Antioxidants hindered phenols

A large number of hindered phenoHc antioxidants are based on the Michael addition of 2,6-di-/ f2 -butylphenol and methyl acrylate under basic catalysis to yield the hydrocinnamate which is a basic building block used in the production of octadecyl 3-(3,5-di-/ f2 butyl-4-hydroxyphenyl)propionate, [2082-79-3], tetrakis(methylene-3(3,5-di-/ f2 butyl-4-hydroxylphenyl)propionate)methane [6683-19-8], and many others (63,64). These hindered phenolic antioxidants are the most widely used primary stabilizers in the world and are used in polyolefins, synthetic and natural mbber, styrenics, vinyl polymers, and engineering resins. 2,6-Di-/ f2 -butylphenol is converted to a methylene isocyanate which is trimerized to a triazine derivative... 

CR adhesives contain 20 wt% solids content. Formulation 100 phr elastomer 4 phr MgO 5 phr ZnO 2 phr hindered phenolic antioxidant 500 phr solvents mixture [2]. 

Nonbound and polymer-bound hindered phenolic antioxidants... 

Figures 10 and 11 show the structure of the hindered phenolic antioxidant Irganox 1010 (Ciba) and its negative ion APCI mass spectra, respectively. Separation was achieved under the following LC conditions Column Aqua Cl 8 (Phenomenex) 3 pm, 150x2.00 mm, 15% carbon loading, proprietary end capping. Column Temp 50°C. Injection volume 5 pi.

One of the present authors (31) has developed a series of additives which combine the features of both free radical inhibitors and flame retardants of the tetrabromophthalimide or chlorendic imide type with hindered phenol antioxidant structures such as the following compounds ... 

Hindered phenol compounds usually possess alkyl groups on ortho and para sites. The alkyl groups are typically t-butyl or methyl in functionality. The lower cost of hindered phenol antioxidants makes them attractive for use in fuel applications. In gasoline, hindered phenols are typically used at treat rates of 5 to 50 ppm. The limitations placed on jet fuel additives often control the rate at which phenolic antioxidants can be used. 

Phenylenediamine (PDA) antioxidants can be used when hindered phenols do not perform or whenever their cost performance overcomes that of hindered phenol compounds. Although PDA compounds can often be as much as four times the cost of a hindered phenol antioxidant, the performance provided by PDAs can frequently exceed that of a hindered phenol compound. 

When cooled or contaminated, hindered phenolic antioxidants and some PDA antioxidants are known to precipitate from solution as concentrated compounds. At temperatures below 60°F (15.5°C), some antioxidants will begin to crystallize and drop from their solvent carrier as relatively pure materials. 

Several stabilizers are useful in minimizing oxidative degradation during thermoplastic processing or in the bulk solid. Phenothiazine, hindered phenolic antioxidants such as butylated hydroxytoluene, butylated hydroxyanisole, and secondary aromatic amines in concentrations of 0.01—0.5% based... 

IR and XANES monitoring of additive performance. A hindered phenol antioxidant and a zinc dialkyldithiophosphate are considered. Changes in hydroxy species (O-H) at 3650 cm1 during the oxidation of antioxidant (2,6-di-tert-butyl-4-methylphenol) showed decay with time (Coates and Setti, 1984, Spitz, 1980). 

Table 3 Major commercial hindered phenolic antioxidants 567...

The compounding ingredients for preparation of adhesion test specimens, magnesia (MgO), zinc oxide, Zalba Special (hindered phenol antioxidant from E. I. duPont de Nemours and Co.), and Bakelite-brand t-butylphenolic resin CK-1634 (Union Carbide Corp.) were used as... 

Compound II. This compound is also a hindered phenol antioxidant (Cyanox 1790, American Cyanamid). Compound II is insoluble in water but has a solubility of 4.6 g/100 mL of ethanol. A saturated solution of this compound in ethanol was prepared, and the fabric pieces were immersed in this solution for 30 min. The samples were then dried in the same manner described in the preceding section. The average add-on was 9%. 

Hindered phenol antioxidants are commonly used in polyols. 

