Compound, polymerizable composition, polymer, and polymerized film

A compound represented by a general formula (I) below,

• in the general formula (I),
• R1 represents a hydrogen atom or a lower alkyl group,
• R2 represents an alkyl group, an alkenyl group, an aryl group, a halogen atom, a hydroxy group, or an amino group,
• R3 represents an alkyl group, an alkenyl group, an aryl group, a halogen atom, an amino group, a carboxy group, or a group having a —SO3−M+ group, or a group that is a combination of an alkyl group, an alkenyl group, an aryl group, an oxygen atom, a —SO3−M+ group, or an arylsulfonylamino group,
• R4 represents a hydrogen atom, an alkyl group, an alkenyl group, an aryl group, a halogen atom, an amino group, or a carboxy group, or a group that is a combination of an alkyl group, an alkenyl group, an aryl group, an oxygen atom, a —SO3−M+ group, or an arylsulfonylamino group,
• M+ represents H+, Li+, Na+, K+, Cs+, or an ammonium salt,
• k is an integer of 0 to 4, and when k is an integer of 2 or more, a plurality of R2's may be the same or different, and may be linked together to form a ring,
• n is an integer of 0 to 4, and when n is an integer of 2 or more, a plurality of R3's may be the same or different, and may be linked together to form a ring,
• m is an integer of 0 to 4, and when m is an integer of 2 or more, a plurality of —SO3−M+ groups may be the same or different,
• with the proviso that n and m satisfy 1≤n+m≤4, and when m is 0, at least one of R3 is a group having a —SO3−M+ group.