Patent ID: 8470953

Claim:
A sealing material for optical elements, comprising: a polysilsesquioxane compound with a ladder structure, which contains a repeating unit of the following formula (A) in the molecule as a major component, wherein R 1 represents a group having a reactive functional group, R 2 represents an alkyl group having 1 to 20 carbon atoms or a phenyl group which may have a substituent, and l, m, and n individually represent 0 or an arbitrary integer, provided that l and n are not 0 at the same time, the polysilsesquioxane compound being obtained by condensing a silane compound (1) shown by the formula (1), R 1 Si(OR 3 ) p (X 1 ) 3-p , wherein R 1 has the same meaning as above, R 3 represents an alkyl group having 1 to 6 carbon atoms, X 1 represents a halogen atom, and p is an integer from 0 to 3, and a silane compound (2) shown by the formula (2), R 2 Si(OR 4 ) q (X 2 ) 3-q , wherein R 2 has the same meaning as above, R 4 represents an alkyl group having 1 to 6 carbon atoms, X 2 represents a halogen atom, and q is an integer from 0 to 3, at a molar ratio of 5:95 to 100:0 in the presence of phosphoric acid, wherein a cured product of the sealing material that has been heated at 150° C. for 100 hours has a transparency to light having a wavelength of 400 nm of 73% or more than that of a cured product before being heated at 150° C. for 100 hours, and has no visually observed cracks after being heated at 150° C. for 24 hours.