MODIFIED VINYL ALCOHOL POLYMER POWDER HAVING REDUCED METHANOL CONTENT AND PRODUCTION METHOD THEREFOR, AND WATER-SOLUBLE FILM AND PACKAGING MATERIAL

The present invention provides an environmentally-friendly and industrially-useful modified vinyl alcohol polymer powder having a structural unit derived from a derivative of an ethylenically unsaturated dicarboxylic acid, and containing a reduced amount of methanol, and a trace amount of a component that does not dissolve in water when the powder is dissolved in water. The invention is also intended to provide a method of production of such a modified vinyl alcohol polymer powder. The present invention relates to a modified vinyl alcohol polymer powder containing a structural unit derived from a derivative (A) of an ethylenically unsaturated dicarboxylic acid in a content (X) of 0.05 mol% or more and 10 mol% or less, and having a degree of saponification of 80.0 mol% or more and 99.9 mol% or less, the modified vinyl alcohol polymer powder has a methanol content of 0.01 weight% or more and less than 3.0 weight% as measured by headspace gas chromatography of 500 mg of the polymer powder, the modified vinyl alcohol polymer powder contains 0.1 ppm or more and less than 2,000 ppm of a component that is insoluble in a 90°C, 5 weight% aqueous solution.