Hindered amine light stabilizers products

There are several claims in literature for the reaction of acetone and ammonia, at temperatures like 50°C, to give triacetoneamine (2,2,6,6-tetramethyl 4-piperidone), using Nafion and other CIERs (Eqn. (10)). This product is the starting material for the renowned hindered amine light stabilizers. 

The hindered-amine light stabilizers for polymers are piperidine derivatives. An example of these products is bis-(2.2,6,6-tetramethyl-4-pipendinyl)sebaeale, tradenained Tinuviii 770, useful as a light stabilizer for polyolefins and styrenics. 

Exposure to solar irradiation (sunlight) may alter their chemical integrity and in due course some physical properties such as mechanical strength (e.g. brittleness) or color (e.g. fading) as well. Additives like industrial ultra violet (UV)-absorbers, hindered amine light stabilizers, radical scavengers and antioxidants are incorporated or applied in these products to effectively reduce or delay such radiation induced deteriorations. 

As with thermal stabilizers, photostabilizers must satisfy basic chemical and physical requirements (see the section titled ""Antioxidant permanence effects of chemical and physical factors ). In addition, they must be photo-stable, i.e., stable to UV-light, to withstand continuous periods of UV-exposure, without being prematurely destroyed or effectively transformed into sensitizing products. There are essentially three classes of compounds that are categorized as photostabilizers/ photoantioxidants UV-absorbers and pigments, peroxide decomposers including nickel complexes, and sterically hindered amine light stabilizers. 

Since their initial production by our laboratories about ten years ago, hindered amine light stabilizers (HALS) have become established as excellent light stabilizers of polymers. This review deals with their synthesis, evaluation and development. 

Hindered Amine Light Stabilizers (HALS) are a new class of highly efficient stabilizers protecting polyolefins and other polymers against light-induced deterioration. They were initially developed into commercial products in our laboratories. In this review we describe the details of how they were synthesized, evaluated and developed. 

Most hindered amine light stabilizers have evolved from the discovery (4) that compounds containing a 2,2,6,6-tetramethylpiperidine moiety can stabilize polymers against photodegradation and this moiety has been incorporated into HALS of various types (Figure 1). Much has been published on the mechanism of action of HALS and the literature in this area has recently been critically reviewed (5,6). While the complete mechanism of action has not been fully elucidated, the high performance of HALS is generally attributed to the ability of their oxidation products to... 

Obviously, in a PA melt, phenols undergo reactions and the reaction products are unable to react with the amide peroxy radical. On the other hand, antioxidants of the hindered amine light stabilizer type interrupt the oxidation reaction of PA6 after an induction period. During this induction period, they are oxidized to the N-oxyl form, which is essentially reactive... 

Additives can also have a similar effect decabromo-diphenyl ether flame retardant in polypropylene was shown to enhance oxidation. Furthermore, where hindered-amine light stabilizers HALS were present in the compound, the degradation product HBr reacted with it to form the ammonium salt that has no photostabilizer effectiveness... 

Many studies on the identification of polymer additives by Py-GC/MS have been published recently for example, an innovative method based on direct analysis of polymers containing polymeric hindered amine light stabilizers (HALS) by using pyrolysis coupled to GC/MS was applied successfully for fast and straightforward identification of these additives. Each of the HALS showed different pyrolysis gas chromatograms containing characteristic pyrolysis products. As a result, HALS additives with very similar chemical structures, e.g., Chimassorb 944 and Chimassorb 2020, could be distinguished. 

Not all antioxidants respond to the OIT test in most cases the phenolic antioxidant concentration can be monitored by measuring the OIT, whereas phosphite antioxidants and hindered amine light stabilizers (HALS) in particular display little response. Because of this, the OIT test is a poor tool for polymer service life predictions as there is no real correlation between the OIT test results and the product s performance in the field. Additional test data such as heat oven aging are often required to supplement the OIT data in order to improve the accuracy of predicting long-term product performance. 

Sterically hindered amine light stabilizers (HALS) constitute another class of light stabilizers that efficiently reduce UV-induced degradation. They are compounds that intercept chemically highly reactive radicals formed hy photochemical reactions and transform them into harmless reaction products. Fig. 3.8. Their effectiveness is not based on a competing physical absorption effect, therefore no minimum layer thickness is required for HALS effectiveness, unlike for the UV absorbers. That makes them suitable for applications such as films and fibers (527). In particular, they provide surface protection, which plays a special role in visible automotive parts. Another essential difference to UV absorbers is the fact that photooxidation is not prevented, but after initial damage its propagation is either reduced or suppressed [510],... 

In order to assess the efficiency of a light stabilizer in its coupling with a phenolic antioxidant, multifunctional hindered amine light stabilizer or some complexes of tetramethylpiperidine with nickel were synthesized [48]. These products were successfiiUy used for the stabUization of monofilament polypropylene and the usage range was expanded to low density polyethylene. For the PVC stabilization, some stilbene compounds such as 4-chloro-a-cyan-3-methyl-stilben (9) were also efficiently used [49]. 

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