Radical polymerization chlorination

Replacement of Labile Chlorines. When PVC is manufactured, competing reactions to the normal head-to-tail free-radical polymerization can sometimes take place. These side reactions are few ia number yet their presence ia the finished resin can be devastating. These abnormal stmctures have weakened carbon—chlorine bonds and are more susceptible to certain displacement reactions than are the normal PVC carbon—chlorine bonds. Carboxylate and mercaptide salts of certain metals, particularly organotin, zinc, cadmium, and antimony, attack these labile chlorine sites and replace them with a more thermally stable C—O or C—S bound ligand. These electrophilic metal centers can readily coordinate with the electronegative polarized chlorine atoms found at sites similar to stmctures (3—6). 

In the free radical polymerization of 1,3-dienes, 1,4 addition dominates 1,2 addition. The proportion of 1,2 (and 3,4 )units decreases in passing from butadiene to its methyl and chlorine substitution products isoprene, 2,3-dimethylbutadiene and chloroprene. The trans configuration of the 1,4 unit from butadiene is formed preferentially, the proportion of trans increasing rapidly with lowering of the polymerization temperature. 

Polymethylstyrene (PMS) and PCMS (both prepared from mixtures of meta and para isomers) were prepared by free radical polymerization of the respective monomers in toluene initiated by benzoyl peroxide at 85°C (12). Chlorination of P-p-MS was carried out in carbon tetrachloride (CC14) at 60 °C in presence of AIBN using the desired amount of S02C12 (13). Chlorination of PMS was carried out in CC14 at 50 °C under irradiation from a 60W incandescent light with the requisite amount of t-BuOCl (14). 

Exercise 29-21 The rate of radical polymerization of ethenylbenzene, induced by benzoyl peroxide in mixtures of tetrachloromethane and benzene, is independent of the concentration of tetrachloromethane. At high concentrations of tetrachloromethane, the average molecular weight of the polymer is greatly reduced and chlorine is found in the polymer. Explain. 

Poly(vinyl chloride), also known as PVC, is prepared by radical polymerization to produce material composed of an average of 10,000 to 24,000 monomer units. It is atactic and therefore amorphous, but it has a relatively high Tg because of the large size of its molecules and its polar carbon-chlorine bonds. It is a rigid material and is used to make pipe, panels, and molded objects. About 68% of PVC is used in the building and construction industry. A more flexible form of PVC is produced by adding a plasticizer such as dioctyl phthalate. This is used to prepare electric wire coatings, film, and simulated leather or vinyl. ... 

Radical polymerization of vinyl chloride and styrene is much easier than that of ethylene because the intermediate radicals are more stable. You saw in Chapter 39 that any substituent stabilizes a radical, but Cl and Ph are particularly good because of conjugation of the unpaired electron with a lone pair on chlorine or the Jt bonds in the benzene ring. 

In principle, the photoreactions of CT s are able to offer a great number of photoinitiator systems for radical polymerization. But, so far, this subject has only received little attention, and the current knowledge relative to the photochemistry of such complexes is poor. In addition to the amine complexes mentioned above, chinoline-bromine [124-127], chinoline-chlorine [128], 2-methylpyridine-chlorine [129], pyridine-bromine [130], IV-vinylpyrrolidone-bromine [131], acridone-bro-mine [132], acridone-chlorine [133], benzophenone-S02 [134], isoquinoline-S02 [135, 136], and 2-methylquinoline-S02 [136] combinations are used for radical polymerization of AN, alkyl methacrylates, acrylic and methacrylic acid, and for... 

Polymaleimide is prepared by free-radical polymerization of maleimide in the presence of divinylbenzene (.5%) or N,N -methylenebisacrylamide (5-10%) as cross-linking agents. PNCS is obtained by addition of chlorine in carbon tetrachloride to a suspension of the polymer in aqueous sodium hydroxide solution,... 

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 ... 

Metal-catalyzed living radical polymerizations of vinylpyridines were investigated with the copper-based systems. One of the difficulties in the polymerization is a decrease of catalytic activity imposed by the coordination of the monomers by the metal complex. Controlled radical polymerization of 4-vi-nylpyridine (M-33) was achieved by an initiating system consisting of a strong binding ligand such as L-32 and a chloride-based system [1-13 (X = Cl)/ CuCl] in 2-propanol at 40 °C.214 The Mn increased in direct proportion to monomer conversion, and the MWDs were narrow (MJMn = 1.1 —1.2). In contrast, 2-vinylpyridine (M-34) can be polymerized in a controlled way with chlorine-capped polystyrene as an initiator and the CuCl/L-1 pair in / -xylene at 140 °C.215 Block copolymers with narrow MWDs (Mw/Mn = 1.1 —1.2) were obtained therein. 

The polystyrene obtained by living cationic polymerization with R—Cl/Lewis acid possesses a carbon-chlorine terminal that is subsequently used for the living radical polymerizations of acrylates and methacrylates to give block copolymers such as B-65 to B-67 376-378... 

Table 5.9 lists the structures of polychloroprenes that form by free-radical polymerization at different temperatures. Chloroprene polymerizes by cationic polymerization with the aid of Lewis acids in chlorinated solvents. When aluminum chloride is used in a mixture of ethyl chloride-methylene chloride solvent mixture at -80 °C, the polymer has 50% 1,4 units. If it is polymerized with boron trifluoride, the product consists of 50-70% 1,4-adducts. A veiy high trans-1,4-poly(2-chloro-1,3-butadiene) forms by X-ray radiation polymerization of large crystals of... 

Nylon 7 and nylon 9 are part of a process developed in Russia to form polyamides for use in fibers. The process starts with telomerization of ethylene. Afree-radical polymerization of ethylene is conducted in the presence of chlorine compounds that act as chain-transferring agents. The reaction is carried out at 120-200 C temperature and400-600 atmospheres pressure. The preferred chain-transferring agents for this reaction are CCI4 and COCh ... 

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