Silanol-free resins

Claim 1

A silicone molding composition with improved thermal shock resistance having therein a base silicone resin having R 1 SiO 3/2 unit and R 2 1 SiO units where R 1 is selected from the class consisting of monovalent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals, a filler and comprising the improvement in which there is present a plasticizing amount of a low-silanol content silicone resin having less than 0.5 weight silanol groups and an R to Si ratio that varies from 1.0:1 to 1.9:1 that is produced by the process comprising (a) adding a mixture of hydrolyzable silanes of the formula, R.sub.a SiX.sub.4-a to water where there is present at least 2 parts of water per part of said silanes and 1 to 5 parts of a water-immiscible organic solvent per part of said silanes at a temperature range of 25° C. to 85° C. and where the silanes are added to said water slowly so as to form a hydrolyzate; (b) continually agitating said mixture; (c) separating the organic layer and adjusting it to 10-40% solids; (d) within 24 hours from the formation of said hydrolyzate catalyzing said organic layer with 300-600 ppm of an alkali metal hydroxide per part of solid, and refluxing the resulting mixture at 100°-160° C.; (e) neutralizing the alkali metal hydroxide in the refluxed mixture with acetic acid; and (f) stripping from the organic layer excess acetic acid and solvent, where R is selected from the group consisting of alkyl radicals of 1 to 8 carbon atoms, cycloalkyl radicals of 5 to 7 carbon atoms, alkenyl radicals of 2 to 8 carbon atoms, mononuclear aryl radicals, mononuclear aryl lower alkyl radicals where the alkyl portion is 1 to 6 carbon atoms and halogenated derivatives of the above radicals, where X is a chlorine radical and a is a whole number that varies from 1 to 2 and such that 40 mole percent to 60 mole percent of the R radicals are selected from the class consisting of mononuclear aryl radicals and mononuclear aryl lower radicals and halogenated derivatives of the foregoing radicals.