| 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 DEG 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 DEG 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). |