Chloroprene Rubber, Poly 2-chloro-l,3-butadiene

2-Chloro-1,3-butadiene (chloroprene) was originally synthesized in 1930. The material can polymerize spontaneously to an elastomer that has good resistance to oil and weathering. Commercial production of chloroprene rubber started in 1932. Since then, many types of polymers and copolymers were developed with the trivial generic name of neoprene. 

Chloroprene is polymerized commercially by free-radical emulsion polymerization. The reaction is carried out at 40°C to a 90% conversion. A typical recipe for such an emulsion polymerization is as follows [127]  

When the polymerization reaches 90% conversion, the reaction mixture is cooled to 20°C and tetraethylthiuram disulfide is added. This is done to prevent the pendant unsaturation in the polychloroprene backbones from cross-linking or forming branches. An unmodified polymer is difficult to process even at a 70% conversion. To overcome this, a sulfur-tetraethylthiuram modification is carried out. 

When the product is treated with the thiuram, an exchange reaction takes place to yield a stable, thiuram-modified polymer of reduced molecular weight. It is believed that the reaction takes place through cleavage of the sulfur links, formed during polymerization in the presence of sulfur, and formation of free radicals [128] 

After the reaction with tetraethylthiuram disulfide is completed, the latex is acidified with acetic acid, short of coagulation. The rubber is then recovered at a low temperature (about — 15°C) in the form of sheets by deposition of the latex oti cooled rotating drums [127, 128]. 

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