AbstractPolyvinylbromide prepared by photopolymerization was fractionated. The molecular weights of the fractions were determined by a method which takes into account the fluorescent light for any polarization of fluorescence and anisotropy of the scattering molecule. The second virial coefficient‐molecular weight relation, the intrinsic viscosity‐molecular weight relation, and the values of the end‐to‐end distance indicate that P.V.B. follows the classical laws for a molecular coil. The molecular distribution curve was determined. The ratio Mw/Mn = 1.8.