Formation of polymethylsiloxanes with alkyl side groups

Hydrosilylation of alpha,w-bis(trimethylsiloxy)methylhydrosiloxane to alkenes in the presence of a catalyst was performed at several temperatures (30-70 degrees C). Comb-type methylsiloxane oligomers with various alkyl substituted groups in the side chains have been obtained. Not all active Si-H groups participate in the reaction. The reaction order, activation energies, and rate constants have been determined. The synthesized oligomers were characterized by H-1, C-13, H-1 COSY NMR, and FTIR spectroscopy. Calculations using the quantum-chemical semiempirical AMI method for modeling reaction between methyldimethoxysilane [Me(MeO)(2)SiH] and hexene-1 were performed to evaluatepossible reaction paths. For all initial, intermediate, and final products, enthalpies of formation as a function of the distance between C-Si bonds are calculated. The hydride addition is energetically more favorable according to the anti-Markovnikov rule than according to the Markovnikov rule. Comb-type oligomers were characterized by gel-permeation chromatography, differential scanning calorimetry, thermogravimetry, and wide-angle X-ray diffractometry. (c) 2007 Wiley Periodicals, Inc.