Hydroxyphenyl benzotriazole

Note Since neither the DBA reagent nor 2-(2-hydroxyphenyl)benzotriazole are intrinsically fluorescent the chromatogram is not affected by interfering signals. 

Figure 8.9 Rotomeric equilibrium between planar and nonplanar form of 2-(2 -hydroxyphenyl)benzotriazole UVAs. After DeBillis et al. [336]. Reprinted with permission from A.D. DeBellis et al., ACS Symposium Series, 805, 453-467. Copyright (2002), American Chemical Society...

Photophysical Studies of Ultraviolet Stabilizers, Particularly in the 2-Hydroxyphenyl Benzotriazole Class... 

Besides these "physical aspects" of the light protection of polymers there are some hints that UV-stabilizers of the o-hydroxyphenyl-benzotriazole type are able to scavenge radicals ("chemical aspects") the production of which could not be suppressed completely by the methods described in this paper (23). 

Figure 4. Transient absorption spectra of 2-hydroxyphenyl benzotriazole and its...

Quantum yields and lifetimes of emission (fluorescence) as well as other principal rates of deactivation have been measured on 2-hydroxy benzophenone and 2-hydroxyphenyl benzotriazole derivatives. Polymerizable UV screening agents have been prepared and copolymerized with acrylics in order to obtain transparent films containing nonfugitive UV screening agents. Preliminary results of studies of photodegradation on these copolymers are also reported here. 

Vinvl-2-hydroxvphenyl)benzotrlazole. Yoshida and Vogl have recently prepared 2-(5-vinyl-2-hydroxyphenyl)benzotriazole by the route shown in Scheme VI (11). 

The 2-(2 -hydroxyphenyl)benzotriazole derivatives, for example, are capable of forming intramolecular hydrogen bonds between a nitrogen atom on the triazole ring and the phenolic proton. This hydrogen bond facilitates the occurrence of a very rapid excited-state... 

Materials. The structures of various o-hydroxyphenyl-benzotriazoles which have been studied extensively by our reseach group are shown in Figure 2. Each of these compounds was synthesized, purified and supplied by Dr. B. Milligan and Mr. P. J. Waters of the CSIRO Division of Protein Chemistry. The derivative 2-(2 -methyl-5 -methoxyphenyl)benzotriazole (MeTIN) was supplied by Dr. R. G. Amiet of the Royal Melbourne Institute of Technology. 

Hydroxyphenylbenzotriazoles have long been used as photostabilizers of polymers. For further details, see the 1990 review by Rabek photostabilizing mechanism of o-hydroxyphenylbenzotriazoles has been well investigated <87JPC1408). The absorption and fluorescence spectra of these photostabilizers have been the subjects of many publications (see Section 4.01.2.9). There are a great number of commercially available 2-(o-hydroxyphenyl)benzotriazoles. They have been widely used in the photostabilization of polypropylene, polystyrene, polyacrylates. 

Ultraviolet absorbers continue to be the most widely used stabilizers. Such products must have long-term stability to ultraviolet light, be relatively nontoxic, heat stable, have little color, must not sensitize the substrate, and must be priced at levels which the plastics processor can tolerate. The principal classes of chemicals meeting these requirements at present are the 2-hydroxybenzophenones, and 2-(2/-hydroxyphenyl)benzotriazoles, substituted acrylates, and aryl esters. Typical compounds representative of these classes are 2-hydroxy-4-octoxybenzophenone, 2-(2 -hy droxy-5 -me thylphenyl) be nzotn azole, ethyl-2-cyano-3,3-diphenyl acrylate, diinethyl / -methoxybenzylidene maJonate, and / -ter -octylphenyl salicylate. 

Additional examples of syntheses of polycyclic triazoles continue to be reported. 2-(2 -Hydroxyphenyl)benzotriazole (84) is prepared in >90% yield from azointermediate (83) by reaction with Raney nickel and DMSO, DMS or thiophene [95JAP07228577]. 2-Methylbenzo-triazole (85) is cyclized under acidic conditions and subsequently converted into the chloro analog (86) by treatment with POCl3 [95FES47],... 

Hydroxyphenyl)benzotriazole Compounds in a One-Step Process L.C. Vishwakarma etal, US Patent 5,739,348 (April 14, 1998)... 

Features of the free-radical initiation processes are similar for both the homopolymerization of functionalized monomers and copolymerization of the latter with conventional monomers. Common chemical initiators were applied. Azo-bis(isobutyro nitrile) was mostly used in bulk polymerization. No interference with phenolic hydroxy groups was observed in polymerization of 2-hydroxybenzo-phenoiKs, acetophenones, salicylates and of their derivatives [47]. The most rigorous eliinination of oxygen from the reaction mixture was necessary to achieve polymerization of monomeric hindered phenolic antioxidants or derivatives of 2-(2-hydroxyphenyl)benzotriazole [48]. An oxygen-free atmosphere is also an advantage for aromatic amines. A higher initiator level and/or increased temperature appear to be necessary to achieve normal polymerization rates with (D-functionalized monomers [46]. 

The deactivation of the UV stabilizers of the 2-(hydroxyphenyl)—benzotriazole class which involve intramolecular hydrogen bonds has been researched in much detail in the... 

Some interest continues in absorber systems. Silane and styrene monomers have been copolymerised with 2-vinylphenyl benzotriazole stabilisers in order to graft the stabilisers into the polymer chain °. When doped into plastics materials they were found to exhibit high surface activity. However, there is a conflicting report from other workers on similar structures where it is claimed that such polymeric stabilisers do not photoprotect the surface of polystyrene . Poly(2,6-dimethyl-l,4-phenylene oxide) has been effectively stabilised with an ortho-hydroxyphenyl benzotriazole stabiliser while in another study these compounds are claimed to be lost rapidly from polycarbonates . Other types... 

Significantly improved UV light stability is found with polymeric substrates stabilized with bis(2,2,6,6-tetramethyl-piperidinyl-4) sebacate, an example of hindered-amine class light stabilizers, compared with those stabilized with conventional light stabilizers. Application areas covered include polyolefin fibers, films and molded sections, polyurethane, and styrenics. Synergistic performance with o-hydroxyphenyl benzotriazoles in these polymers is apparent. 

The mechanism of photodegradation of certain hydroxyphenyl benzotriazole based ultraviolet absorbers has been investigated and a new polymerizable ultraviolet absorber in this group has been synthesized. The photoreactivity is entirely confined at the surface of polymethylmethacrylate films containing the ultraviolet absorbers as pendant groups. A mechanism involving sensitized photooxidation has been proposed to interpret the data. 

Research into the preparation and utility of 1,2,3-triazoles was particularly active in 1997. A computational study using 2-(2 -hydroxyphenyl)benzotriazole, a photostabilizer additive for polymeric materials, and the more computationally tractable model compound, 2-(2 -hydroxyphenyl)triazole, was reported and suggestions regarding the origin of the efficiency... 

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