Hindered amine stabilizers method

Methods of hindered amine stabilizer synthesis are being developed with the purpose of reducing cost and using available raw materials. 

Here are presented only modern trends in the chemistry of photo- and thermostabilizers based on hindered amines, the mechanisms of their action and the methods of selecting stabilizing compositions, including mixtures of hindered amines with other classes of stabilizers. 

Methods are being elaborated for synthesizing multifunctional stabilizers comprising in one molecule the fragments of either hindered amine or a nitroxyl radical and UV absorber, organic phosphite, hindered phenol, thioether, metal derivative, especially those of nickel, etc. 

Elimination of the yellowing introduced by the stable nitroxyl radicals was essential for commercial development of these excellent stabilizers. Since phenolic antioxidants are necessary for the thermal stabilization of polymers during processing, we turned our attention to ways in which unfavorable interactions between the hindered phenols and the stabilizing nitroxyl radicals could be avoided. In this section we describe the discovery of the light-stabilizing activity of hindered amine compounds, an improved synthetic method for these compounds, the synthesis of a number of derivatives, and the evaluation of their stabilizing activity. 

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. 

Sterically hindered amines (HALS) play an important role as stabilizers against the light-induced degradation of polyolefins " the detailed mechanism of their action is still being discussed. Therefore, the method of triplet-sensitized... 

The static method cannot be used for all types of stabilizers. Thiosynergists and sterically hindered amines are not detected [177]. 

Investigations on geo-membranes made from PE-HD indicate that both methods detect the consumption of stabilizers well. For PE-HD with sterically hindered phenols and phosphites, both methods show good correlation with mechanical properties. For PE-HD geo-membranes with thiosynergists and sterically hindered amines, the high-pressure method exhibits better correlation than the conventional static method [180]. 

Because the chemiluminescence method is a tool frequently used to qualify the stabilizing effect in polypropylene of various hindered amine, the analysis of CL kinetic parameters (oxidation induction time, oxidation rate, activation energy of oxidation, CL intensity) could provide reliable information related to the photodegradation state of polypropylene modified with different HALS compounds [76-78]. 

The same method can be used with anilines because para-sulfonation of aromatic amines is possible. This seems surprising because in sulfuric acid essentially all the amine will be protonated. You might expect the resulting ammonium ion to react in the meta position (because NH is no longer electron-rich) but instead the para-sulfonic acid (sulfanilic acid) is formed. At the high temperature of the reaction, it is probable that any meta-substituted product reverts to the starting material, while the para-sulfonic acid accumulates because it is stabilized by delocalization and is less hindered. 

It has been known for a number of years that FD-MS is an effective analytical method for direct analysis of many rubber and plastic additives. Major components and impurities in commercial additives can be assessed quickly, and the FD-MS data can be used to help determine what (if any) additional analytical characterization is needed. Lattimer and Welch showed that FD-MS gives excellent molecular ion spectra for a number of polymer additives, including rubber accelerators (diWocarbamates, guanidines, benzothiazyl, and thiuram derivatives) antioxidants (hindered phenols, aromatic amines) p-phenylenediamine-based antiozonants, processing oils, and phthalate plasticizers. Zhu and Su characterized alkylphenol ethoxylate surfactants by FD-MS. Jackson et al. analyzed some plastic additives (hindered phenol antioxidants and a benzotriazole UV stabilizer) by FD-MS. ... 

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