Low density foams

Claim 1

A viscous liquid composition suitable for use in preparing low density foam polyorganosiloxanes, the composition comprising an A-part and a B-part: the A part consisting essentially of: (A1) at least one viscous liquid high molecular weight uncured vinyl terminated siloxane polymer of the general formula: ##STR11## where R, R 1 , R 2 and R 3 are independently selected from C1-C4 alkyl groups and phenyl groups, and X is an integer of suitable value or range of values so that the polymer is a viscous liquid of viscosity greater than 30,000 cps at 32°-34° C.; (A2) at least one reactive polydimethyl siloxane diluent of viscosity 15-35 centistokes and hydroxyl content of 4-6% by weight, essentially free from carbon-carbon unsaturation and corresponding to the general formula III where "m" is an integer suitably chosen to provide a compound of the specified viscosity: ##STR12## (A3) water; the relevant amounts of water (A3) and reactive diluent (A2) being such that 75-90 mole percent of hydroxyl groups in the composition are derived from water (A3) and correspondingly 25-10% thereof from the reactive diluent (A2); (A4) a complex platinum catalyst; the B part consisting essentially of: (B5) at least one second viscous liquid uncured organosiloxane polymer having the general formula: ##STR13## in which R, R 1 , R 2 , R 3 , R 4 and R 5 are independently selected from hydrogen, alkyl groups (C1-C4) and phenyl groups, at least some of R 2 representing hydrogen; the composition also including (6) an inorganic filler; the amount of said at least one reactive diluent (A2) being from 2-10 parts by weight, per 100 parts by total weight of said vinyl terminated siloxane polymer (A1) an inorganic filler (6); the viscosity of the A-part of the composition being from about 30,000 to about 65,000 cps; the relative amounts of ingredients in the A-part being adjusted within the said ranges so as to give a composition foamable under the action of the complex platinum catalyst (A4) and curable to give a cured foam polyorganosiloxane of density not greater than 14 pcf.