Kinetics and mechanism of the formation of poly[(1,1,3,3- tetramethyldisiloxanyl)ethylene] and poly(methyldecylsiloxane) by hydrosilylation

Abstract

The kinetics of the formation of poly(carbosiloxane), as well as of alkylsubstituted poly(siloxane), by Karstedt's catalyst catalyzed hydrosilylation were investigated. Linear poly(carbosiloxane), poly[(1,1,3,3-tetramethyldisiloxanyl)ethylene], (PTMDSE), was obtained by hydrosilylation of 1,3-divinyltetramethyldisiloxane (DVTMDS) and 1,1,3,3-tetramethyldisiloxane (TMDS), while alkyl-substituted poly(siloxane), poly(methyldecylsiloxane), (PMDS), was synthesized by hydrosilylation of poly(methylhydrosiloxane) (PMHS) and 1-decene. To investigate the kinetics of PTMDSE formation, two series of experiments were performed at reaction temperatures ranging from 25 to 56°C and with catalyst concentrations ranging from 7.0 × 10-6 to 3.1 × 10-5 mol Pt/mol CH=CH2. A series of experiments was performed at reaction temperatures ranging from 28 to 48°C, with catalyst concentrations of 7.0 × 10-6 mol of Pt per mol of CH=CH2, when kinetics of PMDS formation was investigated. All reactions were carried out in bulk, with equimolar amounts of the reacting Si-H and CH=CH2 groups. The course of the reactions was monitored by following the disappearance of the Si-H bands using quantitative infrared spectroscopy. The results obtained showed typical first order kinetics for the PTMDSE formation, consistent with the proposed reaction mechanism. In the case of PMDS an induction period occurred at lower reaction temperatures, but disappeared at 44°C and the rate of Si-H conversion also started to follow the first-order kinetics.