Chloroprene rubber hydrogenation

Another speciality system with a resistance higher than natural rubber to oils and petrol is the group of chloroprene rubbers. The structure is essentially polybutadiene (1.N.12) with a chlorine replacement for a hydrogen atom. Over 80% of the structure is of the form... 

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. 

Synthetic rubbers, CR(chloroprene), SBR (styrene-butadiene) Involve carcinogenic substances in the work environment of production and processing (vulcanisation). CR may generate hydrogen chloride and dioxins when incinerated or burned. 

Using cuprous chloride as catalyst, hydrogen chloride adds to acetylene, giving 2-chloro-l,3-butadiene [126-99-8], chloroprene, C4H5Q, the monomer for neoprene rubber. 

Analysis of the white solid showed a high chlorine content, presumably derived from the catalyst, cuprous chloride, used to form the trimer. Preliminary analytical studies indicated the starting reactant was similar in structure to isoprene, the starting material for synthetic rubber. Because of the structural similarity, the starting material, now known to be 2-chloro-1,3-butadiene, was dubbed chloroprene. In fact, it was derived from the dimer and was found to be readily synthesized from the reaction of the dimer and hydrogen chloride. 

Details polychloroprene was Invented by DuPont scientists on April 17,1930 after Dr. Elmer K. Bolton of DuPont laboratories attended a lecture by Fr. Julius Arthur NIeuwland, a professor of chemistry at the University of Notre Dame. Fr. Nieuwland s research was focused on acetylene chemistry and during the course of his work he produced divinyl acetylene, a jelly that firms Into an elastic compound similar to rubber when passed over sulfur dichlorlde. After DuPont purchased the patent rights from the university, V fellace Carothers of DuPont took over commercial development of Nieuwland s discovery in collaboration with NIeuwland himself. DuPont focused on monovinyl acetylene and reacted the substance with hydrogen chloride gas, manu cturing chloroprene. ... 

The effect of polymer composition on secondary reactions is easily seen in rubber mastication. The greater tendency for gelation and branching in styrene rubber is related to the radicals involved. The radicals from styrene rubber have a greater reactivity than allyl radicals [7] toward a-methylenic hydrogen atoms and double bonds. This behavior has been attributed previously to the pendant vinyl groups in certain synthetic rubbers [8,9]. Poly-chloroprene also forms a gel by addition of radicals to double bonds, whose activity is increased by the chlorine substituent [10]. 

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. 

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