Aging Complexities Induced by the Organotin Catalyst in Foamed Polysiloxane Elastomers

摘要

An organotin ingredient, Tin 2-ethylhexanoate, is used as a catalyst in the synthesis of foamed polysiloxane elastomers. We report on the nature of residual catalyst species and the influence on polymer thermal and nuclear relaxation properties. Our results show that the catalyst plays an active part in the chemistry and is chemically modified as a result. Moessbauer spectroscopy shows that the tin (IV) phase predominates in the as-synthesised material, representing some 67% of the total tin signal, with the remainder being unreacted tin (II) species. Thermal ageing causes changes in the dispersion of the tin species, including oxidation of the tin(II) phase and the in-situ production of stannic oxide. Furthermore, increases in total tin catalyst content appear to induce chain confinement effects, restricting segmental chain dynamics and hindering polymer crystallisation phenomena. It is likely that the soluble tin (II) compounds are catalytically active in polymer hydrolysis and network rearrangement processes, therefore, careful control of the amounts of catalyst used, as well as dispersion, are important for material reliability.