Polychloroprene production

A recent patent ( ) describes reactors used for continuous polychloroprene production which have some interesting features and claims. These reactors are shown in Figures 4 and 5. They include the following features ... 

Neoprenes. Of the synthetic latices, a type that can be processed similarly to natural mbber latex and is adaptable to dipped product manufacture, is neoprene (polychloroprene). Neoprene latices exhibit poor initial wet gel strength, particularly in coagulant dipped work, but the end products can be made with high gum tensile strength, oil and aUphatic solvent resistance, good aging properties, and flame resistance. There are several types of neoprene latex, available at moderately high (ca 50 wt %) and medium soHds content. Differences in composition between the types include the polymer s microstmcture, eg, gel or sol, the type of stablizer, and the total soHds content (Table 22). 

Cationic polymerization with Lewis acids yields resinous homopolymers containing cycHc stmctures and reduced unsaturation (58—60). Polymerization with triethyl aluminum and titanium tetrachloride gave a product thought to have a cycHc ladder stmcture (61). Anionic polymeriza tion with lithium metal initiators gave a low yield of a mbbery product. The material had good freeze resistance compared with conventional polychloroprene (62). 

Polychloroprene consumption woddwide, except for eastern European countries and China, has plateaued at about 250,000 metric tons per year with some continued slow growth expected. Annual production averaged 307,000 metric tons during the 1980s with at least part of the difference being exported to formerly SociaUst countries. Production in Armenia has been limited to a fraction of its capacity of 60 metric tons by environmental problems and, in fact, is currendy shut down. The People s RepubHc of China has three plants with a combined capacity of 20 metric tons (2). 

Neoprene Type TW was shown to have low oral toxicity in rats. The LD q was found to be in excess of 20,000 mg/kg. Human patch tests with Types GN, W, WRT, and WHV showed no skin reactions (169). The FDA status of Du Pont Neoprene polymers is described (172). Although polychloroprene itself has not been shown to have potential health problems, it should be understood that many mbber chemicals that may be used with CR can be dangerous if not handled properly. This is particularly tme of ethylenethiourea curatives and, perhaps, secondary amine precursors often contained in sulfur modified polychloroprene types. Material safety data sheets should be consulted for specific information on products to be handled. 

In 1980 the Goodyear company announced copolymers of cyclopentadiene, cyclo-octene or cyclo-octa-1,5-diene with the Diels-Alder addition product of hexachlorocyclopentadiene and cyclo-octa-1,5-diene. This material has been proposed as an alternative to the polychloroprenes, with lower ( 5°C), and superior ozone resistance... 

The hydrohalide is usually prepared by passing hydrogen chloride into a solution of masticated high-grade raw rubber in benzene at 10°C for about six hours. Excess acid is then neutralised and plasticisers and stabilisers are added. The benzene is removed by steam distillation and the product washed and dried. Alternatively the solution is cast on to a polychloroprene rubber belt, leaving a tough film after evaporation of the solvent. 

Since it is not possible to commercially produce a polymer that is based on the cis 1,4 form, commercial polymers are based on the Irons 1,4 form which has a crystalline melting point, Tm, of +75 °C and a Tg of -45 °C. Pure 1,4 trans polychloroprene thus crystallises readily and would normally be considered to be of limited use for a rubber. Such a polymer, however, does not crystallise when dissolved in a solvent, but will do so when the solvent evaporates. This feature is used to good effect in the production of contact adhesives. 

Polychloroprene latex adhesives, 1 533-534 Polychloroprene latexes, 19 854-861 applications for, 19 857, 859-861 compounding, 19 857-859 global product line of, 19 855 stabilization of, 19 855-857 Polychloroprene polymers branching parameters of, 19 839 commercial, 19 851-852 crystallization of, 19 843-844 cure site for, 19 837... 

Rubber, poly(fluorosilicone), 20 246—247 Rubber, polychloroprene, 79 840 Rubber products, microwave technology in, 76 530... 

