Amine type antioxidants

Antidegradants. Amine-type antioxidants (qv) or antiozonants (qv) such as the phenylenediamines (ppd) can significantly decrease scorch time. This is particulady tme in metal oxide curing of polychloroprene or in cases where the ppd had suffered premature degradation prior to cure. 

A second mechanism in the. aging of CTPB propellants also exists and proceeds concurrently with the reactions proposed above. It consists of an attack at the reactive points of unsaturation in the backbone polymer, which causes additional crosslinking and hence an increase in propellant modulus, particularly at the surface. The exposed surface of CTPB propellants changes, as indicated by an increase in hardness. Heavy metal ions are particularly harmful, and it was found that an increase from 10 to 80 p.p.m. of iron caused a significant increase in surface hardening by catalytic attack on the double bonds. Antioxidants in general provide sufficient protection for polymer storage. In CTPB propellants the antioxidant selected to protect the double bond is very important. Amine-type antioxidants have provided better surface stability than phenolic compounds. 

In addition to the use of the above phenolic and amine type antioxidants, peroxide decomposers are used to harmlessly decompose the peroxides, which otherwise could decompose to give free radical propagating species, e.g., R-0 or H-0 . Examples of such peroxide decomposers, which act synergisticaUy with the phenolic or amine antioxidants, are dilauryl- 3, 3-thiodiproprionate and tris(p-nonylphenyl)phosphite. These and others are also listed in Table 4.10, with their chemical structures being listed in Table 4.11. We note that some of the peroxide decomposers are also accelerators for sulfur vulcanization. 

The oxidation is followed by reaction of the ferrous iron produced, with 2, 2 -dipyridyl to form a coloured complex, the intensity of which is proportional to the concentration of antioxidant present. The procedure has been applied to various phenolic and amine type antioxidants, namely, Succanox 18, BHT, lonol (2,6-di-tert-butyl-p-cresol), and Nonox Cl (N-N-di- 3-napthyl-p-phenylenediamine). A typical application of the procedure is given next, namely to the determination of down to 0.01% of Santonox R in PE. As the Metcalfe and Tomlinson [5] procedure determines Santonox R only in its reduced form, it does not include any Santonox R which may be present in the oxidised form in the original polymer, for example produced by atmospheric oxidation of the additive during polymer processing at elevated temperatures. Total reduced plus oxidised Santonox R can be determined by UV spectroscopic procedures. 

Amine-type antioxidants or antiozonants such as the p-phenylenediamines (PPD) can decrease scorch time. As the PPD degrades and liberates free amine, scorch time decreases and cure rate is increased. 

Additives used in final products accelerator (MTBS) antidegradants (amine type), antioxidant curing agents (ZnO, Zn stearate) fillers (carbon black and mineral fillers, such as silica, clays, talc, whiting), peroxide (e.g. dicumyl) release agent (metal stearates), retarder (MgO) plasticizers (petroleum based oils), sulfur tackifying resins (phenolic, phenol-formaldehyde, phenol-acetylene, hydrocarbon resins UV stabilizer (carbon black) ... 

Aromatic amine-type antioxidants do not usually affect mechanical properties of polymers processed up to 250°C. They are used for dark-colored materials intended only for technical applications. Their efficiency is increased by the presence of OH groups [1]. The most commonly used are secondary amines... 

Table 10.3. Amine-type antioxidants recommended for polyolefins...

Sulfur-containing antioxidant Ip with amine-type antioxidant and mixtures (min) ... 

Amine type antioxidants are summarized in Table 4.2 and some are shown in Figure 4.1. Examples of phenol t5rpe antioxidants are summarized in Table 4.3 and some are shown in Figure 4.2. Examples of anti-rust additives are summarized in Table 4.4. Some of these compounds are shown in Figure 4.3. 

In the EPR loaded with amine type antioxidants, free radicals produced by ionizing radiation on polymer interact with antioxidant with R-NO stable radical formation [55]. The oxidation products increase with decreasing dose rates due to the increased time for oxygen diffusion. 

The procedure has been applied to various phenolic and amine type antioxidants, viz. Succanox 18, butylated hydroxy toluene, lonol (2,6-di-tert-butyl-p-cresol) and Nonox Cl (N-N-di-2-napthyl-p-phenyIenediamine)... 

Antioxidants. The presence of a good antioxidant in Neoprene compounds is essential for adequate protection against oxidation. Hindered w-phenols, such as Wingstay L or Antioxidant 2246, are usually used where minimum discoloration and/or minimum staining is desired. Where discoloration is unimportant, amine type antioxidants are used. 

Gas chromatography has been used for the analysis of phenolic and amine type antioxidants. Antioxidants which have high boiling points cannot be directly by GC but they can be analysed as derivatives such as acetates, trifluoroacetates, trimethyl silyl-ethers, methyl ethers, etc. Trimethyl silane based antioxidants, for example, give good separations on standard silicone based columns (a. 10). 

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