Patent ID: 7589192

Claim:
A pH dependent ion exchange material having at least one monomer selected from the group consisting of M0, M1, M2 and M3 represented by the following formulae, provided that at least one monomer having A and at least one monomer having B are contained therein, the pH dependent ion exchange material having a degree of polymerization of 2-30,000, wherein A is a group —X(CH 2 ) n Y, wherein n is an integer from 1 to 10, X is a functional group which reacts with an activated ester, and Y is a primary, secondary, tertiary amine or a nitrogen-containing aromatic heterocyclic base, B is a group —X′(CH 2 ) n Y′, wherein n is an integer from 1 to 10, X′ is a functional group which reacts with an activated ester, and Y′ is an acid generating group having a pK a value of 4 or less, and R 3 is an alkyl group having 1 to 10 carbon atoms.