Ketone peroxides, organic peroxide initiators

More frequently either methyl ethyl ketone peroxide or cyclohexanone peroxide is used for room temperature curing in conjunction with a cobalt compound such as a naphthenate, octoate or other organic solvent-soluble soap. The peroxides (strictly speaking polymerisation initiators) are referred to as catalysts and the cobalt compound as an accelerator . Other curing systems have been devised but are seldom used. 

Safety. Since organic peroxides can be initiated by heat, mechanical shock, friction or contamination, an enormous problem in safety presents itself. Numerous examples of this problem have already been shown in this article. Additional examples include the foilowing methyl and ethyl hydroperoxides expld violently on heating or jarring, and their Ba salts also are extremely expl the alkylidene peroxides derived from low mw aldehydes and ketones are very sensitive and expld with considerable force polymeric peroxides of dimethyl ketene, -K>-0-C(CH3)2C(0)j-n, expld in the dry state by rubbing even at —80° peroxy acids, especially those of low mw, and diacetyl, dimethyl, dipropkmyl and methyl ethyl peroxides, when pure, must be handled only in small amts and... 

In a systematic ESR and CIDEP study of various alkoxy substituted phenols by photochemical reactions with ketones and with organic peroxides, we have shown (15) that molecular oxygen is not the active radical reactant in the oxidation. Rather, molecular oxygen is necessary to produce peroxy and alkoxy radicals, ROO and RO-which then add onto the phenyl ring to initiate the oxidation processes. The precursor radical R - can be derived from as many ways as one can imagine, both via photo and thermal reactions. 

The heading production of chemical products includes the conversion of allyl alcohol to glycerine with hydrogen peroxide, the production of epoxy-compounds such as epoxy soya oil (plasticizer for PVC) and organic peroxides (e.g. methyl-ethyl-ketone-peroxide, dibenzoylperoxide), which are used as free radical initiators in polymerization processes. The production of amine oxides such as lauryl-dimethyl-amine-oxide with hydrogen peroxide (used as a rinsing agent in dishwashers) is also included. 

The study of the photochemistry of inorganic and organic compounds gives valuable information on their photolysis during which free radicals are formed (10-12). Extensive studies have especially been made in the field of photochemistry of aliphatic ketones,ethers and peroxides (12-14) All these compounds have been found to be good photoinitiators which initiate degradation and crosslinking of polymers. The mechanism of these reactions seems to be simples... 

Many peroxides affect pol mierization, but those used are available in quantity and the choice is based both on economics and performance. It has been shown that the activity of the organic peroxides in any polymerization is related to their decomposition rates at various temperatures. If elevated cure temperatures, 200- 250°F (93-121°C), are used, benzoyl peroxide is preferred. The amount required is about 1.0 per cent. It is preferred because a long catalyzed tank life results at room temperature. If lower temperatures in the 120 180 F (49-82°C) range are employed, hydroperoxides are more effective. Methyl ethyl ketone peroxide and cumene and ter- tiary butyl hydroperoxide all find application. Lauroyl peroxide, cyclohexanone peroxide, and <-butyl perbenzoate are used in limited amounts. Mixtures of two peroxides are often used, one to initiate the reaction and a second to promote the polymerization once it is started. 

In general, polyester resins are synthesized by the reaction between carboxylic acids and alcohols, with three or more reactive groups. Recently, unsaturated polyesters were incorporated in various ways to produce terminal, pendant, and internal double bonds [57-59]. In the case of unsaturated polyesters, maleic anhydride is most commonly used to produce internal unsaturation. The double bond present on unsaturated polyester reacts with a vinyl monomer, mainly styrene, resulting in a 3D crosslinked structure. This structure acts as a thermoset. The crosslinking is initiated through an exothermic reaction involving an organic peroxide, such as methyl ethyl ketone peroxide or benzoyl peroxide (Fig. 3.18). 

The solution, having been made stable in the can, must now be made reactive on the coated surface. In the case of unsaturated polyesters, this is done by introducing factor (3) in relatively large quantities. This is an initiator (p. 65). In thermally cured, as opposed to radiation cured finishes, the substance chosen to decompose and produce free radicals is an organic peroxide. A solution of this material in unreactive solvent forms the activator pack of the two-pack finish. The amount of solvent is chosen to give a suitable finish/activator mixing ratio, e.g. 10 1 by volume. The ketone, diacyl and hydroperoxide types are most frequently used. 

The family of dialkyl peroxides includes dicumyl peroxide, which accounts for one-third of the volume of dialkyls world-wide and is the workhorse of this family of peroxides. Dicumyl peroxide is commonly used as a catalyst in polyester resin systans and for cross-linking polyethylene. Benzoyl peroxide is the most common of the diacyl peroxides. It is also used as a catalyst for curing polyester resins. Hydroperoxides are generally used as a raw material to produce other organic peroxides. The most common peroxides in this family include cumene hydroperoxide and t-butyl hydroperoxide. Ketone peroxides are mixtures of peroxides and hydroperoxides that are commonly used for room-temperature curing of polyester resins. Methyl ethyl ketone peroxide (MEKP) is the major product in this family. Peroxydicarbonates are largely used to initiate polymerization of polyvinyl chloride (PVC). 

Most commercial synthetic polymers are produced by a chain-reaction polymerization process. Some of the many initiators used are various peroxides (e.g. benzoyl peroxide, di-tertiary-butyl peroxide, cyclohexanone peroxide and methyl ethyl ketone peroxide). There are more than 65 commercially available organic peroxides in over 100 formulations. 

To tailor the application properties of the polymer, different initiation systems and chain transfer agents (modifier) are used. Typical initiators are oxygen or organic peroxides. To control the molecular weight distribution of the polymer produced, polar modifiers (aldehydes, ketones or alcohols) or aliphatic hydrocarbons are fed into the monomer stream. 

Feng [344] has described the dibenzoyl peroxide-initiated polymerization of t-butyl vinyl ketone to an amorphous polymer in organic solvents, while several alkyl vinyl ketones have been polymerized in aqueous solutions to low-melting polymers using a potassium persulfate/sodium metabisulfite initiation [345]. Phenyl vinyl ketone was polymerized in an emulsion containing 7.5% soap and 0.2% potassium peroxodisulfate [346]. 

Organic peroxides act through the splitting of the —0—0— bond into free radicals, thereby initiating the polymerization or crosslinking of monomers or polymers. Their exceptionally broad line includes diacyl peroxides, dialkyl peroxides, hydroperoxides, ketone peroxides, peroxyketals, peroxydicarbonates, and peroxyesters. The last two are particularly important in PVC resin manufacture as initiators in the polymerization of vinyl chloride monomer. 

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