PROCESS FOR PREPARING CYCLIC SYN-TETRAMETHYLTETRAVINYLTETRASILOXANE

1343686 Sym-tetramethyltetravinylcyclotetrasiloxane GENERAL ELECTRIC CO 12 June 1971 27642/71 Heading C3S Sym-tetramethyltetravinylcyclotetrasiloxane is prepared by heating a methylvinylpolysiloxane material in the presence of lithium hydroxide and, as a cocatalyst, either triphenylphosphine oxide or a polyether of the formula wherein a is from 0 to 8; b is from 1 to 3; c is from 0 to 8; x is from 2 to 6, the sum (a + c + bx) is from 3 to 18 and the molecular weight does not exceed 350. The methylvinylpolysiloxane material may be a methylvinyldichlorosilane hydrolysis product, a linear methylvinylpolysiloxane or another methylvinylcyclopolysiloxane. By product sym-trimethyltrivinylcyclotrisilbxane and sym-pentamethylpentavinylcyclopentasiloxane may be recycled to provide further yields of the required cyclotetrasiloxane. Preferred polyether cocatalysts are diglyme, triglyme and tetraglyme. If desired the process may be conducted in the presence of high boiling mineral oil solvents. Uses.-The products may be used to form cross-linkable organopolysiloxanes.