Vinyl chlorides cleavage

The vinyl chloride and vinyl bromide copolymer samples were prepared as polymer analogs of PVC. Cleavage of the carbon-halogen bond at LNT should result in the same radical for these polymers. Since secondary C-Cl and C-Br bond dissociation energies are 73 and 59 Kcal/mole respectively, a copolymer of vinyl chloride and vinyl bromide could be regarded as a PVC chain with weak points. The feed ratio of VC/VB was 10/1 by volume. Since the reactivity ratios are (in solution, at 40°C), r = 0.825 for VC and r2 = 1.050 for VB (22), the copolymer composition should be 15 units of vinyl chloride for one unit of vinyl bromide on the average. In addition, the values for r and... 

With perchlorinated substrates first dechlorination to vinyl chlorides occurs and then cathodic cleavage of residual chlorine (Sec. 13.2) with subsequent hydrogenation of the double bond (Eq. (147) ) 3l5 Electrolysis of l-iodo-2-bro-moethane produces ethylene, whereas l,l,l-trifluoro-2-bromochloroethane yields 70% l,l-difluoro-2-chloroethylene 316>. Ethylene and butylene were ob-... 

Arylcopper compounds react with carbon tetrachloride, although no reaction products have been reported (40), and complexes with 1,2-bis-(diphenylphosphino)ethane, (ArCu)a DPPE3, react with 1,2-dichloro-ethane to give vinyl chloride (41). Van Koten and Noltes (281e) have observed a cleavage of the HaC—P bond in a 1 2 reaction of o-(dimetbyl-aminomethyl)phenylcopper with DPPE ([Eq. (76)] the cleavage can be explained by a concerted mechanism which takes place within a complex. A similar mechanism was proposed (281e) to explain the above reaction with 1,2-dichloroethane. 

The majority of packaging plastic materials consists of polyolefins and vinyl polymers, namely polyethylene (PE), polypropylene (PP), polystyrene (PS) and poly(vinyl chloride) (PVC). Obviously, these polymers have many other applications not only as packaging materials. Chemically they are all composed of saturated hydrocarbon chains of macro-molecular size their typical thermal decomposition pathway is free radical one initiated by the homolytic scission of a backbone carbon-carbon bond. In spite of the basic similarity of the initial cleavage, the decomposition of the hydrocarbon macroradicals is strongly influenced by fhe nafure of the side groups of the main chain. 

Competing reactions to addition to a-hetero-substituted alkenes are metallation of vinylic or allylic protons (see 5.5.2.3.2) and cleavage of the carbon-hetero-element bond (see 5.5.2.2.1.). a-Metallations occur with vinylic chlorides, fluorides and ethers no addition of RLi occurs with vinyl fluorides, chlorides or ethers. For vinylic sulfides and selenides, whether metallation or addition (or even carbon-heterobond cleavage) occurs depends on the conditions and reagents. Addition of RLi (R = Et or n-Bu, not Ph) occurs to aryl vinyl sulfides ... 

By comparing the results for chlorinated polypropylene with those for polypropylene, it can be concluded that the two materials undergo very different pyrolytic reactions. Typical for polypropylene is the formation of fragments of the polymeric backbone with formation of monomer, dimer, etc., or with cleavage of the backbone in random places and formation of compounds with 3n, 3n-1, and 3n+1 carbon atoms (see Section 6.1). Pyrolysis of the chlorinated compound leads to a significant amount of HCI and also char. Very few chlorinated compounds are identified in the pyrolysate, since the elimination of HCI leaves very few chlorine atoms bound to carbons. Some aromatic hydrocarbons are formed by a mechanism similar to that of poly(vinyl chloride) pyrolysis. The elimination of HCI leads to the formation of double bonds, and the breaking of the carbon backbone leads to cyclization and formation of aromatic compounds. The reactions involved in this process are shown below for the case of formation of 1,3-dimethylbenzene ... 

Cleavage of —CH—CCl—Substrates containing the vinyl chloride unit are oxidized by ozone in methanol at -78° to methyl esters ... 

A combination of gas chromatography and either electron-impact or chemical ionization mass spectrometry has been used to analyse the products of thermal degradation of poly(vinyl fluoride) and of a number of other polymers [poly(vinyl chloride), aromatic polyimides, polyurethane]. The degradation of poly(vinyl-idene fluoride) has been related to its crystalline form. It is claimed that dehydrofluorination may take place preferentially in crystalline segments containing trans sequences. Thermo-oxidative breakdown is modified if vinylidene fluoride is copolymerized with tetrafluoroethylene or hexafluoroacetone. Dehydrofluorination occurred in both copolymers, but in the latter it was preceded by cleavage of the H from the CHj group in the alpha position to the ether bond followed by scission of the C-0 bond. ... 

The stabilization of poly(vinyl chloride) against light has been reviewed by Wirth and Andreas. Detailed mechanistic studies have indicated the importance of peroxides in the process of photo-oxidation. It was suggested that protection could be successfully achieved by exclusion of radiation of A < 380 nm. E.s.r. examination of irradiated samples demonstrated the intervention of peroxides in the mechanisms with the ultimate formation of carbonyl groups which caused chain scission by Norrish cleavage. Photo-oxidation of samples of poly(vinyl chloride) modified by incorporation of acrylonitrile-butadiene-styrene, methyl methacrylate-butadiene-styrene, and methyl methacrylate-acrylonitrile-butadiene-styrene copolymers has been investigated. Discolouration was accelerated by the presence of the modifiers. Thermal pre-treatment accelerated photo-induced decomposition. Mechanical properties were also examined, and scanning electron microscopy showed surface defects due to decomposition of the modifier. ... 

Thermal chlorination of methane is the most common process for producing CCI4. The perchlorination process (chlorinolysis = Chlorination and pyrolysis) uses the high-temperature chlorination of methane and the chlorinating cleavage of hydrocarbons and their chlorinated derivatives to produce CCI4. In this way, chlorine containing by-products and the residues from other chlorination processes, such as derived from the production of vinyl chloride or of allyl chloride can be converted to a useful product. 

One of the best-documented processes of oxidative cleavage of polymers is ozonization. Although saturated polymers react with ozone to form acids, ketones and peroxides, the process is also accompanied by molar mass degradation. Telechelics can only be synthesized in special cases since oxidative cleavage is generally nonspecific. However, it has been shown that it is possible to synthesize telechelics by the reaction of poly(vinyl chloride) (PVC) with ozone. " Ozonization probably begins at the C=C double bonds, which are present in PVC as structural defects. Indeed, ozonolysis has been used as an analytical method for the characterization of polymers containing C=C double bonds. " ... 

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