Action of Organic Peroxides

Peroxides are vulcanizing agents for elastomers that contain no sites for attack by other types of vulcanizing agents. They are useful for ethylene- 

Elastomers derived from isoprene and butadiene are readily crosslinked by peroxides but many of the vulcanizate properties are inferior to those of accelerated-sulfur vulcanizates. However, peroxide vulcanizates of these diene rubbers may be desirable in applications where improved thermal ageing and compression set resistance are required. 

The initiation step in peroxide-induced vulcanization is the decomposition of the peroxide to give free radicals, thus 

For isoprene rubber, the abstraction route predominates over radical addition. Two polymeric free radicals then unite to give a crosslink. 

Crosslinks could also form by a chain reaction that involves the addition of polymeric free radicals to double bonds [82,88]. 

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Saturated hydrocarbon polymers are also crosslinked by the action of organic peroxides, though branching reduces the efficiency. Polyethylene is crosslinked by dicumyl peroxide at an efficiency of about 1.0, saturated EPR gives an efficiency of about 0.4, while butyl rubber cannot be cured at all. For polyethylene, the reaction scheme is similar to that of the unsaturated elastomers. 

Action of Aliphatic Amines on Slow Oxidation of Acetaldehyde and Ethyl Ether, and on Decomposition of Organic Peroxides in the Gas Phase... 

High pressure is also a factor causing mechanochemical transformations in a polymer. Combined pressure and shear effect turned out to be most efficient (see, for example, reviews of this matter in 87-90). Cros polyethylene containing up to 97 % of gel fraction has been obtained under the action of super-high pressure of the order of 109 Pa in the presence of organic peroxides 87). 

This reaction was studied for many steroid peroxides232-236 and for acene peroxides.238, 237 However, the action of organic bases such as pyridine or triethylamine on 174 led to a diepoxide (190).212... 

Ube proposes a totally different process from the above, starting with cydohexanone. In the first step, cyclohexanone is converted to l.r-peroxydicydohcxylamine by the action of hydrogen peroxide and ammonia, in the presence of the ammonium salt of an organic acid and a peroxide stabilizer (zinc and nickel salt of ethylene diamine tetracetic... 

A large number of organic peroxides and hydroperoxides are known. Peroxo carboxylic acids, e.g., peracetic acid, CH3CO OOH, can be obtained by action of H202 on acid anhydrides. Peracetic acid is commercially made as 10-55% aqueous solutions containing some acetic acid by interaction of 50% H202 and acetic acid, with H2S04 as catalyst at 45-60° the dilute acid is distilled under reduced pressure it is also made by air oxidation of acetaldehyde. The peroxo acids are useful oxidants and sources of free radicals, c.g., by treatment with Fc2 l"(aq). Benzoyl peroxide and cumyl hydroperoxide are moderately stable and widely used as polymerization initiators and for other purposes where free-radical initiation is required. 

From a competitive standpoint, there will be continued efforts at consolidation, through joint ventures, alHances, and acquisitions as the majors look to the growing markets in Asia/Pacific, outside of Japan, and the developing countries. The remaining independent and regional producers of organic peroxides are largely located in coimtries such as Korea, Taiwan, China, and India, and this is where the action will be. 

One of the most important types of addition polymerization is free radical polymerization. This process is initiated by the action of free radicals (electrically neutral species with an unshared electron). Free radicals for the initiation of addition polymerization are usually generated by the thermal decomposition of organic peroxides or azo compounds. The polymerization of unsaturated polyesters with a peroxide catalyst is an example of a free radical polymerization process. 

Effective use of microwave heating in the oxidation of alkenes and alcohols under the action of hydrogen peroxide was described in [177]. The catalyst was MCM l-type mesoporous titanium silicate modified by organic compounds. It was recycled several times without activity loss. 

An amount of enzyme preparation equivalent to 900 mg of wet cells was made up to 25 ml with the above potassium phosphate buffer solution. 150 mg (1.15 mmol) of 5-fluorouracil and 1.0 gram of thymidine (4.12 mmol) were dissolved in 15 ml of the above potassium phosphate buffer solution. The mixture was incubated at 37°C for 18 hours. After this time, enzyme action was stopped by the addition of four volumes of acetone and one volume of peroxide-free diethyl ether. The precipitated solids were removed by filtration, and the filtrate was evaporated under nitrogen at reduced pressure until substantially all volatile organic solvent had been removed. About 20 ml of aqueous solution, essentially free of organic solvent, remained. This solution was diluted to 100 ml with distilled water. 

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