Reaction of benzotriazole ultraviolet light absorbers with free radicals

Gerlock, John L.; Tang, Walter Z.; Dearth, Mark A.; Korniski, Thomas J.

doi:10.1016/0141-3910(95)00027-j

Cited by 40 publications

(20 citation statements)

References 22 publications

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“…[5][6][7][8][9][10][11][12][13][14] Thus many studies have been carried out under more controlled and simplified conditions, including some excellent recent studies in solution by Gerlock and co-workers. 7,8 Known Polar Effects. It has been known for some time that the intramolecular hydrogen bond in benzotriazole-based stabilizers, such as 1, can be disrupted in polar solvents.…”

Section: Introductionmentioning

confidence: 99%

“…[5][6][7][8] Because of the complex environment in which they are employed as well as the length of time required to achieve significant loss of these materials, the study of their photochemistry resulting from direct excitation (as opposed to mechanical loss or autoxidation) has been very difficult to characterize. [5][6][7][8][9][10][11][12][13][14] Thus many studies have been carried out under more controlled and simplified conditions, including some excellent recent studies in solution by Gerlock and co-workers. 7,8 Known Polar Effects.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

DMSO Solvent Induced Photochemistry in Highly Photostable Compounds. The Role of Intermolecular Hydrogen Bonding

et al. 1997

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2-(2′-Hydroxy-5′-methylphenyl)benzotriazole, 1, Tinuvin P, and o-hydroxybenzophenone, 2, are thought to achieve exceptional photostability through highly reversible deactivation associated with their intramolecular hydrogen bonds. Excimer laser excitation (10 mJ, 20 ns at 308 nm) of these molecules in argon-bubbled hexane solution at room temperature affords no discernible transient signals (absorption or emission) between 320 and 800 nm. In DMSO solution under the same conditions, however, strong transient absorptions in the visible (λ max 410 and 425 nm for 1 and 2, respectively) are observed. The transients responsible for the absorptions are quenched by oxygen and acid, and the spectra match well with the ground state difference spectra generated from the corresponding phenolate ions. When a bulky group is incorporated ortho to the hydroxyl function such as in 2-(2′-hydroxy-3′-cumyl-5′-(1,1,3,3-tetramethylbutyl)phenyl)benzotriazole, 3, Tinuvin 928, no appreciable transient absorption is observed even in DMSO solution. These results are consistent with the disruption of the intramolecular hydrogen bond of 1 and 2 (but not 3) as the result of intermolecular hydrogen bond formation with DMSO. The "dramatic" ortho effect implies that the bulky group adjacent to the hydroxyl function sterically shields the intramolecular hydrogen bond from disruption by polar basic environments.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

DMSO Solvent Induced Photochemistry in Highly Photostable Compounds. The Role of Intermolecular Hydrogen Bonding

et al. 1997

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“…Previous work has shown that the loss of UVA from a coating is due primarily to its chemical destruction and not due to exudation from the surface. 17,18 This destruction rate is proportional to the rate of photooxidation, and thus, the UVA is more readily consumed at the surface of the coating where the intensity of light is highest and the rate of photooxidation is the most rapid. A reduction in the rate of photooxidation of the clearcoat by the addition of HALS leads to a shallower gradient in UVA concentration, as seen in Figures 5 and 6.…”

Section: Ultraviolet Light Absorber Retentionmentioning

confidence: 98%

Long-term weathering behavior of UV-curable clearcoats: Depth profiling of photooxidation, UVA, and HALS distributions

Seubert

Nichols

Кучеров

2005

J Coat. Technol. Res.

