The influence of combined 2,2,6,6-tetramethylpiperidine -2-hydroxyphenyl-benzotriazole [1,3,5]triazine polymerizable stabilizers on the photostability of their copolymers with methyl methacrylate as well as the interaction of the photoreactive HALS and UV absorber fragments in the combined molecules have been studied. Chemical bonding of the stabilizers in the polymer was confirmed spectrephotometrically. The participation of the combined stabilizers in the polymerization did not affect considerably the molecular weight and the molecular weight distribution of the copolymers. A significant stabilizing effect against photodegradation was determined. Strong synergistic interaction between different HALS and UV absorber fragment in the combined stabilizers was established. (c) 2006 Wiley Periodicals, Inc.