Pyrolysis radical polymerization

Taylor in 1925 demonstrated that hydrogen atoms generated by the mercury sensitized photodecomposition of hydrogen gas add to ethylene to form ethyl radicals, which were proposed to react with H2 to give the observed ethane and another hydrogen atom. Evidence that polymerization could occur by free radical reactions was found by Taylor and Jones in 1930, by the observation that ethyl radicals formed by the gas phase pyrolysis of diethylmercury or tetraethyllead initiated the polymerization of ethylene, and this process was extended to the solution phase by Cramer. The mechanism of equation (37) (with participation by a third body) was presented for the reaction, - which is in accord with current views, and the mechanism of equation (38) was shown for disproportionation. Staudinger in 1932 wrote a mechanism for free radical polymerization of styrene,but just as did Rice and Rice (equation 32), showed the radical attack on the most substituted carbon (anti-Markovnikov attack). The correct orientation was shown by Flory in 1937. In 1935, O.K. Rice and Sickman reported that ethylene polymerization was also induced by methyl radicals generated from thermolysis of azomethane. 

There are a large number of chain reactions that are significant in industrial processes or play an important role for the environment. Classes of chain reactions that are relevant industrially include hydrogen/halogen reactions and pyrolysis of hydrocarbons, which are both discussed below, and free-radical polymerization discussed in many textbooks on kinetics. As an example of a chain reaction of significant environmental consequence, we will discuss formation of nitric oxide from fixation of atmospheric nitrogen. 

Poly[4(5)vinyl-imidazole] can be obtained by radical polymerization of the corresponding monomer, in turn obtained by decarboxylation of transurocanic acid M> or by pyrolysis of 4 3-acetoxy)ethylimidazole 35). 

As demonstrated in this review, many different conjugated polymers have been intercalated into these and other hosts, using synthetic palhways such as inclusion oxidation, acid-catalyzed polymerization, or radical polymerization followed by pyrolysis of the precursor polymer. 

Even though vinyl chloride was discovered in 1835, polyvinyl chloride was not produced until 1912. It is now one of our most common polymers production in 1984 was over 6 billion pounds. The monomer is made by the pyrolysis of 1,2-dichloroethane, formed by chlorination of ethylene. Free radical polymerization follows Markovnikov s rule to give the head-to-tail polymer with high specificity ... 

A considerable number of papers describe the resulting molecules from the pyrolysis of polystyrene [2-26], etc. These studies include pyrolysis in inert conditions, in the presence of various catalysts [4], in the presence of carbon black [27], pyrolysis of H-T and H-H polymers, pyrolysis of polymers with different average molecular weights, pyrolysis of stereoregular polystyrene [28], pyrolysis of polystyrene obtained by controlled radical polymerization in the presence of 2,2,6,6-tetramethylpiperidine-N-oxyl (stable nitroxide) [29], pyrolysis in the presence of water in subcritical conditions [30], pyrolytic studies for the understanding of large scale processes [31-36], etc. 

Alternatively, refractory wools can be wrapped about the crucibles, however, in some cases pyrolysis on the large surface area can prevent reaction or cause free radical polymerizations of alkenes.(15) In larger than milligram quantities, Ti, V and the more refractory materials are best evaporated by electron beam. (13,14) In any case, for metals it is usual to degas the... 

The pyrolysis of transition metal carboxylates (in the example of Ni " ) has an essential place due to both (a) the quantitative characteristics of the main stages and (b) the properties of the products obtained. Such metallopolymers can be prepared by two principally different routes by the above-mentioned polymer-analogous reactions, namely, by the interaction of polyacryhc acid with metal salts Ni, (PAA-Ni ), Co " ", Fe " ", and so on (method A), or by radical polymerization of the appropriated monomers—for example, nickel acrylate, [Ni(CH2CHCOO)2] , to give nickel polyacrylate (NiPAcr) (method C). The kinetic peculiarities of metallopolymers thermolysis were compared with the behavior of their low-molecular-weight analogues nickel propionate. 

Ohtani, H., Tanaka, M., and Tsuge, S., Pyrol3 is-Gas Chromatographic Study of End Groups in Poly(methyl methacrylate) Radically Polymerized in Toluene Solution with Benzoyl Peroxide as Initiator, J. Anal Appl Pyrolysis, 15,167,1989. 

