Polymer and secondary battery using same

A polymer comprising:

• a plurality of pendant groups,
• wherein each of the pendant groups comprises a carboxyl group or salt thereof, and a group interposed between a main chain and the carboxyl group or salt thereof,
• wherein the group interposed between the main chain and the carboxyl group or salt thereof is a hydrocarbon group, a perfluorocarbon group, a combination of a hydrocarbon group and at least one of an ester group and a carbonate group, or a combination of a perfluorocarbon group and at least one of an ester group and a carbonate group,
• wherein a carbonyl carbon included in the carboxyl group or salt thereof is bonded directly to a carbon included in either the hydrocarbon group or the perfluorocarbon group, and
• wherein in a case where the group interposed between the main chain and the carboxyl group or salt thereof is the hydrocarbon group or the combination of the hydrocarbon group and the at least one of the ester group and the carbonate group, fluorine is bonded to at least a carbon among the carbons included in the hydrocarbon group located at an α-position or a β-position of the carbonyl carbon included in the carboxyl group or salt thereof.