AbstractThe photodegradation of polystyrene (PS) in deoxygenated solutions of CCl4 and CHCl3 by irradiation with ultraviolet light of wavelengths λ ≥ 270 nm is investigated by quasielastic and integral light scattering techniques. Molar mass distributions w(M), number‐ and weight‐average molar masses M̄n and M̄w as well as the average number of chain scissions per macromolecule x(t) as a function of the time of irradiation t were determined. The results obtained prove that efficient photodegradation occurs in CCl4‐ and CHCl3‐solutions of PS, although measurable changes in molar mass of irradiated PS starts to occur only after several hours of irradiation.