Vinylidene Chloride VDC Copolymers

Thermally induced carbon-chlorine bond homolysis gives rise to a carbon-chlorine radical pair. The chlorine atom so produced most typically abstracts an adjacent hydrogen atom to form hydrogen chloride and generate an allylic dichloromethylene unit in the polymer main chain, which may act as an initiation site for further rapid sequential dehydrochlorination 502579 [a.l93]. 

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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. 

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... 

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... 

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. 

Materials The competitive oxygen barrier resins investigated include Dow Chemical Company s vinylidene chloride/vinyl chloride (VDC) copolymer (experimental grade XU 32009.02), Mitsubishi Gas Chemical Company s aromatic nylon MXD-6, Du Pont s amorphous nylon SELAR PA 3426, Rohm Haas s polyacrylic-imide XHTA-50A and two EVOH resins — Kuraray s EVAL EP-E105 (44 mole% ethylene content) and Nippon Gohsei s SOARNOL D (29 mole% ethylene content). ... 

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. 

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 ... 

Table 4.11 Composition results calculated from pyrolysis peak intensities compared with H-NMR results of five compositions of vinylidene chloride (VDC)/vinyl chloride (VC) copolymer ...

Vinylidene Chloride Copolymer Latex. Vinyhdene chloride polymers are often made in emulsion, but usuaUy are isolated, dried, and used as conventional resins. Stable latices have been prepared and can be used direcdy for coatings (171—176). The principal apphcations for these materials are as barrier coatings on paper products and, more recently, on plastic films. The heat-seal characteristics of VDC copolymer coatings are equaUy valuable in many apphcations. They are also used as binders for paints and nonwoven fabrics (177). The use of special VDC copolymer latices for barrier laminating adhesives is growing, and the use of vinyhdene chloride copolymers in flame-resistant carpet backing is weU known (178—181). VDC latices can also be used to coat poly(ethylene terephthalate) (PET) bottles to retain carbon dioxide (182). 

Vinylidene Chloride Copolymer Foams. Low density, fine-celled VDC copolymer foams can be made by extmsion of a mixture of vinylidene chloride copolymer and a blowing agent at 120—150°C (190). The formulation must contain heat stabilizers, and the extmsion equipment must be made of noncatalytic metals to prevent accelerated decomposition of the polymer. The low melt viscosity of the VDC copolymer formulation limits the size of the foam sheet that can be extmded. 

Expandable VDC copolymer microspheres are prepared by a microsuspension process (191). The expanded microspheres are used in reinforced polyesters, blocking multipair cable, and in composites for furniture, marble, and marine appHcations (192—195). Vinylidene chloride copolymer microspheres are also used in printing inks and paper manufacture (196). 

Vinylidene chloride polymers are more impermeable to a wider variety of gases and liquids than other polymers. For example, commercial copolymers are available with oxygen permeabilities of 0.03 nmol/m s-GPa. This is a consequence of the combination of high density and high crystallinity in the polymer. An increase m either tends to reduce permeability. Permeability is affected by the kind and amounts of comonomer as well as crystallinity. A more polar comonomer, e.g., an AN comonomer, increases the water-vapor transmission more than VC when other factors are constant. All VDC copolymers, are very impel meable to... 

Vinylidene chloride-vinyl chloride copolymers were originally developed for thermoplastic molding applications, and small amounts are still used for this purpose. Extrusion of VDC-VC copolymers is the main fabrication technique for filaments, films, rods, and tubing or pipe, and involves the same concerns for thermal degradation, streamlined flow, and noncatalytic materials of construction as described for injection-molding resins. A significant application for vinylidene chloride copolymer resins is in the... 

Vinylidene chloride copolymerizes randomly with methyl acrylate and nearly so with other acrylates. Very severe composition drift occurs, however, in copolymerizations with vinyl chloride or methacrylates. Several methods have been developed to produce homogeneous copolymers regardless of the reactivity ratio (43). These methods are applicable mainly to emulsion and suspension processes where adequate stirring can be maintained. Copolymerization rates of VDC with small amounts of a second monomer are normally lower than its rate of homopolymerization. The kinetics of the copolymerization of VDC and VC have been studied (45—48). 

The maximum rates of crystallization of the more common crystalline copolymers occur at 80—120°C. In many cases, these copolymers have broad composition distributions containing both fractions of high VDC content that crystallize rapidly and other fractions that do not crystallize at all. Poly(vinylidene chloride) probably crystallizes at a maximum rate at 140—150°C, but the process is difficult to follow because of severe polymer degradation. The copolymers may remain amorphous for a considerable period of time if quenched to room temperature. The induction time before the onset of crystallization depends on both the type and amount of comonomer PVDC crystallizes within minutes at 25°C. 

Materials are also blended with VDC copolymers to improve toughness (211—214). Vinylidene chloride copolymer blended with ethylene—vinyl acetate copolymers improves toughness and lowers heat-seal temperatures (215,216). Adhesion of a VDC copolymer coating to polyester can be achieved by blending the copolymer with a linear polyester resin (217). 

In the present section, general comparisons will be presented between these two theories. Both theories will be utilized in a correlative mode. The parameters for barrier polymers will be defined for idealized completely amorphous poly(vinylidene chloride) (PVDC) and a VDC/VC copolymer. It will be shown that physically significant qualitatitive differences exist between the results calculated by the two theories. 

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