1.1 ,This test method describes the test procedures for determining the weight-average molecular weight M_w of polymers by light scattering. It is applicable to all nonionic homopolymers (linear or branched) that dissolve completely without reaction or degradation to form stable solutions. Copolymers and polyelectrolytes are not within its scope. The procedure also allows the determination of the second virial coefficient, A₂, which is a measure of polymer-solvent interactions, and the root-mean-square radius of gyration (s²)^1/2, which is a measure of the dimensions of the polymer chain.