Chloroprene preparation

Poly(2-chloro-1,3-butadlene) or polychloroprene, (-CH2C(CI)=CHCH2-)n, CAS 9010-98-4, is a polymer widely used in practice, for example in automotive industry for the fabrication of belts, gaskets, electrical cables covering, etc. (mainly in vulcanized form). The older procedure for chloroprene preparation starts with acetylene, which is subject to catalytic dimerization followed by addition of HCI to the vinylacetylene molecule. 

Chloro 1 3 butadiene (chloroprene) is the monomer from which the elastomer neoprene IS prepared 2 Chloro 1 3 butadiene is the thermodynamically controlled product formed by addi tion of hydrogen chloride to vinylacetylene (H2C=CHC=CH) The principal product under conditions of kinetic control is the allenic chlonde 4 chloro 1 2 butadiene Suggest a mechanism to account for the formation of each product... 

Dicbloro-l,3-butadiene [1653-19-6] is a favored comonomer to decrease the regularity and crystallization of chloroprene polymers. It is one of the few monomers that will copolymerize with chloroprene at a satisfactory rate without severe inhibition. It is prepared from by-products or related intermediates. It is also prepared in several steps from chloroprene beginning with hydrochlorination. Subsequent chlorination to 2,3,4-trichloto-1-butene, followed by dehydrochlorination leads to the desired monomer in good yield if polymerization is prevented. 

Alternating copolymers of chloroprene have been prepared from a number of donor acceptor complexes in the presence of metal haUdes. 

At higher temperatures under nitrogen, the polymer is reduced to coke with the evolution of hydrogen chloride and organic Hquids such as chloroprene dimer. At temperatures below 275°C, polymers prepared at low temperature, with less 1,2- and 3,4-addition, are less reactive. Dehydrochlorination under nitrogen is not a radical chain process below about 275°C (105). 

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. 

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. 

Park et al. [20] reported on the synthesis of poly-(chloroprene-co-isobutyl methacrylate) and its compati-bilizing effect in immiscible polychloroprene-poly(iso-butyl methacrylate) blends. A copolymer of chloroprene rubber (CR) and isobutyl methacrylate (iBMA) poly[CP-Co-(BMA)] and a graft copolymer of iBMA and poly-chloroprene [poly(CR-g-iBMA)] were prepared for comparison. Blends of CR and PiBMA are prepared by the solution casting technique using THF as the solvent. The morphology and glass-transition temperature behavior indicated that the blend is an immiscible one. It was found that both the copolymers can improve the miscibility, but the efficiency is higher in poly(CR-Co-iBMA) than in poly(CR-g-iBMA),... 

Simple conjugated dienes used in polymer synthesis include 1,3-butadiene, chloroprene (Z-chloro-l -butadiene), and isoprene (2-methyl-l,3-butadiene). Isoprene has been prepared industrially by several methods, including the acid-catalyzed double dehydration of S-methyl-l/S-butanediol. 

The mechanism of chloroprene polymerization is summarized in Scheme 4.11. Coleman et ai9iM have applied l3C NMR in a detailed investigation of the microstructure of poly(chloroprene) also known as neoprene. They report a substantial dependence of the microstructure on temperature and perhaps on reaction conditions (Table 4.3). The polymer prepared at -150 °C essentially has a homogeneous 1,4-tra/rv-niicrostructure. The polymerization is less specific at higher temperatures. Note that different polymerization conditions were employed as well as different temperatures and the influence of these has not been considered separately. 

Uses Its largest uses are for polymeriztion to polybutadiene and copolymerization with styrene to make synthetic rubber (SBR) for tires and other rubber uses. Other uses include the preparation of chloroprene for oil-resistant rubber (neoprene) and hexamethylenediamine for the preparation of nylon. 

II. B polyethylene glycol, ethylene oxide, polystyrene, diisocyanates (urethanes), polyvinylchloride, chloroprene, THF, diglycolide, dilac-tide, <5-valerolactone, substituted e-caprolactones, 4-vinyl anisole, styrene, methyl methacrylate, and vinyl acetate. In addition to these species, many copolymers have been prepared from oligomers of PCL. In particular, a variety of polyester-urethanes have been synthesized from hydroxy-terminated PCL, some of which have achieved commercial status (9). Graft copolymers with acrylic acid, acrylonitrile, and styrene have been prepared using PCL as the backbone polymer (60). 

