Ketone peroxide initiators, decomposition rates

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. 

Acrylic esters and unsaturated polyesters are commercially cured with peroxides or peresters. The choice of per compound is determined on the basis of price, the achievable polymerization rate, and the side products formed. The polymerization rate is determined by the decomposition rate of the initiator, when mixed with the material to be cured, as well as on the free radical yield. In addition, attention should be paid to the fact that many per compounds decompose slowly during storage, thus reducing the polymerization activity per unit initiator mass. For this reason, crystalline per compounds are more stable because of the lower diffusion than amorphous or dissolved per compounds. Side products of initiator compounds can have an unfavorable effect on the long-term thermoset properties dibenzoyl peroxide, for example, forms acids dicumyl peroxide forms ketones. Acids can hydrolyze the ester bonds of polyester chains, causing scission, and ketones can... 

The oxidation of alkanes by r-butyl hydroperoxide (TBHP) has been catalysed by titanium alkoxides, producing the corresponding alcohols and ketones. A radical mechanism is proposed in which r-butoxyl radical formed from TBHP and titanium alkoxide initiates the reaction. The evolution of oxygen (from the decomposition of peroxide) and the abstraction of hydrogen from alkane to form alkyl radical occur competitively. A method for the determination of both the primary and secondary KIEs at a reactive centre based on starting-material reactivities allows the determination of the separate KIEs in reactions for which neither product analysis nor absolute rate measurements are applicable. It has been applied to the FeCls-catalysed oxidation of ethylbenzene with TBHP, which exhibits both a primary KIE and a substantial secondary KIE the findings are in accordance with previous mechanistic studies of this reaction. The oxidation of two l-arylazo-2-hydroxynaphthalene-6-sulfonate dyes by peroxy-acids and TBHP catalysed by iron(III) 5,10,15,20-tetra(2,6-dichloro-2-sulfonatophenyl)porphyrin [Fe(ni)P] is a two-step process. In single turnover reactions, dye and Fe(in)P compete for the initially formed OFe(IV)P+ in a fast reaction and OFe(IV)P is produced the peroxy acid dye stoichiometry is 1 1. This is followed by a slow phase with 2 1 peroxy acid dye stoichiometry [equivalent to a... 

There was no induction period in the solution polymerization of vinyl chloride [52] initiated by the benzoyl peroxide-dimethylaniline system in various solvents such as tetrahydrofuran, ethylene dichloride, dioxane, cyclohexanone, methylethyl ketone, and so forth. The initial rate of polymerization and the conversion was directly and inversely proportional to the temperature, respectively. The polymerization was restricted to only 20% conversion, probably due to the complete consumption of benzoyl peroxide. Without the monomer, the extent of decomposition on benzoyl peroxide reaches a constant value regardless of the temperature and amount of di-methylaniline. It was seen that the greater the amount of dimethylaniline, the faster the initial rate of polymerization and the lower the conversion. The degree of polymerization of vinyl chloride obtained by the redox system benzoyl peroxide-dimethylaniline was generally lower than the polymer obtained by the benzoyl peroxide system alone. The activation energy of the polymerization by the redox system was lower than that of the benzoyl peroxide alone initiated polymerization and found to be 12.5 kcal mol The initial rate of polymerization could be expressed as... 

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