Patent ID: 8858767

Claim:
A polyamic acid of formula (I): wherein each Z independently is in which each R independently is hydrogen, a phenyl group, or a C 1 to C 12 alkyl group; each bond a independently is at position 4 or 5; each bond b independently is at position 4′ or 5′; M is —S—, —O—, —CH 2 —, R 5 being —SO 3 H, or a C 1 to C 12 alkyl group; m is 1 or 2, when m is 1, Y is when m is 2, Y is X is O or S; each of R 1 , R 2 , R 3 , and R 4 , independently, is hydrogen, a C 1 to C 12 alkyl group, a C 1 to C 12 alkoxy group, a C 1 to C 12 ether group, a C 1 to C 12 cyclic alkoxy group, halogen atom, a C 1 to C 12 haloalky group, a hydroxyl group, a trifluoromethoxy group, a trifluoromethyl group, or a phenyl group; and n is an integer ranging from 5 to 1000.