AbstractLow molecular weight silanolates of tetramethylammonium hydroxide and tetrabutylphosphonium hydroxide have been prepared. The kinetics of octamethylcyclo‐tetrasiloxane polymerization induced by either of these bases was studied and the activation energies were determined. It was found that the activities of these catalysts were much greater than that of the potassium silanolate (about 50–150 times). Nevertheless the activation energies did not differ from those found for polymerizations catalyzed by alkali metal silanolates (19.5 kcal./mole). The polymerization rate of the octamethylcy‐clotetrasiloxane‐tetramethylammonium silanolate system is thus comparable to the polymerization rate of the potassium silanolate‐tetradecamethylcycloheptasiloxane system, which is the most reactive of the low molecular cyclic poly (dimethyl siloxanes). Also the decomposition of the silanolates of the onium compounds was studied. It was found that tetramethylammonium silanolate is more stable than the phosphonium compound, the half‐time of decomposition at 100°C. of the former being more than five times that of the latter. Activation energies of the decomposition were also different: 42 kcal./mole for the ammonium compound and 28.5 kcal./mole for the phosphonium compound. This corresponds to a different proposed mechanism of the reaction, as described by Ingold. The most striking feature is that the decomposition follows first‐order kinetics. By analogy with experiments performed by Ingold and his co‐workers, we expected the second‐order kinetics in this medium of low dielectric constant. The first‐order kinetics was found even if excess potassium silanolate was added at 120°C. The rate of decomposition remained unaffected, the half‐time of decomposition being 27 min. This agrees quite well with the value of 24 min. found at the same temperature in the absence