An alternative method for the determination of siloxane activities toward basic equilibration catalysts

The method used is based on the well-known fact that siloxane equilibrates, once formed, do not change their compositions unless some siloxane compound is added, in which case new equilibrium compositions appear. As these composition changes, as well as their dynamics, are caused solely because of the addition of a particular siloxane compound, they are expected to be specific, and should contain information about the siloxane activities toward the applied equilibration catalyst. It was shown that the viscosities of such systems, measured as a function of reaction times, could be used for the determination of the relative activities of siloxanes. Proceeding from this basic assumption, some commonly used siloxanes were tested in equilibrations catalysed with tetramethylammonium hydroxide, TMAH. The siloxanes were: hexamathylcyclotrisiloxane, D3, octamethylcyclotetrasiloxane, D4, tetravinyltetramethylcyclotetrasiloxane, D4Vinyl, hexamethyldisiloxane, MM, and a linear all-methyl oligosiloxane of number average molecular weight of approximately 800. MD8,5M. The following decreasing order of activities toward the TMAH-catalyst was obtained: D3>MD8,5M>D4>D4Vinyl>MM.