REACTION OF BENZOTRIAZOLE ULTRAVIOLET-LIGHT ABSORBERS WITH FREE-RADICALS

The photolysis of benzotriazole ultraviolet light absorber additives ( Bz-UVAs) in acrylic/melamine clearcoats suggests that Bz-UVAs are dest royed by clearcoat-driven photooxidation chemistry. Tinuvin 900 is con verted to parent benzotriazole and phenol ring oxidation products. Bz- UVAs are not destroyed by photolysis in acrylic/melamine clearcoats in the absence of oxygen. Solution photolysis experiments reveal that Bz -UVAs are not attacked by free radicals generated by thermal decomposi tion of azoisobutyronitrile (AIBN) or cumene hydroperoxide (CHP) in et hanol or cyclohexane. Bz-UVAs are also not attacked by free radicals g enerated by photolytic decompostion of AIBN or CHP in cyclohexane. Bz- UVAs, however, are destroyed when AIBN or CHP are photolytically decom posed in ethanol. Photolysis without oxygen leads to Bz-UVA phenol rin g solvent and initiator adducts. Photolysis with oxygen leads to cleav age to form free benzotriazole and to destruction of the phenol ring. It is suggested that an excited state of the non-planar Bz-UVA form ma y be susceptible to free radical attack. Detailed liquid chromatograph y tandem mass spectrometry (LC/MS/MS) product analysis results are rep orted in a companion paper.