A polymer comprising: a first monomer represented by the following Chemical Formula 1; and a second monomer which is different from the first monomer and has at least one sulfonic acid group: in Chemical Formula 1, A is -SO 3 H, -SO 3 - M +, -COOH, -COO - M +, -PO 3 H 2, -PO 3 H - M +, -PO 3 2 -2M +, -O(CF 2) m SO 3 H, - O(CF 2) m SO 3 - M +, -O(CF 2) m COOH, -O(CF 2) m COO - M +, -O(CF 2) m PO 3 H 2, -O(CF 2) m PO 3 H - M +, or -O(CF 2) m PO 3 2- 2M +; m is an integer from 1 to 6; M is a Group 1 element; R1 and R2 are the same as or different from each other, and are each independently a halogen group; n is an integer from 1 to 10; and when m and n are 2 or more, two or more structures in the parenthesis are the same as or different from each other; wherein the second monomer is derived from a compound represented by the following Chemical Formula 2 or Chemical Formula 3: in Chemical Formulae 2 and 3, A1 to A4 are the same as or different from each other, and are each independently a hydroxy group or a halogen group; L1 is a direct bond, CR3R4, C=O, O, S, SO 2, SiR5R6, or a substituted or unsubstituted fluorenylene group; R3 to R6 are the same as or different from each other, and are each independently hydrogen, an alkyl group, fluorine, a haloalkyl group, or a phenyl group; S1 to S3 are the same as or different from each other, and are each independently hydrogen, deuterium, a halogen group, a cyano group, a nitrile group, a nitro group, a hydroxy group, a haloalkyl group, a sulfonic acid group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heterocyclic group; s1, s2, and s3 are each an integer from 1 to 4; m' is an integer from 1 to 5; when s1, s2, s3, and m' are each an integer of 2 or more, two or more structures in the parenthesis are the same as or different from each other; and Chemical Formula 2 and Chemical Formula 3 are substituted with at least one sulfonic acid group. a first monomer represented by the following Chemical Formula 1; and a second monomer which is different from the first monomer and has at least one sulfonic acid group: A is -SO 3 H, -SO 3 - M +, -COOH, -COO - M +, -PO 3 H 2, -PO 3 H - M +, -PO 3 2 -2M +, -O(CF 2) m SO 3 H, - O(CF 2) m SO 3 - M +, -O(CF 2) m COOH, -O(CF 2) m COO - M +, -O(CF 2) m PO 3 H 2, -O(CF 2) m PO 3 H - M +, or -O(CF 2) m PO 3 2- 2M +; m is an integer from 1 to 6; M is a Group 1 element; R1 and R2 are the same as or different from each other, and are each independently a halogen group; n is an integer from 1 to 10; and when m and n are 2 or more, two or more structures in the parenthesis are the same as or different from each other; wherein the second monomer is derived from a compound represented by the following Chemical Formula 2 or Chemical Formula 3: A1 to A4 are the same as or different from each other, and are each independently a hydroxy group or a halogen group; L1 is a direct bond, CR3R4, C=O, O, S, SO 2, SiR5R6, or a substituted or unsubstituted fluorenylene group; R3 to R6 are the same as or different from each other, and are each independently hydrogen, an alkyl group, fluorine, a haloalkyl group, or a phenyl group; S1 to S3 are the same as or different from each other, and are each independently hydrogen, deuterium, a halogen group, a cyano group, a nitrile group, a nitro group, a hydroxy group, a haloalkyl group, a sulfonic acid group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heterocyclic group; s1, s2, and s3 are each an integer from 1 to 4; m' is an integer from 1 to 5; when s1, s2, s3, and m' are each an integer of 2 or more, two or more structures in the parenthesis are the same as or different from each other; and Chemical Formula 2 and Chemical Formula 3 are substituted with at least one sulfonic acid group.