NOVELTY - Polymer film comprises at least one substituted (buta-1,3-dienyl)-dimethyl-amine compounds (I).    USE - The polymer film is useful: as retardation film and ultraviolet absorber (all claimed); as protective films for various members, anti-insect films, films for solar cell modules and films for architectural materials; and as retardation plates for optical compensation of liquid crystal display devices, where ultraviolet absorber is used for liquids, powders and solids useful in glass plates, glass containers, plastic substrates, plastic containers, fibers, papers, inks, paints and architectural materials.    ADVANTAGE - The polymer film: has improved light-fastness and heat resistance; provides ultraviolet absorbers exhibiting high ultraviolet absorbing ability and improved light-fastness compared with the conventional ultraviolet absorbers; and has narrow half bandwidth and precipitous absorption peak, thus excellent in reduced coloration.    DETAILED DESCRIPTION - Polymer film comprises at least one substituted (buta-1,3-dienyl)-dimethyl-amine compounds of formula (X1-CH2-N(CH2-X2)-CH=CH-CH=C(A1)-A2) (I).    either A1, A2 = group having a Hammett's sigma p value of greater than or equal to 0.2; or    A1A2 = cyclic active methylene structure; and    X1, X2 = H, aryl, heterocyclyl, CN, N-alkyl, N-aryl-carbamoyl, alkyl-oxycarbonyl or aryl-oxycarbonyl; or    X1X2 = saturated ring in which N and C atoms are embedded (optionally substituted).    INDEPENDENT CLAIMS are also included for:    (1) a retardation film comprising the polymer having (I) and an optically anisotropic layer of a cured liquid crystal composition;    (2) an ultraviolet absorber comprising at least one of substituted (buta-1,3-dienyl)-dimethyl-amine compound of formula (X1a-CH2-N(CH2-X2a)-CH=CH-CH=C(A1a)-A2a) (III), substituted (buta-1,3-dienyl)-dimethyl-amine compound of formula (IV), substituted (buta-1,3-dienyl)-dimethyl-amine compound of formula (X1c-CH2-N(CH2-X1c)-CH=CH-CH=C(A1c)-A2c) (V), or substituted dibenzyl-(buta-1,3-dienyl)-amine compound of formula (VI);    (3) a merocyanine compound of formula (NC-CH2-N(CH2-CN)-CH=CH-CH=C(A1e)-A1f) (VIII), (V) or (VI); and    (4) preparing a merocyanine compound (VIII), comprising reacting ((E)-3-(bis-cyanomethyl-amino)-allylidene)-bis-cyanomethyl-ammonium monohydrochloride and/or ((1E)-3-(bis(cyanomethyl)iminiumyl)prop-1-en-1-yl)bis(cyanomethyl)azanium dihydrochloride and an active methylene compound.    X1a, X2a = CN, alkyl-oxycarbonyl or aryl-oxycarbonyl (optionally substituted); either    A1a, A2a = group having a Hammett's sigma p value of greater than or equal to 0.2, preferably alkyl-carbonyl, aryl-carbonyl, alkyl-oxycarbonyl, aryl-oxycarbonyl, alkyl-arylsulfonyl, arylsulfonyl, N-alkyl-carbamoyl, N-aryl-carbamoyl or CN (all optionally substituted); or    A1aA2a = cyclic active methylene structure, preferably including substituted (1,3)dioxane-4,6-dione moiety of formula (a), substituted dihydro-pyrimidine-4,6-dione moiety of formula (b), substituted pyrazolidine-3,5-dione moiety of formula (c), substituted 2,4-dihydro-pyrazol-3-one moiety of formula (d) or substituted 3,3-dioxo-3 lambda asterisk6asterisk-(1,3)oxathiolan-5-one moiety of formula (e), where asterisk is linking portion; either    R1, R2 = H or alkyl or phenyl (optionally substituted); or    R1R2 = ring;    X = O or S; either    Y1, Y2 = aryl (optionally substituted); or    Y1Y2 = saturated ring in which N and C atoms are embedded; either    A1c, A2c = alkyl-carbonyl, aryl-carbonyl, alkyl-oxycarbonyl or CN; or    A1cA2c = cyclic active methylene group including (a)-(e); either    A1e, A1f = alkyl-carbonyl, aryl-carbonyl, alkyl-oxycarbonyl or CN; or    A1eA1f = ring having active methylene group including (a)-(e);    B1 = cyclic active methylene structure, preferably (a)-(e); and    X1c = CN or alkyl-oxycarbonyl.