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The long-term weathering performance of two UV-curable clearcoat systems was studied using in-plane microtomy in combination with infrared spectroscopy, UV spectroscopy, and ESR spectroscopy. Oxygen transport characteristics were also studied using the half-time method. The photooxidation versus depth profile was highly dependant on the presence of hindered amine light stabilizers (HALS) for both coating systems. Ultraviolet light absorbers (UVA) had little effect on the photooxidation profile. A photooxidation gradient was formed in both clearcoats due to a reduction in oxygen solubility when compared to standard thermoset clearcoats. This gradient was only seen in formulations not containing HALS.A utomotive clearcoats continue to evolve due to a variety of driving forces that include environmental regulations, customer performance demands, and cost pressures. High-solids solventborne 1K and 2K clearcoats are currently the industry standards in North America. However, super high-solids, powder, waterborne, and slurry clearcoats either have been recently introduced or are in advanced development. Each of these clearcoats offers reduced VOCs in comparison to conventional thermoset clearcoats, but all come with performance or cost compromises as well.Another class of clearcoats being developed, but not yet commercial for automobile bodies, is UV-curable clearcoats. UV-curable clearcoats typically crosslink via free radical polymerization upon exposure to UV radiation. These coating systems are typically mixtures of oligomers, monomers, solvents, one or more photoinitiator (PI), and other additives for weatherability enhancement, including ultraviolet light absorbers (UVA) and hindered amine light stabilizers (HALS). 1 UV-curable coatings are well established in such industries as telecommunications, wood finishing, and flooring manufacturing, but have only recently been seriously considered by the automotive industry for body paint applications. These coatings are of major interest for a variety of reasons, the most widely discussed of which is the potential for outstanding scratch resistance. This improved scratch resistance is mainly due to the extremely high crosslink density that can be achieved by UV-curable coatings. 2,3 In addition, UV-curable clearcoats have the potential to offer lower VOCs, improved process efficiency, shorter curing times, and lower energy consumption. These potential process advantages must be weighed against issues associated with reparability, adhesion, yellowing, and curing shadowed areas on highly contoured objects. One solution that addresses the shadowing issue is to utilize both thermal and UV curing to process the clearcoat. These systems, known as dual cure systems, allow the partial thermal cure of shadowed regions while giving the properties of full UVcure systems in unshadowed regions.Because UV-curable coatings have not been used extensively in outdoor environments, their long-term weathering behavior is largely unknown. The research to date, mainly by Decker, 4-7 Valet, 8...

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“…Therefore, the concentration of primary products is very small, and only highly degraded fragments usually are recovered. Benzophenones have yielded benzoic acid [5,7] and benzotriazoles have yielded benzotriazole [8,9,10] as shown in Figure 4. The phenolic moieties that would result from photolysis reactions such as these would be very unstable and undergo rapid photo-oxidation.…”

Section: Photophysics Of Uv Absorbersmentioning

confidence: 99%

Permanence of UV Absorbers in Plastics and Coatings

Pickett¹

2001

ACS Symposium Series

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Ultraviolet absorbers (UVA's) undergo photo-degradation with quantum yields on the order of 10 -6 even in glassy, unreactive matrices such as poly(methyl methacrylate) (PMMA). The kinetics of UVA loss in a film or coating can be described by the equation: A = log 10 [(1-T 0 )10 (A0-kt) + 1] where A is the absorbance at time t, T 0 is the initial transmission, A 0 is the initial absorbance, and k is a zero order rate constant. The rate constant can be found as the slope of log 10 (10 A -1) plotted vs. exposure. The derivation and implications of these equations and a general review of UVA degradation chemistry are discussed, including the effects of the matrix material, concentration, and hindered amine light stabilizers. The rate of UV absorber loss is of relatively minor consequence when the absorber is used as a bulk additive in a polymer, but is of critical importance in the service lifetime of coatings. The kinetics of photochemical UV absorber loss and use of loss rates in coating lifetime predictions are discussed in detail.

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Reaction of benzotriazole ultraviolet light absorbers with free radicals

Cited by 40 publications

References 22 publications

DMSO Solvent Induced Photochemistry in Highly Photostable Compounds. The Role of Intermolecular Hydrogen Bonding

DMSO Solvent Induced Photochemistry in Highly Photostable Compounds. The Role of Intermolecular Hydrogen Bonding

Long-term weathering behavior of UV-curable clearcoats: Depth profiling of photooxidation, UVA, and HALS distributions

Permanence of UV Absorbers in Plastics and Coatings

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