Poly Vinylidene Chloride

Vinylidene chloride is also produced by the thermal cracking of trichloroethylene at 400°C. 1,1-Dichloroethylene can be quantitatively separated from the resulting mixture with cis and trans 1,2 isomers. 

Since metals such as Fe, Zn, Sn, and Cu catalyze dehydrochlorination, the free radical polymerization must be carried out in glass or stainless steel vessels. 

Copolymers with ethyl acrylate are also commercially available for use as thermoplasts. Fiber-forming copolymers result from the copolymerization of vinylidene chloride with 35-45% acrylonitrile. 

Poly(vinylidene chloride) and its copolymers are very solvent resistant. Consequently, these are used for pipes and filter cloths. In addition, poly(vinylidene chloride) is used for high-abrasive-strength or long-wearing seat covers, noninflammable hair for dolls, and mothballs for the covering of battleships, planes, etc. 

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Acrylonitrile-butadiene-styrene (ABS) copolymer Poly(vinylidene chloride)... 

Poly(vinylidene Chloride). Poly(vinylidene chloride) is prepared according to the following reaction ... 

Properties Flexible and filled Poly(vinylidene chloride) Poly(vinyl formal) ... 

Poly(vinyl chloride) and poly(vinyl acetate) Poly(vinyl chloride), 15% glass-fiber-reinforced Poly(vinylidene chloride) Poly(vinyl formal) Chlorinated poly(vinyl chloride) Poly(vinyl butyral), flexible ... 

Fig. 10. Adsorption ( , O)"desorption (A, A) isotherms of water vapor on poly(vinylidene chloride) (PVDC) carbon before (filled symbols) and after...

Poly(vinylidene chloride). Poly(viayHdene chloride) [9002-85-1] (PVDC), most of which is produced by Dow Chemical, is best known in its saran or PVC-copolymerized form (see Vinylidene chloride and poly(VINYLIDENE chloride)). As solvent or emulsion coating, PVDC imparts high oxygen, fat, aroma, and water-vapor resistance to substrates such as ceUophane, oriented polypropylene, polyester, and nylon. 

Vinylidene chloride copolymers were among the first synthetic polymers to be commercialized. Their most valuable property is low permeabiUty to a wide range of gases and vapors. From the beginning in 1939, the word Saran has been used for polymers with high vinylidene chloride content, and it is still a trademark of The Dow Chemical Company in some countries. Sometimes Saran and poly (vinylidene chloride) are used interchangeably in the Hterature. This can lead to confusion because, although Saran includes the homopolymer, only copolymers have commercial importance. The homopolymer, ie, poly (vinylidene chloride), is not commonly used because it is difficult to fabricate. 

Ninety-six percent of the EDC produced in the United States is converted to vinyl chloride for the production of poly(vinyl chloride) (PVC) (1) (see Vinyl polymers). Chloroform and carbon tetrachloride are used as chemical intermediates in the manufacture of chlorofluorocarbons (CECs). Methjiene chloride, 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene have wide and varied use as solvents. Methyl chloride is used almost exclusively for the manufacture of silicone. Vinylidene chloride is chiefly used to produce poly (vinylidene chloride) copolymers used in household food wraps (see Vinylidene chloride and poly(vinylidene chloride). Chloroben2enes are important chemical intermediates with end use appHcations including disinfectants, thermoplastics, and room deodorants. 

Comparison of Table 5.4 and 5.7 allows the prediction that aromatic oils will be plasticisers for natural rubber, that dibutyl phthalate will plasticise poly(methyl methacrylate), that tritolyl phosphate will plasticise nitrile rubbers, that dibenzyl ether will plasticise poly(vinylidene chloride) and that dimethyl phthalate will plasticise cellulose diacetate. These predictions are found to be correct. What is not predictable is that camphor should be an effective plasticiser for cellulose nitrate. It would seem that this crystalline material, which has to be dispersed into the polymer with the aid of liquids such as ethyl alcohol, is only compatible with the polymer because of some specific interaction between the carbonyl group present in the camphor with some group in the cellulose nitrate. 

Copolymers of acrylonitrile and vinylidene chloride have been used for many years to produce films of low gas permeability, often as a coating on another material. Styrene-acrylonitrile with styrene as the predominant free monomer (SAN polymers) has also been available for a long time. In the 1970s materials were produced which aimed to provide a compromise between the very low gas permeability of poly(vinylidene chloride) and poly(acrylonitrile) with the processability of polystyrene or SAN polymers (discussed more fully in Chapter 16). These became known as nitrile resins. 

Consideration of the structure of poly (vinylidene chloride) (Figure 17.3) enables certain predictions to be made about its properties. 

Poly(ethylene terephtlhalate) Phenol-formaldehyde Polyimide Polyisobutylene Poly(methyl methacrylate), acrylic Poly-4-methylpentene-1 Polyoxymethylene polyformaldehyde, acetal Polypropylene Polyphenylene ether Polyphenylene oxide Poly(phenylene sulphide) Poly(phenylene sulphone) Polystyrene Polysulfone Polytetrafluoroethylene Polyurethane Poly(vinyl acetate) Poly(vinyl alcohol) Poly(vinyl butyral) Poly(vinyl chloride) Poly(vinylidene chloride) Poly(vinylidene fluoride) Poly(vinyl formal) Polyvinylcarbazole Styrene Acrylonitrile Styrene butadiene rubber Styrene-butadiene-styrene Urea-formaldehyde Unsaturated polyester... 

Figure 6. Partly assembled, 5-gallon, low density polyethylene liner in a corrugated carton. Liner is coated with poly(vinylidene chloride) (Saran) to block oxygen entry and prevent loss of aroma used for cola concentrate.

Similarly, oriented crystallisation can be induced by stretching sheets or films of polymers in two directions simultaneously. The resulting materials have biaxially oriented polymer crystals. Typical examples of such materials are biaxially stretched poly(ethylene terephthalate), poly(vinylidene chloride), and poly (propylene). Since the oriented crystals do not interfere with light waves, such films combine good strength with high clarity, which makes them attractive in a number of applications. 

When X = Y, as in polyethylene, poly-(tetrafluoroethylene), polyisobutylene, and poly -(vinylidene chloride), the polymers are highly crystalline products with sharply definable melting points (except for polyisobutylene, which crystallizes readily on stretching but with difficulty on cooling). Oriented specimens of high strength may be obtained, exactly as in the crystalline condensation polymers. 

The head-to-tail arrangement in poly-(vinyl alcohol) is further confirmed by its X-ray diffraction pattern in the crystalline state. Likewise, analysis of the X-ray diffraction of crystalline poly-(vinylidene chloride), (—CH2—CCI2—)x, and of crystalline (stretched) polyisobutylene, [—CH2—C(CH3)2—]x, shows the units to be arranged in these cases also in the expected head-to-tail forms. 

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