Chloroprene monomer

Cuprous salts catalyze the oligomerization of acetylene to vinylacetylene and divinylacetylene (38). The former compound is the raw material for the production of chloroprene monomer and polymers derived from it. Nickel catalysts with the appropriate ligands smoothly convert acetylene to benzene (39) or 1,3,5,7-cyclooctatetraene (40—42). Polymer formation accompanies these transition-metal catalyzed syntheses. 

Fire and uncontroUed polymerization are a concern in the handling of chloroprene monomer. The refined monomer is ordinarily stored refrigerated under nitrogen and inhibited. This is supported by routine monitoring for polymer formation and vessel temperature. Tanks and polymerization vessels are equipped for emergency inhibitor addition. Formalized process hazard studies, which look beyond the plant fence to potential for community involvement, are routine for most chemical processes. 

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. 

Chloroprene monomer will autoxidise very rapidly with air, and even at 0°C it produces an unstable peroxide (a mixed 1,2- and 1,4-addition copolymer with oxygen), which effectively will catalyse exothermic polymerisation of the monomer. The kinetics of autoxidation have been studied [1], It forms popcorn polymer at a greater rate than does butadiene [2],... 

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). 

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 monomer production starts with the catalytic conversion of acetylene to monovinylacetylene, which is purified and subsequently reacts with aqueous hydrogen chloride solution containing cuprous chloride and ammonium chloride to give chloroprene.61... 

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. 

Free-Radical Polymerization. Autopol5mierization of chloroprene monomer occurs readily imder free-radical and photochemical conditions (see Radical Polymerization). The electron-rich and electronegative chlorine atom facilitates the high reactivity of this monomer. Over the temperature range 20-80° C, the initiation depends on the formation of di-radicals or the added free radical that initiates polymerization (see Initiators, Free-Radical). Polymerization proceeds at a rate that follows first-order kinetics with an activation energy of 82 kJ mol (19.6 kcal mol ) and a heat of pol5unerization of 68-75 kJ mol (16-18kcalmol-i)(l,3,7,8). 

The expressions are an outcome of the terminal model theory with several steady-state assumptions related to free-radical fiux (14,23). Based on copolymerization studies and reactivity ratios, chloroprene monomer is much more reactive than most vinyl and diene monomers (Table 1). 2,3-Dichloro-l,3-butadiene is the only commercially important monomer that is competitive with chloroprene in the free-radical copolymerization rate. 2,3-Dichlorobutadiene or ACR is used commercially to give crystallization resistance to the finished raw polymer or polymer vulcanizates. a-Cyanoprene (1-cyano-l,3-butadiene) and /3-cyanoprene (2-cyano-1,3-butadiene) are also effective in copolymerization with chloroprene but are difficult to manage safely on a commercial scale. Acrylonitrile and methacrylic acid comonomers have been used in limited commercial quantities. Chloroprene-isoprene and chloroprene-styrene copolymers were marketed in low volumes during the 1950s and 1960s. Methyl methacrylate has been utilized in graft polymerization particularly for vinyl adhesive applications. A myriad of other comonomers have been studied in chloroprene copolymerizations but those copolymers have not been used with much commercial success. 

The monomer solution makeup involves addition and solubilization of elemental sulfur and rosin (substituted diterpenes) in the chloroprene monomer. The water solution is made in a second vessel. Deionized water, sodium hydroxide, and a dispersant are mixed to form the water solution. The dispersant is a condensation product of naphthalene-sulfonic acid and formaldehyde. The monomer and water solutions are mixed with centrifiigal pumps to form an oil-in-water emulsion. The emulsion formed by virtue of formation of the sodiiun salt of rosin and resin components (abietic and dehydroabietic acids) having hydrophobic and hydrophilic ends. The large carbon-bearing portion of sodium abietate is hydrophobic and thereby solubilizes the monomer. The sodium carboxylate portion of sodium abietate is the hydrophilic end that extends into the aqueous phase and forms the electronic double layer that is critical to emulsion stability (84,85). In the patent example, the emulsion was added to the reactor and the temperatiu-e was increased to 40°C polymerization temperatiu-e (Table 3). 

The emulsion or polymer dispersion containing flammable and toxic chloro-prene monomer was next steam stripped with the aid of a turbanmJar stripper (87). The stripped emulsion contained less than 0.1% residual chloroprene monomer. At this point in the process, the emulsion can be further processed into a dry polymer or sold as a liquid dispersion. 

Residual monomer remaining after polymerization pose a lesser degree of hazard owing to low concentration and the engineering measures implemented in the workplace to prevent personnel exposure to the monomer. Neoprene liquid dispersions contain less than 0.1% residual chloroprene monomer. 

Polychloroprene is produced from the emulsion polymerization of the chloroprene monomer as shown in Figure 4.26. 

Chloroprene monomer Is unstable, highly reactive, and must be stored in refrigeration. Transportation of monomer is limited and most monomer plants are located near the polymer plants... 

Now there are at least six chloroprene plants worldwide. All but one of these plants produce chloroprene from butadiene. However, there is one remaining plant that produces chloroprene monomer using the original acetylene process as shown in Figure 4.27. 

Figure 4.27 Chloroprene monomer produoed by the original acetylene process Standard Classifications...

G-type Neoprene elastomers that are made from the copolymerization of the chloroprene monomer with sulfur and usually stabilized with a thiuram disulfide. 

In the past, acetylene has been dimerized and reacted with hydrogen chloride to form the chloroprene monomer for the polymerization of polychloroprene rubber. However, this synthesis route is not used as much now compared to the direct chlorination of butadiene, the preferred synthesis route. 

Calcium carbide produces acetylene, which has been dimerized into chloroprene monomer (by an older process) to produce polychloroprene rubber through polymerization. However, this synthesis route is quite minor today. 

Chlorine is reacted with butadiene to yield chloroprene monomer, which is polymerized into neoprene rubber. 

Neoprene is produced from the chloroprene monomer, 2-chloro-1,3-butadiene, in an emulsion process. During polymerization, the monomer can add in a number of ways as shown in Table 1. The proportion of each configuration determines the amount of crystallinity in the polymer and its reactivity. 

Neoprene is the common name for the polymers of chloroprene (2-chloro-1,3-butadiene). These are produced by emulsion polymerization. The chloroprene monomer can polymerize in four isomeric forms tram 1,4 addition cis 1,4 addition 1,2 addition, leaving a pendant vinyl group and allylic chlorine and 3,4 addition. Neoprene is typically 88-92% tram, with degree of polymer crystallinity proportional to the trans content. Cis addition accounts for 7-12% of the structure and 3,4 addition makes up about 1%. The approximately 1.5% of 1,2 addition is believed to provide the principal sites of vulcanization. 

Chloroprene monomer production starts with the catalytic conversion of acetylene to... 

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