Vinylidene chloride industrial importance

In addition to homopolymers of varying molecular and particle structure, copolymers are also available commercially in which vinyl chloride is the principal monomer. Comonomers used eommercially include vinyl acetate, vinylidene chloride, propylene, acrylonitrile, vinyl isobutyl ether, and maleic, fumaric and acrylic esters. Of these the first three only are of importance to the plastics industry. The main function of introducing comonomer is to reduce the regularity of the polymer structure and thus lower the interchain forces. The polymers may therefore be proeessed at much lower temperatures and are useful in the manufacture of gramophone records and flooring compositions. 

Vinyl chloride has gained worldwide importance because of its industrial use as the precursor to PVC. It is also used in a wide variety of copolymers. The inherent flame-retardant properties, wide range of plasticized compounds, and low cost of polymers from vinyl chloride have made it a significant industrial chemical. About 95% of current vinyl chloride production worldwide ends up in polymer or copolymer applications. Vinyl chloride also serves as a starling material for Uie synthesis of a variety of industrial compounds. The primary nonpolymeric uses of vinyl chloride are in the manufacture of vinylidene chloride and tri- and tetrachloroethylene. 

In this paper, the water sorption of two commercially available vinylidene chloride copolymers is studied using IGC at low probe concentrations. The copolymers are a poly (vinylidene chloride-vinyl chloride) copolymer (Saran B) and a poly (vinylidene chloride-acrylonitrile) copolymer (Saran F). These copolymers are extensively used in the form of films, coatings, and film laminates in various industrial applications (for example, packaging of foods and pharmaceuticals) where their diffusion characteristics are of prime importance. 

Polyethylene is a special example of a generic class that includes many of the industrially important macromolecules, the vinyl and vinylidene polymers. The chemical repeat unit of a vinylidene polymer is -fCH2—CXY where X and Y represent single atoms or chemical groups. For a vinyl polymer Y is H and for polyethylene both X and Y are H. If X is —CH3, Cl, —CN, — or 0(C=0)CH3, where represents the mono-substituted benzene ring, or phenyl group, and Y is H, the well-known materials polypropylene, poly(vinyl chloride) (PVC), polyacrylonitrile, polystyrene and poly(vinyl acetate), respectively, are obtained. 

The PVDC homopolymer is difficult to process. Thus, copolymers of vinylidene chloride-vinyl chloride, vinylidene chloride-alkyl acrylate, vi-nylidene chloride - acrylonitrile, which are easier to process than PVDC homopolymer, are widely used in industrial processes. The choice of comonomer significantly affects the properties of the copolymer. Table 8 illustrates the reactivity ratios of some important monomers (monomer 1 = VDC) [76]. 

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