2.3- Dichloro-l,3-butadiene

Chloroprene (2-chloro-1,3-butadiene), [126-99-8] was first obtained as a by-product from tbe synthesis of divinylacetylene (1). Wben a mbbery polymer was found to form spontaneously, investigations were begun tbat prompdy defined tbe two methods of synthesis that have since been the basis of commercial production (2), and the first successbil synthetic elastomer. Neoprene, or DuPrene as it was first called, was introduced in 1932. Production of chloroprene today is completely dependent on the production of the polymer. The only other use accounting for significant volume is the synthesis of 2,3-dichloro-l,3-butadiene, which is used as a monomer in selected copolymerizations with chloroprene. 

Continuous polymerization in a staged series of reactors is a variation of this process (82). In one example, a mixture of chloroprene, 2,3-dichloro-l,3-butadiene, dodecyl mercaptan, and phenothiazine (15 ppm) is fed to the first of a cascade of 7 reactors together with a water solution containing disproportionated potassium abietate, potassium hydroxide, and formamidine sulfinic acid catalyst. Residence time in each reactor is 25 min at 45°C for a total conversion of 66%. Potassium ion is used in place of sodium to minimize coagulum formation. In other examples, it was judged best to feed catalyst to each reactor in the cascade (83). 

Polychloroprene is the polymer of 2-chloro-l,3 butadiene. Emulsion polymerization produces an almost entirely trans-1,4 polymer, which is highly crystalline. Less crystalline polychloroprenes are produced by incorporating several wt.% of 2,3-dichloro-l,3 butadiene into the polymer to break up crystalline sequences. 

Dichloro-l 3-butadiene [1653-19-6] M 123.0, b 41-43 /85mm, 98 /760mm. Crystd from pentane to constant melting point about -40 . A mixture of meso and d,l forms was separated by gas chromatography on an 8m stainless steel column (8mm i.d.) with 20% DECS on Chromosorb W (60-80 mesh) at 60 and 80ml He/min. [Su and Ache JPC 80 659 1976]. 

This monomer polymerizes too rapidly in the presence of free radicals to copolymerize easily with most vinyl monomers. However, it readily forms copolymers with 2,3-dichloro-l,3-butadiene, whidi also is a monomer that polymerizes very rapidly. 

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 observation made a long time ago in the case of natural rubber, i.e. the appearance of branchings and crosslinkings during mastication, was found out for PeCL [705] and also for the copolymer of chloroprene with 2,3-dichloro-l,3 butadiene at various temperatures [706]. 

Chloro-2-methyl-l-propene 2,3-Dichloro-l,3-butadiene Hexachlorobutadiene... 

Comonomer 2,3-dichloro-l,3- butadiene sulfur — — — 2,3-dichloro-l,3- butadiene — methaciylic acid... 

Polymerization within a molecular scale porous template has been described in Reference 144 using thioiuea as a host. 2,3-Dichloro-l,3-butadiene-thioiuea complex was obtained and polymerization was induced by y-irradiation. It was found that polymerization occurs in single crystals, and takes place without destroying the original single-trystal habit. Furthermore, it was demonstrated that the highly 1,4-tram-tactic polymer was obtained. 

Neoprene WRT, GRT Copolymers with 2,3-dichloro-l, 3-butadiene" with reduced linearity in the polymer chain thus reducing the tendency of the homopolymer to crystallise rapidly. 

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