Polymerizations of chloroprene

There are only a limited number of commercial apphcations of bulk or solution polymerization of chloroprene. These involve graft polymerization of adhesives and production of Hquid polymers. 

Polychloroprene rubber (CR) is the most popular and versatile of the elastomers used in adhesives. In the early 1920s, Dr. Nieuwland of the University of Notre Dame synthesized divinyl acetylene from acetylene using copper(l) chloride as catalyst. A few years later, Du Pont scientists joined Dr. Nieuwland s research and prepared monovinyl acetylene, from which, by controlled reaction with hydrochloric acid, the chloroprene monomer (2-chloro-l, 3-butadiene) was obtained. Upon polymerization of chloroprene a rubber-like polymer was obtained. In 1932 it was commercialized under the tradename DuPrene which was changed to Neoprene by DuPont de Nemours in 1936. 

Over 5.5 billion pounds of synthetic rubber is produced annually in the United States. The principle elastomer is the copolymer of butadiene (75%) and styrene (25) (SBR) produced at an annual rate of over 1 million tons by the emulsion polymerization of butadiene and styrene. The copolymer of butadiene and acrylonitrile (Buna-H, NBR) is also produced by the emulsion process at an annual rate of about 200 million pounds. Likewise, neoprene is produced by the emulsion polymerization of chloroprene at an annual rate of over 125,000 t. Butyl rubber is produced by the low-temperature cationic copolymerization of isobutylene (90%) and isoprene (10%) at an annual rate of about 150,000 t. Polybutadiene, polyisoprene, and EPDM are produced by the anionic polymerization of about 600,000, 100,000, and 350,000 t, respectively. Many other elastomers are also produced. 

Fig. 19. Polymerization of chloroprene by natural rubber mastication. Effect of time, monomer concentration and temperature on monomer conversion. / 24.2% chloroprene, 15° C 2 24.2% chloroprene, 25°C 3 39.0% chloroprene, 15°C 4 49.0% chloroprene, 15° C (69)...

Chloroprene is a monomer used almost exclusively for the production of polychloroprene elastomers and latexes. It readily forms dimers and oxidizes at room temperature. Occupational exposures occur in the polymerization of chloroprene and possibly in the manufacture of products from polychloroprene latexes. 

In feet this method is similar to the synthesis of block copolymers using trapped radicals produced by polymerization of a monomer in a non-solvent. The existence of occluded radicals with a relatively long life-time was already postulated several years ago by Melville, in the photopolymerization of gazeous methyl methacrylate (149). The polymer deposited on the walls of the vessel was able to initiate the polymerization of chloroprene and of methylisopropenylketon (44,150). 

A method for the controlled emulsion polymerization of chloroprene using dithiocarbamic esters as sulfur-based chain transfer agents is described. The method provides industrially relevant molar masses with Mn s> 50,000 daltons with good yields in acceptable times. It was further determined that when pKa values for the dithiocarbamic acid precursors were less than 12, the thioester was ineffective as a regulator. 

TABLE 1. Effect on the polymerization of chloroprene nsing selected dithiocarbamic esters as sulfnr-based chain transfer agents. 

Sketch the types of structural isomers that can be formed from the polymerization of chloroprene (CH CCl-CHsCH. ... 

The major emulsion processes include the copolymerization of styrene and butadiene to form SBR rubber, polymerization of chloroprene (Fig. t -4) to produce neoprene rubbers, and the synthesis of latex paints and adhesives based mainly on vinyl acetate and acrylic copolymers. The product is either used directly in emulsion form as a paint or else the surfactants used in the polymerization are left in the final, coagulated rubber product. 

CCT suppresses the gel effect in radical polymerization of chloroprene. The polydispersity stays low, <2, up to 80% conversion. Then, because of cross-linking through pendant vinyl group, both the polydispersity and the molecular weight start to grow exponentially. Table 11 summarizes the use of CCT... 

The polymerization of unsaturated halohydrocarbons has been studied most extensively in the case of vinyl chloride and closely related compounds. Kainer 1S6) published a book recently on polyvinyl chloride and mixed polymers of vinyl chloride. In addition to chlorovinyl polymers, Schildknecht includes fluorovinyl polymers in his book Hl). Books covering plastics generally include material on the halohydrocarbon polymers (14, 144)- Several papers ISS, IS, 135,143) have been published in the last couple of years dealing with the polymerization of fluorine-containing compounds. Articles on polymerization of chloroprene 14 ), fluoroprene 1S8), chlorotrifluoroethylene 140), tetrafluoroethylene 1S9), vinylidene fluoride (157), and dichlorodifluoroethylene 1S7) have appeared in recent years. 

Radical-Initiated Homopolymerization. When this homopolymerization is carried out with benzoyl peroxides or other radical formers in a manner analogous to emulsion polymerization of chloroprene, highly crosslinked polymers are formed. They are insoluble in organic solvents such as toluene, benzene, or chloroform. Radical polymerization in toluene, benzene, or hexane leads only to insoluble products. 

In the early part of the 50 years commemorated by this book, there was very little block polymer science or technology to record. Probably the first block polymer reported was in 1938 by Bolland and Melville (23). who found that a film of poly(methyl methacrylate) deposited on the walls of an evacuated tube could initiate the polymerization of chloroprene. Later Melville concluded (24) that... 

