Abstract: A process for producing diorganopolysiloxane gums having a viscosity from 1,000 to 100,000,000 centipoise at 25.degree.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.degree. to 90.degree. 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.

Abstract: A heat vulcanizable silicone rubber composition comprising 5% to 94.75% by weight of an organopolysiloxane polymer, 5 to 75% by weight of an asbestos filler, and 0.25 to 10% by weight of an acrylic ester. The composition also includes a silica filler, a peroxide curing catalyst and a process aid. The preferred acrylic esters are methyl acrylate and trimethylolpropanetrimethacrylate.