Syntheses and properties of sila-functional oligosiloxanes: Synthesis, structure, and spectra of linear and cyclic isocyanato(methyl)oligosiloxanes

Author: Abe Yoshimoto   Kaji Michiko   Arimitsu Koji   Suyama Ken-ichi   Gunji Takahiro  

Publisher: Springer Publishing Company

ISSN: 1569-0660

Source: Silicon Chemistry, Vol.1, Iss.5-6, 2002-09, pp. : 367-375

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Abstract

Synthesis, structure, and spectra of novel linear and cyclic isocyanato(methyl)oligosiloxanes with the silicon number up to eight were investigated. The linear and cyclic oligosiloxanes were synthesized selectively in good or appreciable yields by vapor phase and liquid phase hydrolysis, respectively. They were isolated as liquids by distillation under reduced pressure except for cyclic tetrasiloxane and pentasiloxane which were provided as solids. The cyclic trisiloxane was obtained as a mixture of isomers as confirmed by nuclear magnetic resonance (NMR) spectra. The X-ray analysis of cyclic tetra- and pentasiloxane obtained revealed that they have cis-trans-cis and propeller-like structure, respectively. The infrared (IR) spectra of cyclic siloxanes showed a sharp peak due to ν Si−O−Si and a remarkable shift from the tri- to the tetrasiloxane while peak broadening and almost no shift were observed for the higher homologues. On the other hand, the sharp peak for linear disiloxanes became broad and split into two peaks for the higher homologues, while the peak at low wavenumber shifted even lower as the siloxane linkages increased, yet no corresponding shift is observed for the peak at higher wavenumber. In the 29Si NMR spectra of linear oligosiloxanes, the signals appeared separately at low and high fields in narrow regions, which are ascribed to the terminal silicon atom and the silicon associated with the silylmethyl groups, respectively. These regions hardly changed, regardless of the length of siloxane linkage. Similar trends were observed in the 1H and 13C NMR spectra.