The first studies of this problem were carried out on poly(styrene). For example, in the pyrolysis of radically polymerized poly(styrene), 1,3-diphenylpropane and 1,3,5-triphenylpentane were recovered, but no diphenylethane. Small proportions of 1,1 linkages could not be found since the pyrolysis products could not be recovered quantitatively, and the method of determination was not very sensitive. 

Gore-Tex nonabsorbable monofilament suture is made from a highly crystalhne hnear PIPE. This fully fluorinated thermoplastic is an addition polymer and is formed by the free radical polymerization route in aqueous dispersion under pressure with persulfates and hydrogen peroxide as initiators. The monomer (tetrafluoroethylene) is made from a two-step process the fluorination of chloroform by HF to produce CHClFj which is subsequently dimerized by pyrolysis to form tetrafluoroethylene. FI FE has the highest enthalpy and entropy of polymerization (-156 kJ/mol and -112 J/ mol-deg, respectively) among the vinyls (Joshi and Zwolinski, 1967). Its molecular weight can be as high as 5 x l(p. 

Chemical or radical polymerization Electrochemical polymerization Photochemical polymerization Metathesis polymerization Concentrated emulsion polymerization Inclusion polymerization Solid-state polymerization Plasma polymerization Pyrolysis... 

Acrylonitrile vapor was adsorbed in the degassed (670 K, lO Torr) zeolite crystals at a vacuum line for 60 min at 298 K. To an aqueous suspension of the acrylonitrile-containing zeolite were added aqueous solutions of potassium peroxodisulfate and sodium bisulfite as radical polymerization initiatOTS. The zeolite frameworks could be dissolved with HF to recover the intrazeolite polyacrylonitrile (PAN). IR and NMR data show no damage to the polymers after this treatment For pyrolysis, the zeolite/PAN adducts were heated under nitrogen or vacuum to 920 and 970 K for extended periods. 

It is now clearly demonstrated through the use of free radical traps that all organic liquids will undergo cavitation and generate bond homolysis, if the ambient temperature is sufficiently low (i.e., in order to reduce the solvent system s vapor pressure) (89,90,161,162). The sonolysis of alkanes is quite similar to very high temperature pyrolysis, yielding the products expected (H2, CH4, 1-alkenes, and acetylene) from the well-understood Rice radical chain mechanism (89). Other recent reports compare the sonolysis and pyrolysis of biacetyl (which gives primarily acetone) (163) and the sonolysis and radiolysis of menthone (164). Nonaqueous chemistry can be complex, however, as in the tarry polymerization of several substituted benzenes (165). 

Very little skeletal rearrangement occurs via pyrolysis, a fact inherent in the failure of free radicals to readily isomerize by hydrogen atom or alkyl group migration. As a result, little branched alkanes are produced. Aromatization through the dehydrogenation of cyclohexanes and condensation to form polynuclear aromatics can take place. Additionally, olefin polymerization also can occur as a secondary process. 

A number of papers report investigations of the pyrolytic cleavage of aromatic hydrocarbons. The oxidation and pyrolysis of anisole at 1000 K have revealed first-order decay in oxygen exclusively via homolysis of the O—CH3 bond to afford phenol, cresols, methylcyclopentadiene, and CO as the major products.256 A study of PAH radical anion salts revealed that CH4 and H2 are evolved from carbene formation and anionic polymerization of the radical species, respectively.257 Pyrolysis of allylpropar-gyltosylamine was studied at temperatures of 460-500 °C and pressures of 10-16 Torr. The product mixture was dominated by hydrocarbon fragments but also contained SO2 from a proposed thermolysis of an intermediate aldimine by radical processes.258... 

Pyrolysis of acetylene to a mixture of aromatic hydrocarbons has been the subject of many studies, commencing with the work of Berthelot in 1866 (1866a, 1866b). The proposed mechanisms have ranged from formation of CH fragments by fission of acetylene (Bone and Coward, 1908) to free-radical chain reactions initiated by excitation of acetylene to its lowest-lying triplet state (Palmer and Dormisch, 1964 Palmer et al., 1966) and polymerization of monomeric or dimeric acetylene biradicals (Minkoff, 1959 see also Cullis et al., 1962). Photosensitized polymerization of acetylene and acetylene-d2 and isotopic analysis of the benzene produced indicated involvement of both free-radical and excited state mechanisms (Tsukuda and Shida, 1966). 

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