Chloroprene Polychloroprene

Chloroprene Elastomers. Polychloroprene is a polymer of 2-chloro-l,3-butadiene. The elastomer is largely composed of the trans isomer. There are two basic polymer types the W-type and the G-type. G-types are made by using a sulfur-modified process W-types use no sulfur modification. As a result, G-types possess excellent processing and dynamic properties, and tend to be used in V-belts. However, they have poorer aging properties than W-types. The W-types tend to be used in appHcations requiring better aging, such as roUs and mechanical goods (see Elastomers, SYNTHETIC-POLYCm.OROPRENE). 

Finally, block copolymers have been made in a two-step process. First a mixture of chloroprene and -xylenebis-Ai,Ar-diethyldithiocarbamate is photopolymerized to form a dithiocarbamate terminated polymer which is then photopolymerized with styrene to give the block copolymer. The block copolymer has the expected morphology, spheres of polystyrene domains in a polychloroprene matrix (46). 

Microstructure. Whereas the predominate stmcture of polychloroprene is the head to tail /n7 j -l,4-chloroprene unit (1), other stmctural units (2,3,4) are also present. The effects of these various stmctural units on the chemical and physical properties of the polymer have been determined. The high concentration of stmcture (1) is responsible for crystallization of polychloroprene and for the abiUty of the material to crystallize under stress. Stmcture (3) is quite important in providing a cure site for vulcanization, but on the other hand reduces the thermal stabiUty of the polymer. Stmctures (3),(4), and especially (2) limit crystallization of the polymer. 

The monomer, 2-chlorobuta-1,3-diene, better known as chloroprene, is polymerised by free-radical emulsion methods to give a polymer which is predominantly (-85%) fr<2 s-l, 4-polychloroprene but which also contains about 10% cii-1,4- 1.5%, 1,2- and 1% of 3,4-structures (Figure 11.17). The commercial polymers have a Tg of about -A3°C and a of about 45°C so that at usual ambient temperatures the rubber exhibits a measure of crystallinity. 

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. 

During World War II, polychloroprene was chosen as a replacement for natural rubber because of its availability. Two copolymers of chloroprene and sulphur which contain thiuram disulphide were available (Neoprene GN and CG). One of the first successful applications of these polychloroprene adhesives was for temporary and permanent sole attachment in the shoe industry. However, these polychloroprene cements show a decrease in viscosity on ageing and a black discolouration appears during storage in steel drums. Discolouration was produced by trace amounts of hydrochloric acid produced by oxidation of polychloroprene... 

Chemistry of polychloroprene rubber. Polychloroprene elastomers are produced by free-radical emulsion polymerization of the 2-chloro-1,3-butadiene monomer. The monomer is prepared by either addition of hydrogen chloride to monovinyl acetylene or by the vapour phase chlorination of butadiene at 290-300°C. This latter process was developed in 1960 and produces a mixture of 3,4-dichlorobut-l-ene and 1,4-dichlorobut-2-ene, which has to be dehydrochlorinated with alkali to produce chloroprene. 

Neoprene latex 115 contains a copolymer of chloroprene and methacrylic acid, stabilized with polyvinyl alcohol [15], With respect to other polychloroprene latices, this latex has two major advantages (1) excellent colloidal stability, which gives high resistance to shear and a broad tolerance to several materials ... 

Resistance to weathering. Zinc oxide and magnesium oxide stabilize poly-chloroprene against dehydrochlorination. Further, zinc oxide helps vulcanize the rubber, and magnesium oxide reacts with /-butyl phenolic resin to produce a resinate which improves heat resistance of solvent-borne polychloroprene adhesives. 

Park et al. [20] reported on the synthesis of poly-(chloroprene-co-isobutyl methacrylate) and its compati-bilizing effect in immiscible polychloroprene-poly(iso-butyl methacrylate) blends. A copolymer of chloroprene rubber (CR) and isobutyl methacrylate (iBMA) poly[CP-Co-(BMA)] and a graft copolymer of iBMA and poly-chloroprene [poly(CR-g-iBMA)] were prepared for comparison. Blends of CR and PiBMA are prepared by the solution casting technique using THF as the solvent. The morphology and glass-transition temperature behavior indicated that the blend is an immiscible one. It was found that both the copolymers can improve the miscibility, but the efficiency is higher in poly(CR-Co-iBMA) than in poly(CR-g-iBMA),... 

At present it is believed that intermolecular chemical bonds are formed during the vulcanization of polychloroprene with ZnO not only due to the mobile chlorine in allyl position but also as a result of the reaction of the chlorine located directly at the double bond of the monomeric units chloroprene connected in the chain in 1,4-position as shown in the following scheme43. ... 

FIGURE 4.8 Comparative tensile stress-strain plot of polychloroprene-ordinary zinc oxide (ZnO) and poly-chloroprene-nano-ZnO system. (From Sahoo, S., Kar, S., Ganguly, A., Maiti, M., and Bhowmick, A.K., Polym. Polym. Compos., 2007 (in press). Courtesy of Smithers Rapra Technology Ltd.)... 

