Vinylidene chloride polymers commercial polymerization

Vinylidene chloride is readily polymerized but the homopolymer does not have sufficient thermal stability to withstand melt processing. The homo-polymer is not therefore of commercial importance. However, by the copolymerization of vinylidene chloride with lesser amounts (generally 10-30%) of a vinyl monomer, processable copolymers may be obtained. The comonomers most widely used for this purpose are vinyl chloride and acrylonitrile. 

Up to this point we ve discussed only homopolymers—polymers that are made up of identical repeating units, in practice, however, copolymers are more important commercially. Copolymers are obtained when two or more different monomers are allowed to polymerize together. For example, copolymerization of vinyl chloride with vinylidene chloride (1,1-dichloroethylene) in a 1 4 ratio leads to the polymer Saran. 

Emulsion Polymerization. Emulsion polymerization is used commercially to make vinylidene chloride copolymers. In some applications, the resulting latex is used directly, usually with additional stabilizing ingredients, as a coating vehicle to apply the polymer to various substrates. In other... 

Commercially, suspension polymerizations have been limited to the free radical polymerization of water-insoluble liquid monomers to prepare a number of granular polymers, including polystyrene, poly(vinyl acetate), poly(methyl methacrylate), polytetrafluoroethylene, extrusion and injection-molding grades of poly(vinyl chloride), poly(styrene-co-acrylonitrile) (SAN), and extrusion-grade poly(vinylidene chloride-covinyl chloride). It is possible, however, to perform inverse suspension polymerizations, where water-soluble monomer (e.g., acrylamide) is dispersed in a continuous hydrophobic organic solvent. 

For the fabrication of CMS membranes from commercially available relatively inexpensive polymeric material, Centeno and Fuertes chose poly(vinylidene chloride-co-vinyl chloride) (PVDC-co-PVC) copolymer commercially available imder the trade name of Saran [63]. The polymer solution was spin-coated on a finely polished surface of porous carbon support. In some cases the polymer film was preoxidized in air at 150 or 200°C. The carbonization was carried out at either 500 or 1,000°C. 

The introduction of a comonomer such as vinyl chloride into the polymer chains reduces the crystallinity of the polymer to some extent. Practically, amorphous copolymer is obtained with a 3/1 ratio of vinylidene chlo-ride/vinyl chloride mixture [75]. Both emulsion and suspension free-radical polymerization processes are used for commercial production of PVDC co-... 

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