(b-1) 5 to 50% by mole of glycidyl acrylate, glycidyl methacrylate or an unsaturated glycidyl compound represented by general formula (I) below ##STR3## wherein R is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; Ar is an aromatic hydrocarbon group having 6 to 20 carbon atoms and having at least one glycidyl group; and n is an integer of 1 to 4, and