Types of Organic Peroxides

Some representative examples of commercial sources of organic peroxides as initiators for the manufacture of LDPE are shown in Table 5.11. 

Peroxides are available according to the temperature necessary to form the free radicals and are classified accordingly. These include  

These temperature properties determine the polymerization initiation temperature and the length of time the free-radical initiation process is active. For example, low-temperature peroxides possess a relatively short free-radical half-life and offer a low-temperature initiation but also a lower peak temperature, while a high-temperature peroxide with a relatively long 

Peroxyesters CO, carboxylic acids, acetone, alkanes, tButyl alcohol 

Monop eroxycarb onates COj, alcohols, acetone, alkanes 

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Ferrous ion also promotes the decomposition of a variety of other compounds including various types of organic peroxides [Bamford, 1988],... 

Mixtures of organic peroxides may be classified as the same type of organic peroxide as that of the most dangerous component. However, as two stable components can form a thermally less stable mixture, the self-accelerating decomposition temperature (SADT) of the mixture shall be determined. 

At one time, benzoyl peroxide (BPO) was the favoured initiator for radical polymerizations in non-aqueous media. It is still widely used and it is also important as a component of redox initiating systems it is discussed in some detail in this section. BPO is an example of a diaroyl peroxide and there are many other types of organic peroxides used as initiators of polymerizations, giving end-groups of various types extensive lists are available, e.g. the catalogues and pamphlets issued by AKZO and by the Nippon Oil and Fats Company. 

GC has also been used to determine certain types of organic peroxides. Bukata and co-workers [91] for example, described procedures involving chromatography of heptane solutions of peroxide (Table 4.10) on phthalate/diatomaceous earth or silicone/ diatomaceous earth columns and using helium as the carrier gas. No doubt, this type of procedure could be easily adapted to the examination of solvent extracts of polymers. 

The Arkema Group [15] details the type of functional groups present in their Luperox products and provides information into the decomposition products formed by various peroxide types. These decomposition products may be present in the finished polyethylene for commercial applications. This information is necessary to determine if certain decomposition products may interfere with resin color, stability or odor properties. Table 5.12 lists several types of organic peroxides available today and some of the decomposition reaction products. 

The reaction of acetone with hydrogen peroxide gives various types of organic peroxides of acetone. The simple linear hydroperoxides and hydroxyperoxides form at first and then condense to the linear dimer and trimer analogs. The linear dihydroperoxide 2,2-dihydroperoxypropane (1) and its dimer bis(2-hydroperox-ypropane)peroxide (II) form as a main product in an acetone and hydrogen peroxide mixture, in the absence of an acidic catalyst [1]. 

Table 18. Estimated 1993 Consumption of Organic Peroxides by Principal Types, t...

Organic materials, Sulfuric acid Analytical Methods Committee, Analyst, 1976, 101, 62-66 Advantages and potential hazards in the use of mixtures of 50% hydrogen peroxide solution and cone, sulfuric acid to destroy various types of organic materials prior to analysis are discussed in detail. The method is appreciably safer than those using perchloric and/or nitric acids, but the use of an adequate proportion of sulfuric acid with a minimum of peroxide is necessary to avoid the risk of explosive decomposition. The method is not suitable for use in pressure-digestion vessels (PTFE lined steel bombs), in which an explosion occurred at 80° C. 

Work on the deflagration hazards of organic peroxides has been done using a revised Time-Pressure test, to determine the characteristics of ignition sensitivity and violence of deflagration. Some correlation is evident between these characteristics and the AO content within each structurally based peroxide type. Also, for the same AO content, the nature of the characteristics appears to decrease hi the order diacyl peroxides, peroxyesters, dialkyl peroxides, alkylhydroperoxides [18],... 

Thus the induced H202 dissociation and auto-induced decomposition of organic peroxides (initiators) are accompanied by a change of, at least, one of three reaction parameters (a) stoichiometric equation of the reaction (decomposition products remain typical of the current substance) (b) reaction type and (c) reaction pathway (mechanism) with decomposition overall stoichiometric equation preserved. 

The example demonstrating this type of conjugation is that of organic peroxide and hydroperoxide decomposition induced by radicals. These processes were discussed in Chapter 1. 

Radziszewski, Ber., 1887, 20, 2934 1885, 18, 355 Dubsky, J. prakt. Chem., 1916, [2], 93,137. Tor the hydrolytic activity of hydrogen peroxide towards other types of organic compounds, such as albumin, gelatin, and starch, see Neuberg and Muira, Btochem. Zeitsck, 1911, 36, 37. 

This is called an initiation step. It may happen spontaneously or may be induced by heat or light (see the discussion on p. 279), depending on the type of bond. Peroxides, including hydrogen peroxide, dialkyl, diacyl, and alkyl acyl peroxides, and peroxyacids are the most common source of free radicals induced spontaneously or by heat, but other organic compounds with low-energy bonds, such as azo compounds, are also used. Molecules that are cleaved by light are most often chlorine, bromine, and various ketones (see Chapter 7). Radicals can also be formed... 

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