Accel TP AI3-08293 Butyl namate Carbamic acid, dibutyidithio-, sodium salt Carbamodithioic acid, dibutyl-, sodium salt Dibutyidithiokarbaman sodny EINECS 205-238-0 HSDB 2900 Octopol NB-47 Pennac Pennac SDB Sodium DBDT Sodium dibutylcarbamodithioate Sodium dibutyidittiiocarbamate Sodium N,N-dibutyldithiocarbamate Tepidone Tepidone rubber xcelerator USAF B-35 Vulcacure Vulcacure NB. Ultra accelerator for SBR and natural rubber latex compounds in polymerization of chloroprene rubber, especially for latex compounds where copper staining of zinc salt dithiocarbamates is a problem. 

OTHER COMMENTS an oil-resistant synthetic rubber (neoprene) may be made by the polymerization of chloroprene used as a component of adhesives intended for use in food packaging used for roof coatings used for wire and cable jackets. 

Polychloroprene, developed and sold under the trade name Neoprene by DuPont, was the first commercially successful synthetic elastomer. It is produced by free-radical emulsion polymerization of chloroprene (2-chloro-l,3-butadiene). The commercial material is mainly /raw5-l,4-polychloroprene, which is crystallizable. 

Draw all possible confignrational and stereo isomers resulting from polymerization of chloroprene. 

Various recipes (Morton et al., 1956 Morton and Piirma, 1956) can be used for emulsion polymerization of chloroprene, with potassium persulfate as a popular initiator. A basic recipe (Neal and Mayo, 1954) which illustrates several interesting features about this monomer is shown in Table 2.9. Two... 

Another feature of the emulsion polymerization of chloroprene that distinguishes it from that of the other dienes is the fact that it leads to a predominantly trans-lA chain microstructure. Thus, even at ambient polymerization temperature, the poly chloroprene contains over 90% trans-1,4 units, as shown in... 

Chloroprene rubber, polychloroprene (CR). A syniheXic rubber produced by polymerization of chloroprene (2-chlorobutadiene, CH2=CCl—CH = CH 2). High weather and chemical resistance, better oil resistance than that of natural rubber products. Some applications building sheets, belts, cable insulations, technical rubber goods, contact adhesives. Trade names Baypren (FRG), Neoprene (USA). 

Although all of these attempts had a noble purpose indeed, the means used could hardly be considered a contribution to science, as the transformation of the simple molecules of a diene into the colloidal substance known as rubber was then far beyond the comprehension of chemical science. As a matter of fact, the commercial production of synthetic rubber was already well established, at least in Germany and Russia, before Staudinger laid the basis for his macromolecular hypothesis during the 1920s [9]. Even such relatively modern synthetic elastomers as polychloroprene and the poly(alkylene sulfides) were already in commercial production by 1930-1931. This was, of course, also before Carothers and coworkers pioneering studies on the polymerization of chloroprene [10] ... 

Cochet F, Claverie I.P., GraiUat C., Sauterey F., Guyot A., Emulsion polymerization of chloroprene in the presence of a maleic polymerizable surfactant Control of gel formation at low conversion. Macromolecules, 37(11), 2004, 4081-4086. 

Under similar conditions, the emulsion polymerization of chloroprene proceeds about 700 times faster than that of isoprene. The resulting heat of polymerization therefore must be dissipated as quickly as possible by effective external cooling or by using flow techniques. Alternatively, the reaction rate can be moderated by adding an inhibitor. Sulfur is used commercially for this purpose with chloroprene, although this inhibitor cannot be used in the polymerization of butadiene or isoprene. Coagulation of emulsion is finally brought about by the addition of acids or multivalent salts. The emulsion polymerizates possess only about 1.5% 1,2 structures. 

The free-radical polymerization of chloroprene (2-chloro-l,3-butadiene) is a stereoselective polymerization that has been known for many years. However, this stereochemical fact has been largely ignored or superficially treated in some organic texts. One will note that six stereoregular polymers are possible. A 1,4 addition can give either cis-1,4- or tra%s-l,4-polychloroprene. The 1,2 and 3,4-additions account for the other four possibilities since each addition can be either isotactic or syndiotactic. The macromolecule, which is produced by free-radical synthesis, is practically all trans-l,4-polychloroprene. 

Polychloroprene. To 200 g of emulsion were added 2 g of a 50% water solution of sodium dibutyl dithiocarbamate, 8.3 g of zinc oxide dispersion, and 2 g of a butylated bisphenol A dispersion. The mixture was stirred and films were cast, dried, and cured as above, thereby crosslinking the polymer via two mechanisms the usual zinc oxide vulcanization, and a bisalkylation in which the crosslinking takes place at sites where there are tertiary allylic chlorine atoms formed by 1,2 polymerization of chloroprene monomer. 

Rubber can also be made in the laboratory from polymerizing isoprene in the presence of suitable catalysts that favor formation of the c/s polymer. Rubber produced in this way is virtually indistinguishable from natural rubber. Other substituted dienes can also be polymerized in the laboratory to produce a wide variety of rubberlike, synthetic polymers. In the early 1930s, chemists at the Du Pont chemical company produced a commercially important polymer via the free-radical polymerization of chloroprene. The resulting polymer is sold under the trade name Neoprene. 

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