Vinyl chloride, from decomposition

Molybdenum trioxide is a condensed-phase flame retardant (26). Its decomposition products ate nonvolatile and tend to increase chat yields. Two parts of molybdic oxide added to flexible poly(vinyl chloride) that contains 30 parts of plasticizer have been shown to increase the chat yield from 9.9 to 23.5%. Ninety percent of the molybdenum was recovered from the chat after the sample was burned. A reaction between the flame retardant and the chlorine to form M0O2 012 H20, a nonvolatile compound, was assumed. This compound was assumed to promote chat formation (26,27). 

From the results obtained by thermal decomposition of both low-molecular weight vicinal dichlorides in the gas phase [74,75] and of the copolymers of vinyl chloride and /rthermal instability of PVC to the individual head-to-head structures. Crawley and McNeill [76] chlorinated m-1,4-polybutadiene in methylene chloride, leading to a head-to-head, and a tail-to-tail PVC. They found, for powder samples under programmed heating conditions, that head-to-head polymers had a lower threshold temperature of degradation than normal PVC, but reached its maximum rate of degradation at higher temperatures. 

The ball milling of poly(vinyl chloride) and acrolein gave a product with improved heat stability and electrical properties (25). The milling was performed at 108 rpm and at room temperature for four hours using porcelain balls 1.2-2 cm in diameter. After milling with 20% of acrolein for two hours, the decomposition temperature of the polymer product increased from 150 to 160° C and the darkening temperature from 200 to 220° C. After four hours the two temperatures were, respectively, 220 and 280° C. The ball milled product, also, showed a 37-fold improvement in volumetric resistance and a 15000-fold improvement in surface electrical resistance over the original poly(vinyl chloride). 

For low radiation doses, peroxides accumulate almost linearly with dose. However, after a certain dose has been reached, their concentration tends to level off. This conclusion can be derived from the observed change in the rate of graft copolymerization initiated by polymers subjected to increasing doses of preirradiation in air. Figure 2 illustrates this effect in the case of grafting acrylonitrile onto polyethylene (2). The drop in the yield of peroxide production presumably results from the efficient radiation-induced decomposition of these peroxides. Peroxides are known to decompose under free radical attack, and selective destruction of peroxides under irradiation has been established experimentally (8). This decomposition can become autocatalytic, and sometimes the concentration of peroxides may reach a maximum at a certain dose and decrease on further irradiation. Such an effect was observed in the case of poly (vinyl chloride). Figure 3 shows the influence of preirradiation dose on the grafting ratio obtained with poly (vinyl chlo-... 

Pyrolysis. Vinyl chloride is more stable than saturated ehloroalkanes to thermal pyrolysis. That is why nearly all vmyl chlonde made commercially comes from thermal clehydrochlorination of ethylene dichloride (EDC). When vinyl chloride is heated to 450°C, only small amounts of acetylene form. Decomposition of vinyl chlonde via a free-radical chain process begins at approximately 550°C, and increases with increasing temperature. Acetylene, HC1. chloropiene, and vinylacetylene are formed in about 35% total yield at 680°C. At higher temperatures, tar and soot formation becomes increasingly important. When dry and in contact with metals, vinyl chloride does not decompose below 450°C. However, if water is present, vinyl chloride can corrode iron, steel, and alum in 11m because ofthe presence of trace amounts of HC1. This HC1 may result from the hydrolysis of the peroxide formed between oxygen and vinyl chlonde. 

Entrapped oxygen and water vapor in lubricants can act as anti-wear additives to form protective surface films. Metals are known to catalyze decomposition of certain lubricants, and decomposition temperatures may be reduced by 60°C or more. This is particularly true of bearing surfaces, on which the surface energy may be increased by stress-induced dislocations and by freshly exposed metal surfaces. An example of the way a tribochemical surface is affected by a polymerization process is vinyl chloride. If the load is increased from 0.1 to 0.5 kg in the presence of a vinyl chloride atmosphere, the Auger spectra of iron oxide surface shows a marked increase in the concentration of vinyl chloride on the surface (Buckley, 1981). 

