A copolymer has a polystyrene reduced number average molecular weight of 103-108,
and includes repeating units represented by formulas (1), (2), and (3),
##STR1##
##STR2##
-Ar1- (3)
The copolymer has an excellent solubility in an organic solvent, and a high glass
transition temperature in good valance. Further, a polymer LED has high performance,
such as low-voltage driving and high luminance.
