. . ", R.sub.11, R.sub.12, R.sub.13 and R.sub.14 each independently is hydrogen, alkyl having from 1 to 10 carbon atoms or aryl having from 6 to 10 carbon atoms, Z.sub.1 and Z.sub.2each independently is a moiety including an acid group or a reactive acid derivative, a, m and n each independently is 0 or 1, b, and p each independently is an integer from 1 to 10; and I is a integer from 1 to 3 and M is m" . .