| abstract |
The silicone-based antifoam composition having excellent durability of the antifoam activity even under vigorous agitation or under an alkaline condition comprises three kinds of diorganopolysiloxanes, of which the first is free from aliphatic unsaturation, the second is terminated at both molecular chain ends each with a vinyl diorganosilyl group and the third is terminated at both molecular chain ends each with a diorganosilyl group having a silicon-bonded hydrogen atom, a finely divided silica powder, a platinum compound to catalyze the addition reaction between the silicon-bonded vinyl groups and silicon-bonded hydrogen atoms in the second and the third diorganopolysiloxanes, respectively, and an organosilane compound of the formula R1aYbSi, in which R1 is a monovalent hydrocarbon group, Y is a hydroxy, carboxyl or hydrolyzable group and a and b are each 1, 2 or 3 with the proviso that a+b=4. When the composition, which is in the form of an aqueous emulsion or a dispersion in an organic solvent, is heated at an elevated temperature, the addition reaction takes place between the second and the third diorganopolysiloxanes to increase the stability and antifoam activity of the composition. |