Copolymer and optical film using same

A copolymer, comprising:

• a residue unit A of formula (1);
• and
• a residue unit B of formula (2):
• wherein R1 and R2 each independently represent hydrogen provided that the case where R1 and R2 are both hydrogen is excluded, a cyano group, an ester group (—C(═O)OX1), an amide group (—C(═O)N(X2)(X3)), or an acyl group (—C(═O)X4), where X1 to X3 each independently represent a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 1 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms, and X4 represents a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 1 to 12 carbon atoms, or a cyclic group having 3 to 14 carbon atoms;
• R3 to R7 each independently represent hydrogen, a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 1 to 12 carbon atoms, a cyclic group having 3 to 14 carbon atoms, a halogen, a hydroxy group, a carboxy group, a nitro group, a cyano group, an alkoxy group (—OX5), an ester group (—C(═O)OX6), an amide group (—C(═O)N(X7)(X8)), an acyl group (—C(═O)X9), an amino group (—N(X10)(X11)), or a sulfonyl group (—SOOX12), where X5 to X8 each independently represent a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 1 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms, and X9 to X12 each independently represent hydrogen, a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 1 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms;
• at least one of R3 to R7 is a hydroxy group;
• and
• adjacent substituents among R3 to R7 may form a fused ring structure each other,
• wherein R8 represents an m-membered heterocyclic residue including one or more heteroatoms or a 5-membered or 6-membered ring residue containing no heteroatom, and m represents an integer of 5 to 10;
• and
• the m-membered heterocyclic residue, the 5-membered ring residue, and the 6-membered ring residue may form a fused ring structure with another cyclic structure.