Patent ID: 8026332

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 a phosphoric acid catalyst, 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; wherein the phosphoric acid catalyst is a compound shown by the following formula (3) or the following formula (4), wherein R 5 , R 6 , and R 7 individually represent a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or a phenyl group which may have a substituent, provided that at least one of R 5 , R 6 , and R 7 is a hydrogen atom and provided that at least one of R 5 , R 6 , and R 7 is not a hydrogen atom, wherein R 8 , R 9 , R 10 , and R 11 individually represent a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or a phenyl group which may have a substituent, provided that at least one of R 8 , R 9 , R 10 , and R 11 is a hydrogen atom.