Si NMR differentiated between the various functional linkages in the foams, and showed no significant change of the di- to trifunctional linkage ratios. High-resolution NMR, on solvent extract of foams, showed the presence of water, catalyst, plasticizer, and some silicone oligomers. ATR-FTIR demonstrated changes near the surface of the foam when aged with water and with the presence of the tin catalyst. Gamma irradiation at a low dose had little effect on compression sets. The main changes observed for artificially aged and aged in service foams were related to the presence of the tin catalyst.