Abstract: Substantially water-insoluble silicic acid esters corresponding to the following general formula ##STR1## are used to foam inhibitors in foaming systems. In the above formula, X and Y represent the group --OR or a methyl group, R represents a polypropylene glycol ether group and, optionally, a polyethylene glycol ether group which may be substituted by alkoxyl, amino-alkyl, acyl, acylamino, dialkoxyl and oxyaminoalkyl groups containing from 4 to 24 carbon atoms. The total number of glycol ether groups amounts to between 1 and 100, the number of polypropylene glycol ether groups preferably being at least equal to or larger than the number of ethylene glycol ether groups.

Abstract: This invention is directed to a method of preparing block copolymers useful as foam inhibitors, which method comprises the steps of:(1) mixing (a) from 100 parts by weight of a polydimethylsiloxane that is liquid at 20.degree. C., and (b) from about 2 to 20 parts by weight of a spatially cross-linked polysiloxane resin with a molecular weight of from about 1000 to 10,000;(2) heating said mixture in the presence of a catalyst until the viscosity is at least 200 mPa.s, as measured at 20.degree. C., to form a block polymer;(3) mixing said block polymer with (c) from about 0.5 to 15 parts by weight of a silicon dioxide aerogel; and(4) heating the mixture from step (3).