| Abstract: | A theoretical equation for the dependence of the apparent molecular weight measured by light scattering on the solvent used has been derived with regard to the composition heterogeneity. Terpolymers corresponding to a partial azeotrope were synthesized from styrene, acrylonitrile, and methyl methacrylate with mole fractions of 0.55, 0.16, and 0.29, respectively. The molecular weight measured by light scattering was found to be independent of the solvent used. Therefore the terpolymer was concluded to be apparently homogeneous in composition. The relationship between the molecular weight M of the terpolymer and the volume fraction of the nonsolvent γ in the solvent mixture at the precipitation point in a butanone-methanol-terpolymer system was experimentally proved to follow the equation  where γ0 and b′ are constants. Between the molecular weight and the limiting viscosity number η] of the terpolymer the following relationships are valid at 35°C:  and  |
