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

Claim 1

A process for producing diorganopolysiloxane polymers having a viscosity from 1,000 to 200,000,000 centipoise at 25°C where at least one of the organo groups is an aliphatic or haloaliphatic radical of 3 carbon atoms or more consisting essentially of (a) hydrolyzing in a water and a water-immiscible organic solvent mixture, a silane of the formula, R R' SiX.sub.2 and mixtures of said silane, where R is selected from the class consisting of methyl, ethyl, vinyl and phenyl and R' is selected from the class consisting of alkyl radicals, halogenated alkyl radicals and cycloalkyl radicals of 3 to 8 carbon atoms, X is halogen; (b) separating the water and water-immiscible organic solvent from the hydrolyzate; (c) adding 0.5 to 2% by weight of a catalyst selected from the class consisting of KOH, NaOH, and CsOH to the hydrolyzate and heating the hydrolyzate to 150°C to 200°C; (d) removing overhead a mixture of cyclic polysiloxanes and transferring such cyclic polysiloxanes into a distillation column; (e) separating by distillation at a temperature of 80°-200°C and 1 to 50 mm of Hg vacuum essentially pure tetracyclic polysiloxanes of the formula, (R R' SiO).sub.4 and mixtures thereof, where R and R' are as previously defined; (f) heating the tetracyclic polysiloxanes above 100°C with a nitrogen purge to reduce the water content to less than 10 parts per million; (g) reacting the cyclic tetrapolysiloxanes at a temperature in the range of 0° to 90°C in the presence of 5 to 300 parts per million of a catalyst selected from the class consisting of CsOH and ##EQU5## where R 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 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 a 4 SiO.sub.(4 -a )/2 and mixtures thereof, where R 4 is selected from the class consisting of monovalent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals, a varies from 1.5 to 2.5; until equilibration is reached and (h) neutralizing the catalyst in the reaction mixture after equilibrium has been reached.