Novel modified polymer, its manufacturing method and use

This invention provides a modified polymer which can eliminate the need to select a plurality of monomers or polymers for realizing reverse dispersion, is free from a problem of a glass transition temperature or the like in stretching treatment, and is usable as a starting compound for a new reverse dispersion phase difference film. A polymer having a polyol skeleton as a main chain is reacted with a modification compound such as an aromatic carboxylic acid halide. This reaction can provide a modified polymer comprising a chemical group such as an aromatic carbonyl group attached to an oxygen atom in a polyol skeleton side chain. For example, the polymer may be polyvinyl alcohol, and the modification compound may be benzoic acid chloride. A benzoyl group may be mentioned as the chemical group. A phase difference film having wavelength dispersion characteristics of reverse dispersion is prepared by forming a film from the modified polymer and stretching the film.