Polymerization of organoalkoxysilanes: Kinetics of the polycondensation progress and the effect of solvent properties and salts addition

The kinetics and the produced oligomer patterns of organoalkoxysilanes (AS) were investigated under different conditions by using gas chromatography (GC), because the degree of the polymerization and the siloxane conformations have an effect on the polymer applications. GC peaks were assigned to AS monomers and oligomers by using a mass detector. The pattern of the produced oligomers depended on the catalysts, time, and the solvent, while the kinetics of hydrolysis, re-esterification, condensation, and progress depended on the solvent and type of catalyst. The methoxy and hydrolyzed monomers of trimethylethoxysilane (TMES) were in equilibrium in alkaline and fluorinated media, while the monomers were completely converted to dimers in acidic media. An investigation of the effect of solvent properties (e.g. dielectric constant and viscosity) on the hydrolysis reaction revealed that there was no change in the polarity of the activated complex during spontaneous hydrolysis, and that the reaction was not diffusion controlled.