Process for producing high molecular weight diorganopolysiloxanes for use in heat vulcanizable silicone rubber compositions

摘要

A process for producing diorganopolysiloxane gums having a viscosity from 1,000 to 100,000,000 centipoise at 25°C, where at least one of the organo substituent groups on the silicon atoms is an aliphatic radical of more than three carbon atoms comprising reacting a cyclic tetrasiloxane or a mixture of cyclic tetrasiloxanes at a temperature in the range of 0° to 90° C and in the presence of 5 to 300 parts per million of a catalyst selected from the class consisting of cesium hydroxide and ##EQU1## where R.sup.2 is selected from the class consisting of alkyl radicals of 1 to 8 carbon atoms, cycloalkyl radicals of 4 to 8 carbon atoms and phenyl, B is selected from the class consisting of nitrogen and phosphorous, R.sup.3 is selected from the class consisting of alkyl radicals of 1 to 8 carbon atoms, cycloalkyl radicals of 4 to 8 carbon atoms, phenyl, siloxane chains of the unit formula R.sub.a.sup.4 SiO.sub.4.sub.-a/2 and mixtures thereof, where R. sup.4 is selected from the class consisting of monovalent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals, and a varies from 1.5 to 2.5.