SFC/FTIR, SFC/APCI-MS and MALDI-TOF-MS for the analysis of siloxane-ethylene oxide copolymers
(2000)
Polydimethylsiloxanes (PDMSs) modified by introducing ethylene oxide units with the aim of forming sufficiently water-soluble siloxane compounds were characterized using supercritical fluid chromatography (SFC) coupled with Fourier transform infrared (FTIR) spectroscopy and atmospheric pressure chemical ionization mass spectrometry (APCIMS), and matrix-assisted laser desorptionionization time-of-flight mass spectrometry (MALDITOF-MS). SFC has a domain in analyzing oligomers. Hyphenated techniques enable elucidation of the components. Remarkable is the resolution and short analysis time of MALDITOF-MS. SFC also allows quantification of the basic and reaction products.
A mixture of linear and cyclic methylsiloxanes was analysed to characterize the different types of siloxane structures using gas chromatography (GC), mass spectrometry (MS) and Fourier transform infrared (FT-IR) spectroscopy. Siloxane structures are formed by hydrolysis of dimethyldichlorosilane under controlled conditions in technical applications. In the presence of methyltrichlorosilane or even trimethylchlorosilane, linear polydimethylsiloxanes and mono-, bi- or polycyclic methylsiloxanes are synthesized depending on the reaction conditions. The main structural units are (CH3)3SiO1, (CH3)2SiO and (CH3)SiO3. GC-MS may provide molecular mass information, but it is not able to identify isomeric structures, which are also formed in lower quantities by the mentioned reactions. Coupling GC with FT-IR enables the determination of group frequencies to assign specific structures. Thus, combination of GC with MS and FT-IR may be used in elucidating complex cyclosiloxane compounds. FT-IR measurements were performed with a Tracer unit.