Although not a telomerization, it is mentioned here, that syndiotactic 1,2-polybutadienes were prepared in aqueous emulsions with a 7t-allyl-cobalt catalyst [33]. Similarly, chloroprenes were polymerized using aqueous solutions of [PdCl2(TPPMS)2] and [RhCl(TPPMS)3] as catalysts at 40 °C in the presence of an emulsifier and a chain growth regulator (R-SH, R=Cio-Cis) [35]. Despite the usual low reactivity of chlorinated dienes, these reactions proceeded surprisingly fast, leading to quantitative conversion of 10 g chloroprene in 2 hours with only 50 mg of catalyst (approximate TOP = 3500 h- ). 

We have prepared a series of copolymers under the conditions shown in Table 2. The monomer feed was always a 50 50 ratio of chloroprene to sulfur dioxide. Copolymerizations were carried out in bulk at temperatures from -78 to 100°. Initiators were tertiary butyl hydroperoxide at low temperatures, where it forms a redox system with the SO2 and is more effective than one might otherwise expect. Silver nitrate was used at 0° and 25°, azoiso-butyronitrile at 40° and 60°, and azodicyclohexanecarbonitrile... 

Figure 6. A 90-MHz C-13 spectrum of chloroprene-SOi copolymer prepared at 40°C and having an R value of 1.64...

Solutions of peroxide were prepared by oxidizing to the required extent, quenching the oxidation by cooling, and adding an excess of an inert diluent such as toluene. More than half the toluene was then pumped off while the oxidate was kept at — 20°C. After this procedure had been repeated twice, solutions of peroxide in toluene could be prepared in which the residual chloroprene concentration was about 0.5% (w./w.) of the peroxide. Complete removal of solvent gave faintly yellow viscous peroxidic material which was mildly explosive at room temperature. 

When the NMR spectrum of a 30% (w./v.) solution of peroxide in toluene was recorded at 34°C., absorption was observed between 8 2.74 and 5.46. There were seven main resonances, all multiplets, which were interpreted in terms of aliphatic hydrogen shifted by oxygen. Resonance from ethylenic hydrogen amounted to only a fraction of a proton. However, the sample darkened while in the instrument and probably decomposed extensively. When the spectrum of a solution of peroxide prepared by oxidation to 10.4 mole % was recorded using a cold probe at —35°C. a different picture was obtained. There was complex absorption from both ethylenic and saturated hydrogen which was interpreted as arising from a mixture of 1,2 and 1,4 oxygen copolymers in an approximate jatio of 1 to 2. In this sample the residual chloroprene amounted to 0.15% of the monomer units in the peroxide and dimers of chloroprene to 0.6% of the peroxide. 

Mouse liver microsomal preparations metabolized chloroprene in vitro into a volatile alkylating metabolite (Barbin et al., 1977 Bartsch et al., 1978). 

The capital and process control costs to prepare rubbers must be considered against the cost to process the polyurethanes. The straight raw material cost of the standard rubbers (natural, SBR, and chloroprene) will be less than the polyurethanes cost, but the overall processing cost of the polyurethanes will be lower. 

Sakai and Hashimoto (33) presented experimental results on devolatilization of a mixture of octane/hexane in linear low density polyethylene (LLDPE) from 10% to 0.01%, as well as a rubber slurry of 42% chloroprene and of 58% slurry in carbon tetrachloride in a JSW TEX 65 counterrotating, intermeshing, TSE. The LLDPE mixture was prepared in SSE upstream, where the octane/hexane was added to the melt with a plunger pump, which maintained constant concentration and was fed directly under pressure into the feed throat of the counterrotating, vented, TSE. 

Judging from the results of dynamic mechanical analyses, IPNs showed more effective damping properties than commercial chloroprene rubber at elevated temperatures. In addition, filled IPNs prepared by adding platelet fillers showed even higher attenuation (logarithmic decrement). 

Our third synthesis of the enantiomers of ipsdienol started from the enantiomers of serine as shown in Figure 4.66.116 (A-Serine was converted to epoxide A, which was treated with a Grignard reagent prepared from chloroprene to give hydroxy ester B. Subsequently, B afforded (7 )-ipsdienol (112, >96% ee). Similarly, (R)-serine furnished (S)-112. 

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