. . . . . "nd are allowed to be substituted, and at least one of the groups represented by R1, R2, R3 and R4 is a group containing a double bond, a halogen atom, an epoxy group, an acid anhydride residue, an alkoxy group, an alkoxycarbonyl group, an amino group, an acryloyl group, a methacryloyl group, an acrylamido group, a methacrylamido group or a haloacylamino group; n1, n2 and n3 are each 0 or 1, which" .