Polymers were obtained by free-radical solution polymerization of styrene, carried out by continuous feed-type polymerization. Molecular weights were determined by gel-permeation chromatography, light scattering, and osmotic pressure and viscosity measurements. A study of molecular structures indicated that polymerizations of styrene conducted in solution at relatively low temperatures and to a low degree of conversion can result in varying degrees of branching when certain initiating radicals are present.