Polymerization alkyl peroxides

Cyclic enone, 12 185 Cyclic ethers, 10 567, 569 12 663 polymerization, 14 271 Cyclic fatigue, in ceramics, 5 633-634 Cyclic gas generators, 6 786-787, 789, 827 Cyclic halides, 19 56 Cyclic hexakis(thio-l,4-phenylene), melt polymerization of, 23 705 Cyclic hydrocarbons, 13 687 Cyclic hydroxyalkyl alkyl peroxide, 18 454 Cyclic ion exchange operation, 14 408-413 Cyclic ketones, 12 176, 177 14 590-592. See also Cyclic 1,2-diketones physical properties of, 14 591t hydroxyalkyl hydroperoxides from, 18 450... 

Rust (Ref la) patented the use of this other di-c-alkyl peroxides as polymerization catalysts diesel oil additives Refs 1) Beil-not found la) W.E. Vaughan F.F. Rust, USP 2403771(1946) CA 40, 5757(1946) 2) N.A. Milas D.M. Surgenor,... 

Organic peroxides acyl peroxides (benzoyl, acetyl, lauryl peroxides, etc), alkyl peroxides, hydroperoxides, etc. are used as polymerization initiators. Azocompounds (for example, redox systems, etc. are also widely used as initiators. In... 

Precaution Flamm. uel 21.3%, lei 5.5% may form explosive mixts. in air incompat. with oxidizers can react violently with hydrogen chloride alkyl boron/alkyl hyponitrite compds. initiate polymerization forms peroxides with pure oxygen heat-sensitive Hazardous Decomp. Prods. CO, CO2, hydrogen fluoride heated to decomp., emits toxic fluoride fumes emits toxic fumes underfire conditions... 

In radical polymerization (see Scheme 2), radicals are formed in a first stage determining the rate. Examples used industrially for radical sources, apart from electron radiation, are aroyl peroxides such as bis(2,4-dichlorobenzoyl) peroxide or bis(2,4-methylbenzoyl) peroxide and alkyl peroxides such as dicumyl peroxide or 2,5-dimethyl-2,5-di-/er/-butyl peroxyhexane. In the second stage, the actual crosslinking reaction, a radical addition based on the usual pattern for a radical chain reaction, takes place via the double bonds of the vinyl groups in the polymer. Radical polymerization is today used virtually exclusively for crosslinking solid silicones. 

Dl-te/t-butyl peroxide n. A member of the alkyl peroxide family, used as an initiator in vinyl chloride polymerization, polyester reactions, and as a crosslinking agent. A stable liquid used as a catalyst for... 

Suspension polymerization Diacetyl peroxide, peroxydicarbonates, alkyl peroxyesters and (1)... 

For initiation and molecular weight control in free radical polymerization of ethylene, a combination of several substances can be applied. Typically used free radical initiators belong to the classes of di-alkyl peroxides, peroxy alkyl esters, peroxy-carbonates, or di-acyl peroxides. The choice of the initiator mainly depends on its half lifetime at application temperature. To generate a more or less constant radical concentration level over a wide range of temperatures (e.g., 150-300 °C), a combination of different initiators is commonly applied. A typical mixture consists of a low and high temperature decomposing peroxide dissolved in hydrocarbons. 

Most frequently the polymerization process is initiated by free radicals obtained through the decomposition of hydroperoxides, alkyl peroxides, dialkyl peroxides, acyl peroxides, carboxylic ester peracids, salts of (tetraoxo)sulphuric acid, hydrogen peroxide, aliphatic azo compounds and bifunctional azobenzoin initiators. The rate of decomposition of different initiators into free radicals depends on their stmcture and on temperature. A measure of the efficiency of the initiator in the pol5mierization process is the half-decomposition period. 

Alkyl peroxides are extensively used for the suspension polymerization of styrenic monomers [90—93] and vinyl chloride [94,95]. 

Alkyl borane as the reductant in redox polymerization is well known. It has been used previously in conjunction with alkyl peroxide and peroxyester of carbonic acid. The mechanism of alkyl borane-peroxyester of carboxylic acid is similar to that previously described. Suspension polymerization or copolymerization of vinyl chloride by the redox system such as monotertiary butyl permaleate-EtsB or BU3B or iso-BusB has been reported in patent literature [198]. 

Because high temperatures are required to decompose diaLkyl peroxides at useful rates, P-scission of the resulting alkoxy radicals is more rapid and more extensive than for most other peroxide types. When methyl radicals are produced from alkoxy radicals, the diaLkyl peroxide precursors are very good initiators for cross-linking, grafting, and degradation reactions. When higher alkyl radicals such as ethyl radicals are produced, the diaLkyl peroxides are useful in vinyl monomer polymerizations. 

Dialkyl peroxides have the stmctural formula R—OO—R/ where R and R are the same or different primary, secondary, or tertiary alkyl, cycloalkyl, and aralkyl hydrocarbon or hetero-substituted hydrocarbon radicals. Organomineral peroxides have the formulas R Q(OOR) and R QOOQR, where at least one of the peroxygens is bonded directly to the organo-substituted metal or metalloid, Q. Dialkyl peroxides include cyclic and bicycflc peroxides where the R and R groups are linked, eg, endoperoxides and derivatives of 1,2-dioxane. Also included are polymeric peroxides, which usually are called poly(alkylene peroxides) or alkylene—oxygen copolymers, and poly(organomineral peroxides) (44), where Q = As or Sb. 

R = alkyl, R = H) can be condensed, using acid, dehydrating agents (eg, phosphoms pentoxide), or vacuum to form polymeric peroxides (3). Most such polymeric peroxides decompose explosively. 

As has already been indicated, a thorough discussion of the mechanism of metal, metal alkyl-, oxygen- or peroxide-induced polymerizations is beyond the scope of this article. Chiefly for purposes of comparison, it seems worthwhile to present a brief outline of the free radical type of mechanism which best explains these reactions and which probably is valid also for the photochemical and thermal polymerizations, particularly in the lower temperature range. 

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