Chloroprene, properties

Chloroprene Elastomers. Polychloroprene is a polymer of 2-chloro-l,3-butadiene. The elastomer is largely composed of the trans isomer. There are two basic polymer types the W-type and the G-type. G-types are made by using a sulfur-modified process W-types use no sulfur modification. As a result, G-types possess excellent processing and dynamic properties, and tend to be used in V-belts. However, they have poorer aging properties than W-types. The W-types tend to be used in appHcations requiring better aging, such as roUs and mechanical goods (see Elastomers, SYNTHETIC-POLYCm.OROPRENE). 

Chlorinated polyethylene (CPE) has excellent o2one, oil, and heat resistance. In addition chlorinated polyethylene has replaced chloroprene elastomers. CPE has a lower specific gravity than chloroprene compounds and produces compounds that are similar to CR in properties but with lower costs. In addition, due to high levels of chlorine in the polymer, the flame resistance of the compounds of CPE are high. 

Ozonc-rcsjstant elastomers which have no unsaturation are an exceUent choice when their physical properties suit the appHcation, for example, polyacrylates, polysulfides, siHcones, polyesters, and chlorosulfonated polyethylene (38). Such polymers are also used where high ozone concentrations are encountered. Elastomers with pendant, but not backbone, unsaturation are likewise ozone-resistant. Elastomers of this type are the ethylene—propylene—diene (EPDM) mbbers, which possess a weathering resistance that is not dependent on environmentally sensitive stabilizers. Other elastomers, such as butyl mbber (HR) with low double-bond content, are fairly resistant to ozone. As unsaturation increases, ozone resistance decreases. Chloroprene mbber (CR) is also quite ozone-resistant. 

Selected physical properties of chloroprene are Hsted in Table 1. When pure, the monomer is a colorless, mobile Hquid with slight odor, but the presence of small traces of dimer usually give a much stronger, distinctive odor similar to terpenes and inhibited monomer may be colored from the stabilizers used. Ir and Raman spectroscopy of chloroprene (4) have been used to estimate vibrational characteristics and rotational isomerization. 

Microstructure. Whereas the predominate stmcture of polychloroprene is the head to tail /n7 j -l,4-chloroprene unit (1), other stmctural units (2,3,4) are also present. The effects of these various stmctural units on the chemical and physical properties of the polymer have been determined. The high concentration of stmcture (1) is responsible for crystallization of polychloroprene and for the abiUty of the material to crystallize under stress. Stmcture (3) is quite important in providing a cure site for vulcanization, but on the other hand reduces the thermal stabiUty of the polymer. Stmctures (3),(4), and especially (2) limit crystallization of the polymer. 

If flammabiHty is an issue, Hquid chloroprene polymers (eg, Du Pont PB or Denki LCR-H-050) can be used. They cocure and, for that reason, are nonvolatile and nonextractable. They are particularly useful in hard compounds where they do not detract from physical properties as much as nonreactive plastici2ers (132,133). Methacrylate esters have been used as reactive plastici2ers (qv). Por example, hexa(oxypropylene)glycolmonomethacrylate can be used as a reactive plastici2er to enhance flex life without increasing hardness (134). 

The type of chloroprene polymers used is perhaps best illustrated by the variety of special products, designed for adhesive appHcations, that Du Pont has developed. These are described ia Table 8. Standard polymer grades are also often used, especially to modify adhesive properties and to reduce cost. 

Table 7. Effect of Wollastonite treatment method on the mechanical properties of filled chloroprene [242]...

A convenient term for any material possessing the properties of a rubber but produced from other than natural sources. A synthetic version of natural rubber has been available for many years with the same chemical formula, i.e., cis-1,4-polyisoprene, but it has not displaced the natural form. See also Butyl Rubber, Chloroprene Rubber, Ethylene-Propylene Rubber, Nitrile Rubber, Silicone Rubber and Styrene-Butadiene Rubber. 

