Patent ID: 8415277

Claim:
A bi-functional compound that is positively charged at a first pH and negatively charged at a second pH, the bi-functional compound represented by Formula I below: Q-X-Q 1 (Formula I) wherein Q or Q 1 or a combination comprising at least one of the foregoing, X is a compound represented by wherein L is a bond, —O—, —CO—, —S—, —SO 2 —, —CH 2 —, —C(CH 3 ) 2 —, —C(CF 3 ) 2 —, or a combination comprising at least one of the foregoing, wherein the carbonyl group and the carboxyl group are substituted at any available carbon position except for a ring connection portion, a combination comprising at least one of the foregoing, or wherein the bi-functional compound that is positively charged at a first pH and negatively charged at a second pH, wherein the bi-functional compound is linked to at least one monomer comprising monomers represented by M0, M1, M2, M3, or a combination comprising at least one of the foregoing, below, and wherein the bi-functional compound comprises at least one of a monomer with A and at least one of a monomer with B, wherein A is a group represented by —OH or —X 2 —R 11 —Y 2 where X 2 is O—, —S—, —NR 12 —, or a combination comprising at least one of the foregoing, where R 12 is hydrogen, halogen, a substituted or unsubstituted C 1 -C 10 alkyl, or a combination comprising at least one of the foregoing, R 11 is a substituted or unsubstituted C 1 -C 10 alkylene, a substituted or unsubstituted C 3 -C 10 cycloalkylene, a substituted or unsubstituted C 2 -C 10 alkenylene, a substituted or unsubstituted C 2 -C 10 alkynylene, or a combination comprising at least one of the foregoing, and Y 2 is —COOH, —SO 3 H, —SO 2 H, —SOH, —H 2 PO 4 , —HPO 4 − , —PO 4 2− , or a combination comprising at least one of the foregoing, and B is or a combination comprising at least one of the foregoing, and wherein the bi-functional compound comprising A and B has a polymerizationdegree of about 2 to about 30,000.