Patent ID: 7160972

Claim:
A thermally stable polysiloxane composition which is a cross-linked product of a Part A composition, of a Part B composition and of a Part C composition comprising a catalyst that catalyzes the cross-linking of Part A with Part B, the Part A composition comprising a polysiloxane having 60 to 75 percent by weight phenyl groups; the Part B composition comprising a polysiloxane having 50 to 80 percent by weight phenyl groups; the polysiloxane composition having the properties: (1) of optical clarity as measured by 90% or greater transmission of light of 400 nm wavelength in a 1.0 centimeter path; (2) thermal stability in that the composition still has 90% or greater transmission of light of 400 nm wavelength in a 1.0 centimeter path after exposure to 150° C. for 6 hours, and (3) refractive index at 589 nm of 1.545 or greater, and wherein Part A is a copolymer including methylphenylvinyl-Si—O 1/2 , diphenyl-Si—O, methylvinyl-Si—O and pheny-Si—O 3/2 units, and where Part B is a copolymer including dimethylHydrido-Si—O 1/2 units, diphenyl-Si—O units, phenyl-Si—O 3/2 units, and where the composition includes covalent cross-linked bonds between Part A and Part B, the cross-links having been formed between vinyl and hydride containing units.