A mechanistic study of cyclic siloxane pyrolyses at low pressures.

Matrix isolation IR spectroscopy has been used to study the vacuum pyrolysis of hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4) and decamethyl cyclopentasiloxane (D5), and the results interpreted in the context of various kinetic models. In particular, it is shown that the significant pyrolysis products--which include CH3, CH4, C2H2, C2H4, C2H6 and SiO--may be satisfactorily accounted for by radical reactions involving dimethylsiloxane (D1), and estimates are made of the various chain lengths for the proposed reactions based on a range of ambient conditions.