Nonstaining hindered phenols

Stabilizers. Antioxidants provide protection against UV light and thermal oxidative degradation. Hindered phenols are the most common nonstaining antioxidants. For SBR latices, two additional type of stabilizers must be used. 

Cterically hindered phenols are used widely today as effective non- discoloring, nonstaining antioxidants for hydrocarbon systems, particularly rubbers and plastics. These compounds may be grouped in two broad classifications—monocyclic phenols represented by a compound such as 2,6-di-fer -butyl-4-methylphenol (I) and polycyclic phenols such as 2,2 -methylenebis(4-methyl-6-terf-butylphenol) (II). (Throughout this chapter, X represents tert-butyl). 

There are two major classes of antioxidants and they are differentiated based on their mechanism of inhibition of polymer oxidation chain-terminating or primary antioxidants and hydroperoxide-decomposing secondary antioxidants [5]. Primary or free-radical scavenging antioxidants inhibit oxidation via very rapid chain-terminating reactions. The majority of primary antioxidants are hindered phenols or secondary aryl amines. Generally, hindered phenols are nonstaining, nondiscoloring, and are available in a wide... 

Nonstaining antioxidants This ciass of antioxidants is subdivided into four groups phosphites, hindered phenols, hindered bisphenols, and hydroquinones. Hindered bisphenols such as 4,4 -thiobis(6-r-butyl-m-cresol) are the most persistent of the four classes of material. Because of then-lower molecular weight, hindered phenols tend to be volatile. Phosphites tend to be used as synthetic rubber stabilizers, and hydroquinones such as 2,5-di-re t-amylhydroquinone are used in adhesives ... 

Hevastain 21 Nonstaining Antioxidant is a hindered phenolic compound which is produced by alkylating phenols with selected olefinic monomers. 

Primary antioxidants act by trapping radicals and preventing the initiation of oxidative chain reactions. Sterically hindered phenols are widely valued for their lower nonstaining properties. Secondary stabilizers (e.g., phosphite esters and special thioesters) decompose peroxides, which are responsible for autocatalytic effects. 

In accordance with general experience, nonstaining antioxidants from the class of stearically hindered phenols or bisphenols are less effective. 

Hindered phenolics, because of their nonstaining qualities, are the most preferred type of primary antioxidant for light colored applications such as footwear. This group can be further categorized into simple phenolics (1), bisphenolics (2), polyphenolics (3), and thiobisphenolics (4), as shown on the following page [17]. 

Antioxidants used in rubber compounds often are classified as staining or nonstaining depending on whether or not they develop color in use. In a carbon black-loaded tire tread, a staining material has no drawback. But in the white sidewalls, it is important to use additives that are colorless to start with and stay colorless as they protect against oxidation. Phenylenediamine derivatives are very effective antioxidants but discolor (stain) severely. Where light colors must be preserved, a sulfur-cross-linked, hindered phenol that does not discolor is preferable ... 

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