Polymer-reactive antioxidant

Reactions of Polymer-Reactive Antioxidants. Three different modifications of this approach have been reported. 

Another polymer reactive antioxidant which can be combined with rubber during vulcanization involves the 1,3 addition reaction of nitrones to the double bond in rubbers, reaction 4 (11). 

Another example where antioxidant performance can be improved dramatically lies in the mechanochemlcally initiated addition of reactive antioxidants on rubbers (5.10) or unsaturated thermoplastics such as ABS (12). For example, using thiol antioxidants 2 and 3 as the reactive antioxidants, Kharasch-type addition of the thiol function to the polymer double bond takes place during melt processing to give bound antioxidant adduct (see Equation 1) the polymer becomes much more substantive under aggressive environments. 

Radiation chemistry in polymer research, 168-169 Reactive macroalkyl radicals, formation, 409 Reactive modifiers addition of reactive antioxidants on rubbers, 417 adhesion, 420,422 demanding applications, 414,416 improving additive performance during melt processing, 412 polymer bound antioxidant, 418-419/ Reduced poly(vinyl chloride),... 

A strategy that is based on the use of reactive antioxidants can also be explored to achieve stabilisation of polymers suitable for human-contact applications. Reactive antioxidants which become an integral part of the macro-molecular chain can result in non-migratory stabiliser systems that would be unaffected by extractive hostile contact media. 

In general, reactive antioxidants are compounds that contain one or more antioxidant functions (the antioxidant, AO, component) and one or more chemical functions capable of reacting either with monomers (same or different) or with polymers (the reactive, Rv, component). The AO function is... 

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-... 

Reactivity With Nitroso Compounds. Functionalization of diene based rubbers with aromatic nitroso compounds bearing aminic or phenolic moieties 174, like with iV,A-diethyl-4-nitrosoaniline, 4-nitrosodiphenylamine, 4-nitrosodiphenylhy-droxylamine or 4-nitrosophenol represents an effective way for the synthesis of polymer-bound antioxidants [233], The respective nitroso compound can be mixed with rubbers during compounding or with concentrated rubber latexes. The chemical attachement of stabilizing active moieties takes place during subsequent... 

Low molar mass antioxidants are known to suffer from physical loss and research in recent years has, therefore, focused on finding substantive alternatives. For example, reactive antioxidants, which can be chemically anchored on the polymer backbones to prevent physical loss during processing or in-service, have been explored as nonmigratory antioxidants. Clearly, there are many factors that need to be considered before choosing antioxidants in end-use applications. The success of an antioxidant package is critically dependent on the underlying chemical and physical factors that influence antioxidant performance in different substrates and environments. 

In general, reactive antioxidants are compounds that contain one or more antioxidant functions (the antioxidant, AO component) and one or more chemical functions that are capable of reacting either with monomers (same or different) or with polymers (the reactive, Rv, component). The AO function is based on any antioxidant moiety (see examples A-D in Scheme 7), whereas the reactive moiety can either be a polymerizable (e.g., Rv functions 1-4) or nonpoly-merizable (e.g., Rv functions 5-7) groups, and may or may not contain a spacer (an inert flexible and short chemical link connecting the antioxidant moiety to the reactive function). 

Reactive antioxidants may either be copolymerized with monomers during polymer synthesis or grafted on preformed polymers they are therefore linked to the polymer. Although the copolymerization route has been successfully exploited, " it has not received greater attention because of cost incurred in the synthesis and production of tailor-made speciality materials for low-volume specific applications. On the... 

Compared to conventional antioxidants, reactive antioxidants that are capable of becoming covalently bound to the polymer backbone are not readily lost from polymers during fabrication and in-service. There is a lot of evidence that demonstrates the performance (in terms of polymer protection) of immobilized antioxidants in practice, especially when polymer products are subjected to harsh environment, e.g., exposure to high temperatures, UV-light and leaching solvents. It is clear from this that high mobility of low molar mass antioxidants is not a necessary prerequisite to achieving stabilization and attachment of antioxidants to polymers can be industrially beneficial. 

Reactive antioxidants grafted on polymer melts behave in a similar way to low molar mass conventional antioxidants, but offer many additional advantages. The polymer-linked antioxidants do not suffer from the problem of compatibility, volatility, and migration, i.e., they do not suffer physical loss even under highly aggressive and extractive environments. Such antioxidant systems would be much more riskfree and environmentally friendly. The ability to produce highly grafted antioxidant concentrates (master batches), which can be used in conventional (the same or different) polymers, as normal additives would extend the use of reactive antioxidants to new areas of application. 

Al-Malaika, S. Reactive antioxidants for polymers. In Reactive Modifiers in Polymers Al-Malaika, S., Ed. Blackie Academic Professional London, 1997 266-302. 

It is concluded that the modification of rubbers after manufacture with chemically reactive antioxidants offers the most promising procedure for producing concentrates of polymer-bound antioxidants that can be used as conventional additives. 

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... 

Al-Malaika, S., Scott, G. and Wirjosentono, B. (1993) Mechanisms of antioxidant action Polymer-bound hindered amines by reactive processing, part III - Effect of reactive antioxidant structure. Polymer Degrad. Stab, 40, 233-238 Al-Malaika, S., Ibrahim, A.Q. and Al-Malaika, S. (1988) Mechanisms of antioxidant action Photoantioxidant activity of polymer-bound hindered amines I Bis maleate esters. Polymer Degrad. Stab., 22, 233-239 Al-Malaika, S. and Scott, G. (1995) US Patent 5382633. 

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... 

Reaction of reactive antioxidants with conventional polymers. 

One approach to overcoming the problem of antioxidant physical loss is to use reactive antioxidants which attach chemically to the polymer melt during processing (reactive processing). The grafted antioxidant... 

Secondary aromatic amines are very reactive antioxidants [91-94] and, as with the phenolic antioxidants, the primary radical can react with radicals, leading to various decomposition products. The main drawback of this type of antioxiiimt is that many of these decomposition products are colored. For this reason their application is mainly limited to carbon black-filled polymers. 

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