Patent ID: 7282270

Claim:
A curable organopolysiloxane composition comprising: (A) a straight-chain organopolysiloxane having per molecule at least two silicon-bonded alkenyl groups and at least one silicon-bonded aryl group; (B) a branched-chain organopolysiloxane having an average unit formula: (R 2 SiO 3/2 ) a (R 2 2 SiO 2/2 ) b (R 2 3 SiO 1/2 ) c (SiO 4/2 ) d (XO 1/2 ) e where each R 2 is the same or different substituted or unsubstituted monovalent hydrocarbon group, 0.1 to 40 mole % of all R 2 's are alkenyl groups, more than 10 mole % of all R 2 's are aryl groups, X is a hydrogen atom or an alkyl group, a is a positive number, b is 0 or a positive number, c is 0 or a positive number, d is 0 or a positive number, e is 0 or a positive number, b/a is 0 to 10, c/a is 0 to 0.5, d/(a+b+c+d) is 0 to 0.3, and e/(a+b+c+d) is 0 to 0.4, and where component (B) is used in a weight ratio of 1/99 to 99/1 based on the weight of component (A); (C) an organopolysiloxane having per molecule at least two silicon-bonded hydrogen atoms, where component (C) is used in an amount of 1 to 200 parts by weight for each 100 parts by weight of the total weight of parts (A) and (B); and (D) a hydrosilylation catalyst in an amount sufficient to promote curing of the composition.