Method of preparing a curable polyorganosiloxane composition

A method of preparing a curable polyorganosiloxane composition, the method comprising:

• (a) kneading a uniform mixture of an alkenyl group-containing polyorganosiloxane, a polyorganohydrogensiloxane, and a platinum group metal compound, and
• (b) defoaming the resultant kneaded mixture from step (a) under reduced pressure, wherein
• (A) the alkenyl group-containing polyorganosiloxane comprises
• (i) a linear polyorganosiloxane represented by a formula (I) as follows:
• wherein each R group is independently a R1 group or a R2 group, and at least two R groups are R1 groups;
• each R1 group is independently a C2-C6 a\keny\ group;
• each R2 group is independently a C1-C6 alkyl group;
• and n is a value that yields a viscosity at 23° C. of 50 to 2,500 cPs, and
• (ii) a branched polyorganosiloxane comprising a SiO4/2 unit and a R′3SiO1/2 unit, and optionally a R′2SiO unit and/or a R′SiO3/2 unit, wherein each R′ group independently represents an unsubstituted or substituted, monovalent aliphatic group or alicyclic group, and at least three R′ groups per molecule are alkenyl groups,
• the alkenyl group-containing polyorganosiloxane having a weight ratio of the branched polyorganosiloxane to the linear polyorganosiloxane of 2.0 to 3.0, and, when the optional R′SiO3/2 unit is present in the branched polyorganosiloxane, a weight ratio of the SiO4/2 unit and the R′SiO3/2 unit is 25 to 50% by weight based on the total weight of the linear polyorganosiloxane and the branched polyorganosiloxane;
• and
• (B) a number of hydrogen atoms bonded to a silicon atom of the polyorganohydrogensiloxane exceeds 2.