Foamable polyorganosiloxane compositions

Claim 1

A foamable polyorganosiloxane composition exhibiting a viscosity of at least 0.5 Pa.s at 25° C., said composition consisting essentially of the product obtained by homogeneously blending together (A) a polydimethylsiloxane containing at least two vinyl radicals per molecule and exhibiting a viscosity of from 0.1 to 100 Pa.s at 25° C.; (B) an organohydrogensiloxane containing an average of at least 3 silicon-bonded hydrogen atoms per molecule in an amount sufficient to cure said composition in the presence of a hydrosilation catalyst; (C) a catalytically effective amount of a platinum-containing hydrosilation catalyst, (D) from 0.2 to 25%, based on the weight of said polyorganosiloxane composition, of a foam stabilizer consisting essentially of a resinous, benzene-soluble organosiloxane copolymer comprising SiO 4/2 units, (CH 3 ) 3 SiO 1/2 units and fluorine-containing units selected from the group consisting of R a R b 'SiO.sub.(4-a-b)/2 , R"[Si(R') b O.sub.(3-b)/2 ] 2 and combinations thereof, where R is a monovalent organic radical containing at least four perfluorinated carbon atoms, R' is an alkyl radical containing from 1 to 3 carbon atoms, R" is a divalent organic radical containing at least four perfluorinated carbon atoms, R and R" are bonded to the silicon atoms of their respective fluorine-containing units by means of a sequence of at least two methylene radicals or a silicon-bonded oxygen atom that is, in turn, bonded to a sequence of at least two methylene radicals, a is 1 or 2, b is 0, 1 or 2 and the sum of a and b is 3 or less, the molar ratio of all units other than hydroxyl and said SiO 4/2 units to said SiO 4/2 is from 0.7:1 to 1.1:1 inclusive, and the molar ratio of the (CH 3 ) 3 SiO 1/2 units with respect to said fluorine-containing units and any remaining units other than said SiO 4/2 units is such that (a) the surface tension exhibited by a 10% by weight solution of (D) in a trimethylsiloxy endblocked polydimethylsiloxane exhibiting a viscosity of 0.01 Pa.s at 25° C. is less than 2.2×10 -4 newtons per cm at 25° C., and (b) said 10% by weight solution requires the addition of from 0 to 5 weight % of xylene to achieve clarity at 25° C. and; (E) an amount of a blowing agent sufficient to convert said composition to a foam during exposure of said composition to atmospheric pressure and a temperature of at least 0° C.