Investigations into the Formation and Cleavage of Siloxanes

Abstract

The hydrolysis of dimethyldichlorosilane and methylphenyldichlorosilane, with an excess of water, was carried out under various conditions. The initial product, a silane diol, usually undergoes condensation very readily to give mixtures of open chain ,∝,ω-siloxane diols and cyclic siloxanes. These mixtures were quantitatively analysed by column and gas chromatography, the proportions of cyclic to linear siloxanes and the proportions of cyclic trimer, tetramer, and pentamer being obtained. With the methyl phenyl cyclosiloxanes, which exist in stereoisomeric forms, product isomer ratios were also determined. The effects of varying the solvent, temperature, concentration, time for reaction, etc., on the product ratios are discussed from the point of view of competing reactions during the condensation of the initial hydrolysis products, relative stability of possible products, further reaction of products with the hydrochloric acid present, etc. On treatment with acid or base, oligomeric cyclic siloxanes can be polymerised to high molecular weight materials. In this work, the initial stage of the reaction of some cyclic siloxanes with acid and base was investigated. The acid reaction was pursued mainly with regard to the effect of acid on the initially formed cyclic products in the hydrolysis of diorganodichlorosilanes. Analytical results obtained by thin layer, column and gas chromatography, and proton resonance spectroscopy are mentioned. It was found that, in general, the initial effect of acid or base on a cyclic trimer was to convert it to the corresponding cyclic tetramer. Many low molecular weight open chain stannosiloxanes have been reported, but little mention has been made of cyclic types. A brief examination of some potential methods for the preparation of cyclic polyphenylstannosiloxanes is described