"wherein P is an organic dyestuff residue, a heterocyclic ring residue or an aromatic polycyclic compound residue, X is a divalent binding group composed of a chemically rational combination of 2 to 15 atoms selected from S, C, N, 0 and H, Y is a direct bond or a divalent binding group selected from --NR-- (in which R is H or an alkyl group having 1 to 18 carbon atoms) or --O--, Z is an alkylene gr" . . . .