Dechlorination of poly (vinyl chloride) (PVC) prepared by polymerisation of vinyl chloride (VC) with butyllithium (BuLi) was investigated under the conditions of high pressure and high temperature water. Dechlorination was induced completely and polyene product was formed from PVC under high pressure and high temperature. The polymers obtained from polymerisation of VC with the BuLi revealed different decomposition behaviour from that obtained with radical initiator such as lauryl peroxide. This was attributed to the different chemical structure of the sample PVC. Complete dechlorination of PVC could be achieved in hot water under the conditions of 19.3 MPa and 300 deg.C. 3 refs. 

Elimination of carbon dioxide from carboxyl, water from alcoholic hydroxyl, carboxylic acid from alkanoate, and hydrogen chloride from chlorine side groups or chain ends are typical thermal decomposition reactions in the temperature range 250-350°C. Hydrogen chloride is an important product of poly(vinyl chloride) because every second carbon atom of the hydrocarbon polymer chain is chlorine substituted. But hydroxyl, alkanoate and free carboxylic acid groups normally occur only at the ends of the macromolecular chains in customary plastics, thus the contribution of their elimination to the volatile pyrolysis products is negligible. 

Yates and Hughes photochemically stimulated the radical-chain decomposition of 1,2-dichloroethane to vinyl chloride and hydrogen chloride. They obtained an overall activation energy of 12.5 kcal.mole from which they deduced an activation energy of 23.0 kcal.mole" for the step... 

The earliest investigations on vinyl chloride using Zieglei Natta catalysts suggested that they were rather unsatisfactory initiators of polymerization. Yields and molecular weights were low, possibly due to participation of monomer in side reactions with catalyst components, and it was considered that polymerization resulted from free radicals produced by decomposition of unstable organo-metal compounds. 

Some studies show that pyrolysis of certain polymer blends can be influenced by the migration of a small molecule or a small radical formed from one type of polymer and affecting the other type. For example, poly(methyl methacrylate) (PMMA) in blends with poly(vinyl chloride) (PVC) shows higher resistance to heat. The thermal decomposition of PVC generates HCI, which interacts with the PMMA forming anhydride units in the middle of PMMA chains, as shown below ... 

In addition to comonomers, nylons are frequently used in blends. The pyrolysis of blends typically shows little interaction between the compounds generated from the individual blend components. However, a study on the co-pyrolysis of several polyamides in the presence of PVC showed interactions [40]. The study was done on nylon-12, nylon-6,6 and poly(1,4-phenylene terephthalamide) (Kevlar) in the presence of poly(vinyl chloride). Polyamide-PVC mixtures (typical mass ratio 1 1) were pyrolyzed at 700 and 900°C. It was found that the presence of PVC promoted the hydrol ic decomposition routes of amide groups and volatile nitrile formation from all examined polyamides due to the hydrogen chloride eliminated from PVC under pyrolysis. In the presence of PVC, an elevated yield of alkenenitriles was observed from nylon-12. For Kevlar in the presence of PVC, it was noticed the evolution of benzeneamine, benzoic acid, benzenenitrile and benzeneisocyanate. At 900°C in the presence of PVC, an enhanced evolution of HCN from nylon-12 and nylon-6,6 was noticed. 

Most preparations of cyclopropanes involving catalytic decomposition of diaryldiazomethanes have been carried out by using zinc(II) chloride. The best result was achieved when diphenyldiazomethane was decomposed in the presence of ethyl vinyl ether at 25 °C l-ethoxy-2,2-diphenylcyclopropane was isolated in 52 /o yield.In general, the yield of the cyclopropane is sensitive to the temperature at which the reaction is carried out the lower the temperature, the lower the amount of the cyclopropane. Thus, when zinc(II) chloride catalyzed decomposition of diphenyldiazomethane was carried out in the presence of cyclopentadiene, the yield of 6,6-diphenylbicyclo[3.1.0]hex-2-ene (4) drops from 35 /o to 23"/o when the temperature is lowered from 22 °C to <... 

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