Polymeric hindered amine light stabilizers (HALSs), in which the HALS functionality was attached to the terminal isocyanate chain end of poly(styryl-co-styryl isocyanate), were synthesized by a two-step process. First, cinnamoyl azide was prepared and copolymerized with styrene by a free-radical copolymerization method. Polymeric low-molecular-weight and high-molecular-weight 2,2,6,6-tetramethyl-4-pipridinol-graft-poly(styryl-co-styryl isocyanate) and 4-amino-2,2,6,6-tetramethyl piperidine-graft-poly(styryl-co-styryl isocyanate) were synthesized by a grafting method. The photodegradation and stabilization of different grades of high-impact polystyrene (HIPS) were studied at 55degreesC in air at different time intervals, and the photostabilizing efficiency of polymeric HALSs was compared with conventional light stabilizers, such as 2,2,6,6-tetramethyl-4-pipridinol and bis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate. Polymeric HALSs showed significant improvements in the photostabilization of HIPS. The solubility and diffusion coefficient of polymeric HALSs were studied. The morphological changes in HIPS caused by photooxidation were also studied. (C) 2003 Wiley Periodicals, Inc.