Characterization of poly(dimethylsiloxane)s by time-of-flight secondary ion mass spectrometry

A series of poly(dimethylsiloxane)s (PDMS) terminated by trimethylsilyl groups, and having molecular weights from 600 to 20 000, were characterized by time-of-flight secondary ion mass spectrometry. The fragmentation patterns of the PDMS were examined. The predominant fragmentation pathway involves formation of cyclic fragments, probably via an intermediate with a four-membered ring. The relative intensities of the clusters in the PDMS fragmentation patterns were investigated as a function of sample molecular weight. The relative intensities of cyclic fragments increase with increasing polymer molecular weight. Poly(dimethylsiloxane)s containing different end groups were also investigated to determine the effect of the terminal groups on fragmentation. The terminal groups in PDMS were identified by analysis of low mass range spectra. Effects of nitrogen-containing end groups were found on the fragmentation of PDMS. Large fragments with intrinsic positive charge were observed in the spectra of PDMS terminated by (aminopropyl)dimethylsiloxy and (amidopropyl)dimethylsiloxy groups.