| abstract |
A method of preparing a curable polyorganosiloxane composition including kneading a uniform mixture of an alkenyl group-containing polyorganosiloxane, a polyorganohydrogensiloxane, and a platinum group metal compound, and defoaming the kneaded mixture under reduced pressure, the alkenyl group-containing polyorganosiloxane includes a linear polyorganosiloxane of the formula (I): n nR is R 1 or R 2 , and at least two Rs are R 1 ; R 1 is C 2 -C 6 alkenyl; R 2 is C 1 -C 6 alkyl; and n is a value that yields a viscosity at 23° C. of 10 to 10,000 cPs, a branched polyorganosiloxane containing SiO 4/2 and R′ 3 SiO 1/2 units, optionally a R′ 2 SiO and/or a R′SiO 3/2 , R′ represents a monovalent aliphatic or alicyclic, and at least three R′ groups per molecule are alkenyls, the alkenyl group-containing polyorganosiloxane having a weight ratio of the branched to linear polyorganosiloxane of 1 to 5; and a number of hydrogens bonded to a silicon atom of the polyorganohydrogensiloxane exceeds 2. |