NOVELTY - Polymer film comprises at least one species of a merocyanine unit (A).    USE - The polymer film is useful in the phase difference film, polarizing plate, and LCD device (all claimed), and for applications including protective film of various component, insect repellent film, film for solar battery module and architectural film.    ADVANTAGE - The polymer film exhibits: high retardation along thickness direction even with a small amount of addition, while ensuring a desired level of wavelength dispersion; and improved UV absorption properties. (A) has high affinity with hydrophilic polymers and high birefringence.    DETAILED DESCRIPTION - Polymer film comprises at least one species of a merocyanine unit (A) of formulae (R3-(O-C(=O)-Y1-N(-R1)-CH=CH-CH=C(-CN)2)n) (I) and (R3-(C(=O)-O-Y1-N(-R1)-CH=CH-CH=C(-CN)2)n) (II).    R1 = 1-6C unsubstituted alkyl or 6-12C unsubstituted aryl;    Y1 = 1-6C alkylene or arylene (both optionally substituted), where one carbon atom or more non-adjacent carbon atoms in the alkylene group is substituted by oxygen atoms;    n = 1-3; and    R3 = alkyl or aryl (both optionally substituted), where one carbon atom or more non-adjacent carbon atoms in the alkyl group is substituted by oxygen atoms (n = 1), or n-valent linking group comprising one or more atoms (n = 2-3).    INDEPENDENT CLAIMS are included for:    (1) a phase difference film comprising the polymer film, and an optically anisotropic layer (11) configured by curing a liquid crystal composition;    (2) a polarizing plate comprising the polymer film;    (3) a LCD device comprising the polymer film;    (4) an high retardation along thickness direction (Rth) inducing agent comprising (I) and (II); and    (5) a merocyanine-based compound (B) of formulae (R3-(O-C(=O)-CH2-N(-CH3)-CH=CH-CH=C(-CN)2)n) (III) and (R3-(C(=O)-O-CH2-N(-CH3)-CH=CH-CH=C(-CN)2)n) (IV).    DESCRIPTION OF DRAWING(S) - The figure shows a schematic cross sectional view of a phase difference film.    Retardation film (10)    Optically anisotropic layer (11)    Support. (12)