Influence of Polymer Matrixes on the Photophysical Properties of UV Absorbers

The copolymerization parameters for monomer pairs of the copolymerizable UV absorbers MA-TIN 1 (2-[2-hydroxy-3-tert-butyl-5-(O-[2-hydroxy-3-(2-methylpropenoyloxy)-propyl]-2-carbonyloxyethyl)phenyl]-benzotriazole) and MA-TZ 1 (2,4-bis(2,4-dimethylphenyl)-6-[2-hydroxy-4-(2-hydroxy-3-[2-methylpropenoyloxy])-propoxyphenyl]-1,3,5-triazine) with styrene and methyl methacrylate were determined. The UV absorbers were present to a higher extent in the copolymers than they are when simply present as mixtures of monomeric UV absorbers in the monomer feed. At higher temperatures, the radiationless deactivation from the excited proton-transferred singlet state becomes more efficient for the UV absorbers physically admixed to the polymer than for the respective polymeric UV absorbers. MA-TZ 1 embedded in poly(methyl methacrylate) shows an equal increase of phosphorescence intensity with UV irradiation time as the decrease of the proton-transferred fluorescence. By combining fluorescence and phosphorescence measurements it becomes possible to estimate the proportion of UV stabilizer molecules with an intermolecular hydrogen-bridge to poly(methyl methacrylate) and which are not suitable for light protection of polymers at room temperature. At low pressure and temperature, the increase of light-induced phosphorescence was delayed. This "phosphorescence induction" phenomenon can be put down to the free volume of polymer matrixes, in which various UV absorbers have been incorporated. The emission spectroscopic results are applicable to products which are customary in trade, as shown by investigations on a clear coat hinder system.