At present, the UV absorbers used in polymer materials mainly include benzotriazoles, benzophenones, salicylates and triazines. Among them, the amount of benzotriazole UV absorbers is the largest and the application range is the widest.
Compared with benzotriazole UV absorbers, triazine UV absorbers are the latest class of products.
These products have the advantages of high efficiency (low addition and good effect), low color (making it more widely used), high processing temperature, good compatibility (good dispersion and easy chemical modification of the molecule itself) and excellent broad-spectrum (in the UVA and UVB ultraviolet range with a high molar absorption coefficient).
These advantages make triazine UV absorbers become the development direction of UV absorbers. Its basic structural skeleton is shown in Figure 1.
Note: R1, R2, R3, and R4 are mostly alkyl or H. R5 is mostly alkyl or hydroxy ether, etc., such as UV-1 164, UV-1 577, UV-400, UV-405, etc.
The European Chemicals Agency (ECHA) listed four benzotriazole UV absorbers (UV320, UV 327, UV 328, UV 350) on the Substance of Very High Concern (SVHC) list in 2014 and 2015. The use of benzotriazole UV absorbers is strictly restricted.
And as early as 2007, Japan has begun to ban the production and import of benzotriazole UV absorbers and products containing such substances. As a result, benzotriazole UV absorbers are being gradually replaced. The R&D and production scale of triazine UV absorbers is expanding day by day.
At present, China has fewer enterprises with the technology to produce triazine UV absorbers. Many are still in the research and development stage. The demand for research and development of this type of UV absorber production technology is increasing day by day.
Triazine UV absorber product introduction
At present, there are not many types of commercial triazine UV absorbers. There are mainly the following: UV-1577, UV-1164, UV-400, UV-405, UV-1600, UV-479, UV-477, UV-460, UV-5 (also known as triazine-5) and UV-425 (also known as triazine-425), etc.. Their chemical structures are similar, and all of them take the structure in Figure 1 as the basic skeleton, only the substituents are different. The corresponding substituents of each of the above products are shown in Table 1.
Note: EH stands for ethylhexyl, i.e., isooctyl.
Among the above products, UV-1 164, UV-400 and UV-405 have the same intermediate (Intermediate 1), i.e., 4,6-bis(2,4-dimethylphenyl)-2-(2,4-dihydroxyphenyl)-1,3,5-triazine (R1=R2=R3=R4=CH3, R5=H in Figure 1). UV-1577 and UV-5 have the same intermediate ( Intermediate 2), namely 4,6-diphenyl-2-(2,4-dihydroxyphenyl)-1,3,5-triazine (R1=R2=R3=R4=R5=H). UV-1600 and UV-479 have the same intermediate (Intermediate 3), namely 4,6-bis(biphenyl-1-yl)-2-(2,4-dihydroxyphenyl)-1,3,5-triazine (R1=R4= Phenyl, R2= R3= R5= H). UV-1600 and UV-479 are the two newest of the many triazine UV absorbers. Launched by BASF in China in 2012. The two biphenyls act as substituents, increasing the degree of conjugation of the entire molecule, narrowing the optical band gap of the molecule itself, red-shifting the absorption, and increasing the molar absorption coefficient.
According to BASF, the anti-UV performance of the two is the best among similar UV absorbers.
UV-5, UV-460 and UV-477 have the same intermediate, namely 2,4,6-tris(2,4-dihydroxyphenyl)-1,3,5-triazine (R1=R2=R3=R4=OH, R5=H). The main difference is that UV-5 contains three alkyl chains while UV-460 contains four alkyl chains (all n-butyl).
UV-477 also contains three substituents, which is the same as the substituent (R5) of UV-479, namely 2-propionic acid isooctyl group.
UV-5 was originally developed mainly for use in PVC agricultural films, but because its molecule itself contains three hydroxyl groups (hydroxyl groups are color-generating groups), the product itself is heavily colored, leading to severe limitations in its application to light-colored products. UV-460 adds an alkyl chain to UV-5 (while reducing one hydroxyl group), making the product itself lighter in color and thus can be used in a wider range of polymer materials. UV-477 is currently mainly used in high-performance coatings.
In addition to the above-mentioned grades, there is also a less widely used grade of triazine UV absorber with some differences from the above structure, namely UV-627. Its structure is shown in Fig. 2. Recently, its synthesis process has been studied by the Suzuki cross-coupling method at Zhonghao (Dalian) Chemical Research and Design Institute Co. The Suzuki cross-coupling method uses a catalytic amount of nickel catalyst, which avoids the use of large amounts of aluminum trichloride.