Hindered amine light stabilizers structures

Hindered Amine Light Stabilizers Structures are given in the Appendix. 

Figure 3. Structural variants of hindered amine light stabilizers.

The most important classes of UV stabilizers are UV absorbers (U VAs), quenchers and hindered amine light stabilizers. In this chapter an overview is given about the types of UV stabilizers in use, their mechanisms of action as well as possible synergistic and antagonistic effects. In the last part for a selected number of polymers the effectiveness of different stabilizers is shown. The chemicals structures of all stabilizers mentioned in this chapter are shown in Appendix 17.9. 

Ultraviolet-light stabilizers are of two types those that preferentially absorb UV, thus shielding the polymer structure from UV light and those that protect by quickly scavenging the free radicals as they form. The latter belong to a group of compounds known as hindered amine light stabilizers (HALS). 

Figure 10.5 General chemical structure of a representative hindered amine light stabilizer (HALS).

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. 

With a few exceptions, such as hydroxybenzoate derivatives, most conventional phenolic antioxidants suffer from low photostabUiy and could not be used for photostabilization. This problem was solved with the introduction and development of hindered amine light stabilizers (HAS) [49]. Because this class of compounds was originally developed for photostabilization, they are frequently referred as hindered amine light stabilizers or HALS. HAS are commercialized under a variety of structures, most of which contain one or several 2,2,6,6-tetramethylpiperidine moieties linked together to form polynuclear species. The stmcture of a typical commercial HAS, Chimassorb 944, is shown in Figure 15.21. 

Hindered amine light stabilizers (HALS) were developed as photostabilizers and/or metal deactivators. It was soon determined that the oxime structure functioned as an AO as well. In fact, these AOs are almost self-regenerating so they last for long times. They also serve their original functions, thus they often do double and even triple duty. These additives are responsible for high performance PP used... 

The basic structure of hindered amine light stabilizers consists of 2,2,6,6-tetramethylpiperidine. The term hindered refers to the four methyl groups shielding the nitrogen atom. If the structure is hindered less, considerable loss in efficiency is observed. 

Here we report the use of a readily prepared polymer immobilised TEMPO as a catalyst for alcohol oxidations.15 It was derived from a commercially available oligomeric, sterically hindered amine, poly[[6-[(l,l,3,3-tetramethylbutyl)amino]-l,3,5-triazine-2,4-diyl] [2,2,6,6-teramethyl-4-piperidinyl)-imino]-1,6-hexane-diyl[(2,2,6,6-tetramethyl-4-piperidinylimino]], better known as Chimassorb 944 (MW 3000 see figure 3 for structure). This compound is used as an antioxidant and a light stabiliser for plastics. It contributes significantly to the long-term heat stability of polyolefins and has broad approval for use in polyolefin food packaging.16... 

Some antioxidants also give protection to polymers against the effect of light both by their inherent structure or by a synergetic effect with light stabilizers [47a] while the sterically hindered amines are quite efficient as antioxidants [47b]. 

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