CHARACTERIZATION OF POLY(DIMETHYLSILOXANE)S BY TIME-OF-FLIGHT SECONDARY-ION MASS-SPECTROMETRY

A series of poly(dimethylsiloxane)s (PDMS) terminated by trimethylsily l groups, and having molecular weights from 600 to 20 000, were charac terized by time-of-flight secondary ion mass spectrometry. The fragmen tation patterns of the PDMS were examined. The predominant fragmentati on pathway involves formation of cyclic fragments, probably via an int ermediate with a four-membered ring. The relative intensities of the c lusters in the PDMS fragmentation patterns were investigated as a func tion of sample molecular weight. The relative intensities of cyclic fr agments increase with increasing polymer molecular weight. Poly(dimeth ylsiloxane)s containing different end groups were also investigated to determine the effect of the terminal groups on fragmentation. The ter minal groups in PDMS were identified by analysis of low mass range spe ctra. Effects of nitrogen-containing end groups were found on the frag mentation of PDMS. Large fragments with intrinsic positive charge were observed in the spectra of PDMS terminated by (aminopropyl)dimethylsi loxy and (amidopropyl)dimethylsiloxy groups.