Vinylidene chloride VDC

Toxicology. Vinylidene chloride (VDC) causes central nervous system (CNS) depression at high levels, and repeated exposure to lower concentrations results in liver and kidney damage in experimental animals. 

Vinylidene chloride (VDC) is prepared commercially by the dehy-drochlorination of 1,1,2-tnchloroethane with lime or caustic in slight excess (2-10%). A continuous liquid-phase reaction at 98-99°C yields 90% VDC. Commercial grades contain 200 ppm of the monomethyl ether of hydroquinone (MEHQ). 

Vinylidene chloride (VDC) is prepared commercially by the dehydrochlorination of 1,1,2-trichloroethane with lime or caustic in slight excess (2—10%) (3,9). A continuous liquid-phase reaction at 98—99°C yields 90% VDC. Caustic gives better results than lime. Vinylidene chloride is purified by washing with water, drying, and fractional distillation. It forms an azeotrope with 6 wt % methanol (10). Purification can be achieved by distillation of the azeotrope, followed by extraction of the methanol with water an inhibitor is usually added at this point. Commercial grades contain 200 ppm of the monomethyl ether of hydroquinone (MEHQ). Many other inhibitors for the polymerization of vinylidene chloride have been described in patents, but MEHQ is the one most often used. The inhibitor can be removed by distillation or by washing with 25 wt % aqueous caustic under an inert atmosphere at low temperatures. 

Homo and copolymers of vinylidene chloride (VDC) possess extremely high barrier properties to gases, water and aromas as well as good resistance to water and solvents. The barrier properties of polyvinylidene chloride (PVDC) come from the dense packing of its polymer chains (without voids or branching) which are crystalline in their stable form. The chlorine content of the high density polymer is 73 % (1.80-1.97 g/cm3, crystalline). 

The copolymers of vinylidene chloride (VDC) and BMA have high flexibility. Their tensile strength and toughness can be further improved by including proper amounts of VDC and BMA homopolymers. The melt mixing method cannot be used because the melting point of PVDC is high (nearly 200°C) [31]. The inclusion of the homopolymers via the concentrated emulsion method can, however, be easily achieved. Three preparation procedures were employed to... 

The composition of a vinylidene chloride (VDC)/vinyl chloride (VC) co-polymer, calculated as a function of conversion using such a program, is shown in Figure 6-22. 

Sample copolymers of vinylidene chloride (VDC) [19] and vinyl chloride (VC) are being used in the experimental part of this study, which complements the calculations being performed on similar systems by a variety of techniques. 

With the growing demand for coextruded products, barrier plastics have shown significant growth in the last several years. Historically, the high barrier resins market has been dominated by three leading materials — vinylidene chloride (VDC) copolymers, ethylene vinyl alcohol (EVOH) copolymers, and nitrile resins. Since 1985, however, there has been a lot of interest worldwide in the development of moderate to intermediate barrier resins, as apparent from the introduction of a number of such resins, notably, aromatic nylon MXD-6 from Mitsubishi Gas Chemical Company, amorphous nylons SELAR PA by Du Pont and NovamidX21 by Mitsubishi Chemical Industries, polyacrylic-imide copolymer EXL (introduced earlier as XHTA) by Rohm and Haas and copolyester B010 by Mitsui/Owens-Illinois. 

General Description Polyvinylidene Chloride (PVDC) resin is a copolymer of vinylidene chloride (VDC) with vinyl chloride or other monomers Dow Plastics vinyl chloride and vinylidene chloride, Saran, is usually supplied as a white, free-flowing powder. Dow Saran polymers are known worldwide for their gas-moisture, and chemical-barrier properties, and for their ignition-resistant properties. 

Polyvinylidene Chloride Stereoregular thermoplastic polymer of vinylidene chloride has good abrasion and chemical resistance and barrier properties. Vinylidene chloride (VDC) content always exceeds 50%. Proeessed by molding and extrusion. Used in food paekaging films, bag liners, pipes, upholstery, fibers, and eoatings. Also called PVDC. 

A similar type of automatic viscometer, with a capillary diameter of 0.4 or 0.5 mm and a length of 200 mm, was applied to copolymers of vinyl chloride (VC), methyl acrylate, and MMA with vinylidene chloride (VDC) [33]. At the peak maximum the viscosity was not very different from that of the whole polymer. The viscosities increased with the decrease in VDC content. From the plot of [fj ] and the slope a and intercept K were obtained and corrections were made according to ... 

Moreton [68] used vinylidene chloride (VDC) in an attempt to produce a precursor, which would principally oxidize fast and, hopefully, achieve carbonization without oxidation, but unfortunately, the carbon fiber properties obtained were poor. It was hoped that the presence of the VDC monomer units would provide sites for potential cross-linking of the ladder polymers, thereby hastening the oxidation process. 

Several examples of NMR studies of copolymers that exhibit Bernoullian sequence distributions but arise from non-Bernoullian mechanisms have been reported. Komoroski and Schockcor [11], for example, have characterised a range of commercial vinyl chloride (VC)/vinylidene chloride (VDC) copolymers using carbon-13 NMR spectroscopy. Although these polymers were prepared to high conversion, the monomer feed was continuously adjusted to maintain a constant comonomer composition. Full triad sequence distributions were determined for each sample. These were then compared with distributions calculated using Bernoullian and first-order Markov statistics the better match was observed with the former. Independent studies on the variation of copolymer composition with feed composition have indicated that the VDC/VC system exhibits terminal model behaviour, with reactivity ratios = 3.2 and = 0.3 [12]. As the product of these reactivity ratios is close to unity, sequence distributions that are approximately Bernoullian are expected. 

The thermal degradation of poly(vinylidene chloride) and vinylidene chloride (VDC) copolymers usually occurs with the evolution of hydrogen chloride at elevated temperature. For the homopolymer, the degradation occurs rapidly when heated to its melting point, making it difficult to formulate through extrusion processes. As a consequence, only the copolymers with vinyl chloride, alkyl acrylate and acrylonitrile, etc., are of commercial... 

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