Curable organopolysiloxane composition and cured product thereof

1. A curable organopolysiloxane composition comprising:

(A) a solvent-soluble organopolysiloxane obtained by conducting a hydrosilylation reaction between

(i) an organopolysiloxane that contains in one molecule at least two alkenyl groups and is represented by the following average structural formula:

R 1 a SiO (4-a)/2

 (wherein R 1 represents a substituted or unsubstituted monovalent hydrocarbon group, the content of alkenyl groups in all groups represented by R 1 is within the range of 0.1 to 40 mole %, and “a” is a positive number that satisfies the following condition: 1≦a<2), and

(ii) a diorganopolysiloxane represented by the following general formula:

HR 2 2 SiO(R 2 2 SiO) n R 2 2 SiH

 (wherein R 2 designates substituted or unsubstituted monovalent hydrocarbon groups that can be identical or different and that are free of unsaturated aliphatic bonds, and “n” is an integer ranging from 0 to 1,000) {constituent (ii) is used in such an amount that the content of silicon-bonded hydrogen atoms of this constituent is less than 1 mole per 1 mole of alkenyl groups of constituent (i)}, the reaction being carried out in the presence of (iii) a hydrosilylation catalyst;

(B) an organohydrogenpolysiloxane represented by the following average structural formula:

R 2 b H c SiO (4-b-c )/2

 (wherein R 2 is the same as defined above, and “b” and “c” are positive numbers that satisfy the following conditions: 0.7≦b≦2.1; 0.001≦c≦1.0; and 0.8≦(b+c)≦2.6); {component (B) is used in such an amount that the content of silicon-bonded hydrogen atoms of this component is in the range of 0.1 to 10 moles per 1 mole of alkenyl groups of component (A)}; and

(C) a hydrosilylation catalyst used in a catalytic amount.

2. The curable organopolysiloxane composition of claim 1 , wherein the content of aryl groups in all groups represented by R 1 of constituent (i) is at least 10 mole %.

3. The curable organopolysiloxane composition of claim 2 , wherein the alkenyl groups of constituent (i) are vinyl or allyl groups, and the aryl groups of constituent (i) are phenyl groups.

4. The curable organopolysiloxane composition of claim 2 , wherein groups represented by R 2 of constituent (ii) are methyl groups.

5. The curable organopolysiloxane composition of claim 1 , wherein groups represented by R 2 of constituent (ii) are methyl groups.

6. The curable organopolysiloxane composition of claim 1 , wherein constituent (ii) participates in reaction with constituent (i) in such an amount that 0.05 to 0.95 moles of silicon-bonded hydrogen atoms of constituent (ii) are used per 1 mole of alkenyl groups of constituent (i).

7. A cured product obtained by curing the curable organopolysiloxane composition according to claim 1 .

8. The cured product of claim 7 having an index of refraction equal to or greater than 1.5 at 25° C. in visible light.

9. The cured product of claim 7 having an optical transmittance equal to or greater than 80% at 25° C.

10. The cured product of claim 7 having an ultraviolet-ray transmittance equal to or lower than 10% at 25° C. in the wavelength range of 200 nm to 250 nm.

11. The curable organopolysiloxane composition of claim 1 , wherein groups represented by R 2 of constituent (ii) are alkyl groups.