Synthetic structural and kinetic studies of polyethoxy-silanes

Abstract

Polyethoxy-silanes are of considerable commercial interest in Brake Fluid formulations. The synthesis of a polymeric Brake Fluid base material, known industrially as Silane Racing Fluid (SRF) isreported, along with the preparation of a series of reference compounds. The fluid contained a mixture of polymeric glycol silanes with theformula andn = 0,1,2, etc. The molecular weights of these compounds weredistributed over a range from 164 to at least 1200. The referencecompounds synthesised were monomeric, with the structure MenSi(OR1 where n = 0,1 ,2 and -OR1 represents varying chain length glycol units, including. The compounds prepared were characterised using a variety of analytical techniques including Si NMR, Size Exclusion Chromatography (SEC) and Mass Spectrometry. The partial hydrolysis of SRF and several of the reference compounds, including is also described. Reactions were monitored qualitatively by Si NMR spectroscopy. Molar ratios of water to si lane were in the range of 2:1 to ~14:1. The technique allowed the identification 'in situ' of labile partial hydrolysis products, before they condensed to more stable siloxanes. In further studies the hydrolysis of several polyethoxy-silanes is reported, in dilute aqueous solution. The reactions were monitored quantitatively by two techniques, ultra-violet spectrophotometry and an extraction method. In the spectrophotometric experiment the hydrolysis of was studied. Pseudo first order kinetics was observed, which was found to be specific Acid/Base catalysed over the pH range studied (4-9). The extraction method relied upon n-hexane specifically extracting the starting material. An Infra-red spectrometer was used to determine the quantity of starting material present after extraction, by monitoring the Si-O-C stretching frequency ~1100 cm. Pseudo first order rate constants were obtained for the hydrolysis of and (0Me)3 . The results indicated specific Acid/Base catalysis over the pH range studied (5-9). The kinetic results described are in good agreement with recent studies reported using Trialkoxysilanes.