ANALYSIS OF A MIXTURE OF LINEAR AND CYCLIC SILOXANES BY CRYO-GAS CHROMATOGRAPHY FOURIER-TRANSFORM INFRARED-SPECTROSCOPY AND GAS-CHROMATOGRAPHY MASS-SPECTROMETRY

A mixture of linear and cyclic methylsiloxanes was analysed to charact erize the different types of siloxane structures using gas chromatogra phy (GC), mass spectrometry (MS) and Fourier transform infrared (FT-IR ) spectroscopy. Siloxane structures are formed by hydrolysis of dimeth yldichlorosilane under controlled conditions in technical applications . In the presence of methyltrichlorosilane or even trimethylchlorosila ne, linear polydimethylsiloxanes and mono-, bi- or polycyclic methylsi loxanes are synthesized depending on the reaction conditions. The main structural units are (CH3)(3)SiO1/2, (CH3)(2)SiO and (CH3)SiO3/2. GC- MS may provide molecular mass information, but it is not able to ident ify isomeric structures, which are also formed in lower quantities by the mentioned reactions. Coupling GC with FT-IR enables the determinat ion of group frequencies to assign specific structures. Thus, combinat ion of GC with MS and FT-IR may be used in elucidating complex cyclosi loxane compounds. FT-IR measurements were performed with a Tracer unit .