The reaction of hydride polyaddition of methylhydridesiloxanes to conjugated cyclohexa-1,3-diene, in the presence of catalytic amount of platinum hydrochloric acid, has been investigated at several temperatures. The polyorganosiloxanes with cyclohexenyl fragments in the side chain, completely soluble in organic solvents, were synthesized. The hydride polyaddition reaction order, activation energies, and rate constants were found. By quantum-chemical half-empirical method AMI, the electronic characteristics of cycloliexa-1,3-diene: the charges on the carbon atoms and bonds orders were calculated. For full characterization of hydrositylation reaction, calculations for modeling reaction between methyldimethoxysilane and cyclohexa-1,3-diene were carried out using Gaussian 03 program package. The geometries of reactants, transition states, and products were optimized using PM3 semiempirical method followed by single-point calculations at B3LYP/6-31G(d) level of density functional theory. It was concluded that the course of hydride addition of modeling reaction of methyldimethoxysilane to cyclohexa-1,3-diene energetically is more favorable by 1,4-addition. The synthesized oligomers were characterized by FTIR, H-1- and C-13-NMR spectroscopy, thermogravimetry, gel permeation chromatography, differential scanning calorimetry, and wide-angle X-ray diffractometry. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 116: 1131-1137, 2010