Sealing material for optical element and sealed optical element

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 R1 represents a group having a reactive functional group, R2 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), R1Si(OR3)P(X1)3-p, wherein R1 has the same meaning as above, R3 represents an alkyl group having 1 to 6 carbon atoms, X1 represents a halogen atom, and p is an integer from 0 to 3, and a silane compound (2) shown by the formula (2), R2Si(OR4)q(X2)3-q, wherein R2 has the same meaning as above, R4 represents an alkyl group having 1 to 6 carbon atoms, X2 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 R5, R6, and R7 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 R5, R6, and R7 is a hydrogen atom and provided that at least one of R5, R6, and R7 is not a hydrogen atom,
• wherein R8, R9, R10, and R11 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 R8, R9, R10, and R11 is a hydrogen atom.