Metal Deactivators, Complexing Agents

Metal deactivators are used to form a complex with catalytically active metal compounds so that the complex has no or only insigniflcant catalytic activity. Of special importance are the chelating agents, because their metal complexes exhibit particularly high stability [531]. 

A common feature of chelating agents is their polyfunctionality, which is due to the presence of several ligand atoms alone or together with ionizable groups, such as hydroxyl or carboxyl groups [531]. 

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Metal Deactivation. Compounds capable of forming coordination complexes with metal ions are needed for this purpose. A chelating agent such as ethylene-diaminetetraacetic acid (EDTA) is a good example. 

Retard efficiently oxidation of polymers catalysed by metal impurities. Function by chelation. Effective metal deactivators are complexing agents which have the ability to co-ordinate the vacant orbitals of transition metal ions to their maximum co-ordination number and thus inhibit co-ordination of hydroperoxides to metal ions. Main use of stabilisation against metal-catalysed oxidation is in wire and cable applications where hydrocarbon materials are in contact with metallic compounds, e.g. copper. 

Synergy between primary and secondary anti-oxidants occurs and often a mixture is employed. Also included are metal complexing agents, e.g., EDTA (ethylenediaminetetraacetic acid), citric acid, the purpose of which is to deactivate extraneous metal ions that catalyse polymer oxidation. 

Complexing agent that deactivates or reduces the ability of metal ions to initiate or to catalyze the degradation of a polymer. 

Heat treatment is effective in deactivating the enzymes. Metal complexing agents may deactivate the enzyme by making the copper unavailable. 

The reactivity of metals in Reactions 11 and 12 can be influenced by the gegenion or by complexing agents (26-29). Generally, coordinated metals are less reactive. Thus, the cobaltic ethylenediaminetetraacetic acid complex is not reduced by hydroperoxides (30), although cobaltic carboxylates are reduced very rapidly (28, 31). Coordination of metallic catalysts has been generally employed for their deactivation (32). On the other hand, researchers (10) have reported that the coordination of tran-... 

Complexing agents N,N -bis(o-hydroxybenzal)oxalyl dihydrazide Metal deactivation (not apphcable)... 

The most important costabilizers in PVC formulations used mainly in combination with mixed metal salts are alkyl-aryl-phosphites to improve early color. Epoxy compounds, for example, epoxidized fatty esters such as epoxidized soy bean oil, react directly with HCl or substitute labile chlorine atoms, for example, in the presence of zinc ions. Furthermore, the epoxidized fatty esters act as plasticizers. Polyols such as pentaerythritol or dipentaerythritol and P-diketones act as complexing agents and deactivate the negative effect of the formed zinc chloride. Hydrotalcites... 

Complexing Agents Metal Deactivators. Transition metals (elements with more than one valence state) catalyze oxidation reactions by complex redox (reduction-activation) mechanisms,... 

Complexing agent Af,iV -bis(o-hydroxybenzyl) oxalyl dihydrazide Metal deactivation (Not applicable)... 

Deactivators. Metal deactivators combine with metal ions to limit the potential for chain propagation. Metal deactivators are commonly used in polyolefin inner coverings in wire and cable applications where the plastic comes in contact with the metal. In effect, the deactivator acts as a chelating agent to form a stable complex at the metal interface, thereby preventing catalytic activity. The most common deactivators contain an oxamide moiety that complexes with and deactivates the metal ions. Atypical product is Ciba s IRGANOX MD-1024. 

The presence of metal ions can act to increase the oxidation rate, even in the presence of antioxidants. Metal deactivators are often added to prevent this from taking place. Chelating agents are added to complex with the metal ion. 

Chelating agents can be used as metal deactivators. But prior to their use in a given plastic formulation, it is necessary to know the entire composition of the mixture. The activity of some metals bound in complexes might exceed that of simple systems and thus accelerate self-oxidation. For example, bis-salicyli-dene-ethylenediamine, when used with hydrocarbons, strongly accelerates their oxidation in the presence of iron and cobalt ions, but in the presence of copper, in concentration four times larger than that of the metal, it inhibits selfoxidation of hydrocarbons [59]. 

Metal deactivators act as complex forming agents. When the metal is complexed, it loses its ability to imdergo a redox reaction. An example of such a complex is shown in Figure 19.8. 

The photoelectrochemical kinetic scheme involves a photochemical reaction that is followed by an electrochemical reaction. The photochemical reaction is used to produce or deactivate the reducing agent. Catalytic metallic nuclei are formed in the subsequent electrochemical reaction. For example, the Fe reducing agent (Red) needed for reaction (8.24) is generated in the photochemical reduction of complexed Fe ions. This redox photolysis is the ligand-to-metal charge transfer with the overall reaction of oxidation of [ 204] ... 

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