Hindered amine stabilizers polymers

Schwetlick, K. Habicher, W. D. Antioxidant action mechanisms of hindered amine stabilizers. Polym. Degrad. Stab. 2002, 78, 35-40. 

Gijsman, P. Gitton, M. Hindered amine stabilizers as long-term heat stabilizers for polypropylene. Polym. Degrad. Stab. 1999, 66, 365— 371. 

There is much to learn and admire in the hindered amine story. Chemists can take pride in how effectively they have worked together across national boundaries to make hindered amine stabilizers an important product group for the stabilization of polymers. This introduction is a modest effort to review some of the early history of stable-free radicals including triacetoneamine-N-oxyl. This chapter was intended to serve primarily as an introduction to the hindered amine review which took place at the symposium and intentionally avoids covering material which other participants were expected to present. It is a "light-touch" overview. 

And so, the work on mechanisms of autooxidation at the British Rubber Producers Association, the early work on the synthesis and reaction of stable free radicals, the recognition of the rale of stable free radicals in polymer stabilization, the discovery of stable triacetonamine-N-oxyl, and the search for practical candidates for commercialization, have led to the development of hindered amine stabilizers, a new class of polymer stabilizers. They are effective in many polymers against photodegradation and also are effective against thermooxidation in some polymers. The structures of the current commercially available products for polymer stabilization may be seen in Figure 7. These compounds are effective in meeting the stabilizer requirements in many commercial polymers however, others are under development to satisfy requirements not being met by them. 

Hindered amine stabilizers have been the single most important development of the last decade in polymer stabilization" -Peter P. Klemchuk. 

Scheme 5. Structures of hindered amine stabilizers for polymers. Continued on next page.

The nitroxide concentration rises rapidly to a maximum then slowly decays. The slow decay of the nitroxide concentration In the hindered amine doped coatings together with the high rate of Initiation demonstrates the Importance of nitroxide regeneration as a stabilization mechanism. The effectiveness of the hindered amine stabilizers Is a function of the kinetic chain length and of the lifetime of the stabilizer In the coating. The results found here are contrasted with degradation and stabilization studies In other polymers such as polypropylene and polyethylene. 

POLYMER degradation and stabilization have become increasingly of interest to an international audience, and contributions to the body of knowledge have come from scientists worldwide. The symposium upon which this book is based was billed as international to encourage the participation of scientists from many countries, especially because it was the first Polymer Degradation and Stabilization Meeting of the Polymer Division of the American Chemical Society since March 1977 in New Orleans, and also because a major subject of the symposium, hindered amine stabilizers, had resulted from extraordinary international cooperation. 

If a stabilizer is present then this reaction sequence is modified (Figure 2) by the competing reactions for the removal of polymer alkyl (P-) and alkyl peroxy (POO) radicals. The nitroxide, R2NO, whether pre-formed, as in the case of TMDBIO above, or formed in situ through the oxidation of a hindered amine stabilizer, may scavenge only carbon centred radicals, P-. The hindered phenol antioxidant, AH, in contrast, will scavenge only oxygen centred radicals, and in... 

A mechanism involving charge-transfer complexes formed by HAS, polymer, O2, and ROO, i.e. [HAS - -02], [polymer - - -O2], [HAS - -ROO ], has been proposed [111]. It is considered to contribute in the early stages of the hindered amine stabilization mechanism [87]. The oxidation of TMP derivatives as illustrated in Scheme 9.15 commences when the polymer is processed. It continues later, when the polymer is exposed to light. 

Hindered Amine Stabilizers as Sources of Markers of the Heterogeneous Photooxidation / Photostabilization of Carbon Chain Polymers... 

Hindered amine stabilizers (HAS) are the most common class of the curative additives and their application is the state-of-the-art in photoprotection of carbon-chain polymers, polyolefins in particular. HAS shape future polymer development, promote their consumption in new areas and expand material performance by increasing its lifetime. Application of HAS is based on a long-term effective development and is connected with commercial benefits for polymers. An optimized technical application of HAS required explanation of their chemistry and activity mechanisms in different phases of the oxidative degradation of polyolefins [14-17]. 

In this article the focus will be on the application of one-dimensional (1-D) and two-dimensional (2-D) spectral-spatial ESRI to the photo- and thermal degradation of poly(acrylonitrile-butadiene-styrene) (ABS) (19-55,58-63). The ESRI approach was applied to ABS because it represents a polymer that is exceptionally important in technological applications, yet is also vulnerable to photo- and thermal degradation, and can be used only in the presence of protective additives. Hindered amine stabilizers (HAS), for instance bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate (Tinuvin 770, (8)), are added for stabilization of polymeric materials (101,102). 

ESR SPECTRA OF NITROXIDES DERIVED FROM HINDERED AMINE STABILIZERS IN AGED HETEROPHASIC POLYMERS... 

Many polymer light stabilizers along with their relevant main functions have additional capacity to be heat stabilizers or antioxidants. These molecules often simultaneously bear fragments responsible for polymer protection against the destructive effects of both light and thermal oxidations. For instance, a number of hindered amine stabilizers (HAS) serve as both light and heat stabilizers [40-51]. 

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