Effect of silanol on the thermal stability of poly[methyl(trifluoropropyl)siloxane]

Poly[methyl(trifluoropropyl)siloxane] (PMTFPS), which is an essential polymer in oil-resistant rubber materials, exhibits unsatisfactory thermal stability. In this article, PMTFPSs with methyl and hydroxyl terminal groups are prepared, and their thermal stabilities are investigated via thermogravimetric analysis and pyrolysis-gas chromatography-mass spectrometry in an inert atmosphere. Additionally, the degradation mechanisms are discussed in terms of molecular structural characteristics (bond length and bond angle) and reaction driven forces (electrostatic potential and atom charge) based on quantum chemistry calculations. PMTFPS is found to degrade mainly into cyclic monomers through (a) the Si-O rearrangement reaction in the middle of the chain and (b) the back-biting reaction from the end of the chain. PMTFPS with silanol terminal groups is more likely to degrade according to pathway (b), resulting in more cyclotrisiloxane. Furthermore, the silanol from nano-silica accelerates the degradation of PMTFPS, and the mechanism of this process is presented.