Optical element

Patent Granted PROBLEM TO BE SOLVED: To provide an optical element material excellent in thermooptic coefficient, solvent resistance, and heat resistance, and further having stable quality controlled in molecular weight. ; SOLUTION: The optical element is prepared using a polymer prepared using a cage silsesquioxane derivative represented by formula (1-0) where R is independently a 1-40C alkyl, a 6-40C aryl any hydrogen of which may be substituted by a halogen or a 1-20C alkyl, or a 7-40C arylalkyl in which any hydrogen in an aryl may be substituted by a halogen or a 1-20C alkyl.