Grafting of antioxidants

A1 Malaika et a/.35" 754 have reported on the grafting of antioxidant moieties onto PP as mono- (e.g. 33) or bis-(meth)acrylic derivatives (34). Moderate grafting yields (10—40%) and some homopolymerization was observed in the case of the monoacrylate. However, with the bis-acrylate (34) close to 100% grafting yield was reported. 

Direct grafting of antioxidants on polypropylene has been accomplished by treatment with 3,5-di- erf-butyl-4-hydroxylbenzyl acrylate and a photoactivator such as benzophenone (7). 

A1 Malaika et have reported on the grafting of antioxidant moieties... 

It is important to point out here that there are different approaches to the grafting of antioxidants on polymers, each with its set of advantages and disadvantages. However, the behavior of grafted reactive antioxidants is similar to that... 

It has been observed that complete immobilisation of the stabiliser through a graft leads to deactivation. However, proper selection of the ratio of phenolic to graftable groups leads to a polymer-bound product which retains sufficient mobility to provide a high level of antioxidant activity. An n/m ratio of 5-10 provides an optimal balance of graftability and antioxidant activity [144]. 

Kim el al. [582] have described maleimide-based antioxidants melt grafted onto low-MW PE. IR spectroscopic methods and titration were used for the quantitative determination of the extent of grafting of the monomeric antioxidant. Smedberg el al. [583] have characterised polymer-bound stabilisers by FTIR and NMR. The binding of antioxidants and photostabilisers to polyurethanes was verified by tJV/VIS spectroscopy [584]. 

Non-polymerisable monofunctional antioxidants were subsequently used to avoid the problem of homopolymerisation of the antioxidant. For example, melt grafting of the two maleated antioxidants, BPM and APM, on PP was shown to lead to high grafting efficiencies (up to 75% in the former and >90% in the latter) which were attributed to the non-polymerisable nature of the maleate (maleimide) functions [57, 59, 60]. The performance of these antioxidants, especially under extractive organic solvent conditions, was also shown to far exceed that of conventional antioxidants with similar antioxidant functions. Table 2, for example, shows the advantages of the grafted... 

The use of reactive antioxidants containing two polymerisable polymer-reactive functions in the same antioxidant molecule is outlined here. Careful choice of the processing parameters, the type, and the amount of free radical initiator can lead to very high levels of antioxidant grafting [53, 57]. For example, melt grafting of concentrates (e.g. 5-20 wt%) of the di-acrylate hin-... 

Increase in TAC is not always a good prognostic it may simply indicate an initial response to oxidative stress, as with concentrations of individual antioxidants and activities of antioxidant enzymes, or when it is due to disturbances in uric acid metabolism. Because uric acid is the main determinant of TAC of blood plasma, TAC increases in situations when the concentration of urate is increased, for example, in metabolic disorders and kidney failure. TAC is increased in urine from renal transplant recipients with delayed graft function (SI6). Ischemia of small intestine leads to an increase in TAC of rat blood serum, which is maximal (almost twofold) immediately after termination of 45-min ischemia (S22). TAC of blood plasma of rats poisoned with a high dose of carbon tetrachloride (1200 mg/kg, intraperitoneal injection, measurement 16 hr after injection) was significantly (over twofold) increased (Kl). These apparently paradoxical effects can be explained, however, by release of antioxidants from cells undergoing necrosis. Increase in TAC after intensive physical exercise also may be a marker of tissue... 

Reactions of Reactive Antioxidants with Polymers by Normal Chemical Procedures. Grafting of vinyl antioxidants e.g., VI, into rubbers has been used to produce modified rubber latices (26). Even simple... 

The same process can be used to graft vinyl antioxidants to polymer chains during processing of elastomer or to initiate the formation of polymer adducts with thiol antioxidants (21, 22, 24). 

U.V. Stabilizers.—Many of the papers discussed in preceding sections contain discussion of the nature and mechanism of u.v. stabilizers. A brief survey of antioxidants and stabilizers used in the plastics industry has appeared,28 and some new photostabilizers, including a polymeric u.v. absorber and a surface-grafted antioxidant, have been proposed.280 The mechanism of nickel chelate stabilizers has been further discussed,281 and the diffusion of and loss of light stabilizers in poly(olefins) described.282 As part of an attempt to understand the transformations of stabilizers during the ageing of polymers, the photooxidation of 2,6-di-t-butyl-4-methylphenol sensitized by Methylene Blue has been studied.283 U.v. light protection by sunscreens, with mechanisms of interest to the polymer field, has been described.284... 

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