Many of the synthetic elastomers now made are still polymerized by a free radical mechanism. Polychloroprene, polybutadiene, polyisoprene, and styrene-butadiene copolymer are made this way. Initiation by peroxides is common. Many propagation steps create high molecular weight products. Review the mechanism of free radical polymerization of dienes given in Chapter 14, Section 2.2. 

These steps are typical for most of the synthetic elastomers. The use of sulfur for vulcanization is common for the production of most elastomers. Magnesium and zinc oxides are often used for the cross-linking of polychloroprene (CR). Saturated materials such as EPM and fluoroelastomers are cross-linked using typical organic cross-linking agents such as peroxides. 

The vulcanization of polychloroprene (Neoprene) is carried out in different ways. Vulcanization by sulfur, even with an accelerator, is not practiced to a large extent. Vulcanizations by metal oxides (without diamine), either alone or in combination with sulfur (sometimes together with an accelerator), give the best physical properties for the crosslinked product. Halogenated butyl rubber is crosslinked in a similar manner. The mechanism for crosslinking by metal oxide alone is not established [Stewart et al., 1985 Vukov, 1984]. 

The molecular weight distribution of peroxide formed at 4% oxidation was determined with a Waters gel permeation chromatograph. The peroxide was prepared as a 0.7% (w./v.) solution in tetrahydrofuran, and the molecular weight distribution then obtained is shown in Figure 2. By analogy with polychloroprene count 25 is equivalent to about 140 monomer units in the peroxide, and the peak maximum is at about 18 units—i.e., a molecular weight of 2000. The incipient peaks at counts 34, 36, and between 32 and 33 result from products of peroxide decomposition. 

Elastomers, synthetic-polychloroprene Elastomers, synthetic-ethylene-propylene-diene rubber). Tires, hoses, bdts, molded and extmded goods, and asphalt products consume ca 80% of the redaimed mbber manufactured. Typical properties of reclaimed mbbers are shown in Table 5. 

Metal Oxides. Halogen-containing elastomers such as polychloroprene and chlorosulfonated polyethylene are cross-linked by their reaction with metal oxides, typically zinc oxide. The metal oxide reacts with halogen groups in the polymer to produce an active intermediate which then reacts further to produce carbon—carbon cross-links. Zinc chloride is liberated as a by-product and it serves as an autocatalyst for this reaction. Magnesium oxide is typically used with ZnCl to control the cure rate and minimize premature cross-linking (scorch). 

When irradiating a 1 1 blend of polychloroprene and poly(butadiene-acry-lonitrile) (NBR) reinforced by 50 phr furnace black and containing 5-15 phr of tetramethacrylate of bisglycerol phtalate, the product exhibited a tensile strength of 20 MPa (2,900 psi) at a dose of 15 Mrad (150 kGy) with values of elongation at break in the range of 420-480%. These values are equal to or better than those obtained from similar compounds cured chemically. ... 

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). 

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). 

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. 

Ethylenethiourea has a wide variety of uses in addition to vulcanization, a principal application since 1948. The curing process converts most of the ETU to other compounds, but traces of it are still found in the rubbers. Neoprene (polychloroprene) is found largely in automotive parts, wire and cable insulation, construction and adhesives. Consumer products containing neoprenes include container seals (e.g., aerosol dispensers) and shoes. It is also an intermediate in the manufacture of antioxidants, dyes, fungicides, insecticides, pharmaceuticals, synthetic resins, and a constituent of plating baths. 

Polychloroprene. Polychloroprene dispersions have a range of qualities similar to those of solvent-based polychloroprene adhesives and a similar range of uses. As an example, the bonding of vinyl materials with phenolic resin/paper decorative laminates often is carried out with these products. It is necessary to incorporate acid-acceptor dispersions of metallic oxides, and the dispersions in general do not provide such long open times as solvent-based polychloroprene adhesives. 

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