Anti-Discoloration Effect of Polyammonium Electrolyte on Organic UV Absorbers

One of the causes that hydroxyphenylbenzotriazole- and hydroxybenzophenon-type UV absorbers tend to turn yellow, when they are blended with resin and molded, is believed to be the affection on the phenolic hydroxyl group of alkaline or metal components. In organic solutions containing the UV absorbers, the yellowing can be exhibited by the addition of tetrabutylammonium hydroxide or titan tetra-n-butoxide, which can remove H+ from the phenolic hydroxyl group. The yellow hue of the solution was disappeared by addition of the polyelectrolyte comprising poly[oxyethylene(dimethylimino)propyl(dimethylimino)ethylene] cation and bis(2-ethylhexyl)sulfosuccinate anion to form the polyion complex with the deprotonated UV absorber. The anti-discoloration effect may be attributed to the localization of the negative charge at around the oxygen atom in the phenolic group by the positive charge of the polyammonium. The polyammonium electrolyte can be blended with poly(vinylbutyral) and poly(vinylchloride), and can be applied successfully to prepare a non-yellowing plastic film with a high absorptivity of the UV light.