Polychloroprenes preparation

FIGURE 1.4 Glass transition temperature (Tg) and melt temperature (Ziu) of polychloroprene prepared at various temperatures. 

Latex mbber foams are generally prepared in slab or molded forms in the density range 64—128 kg/m (4—8 lbs/fT). Synthetic SBR latexes have replaced natural mbber latexes as the largest volume raw material for latex foam mbber. Other elastomers used in significant quantities are polychloroprene, nitrile mbbers, and synthetic i j -polyisoprene (115). 

Processing ndProperties. Neoprene has a variety of uses, both in latex and dry mbber form. The uses of the latex for dipping and coating have already been indicated. The dry mbber can be handled in the usual equipment, ie, mbber mills and Banbury mixers, to prepare various compounds. In addition to its excellent solvent resistance, polychloroprene is also much more resistant to oxidation or ozone attack than natural mbber. It is also more resistant to chemicals and has the additional property of flame resistance from the chlorine atoms. It exhibits good resiUence at room temperature, but has poor low temperature properties (crystallization). An interesting feature is its high density (1.23) resulting from the presence of chlorine in the chain this increases the price on a volume basis. 

The hydrohalide is usually prepared by passing hydrogen chloride into a solution of masticated high-grade raw rubber in benzene at 10°C for about six hours. Excess acid is then neutralised and plasticisers and stabilisers are added. The benzene is removed by steam distillation and the product washed and dried. Alternatively the solution is cast on to a polychloroprene rubber belt, leaving a tough film after evaporation of the solvent. 

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. 

Neoprene XD. Developed in the 1980s, this polychloroprene family was prepared using special xanthogendisulphides as chain modifiers, offering improved processability and vulcanizate properties. In solution, these polychloroprenes show slow crystallization and high temperature resistance. 

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),... 

Diene polymers refer to polymers synthesized from monomers that contain two carbon-carbon double bonds (i.e., diene monomers). Butadiene and isoprene are typical diene monomers (see Scheme 19.1). Butadiene monomers can link to each other in three ways to produce ds-1,4-polybutadiene, trans-l,4-polybutadi-ene and 1,2-polybutadiene, while isoprene monomers can link to each other in four ways. These dienes are the fundamental monomers which are used to synthesize most synthetic rubbers. Typical diene polymers include polyisoprene, polybutadiene and polychloroprene. Diene-based polymers usually refer to diene polymers as well as to those copolymers of which at least one monomer is a diene. They include various copolymers of diene monomers with other monomers, such as poly(butadiene-styrene) and nitrile butadiene rubbers. Except for natural polyisoprene, which is derived from the sap of the rubber tree, Hevea brasiliensis, all other diene-based polymers are prepared synthetically by polymerization methods. 

Colloidal particles, foams used to collect and separate, 12 22 Colloidal powders, 23 55-56 Colloidal silica, 22 380, 382, 384 applications of, 22 394 modification of, 22 393-394 preparation of, 22 392-393 properties of, 22 391-392 purification of, 22 393 Colloidal silica gels, 23 60 Colloidal solids, 7 293-294 Colloidal stability, 7 286-291 10 116 22 55 Colloidal stabilizers, in polychloroprene latex compounding, 19 857 Colloid mills, 8 702 10 127 Colloids, 7 271-303 23 54. See also Polymer colloids analysis, 7 296 applications, 7 292-296 conducting, 7 524... 

Yet as the many sided debate went on, Wallace Carothers started a series of investigations in 1928 which would eventually establish the macromolecular concept. His objective from the beginning was to prepare polymers of known structure through the use of established reactions of organic chemistry (85). In the brilliant years before his untimely death in 1937, he studied the preparation and properties of polyesters, polyanhydrides, polyamides, and polychloroprene (28). 

In the polymer prepared at -78°, the R value is nearly one and so almost the only sequence present is SMS. This enables this assignment to be made with confidence. The homopolymer type sequence, —MMM—, can be assigned by reference to the paper of Coleman, et a. ( ) on polychloroprene, to which we have already made reference. The sequences MMS and SMM can be assigned as shown by appealing to chemical shift rules similar to those we have already discussed for polystyrene sulfone ... 

