Polynuclear antioxidants, phenolic

T o stabilize polypropylene against oxidation by atmospheric oxygen, phenolic mononuclear and polynuclear antioxidants containing one hydroxyl group on the aromatic nucleus are used successfully. Thus far the behavior of antioxidants having the structure of polyhydric phenols has not been studied extensively for stabilizing polyolefins. We have systematically observed the properties of dihydric mononuclear phenols with the structure of pyrocatechol and hydroquinone in isotactic poly-... 

Various polyesters derived from phosphorous or phosphoric acids were prepared. Efiicient polyphosphites were synthesised in the early 196(. Polyphosphite prepared from 152 and 4,4 -isopropylidenebis(cyclohexanol) was tested as a thermal stabilizer for PC [199] or as secondary AO for radiation sterilized EPM [200]. Built-in phosphites obtained by transesterification of triallcylphosphite with 4,4 -isopro-pylidenebisphenol or 4,4 -thiobisphenol possess antioxidant properties in polyolefins. Stabilizer containing phosphite moiety 153 was prepared from tris(2-hydroxy-ethyl)isocyanate, decyl alcohol and triphenylphosphite [201]. Various phosphites were derived firom polynuclear phenols or dihydric phenols. For example, a polycondensate prepared by reaction of phosphorus trichloride with 2,5-di-rert-butylhydroquinone was tested as heat and light stabilizer for PP [202], A linear polyester with a built-in phenolic moiety was synthesised from (2,6-di-tm-butyl-4-methylphenyl)bis(6-hydroxyhexyl)phosphite and dimethyl terephthalate [203]. 

The above result, that the antioxidant response in two-stage hydroprocessed oils is clearly better than in solvent-refined base stocks, has recently been confirmed [76]. It was demonstrated that phenolic-based formulations, blended into two-stage hydroprocessed oils, gave the greatest oxidative stability when total and polynuclear aromatics were lowest. Most fully formulated turbine oils make use of the synergistic interaction between phenolic and aminic antioxidants, see Reaction (4.70). Thus, depending on the performance requirements and the base oil composition, phenol/amino ratios of 1 1 to 4 1 are used [77],... 

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. 

Because of the variety of degradation reactions, POM is stabilized using multi-component systems consisting of antioxidants and compounds that bind the secondary products (e.g., formaldehyde, protons) of autoxidation. The stabilizers allow numerous combinations that often have synergetic effectiveness. Sterically hindered phenols are mostly used as antioxidants here, polynuclear phenols are preferred because of their low migration tendency. In addition, sterically hindered amines are used as radical scavengers. 

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