Tetramethylpiperidine-N-oxyl radical

The success story of HALS began in 1959, when the preparation of a stable 2,2,6,6-tetramethylpiperidine-N-oxyl radical (Figure 1) was described. Soon it was found that this stable nitroxyl radical is a very efficient stabilizer which is able to inhibit chain oxidation of organic materials. A principal disadvantage of the stable nitroxyl radical was its deep red-brown colour - a feature that completely precluded nitroxyls from practical use in polymer stabilization. 

Cimino P, Pavone M, Barone V (2007) Halogen bonds between 2,2,6,6-tetramethylpiperidine-N-oxyl radical and C=HyFzI species DFT calculations of physicochemical properties and comparison with hydrogen bonded adducts. J Phys Chem A 111 8482-8490... 

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