Hydroperoxide decomposers, polymeric

The alkenyl hydroperoxides and polymeric dialkyl peroxides are fairly stable at ambient temperature but decompose appreciably at the reaction temperatures studied. Thermal stabilities of the alkenyl hydroperoxides and dialkyl peroxides in the olefin solution were determined by heating the solution at 110°C. under nitrogen. The peroxide numbers were plotted vs. time to estimate the half-lives in solution. The thermal decomposition half-lives of these alkenyl hydroperoxides are compared with values from the literature for acyclic and cyclic hydroperoxides in Table IV. Secondary acyclic alkenyl hydroperoxides appear to be less... 

It is generally agreed that alkenyl hydroperoxides are primary products in the liquid-phase oxidation of olefins. Kamneva and Panfilova (8) believe the dimeric and trimeric dialkyl peroxides they obtained from the oxidation of cyclohexene at 35° to 40° to be secondary products resulting from cyclohexene hydroperoxide. But Van Sickle and co-workers (20) report that, The abstraction/addition ratio is nearly independent of temperature in oxidation of isobutylene and cycloheptene and of solvent changes in oxidations of cyclopentene, tetramethylethylene, and cyclooctene. They interpret these results to support a branching mechanism which gives rise to alkenyl hydroperoxide and polymeric dialkyl peroxide, both as primary oxidation products. This interpretation has been well accepted (7, 13). Brill s (4) and our results show that acyclic alkenyl hydroperoxides decompose extensively at temperatures above 100°C. to complicate the reaction kinetics and mechanistic interpretations. A simplified reaction scheme is outlined below. 

Different types of antioxidants are used for the stabilization of polymers H-donors, radical scavengers and hydroperoxide decomposers. They interfere in different ways during the auto-oxidation cycle of polymeric materials (Scheme 2). 

R + OOH) is very slow. The hydroperoxide decomposes thermally into an RO radical and an HO radical, both of which initiate the polymerization of vinyl monomers. The HO radical causes unwanted homopolymerization as well as the desired graft polymers. These homopolymers are difficult to separate from the graft polymer mixture, and thus it is impossible to determine the graft yield with any certainty. In addition, homopolymers and graft polymers are generally incompatible over wide areas of the graft polymer composition, causing a deterioration in the mechanical properties. The hydroperoxide radical can be decomposed chemically, however, when the OH radical is not formed, and only the RO radical is left to initiate polymerization ... 

Hydroperoxides are soluble in both the aqueous and monomer-polymer phases and thus distribute themselves between the two phases. Thus, in principle, the hydroperoxides could decompose in either phase to form a hydroxyl radical and another oxygenated radical according to the particular hydroperoxide used. It has been postulated, however, that, in the emulsion polymerization of styrene, cumene hydroperoxide decomposes at the interface between the monomer polymer and aqueous phase, with the hydroxyl radical going into the aqueous phase and the nonpolar oxygenated radical remaining in the monomer-polymer phase (20). This interfacial decomposition would explain the increased rate of decomposition in emulsion polymerization as compared with bulk or solution polymerization under the same conditions. In this case, too, the distribution of hydroperoxide between the two phases may be altered by ingredients dissolved in both phases. 

Sulphur dioxide may decompose polymeric hydroperoxide groups (POOH) to polymeric peroxides (POOP) and/or polymeric esters of sulphuric acid (POSO2OH) ... 

Treatment of 2-methylthiirane with t-butyl hydroperoxide at 150 °C in a sealed vessel gave very low yields of allyl disulfide, 2-propenethiol and thioacetone. The allyl derivatives may be derived from abstraction of a hydrogen atom from the methyl group followed by ring opening to the allylthio radical. Percarbonate derivatives of 2-hydroxymethylthiirane decompose via a free radical pathway to tar. Acrylate esters of 2-hydroxymethylthiirane undergo free radical polymerization through the double bond. 

One of the earliest examples of this methodology involves the reaction of a polymeric anion (formed by living anionic polymerization) with molecular oxygen to form a polymeric hydroperoxide which can be decomposed either thermally or, preferably, in a redox reaction to initiate block polymer formation with a second monomer (Scheme 7.25). However, the usual complications associated with initiation by hydroperoxides apply (Section 3.3.2.5). 

It is well known that phosphites or sulfides added to stabilizers of polymeric materials considerably enhance the stabilizing effects. Destruction of polymers is caused by the action of peroxides resulting from oxidation at the defects of polymeric chains. The additives decompose hydroperoxides according to the following equations ... 

Peroxy esters 67 were prepared in situ by the reaction of phosphonochloridate and terf-butyl hydroperoxide in diethyl ether. The peroxy ester 67 (R = Ph) is stable for several days at 5 °C in diethyl ether. Most peroxyphosphates 67 with an RO group other than ferf-butylperoxy are unstable even for short periods . This synthetic method was successfully applied for synthesis of ring peroxyphosphates 70 and 71 as colorless oils. They are very unstable and decompose at 25 °C to yield polymeric products and volatile side products . ... 

In the presence of approximately 1% cobalt naphthenate in benzene, only 4 hours at 100°C. were required to decompose the hydroperoxide almost completely. The yields of products from decompositions catalyzed by some commonly used cobalt and vanadium (1) compounds are given in Table I. Polymerization appears to be the major reaction. 

Beniska and Staudner (55) described a different method for the grafting of vinyl polymers on plasticized rubber. In a first stage they performed a degradation at 20-25° C in the presence of oxygen and hydroperoxide groups. The hydroperoxides are decomposed by heat (at 90, 100, and 120°C) with formation of macroradicals which initiate polymerization of monomers. It is claimed that with increasing time of plasticizing and temperature, the conversion of monomers increased. 

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