Polymer stabilization antioxidants

Phosphites. Tertiary phosphites are also commonly used and are particularly effective ia most mixed metal stabilizers at a use level of 0.25—1.0 phr. They can take part ia a number of different reactions duting PVC processing they can react with HCl, displace activated chlorine atoms on the polymer, provide antioxidant functionaHty, and coordinate with the metals to alter the Lewis acidity of the chloride salts. Typical examples of phosphites are triphenyl phosphite [101 -02-0], diphenyl decyl phosphite [3287-06-7], tridecyl phosphite [2929-86-4], and polyphosphites made by reaction of PCl with polyols and capping alcohols. The phosphites are often included in commercial stabilizer packages. 

Additioaal uses for higher olefias iaclude the productioa of epoxides for subsequeat coaversioa iato surface-active ageats, alkylatioa of benzene to produce drag-flow reducers, alkylation of phenol to produce antioxidants, oligomeriza tion to produce synthetic waxes (qv), and the production of linear mercaptans for use in agricultural chemicals and polymer stabilizers. Aluminum alkyls can be produced from a-olefias either by direct hydroalumination or by transalkylation. In addition, a number of heavy olefin streams and olefin or paraffin streams have been sulfated or sulfonated and used in the leather (qv) iadustry. 

Many antioxidants ia these classes are volatile to some extent at elevated temperatures and almost all antioxidants are readily extracted from their vulcanizates by the proper solvent. These disadvantages have become more pronounced as performance requirements for mbber products have been iacreased. Higher operating temperatures and the need for improved oxidation resistance under conditions of repeated extraction have accelerated the search for new techniques for polymer stabilization. Carpet backiag, seals, gaskets, and hose are some examples where high temperatures and/or solvent extraction can combine to deplete a mbber product of its antioxidant and thus lead to its oxidative deterioration faster (38,40). 

These stabilizers function as light-stable antioxidants to protect polymers. Their antioxidant activity is explained by the foUowiag sequence (16) ... 

EB irradiation of polymeric materials leads to superior properties than the 7-ray-induced modification due to the latter having lower achievable dose rate than the former. Because of the lower dose rate, oxygen has an opportunity to diffuse into the polymer and react with the free radicals generated thus causing the greater amount of chain scissions. EB radiation is so rapid that there is insufficient time for any significant amount of oxygen to diffuse into the polymer. Stabilizers (antirads) reduce the dose-rate effect [74]. Their effectiveness depends on the abUity to survive irradiation and then to act as an antioxidant in the absence of radiation. 

Nitroxyl radicals are formed as intermediates in reactions of polymer stabilization by steri-cally hindered amines as light stabilizers (HALS) [30,34,39,59]. The very important peculiarity of nitroxyl radicals as antioxidants of polymer degradation is their ability to participate in cyclic mechanisms of chain termination. This mechanism involves alternation of reactions involving alkyl and peroxyl radicals with regeneration of nitroxyl radical [60 64],... 

Polymer stabilization is another area in which the peroxide-decomposing and chain-breaking antioxidant properties of diorganotellurides has found utUity. Alone or in combination with phenol and phosphate antioxidants, electron-rich dialkylamino-substirnted diaryltellurides and alkylaryltellurides provided greatly enhanced polymer stability for a thermoplastic elastomer and for polypropylene. The effects were unique to the tellurides, with selenides not providing similar protective effects. ... 

A variety of methods for evaluating antioxidants in polypropylene has been developed during the past several years. Polymer producers, end-use manufacturers, additive suppliers, academicians, and others have developed widely disparate test methods, all of which presumably yield the same results—i.e., the test methods rate the antioxidants and antioxidant systems in the same relative order of effectiveness. Many of these test methods are useful tools in distinguishing unstabilized polymer, moderately stabilized polymer, and highly stabilized polymer systems. Today, all of the polypropylene producers offer highly stabilized polymers. Effective antioxidants are available from several additive suppliers. How does one select the best antioxidant or polymer formulation for a particular end use This paper compares the results obtained by various test methods used to evaluate the two basic types of oxidative stability, processing stability and end-use or environmental stability. The correlation or lack... 

Plastics have to be stabilized to withstand chemical and physical stresses during different phases of their lifetime. Stabilizers protecting plastics against particular degradation processes were developed and commercialized by various companies. According to their principal activity mechanisms, polymer stabilizers are conventionally classified as antioxidants, photoantioxidants, photostabilizers, heat stabilizers and... 

Shelton J R (1981) Organic sulfur compounds as preventive antioxidants. In Developments in polymer stabilization-4, Scott G (Ed), Applied Science Publishers London, pp 23-70. 

The potentially beneficial properties of antioxidants have been a common subject in the popular press. Such compounds have the ability to eliminate toxic free radical species in living systems. Antioxidants are claimed to have cytoprotective properties in the inhibition of cancer, heart disease, and various skin disorders, and are often simply labeled as antiaging. There is a host of benzofuran examples in the recent literature that find application in all of these areas as potential pharmaceuticals, cosmetics, and polymer stabilizers. 

The Arrhenius plot is valid for the temperature dependence of the diffusion coefficient D in a particular combination polymer/stabilizer. The value of D is independent of stabilizer concentration and was mostly determined by quantification of data dealing with the transfer of a stabilizer from a doped into a virgin polymer. The values of D of antioxidants in PP decrease approximately with increasing molecular weight of AO, with branching of substituents, increasing difference between the polarity of the polymer and that of stabilizer. A generalization is, however, very difficult [27, 30]. 

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... 

There are many publications showing the applications of SFE to the determination of polymer additives. Antioxidants such as Irganox 2246, BHT and others, as well as UV stabilizers such as Tinuvin P, have been effectively extracted with supercritical CO2. Extraction conditions varied from 15 to 25 MPa at 60°C and with a total time of 30 min [1], If microwaves are applied to extract these compounds, a mixture of sol-... 

Cobalt complexes find various applications as additives for polymers. Thus cobalt phthalocyanine acts as a smoke retardant for styrene polymers, and the same effect in poly(vinyl chloride) is achieved with Co(acac)2, Co(acac)3, C02O3 and C0CO3. Co(acac)2 in presence of triphenyl phosphite or tri(4-methyl-6-f-butylphenyl) phosphite has been found to aa as an antioxidant for polyenes. Both cobalt acetate and cobalt naphthenate stabilize polyesters against degradation, and the cobalt complex of the benzoic acid derivative (12) (see Section 66.4) acts as an antioxidant for butadiene polymers. Stabilization of poly(vinyl chloride)-polybutadiene rubber blends against UV light is provided by cobalt dicyclohexyldithiophosphinate (19). Here again, the precise structure does not appear to be known. 

There are many examples in the literature on applications of 1,4-hydroquinones as polymer stabilizers and as antioxidants. The natural ubiquinols are 2,3-dimethoxy dialkyl derivatives of these hydroquinones and these natural compounds are now known to be of great importance in biological systems. We select a few examples of 1,4-hydroquinones as antioxidants to illustrate the effect of structure (e.g. substituents) on their reactivity, but especially to emphasize the role that hydrogen bonding plays in the reactivity of catechols, 1,4-hydroquinones and methoxy derivatives. 

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