GB784424A - Manufacture of silicone oils - Google Patents

Abstract

End-blocked polysiloxane oils are obtained by equilibrating linear or cyclic polysiloxanes in which the organic groups are hydrocarbon, with disiloxanes in which the organic groups are also hydrocarbon in the presence, as catalyst, of a cation exchanger which may be a synthetic resin or silicate or a cation exchanger based on carbon. The cation exchanger may also contain basic groups. The catalyst may be removed by simple filtration. In examples: (1) 500 gr. of a 33 cs. polydimethylsiloxane are heated under reflux at 140 DEG C. for 4 hours with 6.5 gr. hexamethylsiloxane in the presence of 15 grams of a sulphonated carbon cation exchanger. The product is an oil of 360 cs. viscosity. Examples 2, 3 and 5 are similar but using different cation exchangers. (4) 1450 gr. octamethylcyclotetrasiloxane and 1450 gr. hexamethyldisiloxane are refluxed at 111 DEG C. for 4 hours in the presence of a neutral acid-activated bleaching earth and the product distilled to remove a distillate containing the trisiloxane. The residue has a viscosity of 30 cs. (6) 500 grams of a 1440 cs. polydimethylsiloxane is heated at 140 DEG C. for 4 hours with 25 gr. of hexamethyldisiloxane in the presence of 15 gr. bleaching earth to give an oil of viscosity 45.5 cs. The Specification refers to prior art in which the equilibrating reaction is carried out in the presence of a mineral acid absorbed on bleaching earth, and in which final traces of catalyst in the equilibrated reaction product are removed by treatment with bleaching earth.