This name has been widely adopted for the elastomer obtained by polymerising chloroprene, i.e., polychloroprene. It is however the trade name of those types of polychloroprene produced by the Du Pont Co.which were originally called Duprene . Chloroprene rubber (CR) is the preferred term, but polychloroprene (PCP) is also popular. 

This is reacted with hydrogen chloride to produce chlorobutadiene (chloroprene) which is polymerised to polychloroprene. See Neoprene. Vinyl Chloride... 

Neoprene or polychloroprene is formed by the free radical polymerisation of chloroprene. 

Besides butadiene, another important monomer for the synthetic elastomer industry is chloroprene, which is polymerized to the chemically resistant polychloroprene. It is made by chlorination of butadiene follow by dehydrochlorination. As with most conjugated dienes, addition occurs either 1,2 or 1,4 because the intermediate allyl carbocation is delocalized. The 1,4-isomer can be isomerized to the 1,2-isomer by heating with cuprous chloride. 

Gas chromatography has been used to determine chloroprene as a residual monomer in polychloroprene latexes, with a sensitivity of less than 0.002 wt % (Bunyatyants et al., 1976). 

Chloroprene production can be equated approximately to the amount of polymer produced. World production of dry polychloroprene was 135 thousand tonnes in 1960, 254 thousand tonnes in 1970, 314 thousand tonnes in 1980 and 321 thousand tonnes in 1989 (Stewart, 1993). World polychloroprene capacity in 1983 was reported to be (thousand tonnes) United States, 213 Germany, 60 France, 40 United Kingdom, 30 Japan, 85 and centrally plarmed economy countries, 220 (Kleinschmidt, 1986). Current capacities are reported to be (thousand tonnes) United States, 163 Germany, 60 France, 40 United Kingdom, 33 Japan, 88 central Europe and the Commonwealth of Independent States, 40 and People s Republic of China, 20 (International Institute of Synthetic Rubber Producers, 1997). 

During 1973, at a chloroprene polymerization plant in the United States, airborne concentrations of chloroprene were found to range from 14 to 1420 ppm [50-5140 mg/m ] in the make-up area, from 130 to 6760 ppm [470-24 470 mg/m in the reactor area, from 6 to 440 ppm [22-1660 mg/m ] in the monomer recovery area and from 113 to 252 ppm [409-912 mg/ni l in the latex area (Infante et al., 1977). Concentrations in the air inside a Russian polychloroprene rubber plant were 14.5-53.4 mg/m (Mnatsakayan et al., 1972). In a Russian chloroprene latex manufacturing facility, chloroprene concentrations varied from 1 to 8 mg/m (Volkova et al., 1976). 

Exposure to residual chloroprene monomer in polychloroprene latex and polymer has also been described. In 1977, mean airbome concentrations of chloroprene of up to 0.2 ppm [0.72 mg/m3] were reported in a roll building area at a metal fabricating plant in the United States where polychloroprene was applied extensively to metal cylinders before vulcanization (Infante, 1977). Workers in a Russian shoe factory were reportedly often exposed to chloroprene concentrations of 20-25 mg/m (Buyanov Svishchcv, 1973). 

Chloroprene has been detected in industrial wastewater and nearby groundwater in the People s Republic of China (Huang et al., 1996), in wastewaters from polychloroprene and dichlorobutadiene production plants in Russia (Avetisyan et al., 1981 Geodakyan et al., 1981) and in waste gas from a chloroprene plant in Japan (Kawata et al., 1982). 

It is reported that dry polychloroprene no longer contains detectable chloroprene (detection limit, 0.5 ppm). In polychloroprene latexes, residual chloroprene is less than 1%, varying with the manufactunng process and intended use (DuPont Dow Elastomers, 1998). 

One case has been reported of liver angiosarcoma (pathologically confirmed) in a worker exposed to polychloroprene who had no known occupational exposure to vinyl chloride (lARC, 1987b) or medical exposure to thorotrast (Infante, 1977). [It is unclear whether and how much this worker was exposed to chloroprene monomer.]... 

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. 

Copolymenzation -of chloroprene [ELASTOMERS, SYNTHETIC - POLYCHLOROPRENE] (Vol 8) -ofion-exchange resins [ION EXCITANGE] (Vol 14) -of isobutylene [ELASTOLffiRS, SYNTHETIC - BUTYL RUBBER] (Vol 8)... 

Butadiene is a colorless, odorless, flammable gas, with a boiling point of -4.7°C and is used for the manufacture of polybutadiene, nitrile rubber, chloroprene, and various other polymers. An important synthetic elastomer is styrene-butadiene rubber (SBR) in the automobile tire industry. Specialty elastomers are polychloroprene and nitrile rubber, and an important plastic is acrylonitrile/butadiene/styrene (ABS) terpolymer. Butadiene is made into adiponitrile, which is converted into hexamethylenediamine (HMDA), one of the monomers for nylon. 

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