The molecular weight distribution of peroxide formed at 4% oxidation was determined with a Waters gel permeation chromatograph. The peroxide was prepared as a 0.7% (w./v.) solution in tetrahydrofuran, and the molecular weight distribution then obtained is shown in Figure 2. By analogy with polychloroprene count 25 is equivalent to about 140 monomer units in the peroxide, and the peak maximum is at about 18 units—i.e., a molecular weight of 2000. The incipient peaks at counts 34, 36, and between 32 and 33 result from products of peroxide decomposition. 

The formation of coagulum is observed in all types of emulsion polymers (i) synthetic rubber latexes such as butadiene-styrene, acrylonitrile-butadiene, and butadiene-styrene-vinyl pyridine copolymers as well as polybutadiene, polychloroprene, and polyisoprene (ii) coatings latexes such as styrene-butadiene, acrylate ester, vinyl acetate, vinyl chloride, and ethylene copolymers (iii) plastisol resins such as polyvinyl chloride (iv) specialty latexes such as polyethylene, polytetrafluoroethylene, and other fluorinated polymers (v) inverse latexes of polyacrylamide and other water-soluble polymers prepared by inverse emulsion polymerization. There are no major latex classes produced by emulsion polymerization that are completely free of coagulum formation during or after polymerization. 

Due to the high nucleophilicity of oxazoline monomers, their polymerization may be initiated by C—Cl bond even in the absence of silver salt. Thus, chloromethylated polystyrene [290] or polychloroprene [291] were used to prepare corresponding graft copolymers. More recently, polyoxazoline was grafted on poly(vinyl ether)s containing certain proportion of chloroethyl groups [292],... 

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. 

Commercial samples of l,4-c/5 -polybutadiene (SKD, E-BR) polybutadiene (Diene 35 NFA, BR) l,4-c/5 -polyisoprene (Carom IR 2200, E-IR), and polychloroprene (Denka M 40, PCh) were used in the experiments (Table 10.1). The 1,4-irara-polyisoprene samples were supplied by Prof A. A. Popov, Institute of Chemical Physics, Russian Academy of Sciences. All rubbers were purified by three-fold precipitation from CCl solutions in excess of methanol. The aforementioned elastomer structures were confirmed by means of H-NMR spectroscopy. Ozone was prepared by passing oxygen flow through a 4-9 kV electric discharge. 

Table 15.5 shows the results of Mochel [22] for the effect of conversion upon the gel content of polychloroprene rubbers prepared by emulsion polymerization at 40 °C. In section (a) of this table are shown results for polymers produced in the absence of added sulfur section (b) shows results for polymers produced with the addition of 0.6 parts of sulfur per 100 parts by mass of chloroprene, before chemical peptization of the polymer. In both types of reaction system, polymer gel begins to form quite early in the reaction. However, these results indicate that sulfur has a slight tendency to act as a modifier during the polymerization, in that the onset of gel-formation is delayed when sulfur is present. Also delayed is the pdnt at which the polymer is virtually entirely gel. Mochel et al. [23] have reported results for the molar mass distribution of a thiuiam-modified polychloroprene rubber produced by emulsion polymerization at 40 °C,... 

Table 15.5 Preparation of polychloroprene rubbers by emulsion polymerization at 40 C variation of gel content with conversion (Modiel [22])...

The irradiation of mixed lattices for subsequent combination of the mptured chains is another approach it has been carried out with natural rubber and poly(vinyl chloride) lattices to prepare graft (and block) copolymers in fairly high yields without the problem of monomer recovery. The same method has been used to graft polychloroprene onto synthetic polyisoprene dispersions and onto polybutadiene lattices of various compositions. 

The polymer, formed by this technique, consists of about 85% trans-1,4 units, 10% cw-1,4 units, 1.5% 1,2 units, and 1.0% 3,4 units. The polymer is essentially linear with a molecular weight equal to approximately 100,000. The sulfur-modified polychloroprenes are sold under the tradename Neoprene-G. An unmodified version prepared with mercaptan chain-transferring agents (Neoprene W) is a polymer with a molecular weight of about 200,000. ... 

Angier and Watson [A7, A9] found that graft copolymers could be prepared by masticating elastomer blends in the absence of oxygen. The systems studied included natural rubber/polychloroprene, natural rubber/ butadiene-styrene copolymer, and polychloroprene/butadience-styrene copolymer. The mechanism hypothesized was... 

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