Reduction phenol phosphite

Here we discuss a new class of polypropylene stabilizers—the polymeric phenolic phosphites. These compounds exhibit unique, broad-spectrum activity which may allow simplification of polypropylene stabilizer systems. The most active species are synergistic with thiodipro-pionate esters, are effective processing stabilizers when used alone or with other compounds, and contribute to photostability. Compounds of this type appear to function as both free radical scavengers and peroxide decomposers, and through a mechanism not yet completely understood, allow significant reductions in the concentration of ultraviolet absorbers required to achieve high levels of photostability. 

The addition of HP-136 to the classic binary phenol/phosphite systems significantly improves performance both in melt flow and colour, enabling a producer and converter to tailor the formulation to meet specific cost targets. In some cases it is possible to reduce the concentration of the classic binary system by more than 50%, In combination with high-performance phosphites there is also a dramatic improvement, with significant reductions in overall concentration of stabilizer without loss of performance. 

The coupling reaction between phenol and ethylene to give ortho-ethylphenol is catalyzed by (triphenylphosphite)ruthenium complex [20]. In this reaction, the ortho C-H bond of triphenylphosphite is cleaved by orthometallation, and then insertion of ethylene followed by reductive elimination lead to the formation of triarylphos-phite having an ortho-ethylphenoxo group. Transesterification between the phosphite and phenol then releases (ortho)-ethylphenol by reproducing triphenylphosphite (Scheme 14.8). 

Reduction of phenols. The reagent provides a means for the reduction of a phenol to the parent hydrocarbon. A solution of the phenol and diethyl hydrogen phosphite in carbon tetrachloride is treated with trielhylamine and allowed to stand... 

As for the unfilled PA6, for glass filled black PA6 the addition of just a phenolic antioxidants and a phosphite causes already a reduction of the UV degradation rate during accelerated aging. Addition of HALS leads to a further reduction of the rate of gloss loss during weathering (see Fig. 17.12). In this case, the combination of a low... 

In polypropylene tape applications. HP-136 is very effective when used with a classic phenolic or in a ternary blend and. compared with a traditional binary blend, data indicate that there is potential for a 50% reduction in total stabilizer concentration, with comparable melt flow stability, improvement in colour, and an improvement in water carry-over, again providing a significant margin for optimization of formulation. In polypropylene fibre applications, a combination of HP-136 with a hindered amine and a phosphite shows melt flow and colour comparable with a traditional binary system, but superior gas-fade resistance and UV stability in phenol-free blends. This improvement is seen at 40% less concentration. 

The phosphite efficiency in hydroperoxide reduction decreases in the order phosphites > alkyl phosphites > aryl phosphites > hindered aryl phosphites. Hindered aryl phosphites can also act as chain breaking primary antioxidants when substituted by alkoxy radicals but their activity is lower than that of hindered phenols but in oxidizing media at high temperatures the hydrolysis of aryl phosph(on)ites takes place and produces hydrogen phosph(on)ites and phenols which are effective chain-breaking antioxidants. Multifunctional stabilizers such as those containing HAS-phosph(on)ites moieties show a superior efficiency due to the intramolecular synergism—Table 6 [49]. 

It is well known that polymerization catalyst residues can induce the degradation of polymers, which can result in a faster conversion of present phenolic antioxidants and thus to discoloration. A possible mechanism of action of phosphites is that they form a complex with these metal ions and reduce their negative influence. This can lead to a slower conversion of the phenolic antioxidant and thus reduction of the formation of their yellow conversion products. 

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