INVESTIGATIONS ON POLYMERIC AND MONOMERIC INTRAMOLECULARLY HYDROGEN-BRIDGED UV ABSORBERS OF THE BENZOTRIAZOLE AND TRIAZINE CLASS

Various copolymers of MA-TPN )-propyl]-2-carbonyloxyethyl)phenyl]benzo triazole, and MA-TZ methylpropenoyloxy])propoxyphenyl]-1,3,5-triazine, with styrene, methyl methacrylate, and methacrylic acid have been syn thesized by radical polymerization. Their absorption spectra in the lo ng-wavelength UV region appear unchanged compared to those of the mono meric UV absorbers, indicating the stabilizer chromophore to remain un impaired in the course of the polymerization. Both the monomeric and t he polymeric stabilizers exhibit a strongly Stokes-shifted, temperatur e-dependent, low-quantum-yield fluorescence which arises from an inter mediate species formed by intramolecular proton transfer. The intramol ecular hydrogen bond which is essential for the photostability of this type of UV absorbers thus is still intact in the copolymers. Activati on energies for the radiationless deactivation process can be evaluate d from the temperature dependence of the proton-transferred fluorescen ce. These energies lie between 4 and 5 kJ/mol for most of the benzotri azole and triazine stabilizers investigated and show hardly any matrix dependence. Fluorescence-decay measurements with crystalline MA-TIN 1 at different temperatures reveal a close correspondence of the temper ature dependence between decay times and relative quantum yields. The radiationless process thence is concluded to originate from the proton -transferred level S-1'. The decay time at room temperature is estimat ed at 70 ps, close to the value for crystalline TIN P. The proton-tran sfer-red fluorescence of MA-TIN 1, in contrast, exhibits a biexponenti al decay profile.