Table 2. Properties of modeling unfilled elastomeric compositions on the basis of chloroprene rubber in vulcanization optimum...

ZnCFO is the effective vulcanization active component of the sulfur, thiuram, peroxide and metaloxide vulcanization systems for isoprene, nitrile-butadiene and chloroprene rubbers at the same time it is not effective in resin vulcanization system for butyl rubber. On a degree of positive influence on the properties of elastomeric compositions vulcanization systems with ZnCFO are arranged in a line ... 

Influence of Interpolymer Properties. As stated earlier, the physical and chemical properties of interpolymers markedly influence the reaction rate after the induction period. If the monomer present yields a polymer comparable in viscosity with the initial mixture the rate of scission will not accelebrate. For example, the polymerization rate of chloroprene on mastication with natural rubber does not increase as markedly with conversion (69), see Fig. 19, as with methyl methacrylate and styrene. The reason is the chloroprene-rubber system remained elastic and softer than the original rubber. 

The similarity of the reaction rate-time curve of chloroprene (Figure 8) to the styrene curve is possibly caused by the similar properties of these monomers with respect to water solubility, solubility of the polymer in the monomer, and the absolute reaction rate values. 

Chloroprene rubber (CR) is well known for its high gum vulcanizate strength arising from strain-induced crystallization. The uncured rubber also shows storage hardening due to slow crystallization. It has excellent physical properties, weather... 

Chloroprene rubber also generally offers good compression set properties. A higher percent of the compression set means a permanent deformation of the rubber matrix in a compressed form. The filled vulcanizates show a marked... 

Another chlorinated compound which, like vinyl chloride, is used only in its polymeric form, is chloroprene (2-chloro-l,3-butadiene), which is polymerized to make neoprene, first produced in 1940. As far as is known (17) y the monomer is made commercially only from acetylene via addition of hydrochloric acid to monovinylacetylene in the presence of cuprous chloride, but syntheses from butylenes or butadiene have been described. The production of chloroprene exceeded 100,000,000 pounds per year at the wartime peak and has been somewhat lower since then, but in view of the many valuable properties of the neoprene rubber it will continue to be important. 

Chloroprene rubber (Neoprene—trade name of DuPont) was one of the earliest synthetic rubbers, first commercialized in 1932. It has a wide range of useful properties but has not become a true general purpose synthetic rubber, probably because of its cost. It does possess properties superior to those of a number of general purpose polymers, such as oil, ozone, and heat resistance but for these properties other specialized polymers excel. Polychloroprene thus is positioned between the general purpose elastomers and the specialty rubbers. 

Wallace Carothers will be the subject of one of our Polymer Milestones when we discuss nylon in Chapter 3. Among his many accomplishments in the late 1920s and early 1930s, Carothers and his coworkers made a major contribution to the discovery and eventual production of the synthetic rubber, polychloroprene. It was synthesized from the diene monomer, chloroprene, CH2=CCI-CH=CHr Chloroprene, which is a very reactive monomer—it spontaneously polymerizes in the absence of inhibitors— was a product of some classic studies on acetylene chemistry performed by Carothers and coworkers at that time. In common with butadiene and iso-prene, in free radical polymerization chloroprene is incorporated into the growing chain as a number of different structural isomers. Elastomeric materials having very different physical and mechanical properties can be made by simply varying the polym-... 

If a rubber-like polymer is used as the vinyl polymer, this IPN will show good damping properties at elevated temperatures. So, butyl acrylate, ethylene glycol dimethacrylate, phenolic novolac, and bisphenol A type epoxies were used as IPN components. The dynamic mechanical properties of these IPNs were examined first, because the loss tangent is very important to damping properties. Then the damping properties of IPN and commercial chloroprene rubber were measured at various temperatures. 

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). 

The modern materials called synthetic rubber are not really synthetic rubber, since they are not identical with the natural product. They are, rather, substitutes for rubber—materials with properties and structure similar to but not identical with those of natural rubber. For example, the substance chloroprene, C4H.CI, with the structure... 

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