Features of the free-radical initiation processes are similar for both the homopolymerization of functionalized monomers and copolymerization of the latter with conventional monomers. Common chemical initiators were applied. Azo-bis(isobutyro nitrile) was mostly used in bulk polymerization. No interference with phenolic hydroxy groups was observed in polymerization of 2-hydroxybenzo-phenoiKs, acetophenones, salicylates and of their derivatives [47]. The most rigorous eliinination of oxygen from the reaction mixture was necessary to achieve polymerization of monomeric hindered phenolic antioxidants or derivatives of 2-(2-hydroxyphenyl)benzotriazole [48]. An oxygen-free atmosphere is also an advantage for aromatic amines. A higher initiator level and/or increased temperature appear to be necessary to achieve normal polymerization rates with (D-functionalized monomers [46]. 

Antioxidants. Hindered phenol antioxidants such as 2,6-ditertiary butyl-4-methylphenol (BHT) controls the exotherm in the reaction between diol and diisocyanate. When acidic flame retardants are present in the formulation, amine antioxidants are preferred (Seymour, 1992). 

A hindered phenol commonly used as an antioxidant is 2,6-di-terf-butyl-4-meth-ylphenol (also known as butylated hydroxy toluene or "BHT"). Structures of BHT and other hindered phenol antioxidants are shown in Figure 8.3. Many of these complex structures have lengthy lUPAC names and are frequently called by trade names assigned by manufacturers, e.g., Irganox 1135 from Ciba (now BASF). 

Figure 8.3 Structures of hindered phenol antioxidants. (Reproduced with permission from J. Fink, A Concise Introduction to Additives for Thermoplastic Polymers, Wiley-Scrivener Publishing, Salem, MA, 2010).

High molecular weight hindered phenolic antioxidant with photo-and thermo-stability. Provides low volatility and resistance to extraction from polymer compounds. Suitable for PP, PE, polystyrene, ABS, PVC, nylon, and polyurethane. Also used as a radical scavenger providing stabilization for polyolefins. 

Metal deactivator that acts as a hindered phenolic antioxidant. Used in conjunction with phenolic antioxidants, phosphites/ phosphonites, thio-synergists and other co-additives. Most suited for PA PE, Rubbers and PP applications. 

Non-discoloring, metal deactivator and antioxidant, acts as a hindered phenolic antioxidant. Typical end use applications include wire and cable insulation, film and sheet manufacture as well as automotive parts. 

CAO-5 [Aqualon]. TM for the hindered phenolic antioxidant 2,2 -methylene-bis(4-methyl-... 

The use of antioxidants in human-contact applications, e.g., food-contact, medical, and pharmaceutical, present a challenge in terms of their safety and level of migration into the contact media, e.g., food and body fluids. The biological antioxidant vitamin E, which is a suitable candidate for such areas of application, is a fat-soluble, and sterically hindered phenol antioxidant with the most bioactive form of the vitamin being the a-tocopherol (Table 1, AO 10). 

Klemchuk, P.P. Horng, P.L. Transformation products of hindered phenolic antioxidants and color development in polyolefins. Polym. Deg. Stab. 1991, 34, 333-346. 

Xylenol on butylation with isobutylene produces 2,4-dimethyl-6-t-butyl phenol, a hindered phenol antioxidant. 

It was noted that the efficiency is increased in the presence of amines (Scott, 1993b), so the effectiveness in conjunction with aromatic amine free-radical (CB-D) stabilizers or the amine end groups of nylon would be expected. It is also noted that cuprous salts are often used as the iodide, and the effective alkyl-scavenging ability of iodo compounds has been demonstrated (Henman, 1979). Copper salts are also effective in the melt stabilization of polyesters, but in this case the effectiveness is improved by using a hindered phenol antioxidant. This performance is in contrast to the strong prodegradant effect of copper and other transition metals on the polyolefins as discussed later. 

Figure 1.42. Weight loss from polyacetal during processing due to liberation of formaldehyde and inhibition by an acid scavenger combined with a hindered phenol antioxidant. Adapted from Zweifel (1998).

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