Characterization of degradation products of poly[(3,3,3-trifluoropropyl)methylsiloxane] by nuclear magnetic resonance spectroscopy, mass spectrometry and gas chromatography

Poly[(3,3,3-trifluoropropyl)methylsiloxane] (PTFPMS) was treated with the solvents acetone, ethyl acetate and methanol and its degradation products were analyzed with multiple techniques. ¹H, ²⁹Si and ¹⁹F nuclear magnetic resonance (NMR) spectroscopy were useful for the characterization of the intact polymers and for the determination of cyclosiloxanes. Cyclosiloxanes with a ring size of up to 23 were quantified by gas chromatography. The only degradation products found were TFPmethyl-cyclosiloxanes. 1,3,5,7-Tetrakis(TFPmethyl)-cyclotetrasiloxane was predominant, and (TFPmethyl)cyclotri-, penta- and hexasiloxane could be detected at lower concentrations. The identity of cyclic degradation products with a ring size of up to 6 was unambiguously confirmed by direct infusion mass spectrometry. The TFPmethyl-cyclosiloxanes were successfully ionized by electrospray ionization in the negative mode. None of the techniques applied gave hints to other degradation products such as short linear oligomers. Almost complete degradation of PTFPMS occurred in acetone and methanol, while degradation is distinctly reduced in ethyl acetate.