Polyvinyl acetal and laminated glass interlayer comprising same

A polyvinyl acetal which is obtained by acetalizing polyvinyl alcohol, wherein the polyvinyl alcohol has a degree of saponification of 50 to 99.99 mol%, a viscosity-average polymerization degree of 200 to 5000, and a content of alkali metal salt of carboxylic acid of 0.5 mass% or less by mass of alkali metal, and wherein when the polyvinyl alcohol is heated for three hours at 120°C and subjected to gel permeation chromatography, a peak top molecular weight (A) measured by a differential refractive index detector and a peak top molecular weight (B) measured by an absorbance detector (measurement wavelength 280 nm) satisfy formula (1), (A-B)/A<0.75 (1), and absorbance at the peak top molecular weight (B) is 0.25×10 -3 to 3.00×10 -3 . Accordingly, a polyvinyl acetal can be provided from which a film that has a reduced amount of coarse particles generated in the process of acetalization, lower coloring due to heat and less foreign matters (undissolved fractions) can be obtained.