Poly vinylidine chloride

The monomer, vinylidine chloride, can be prepared by dehydrochlorination of 1,1,2-trichloro-ethylene  

It is a colorless liquid that boils at 32 °C. Also, it is rather hard to handle as it polymerizes on standing. This takes place upon exposure to air, water, or light. Storage under an inert atmosphere does not completely prevent polymer formation. 

Poly(vinylidine chloride) can be formed in bulk, solution, suspension, and emulsion polymerization processes. The products are highly crystalline with regular structures and a melting point of 220 °C. The structure can be illustrated as follows  

This regularity in structure is probably due to little chain transferring to the polymer backbone during polymerization. Such regularity of structure allows close packing of the chains and, as a result, there are no effective solvents for the polymer at room temperature. 

Copolymers of vinyl chloride with vinylidine chloride are similar in properties to copolymers with vinyl acetate. They contain from 5 to 12% of poly(vinylidine chloride) and are intended for use in stabilized calendaring. 

Copolymers containing 60% vinyl chloride and 40% acrylonitrile are used in fibers. The fibers are spun from acetone solution. They are nonflammable and have good chemical resistance. 

Vinylidine chloride homopolymers form readily by free-radical polymerization, but lack sufficient thermal stability for commercial use. Copolymers, however, with small amotmts of comonomers find many applications. 

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FIGURE 7-50 H NMR spectra of (A) poly(vinylidine chloride) homopolymer (B) polyisobutylene... 

Composites of polypyrrole and poly(vinyl chloride) have been prepared by several groups (64-67). Polythiophene-poly(vinyl chloride) composites have also been prepared (68). The electropolymerization of pyrrole on poly(vinyl chloride)-coated electrodes yielded composites with mechanical properties (tensile strength, percent elongation at break, percent elongation at yield) similar to poly(vinyl chloride) (65) but with a conductivity of 5-50 S/cm, which is only slightly inferior to polypyrrole (30-60 S/cm) prepared under similar conditions. In addition, the environmental stability was enhanced. Morphological studies (69) showed that the polypyrrole was not uniformly distributed in the film and had polypyrrole-rich layers next to the electrode. Similarly, poly(vinyl alcohol) (70) poly[(vinylidine chloride)-co-(trifluoroethylene)] (69) and brominated poly(vinyl carbazole) (71) have been used as the matrix polymers. The chemical polymerization of pyrrole in a poly(vinyl alcohol) matrix by ferric chloride and potassium ferricyanide also yielded conducting composites with conductivities of 10 S/cm (72-74). 

Fig. 43. Pyrolysis of (i) polyvinylchloride and (ii) poly(vinylidine chloride) in a nitrogen atmosphere [ 142 ].

Discuss the chemistry of poly(vinyl chloride) and poly(vinylidine chloride). 

Discuss chlorination of poly(vinylidine chloride) and poly(vinyl fluoride). 

The rates of thermal decompositions of poly(vinylidine chloride)s were shown to depend upon the method by which the polymers were prepared [497]. Those that were formed from very pure monomers by mass polymerization are most stable. Polymers prepared by emulsion polymerizatiOTi, on the other hand, degrade fastest. The mechanism of degradation of poly(vinylidine chloride) was proposed to be as follows [498-500] ... 

At higher chlorine levels, where vicinal chlorine groups may occur, one may also include a term for poly(vinylidine chloride) (Tg = 226°C). The relationship of glass-transition temperature to chlorine content for a CSM with random chlorine substitution is shown in Figure 1. 

The mechanical properties of protein-based materials are substantially lower than those of standard synthetic materials, such as poly(vinylidine chloride) or polyester (Table 11.11). The mechanical properties of protein-based materials were measured and modeled as a function of film characteristics [60,106,107]. For stronger materials, (e.g., based on wheat gluten, corn gluten and myofibrillar proteins), critical deformation (DC = 0.7 mm) and elastic modulus (K = 510 N/m) values are slightly lower than those of reference materials such as LDPE (DC = 2.3 mm K = 135 N/m), cellulose (DC = 3.3 mm K = 350 N/m), or even PVC films. Mechanical properties of corn gluten-based material are close to those of PVC. 

Another widely used approach is the in situ polymerization of an intractable polymer such as polypyrrole onto a polymer matrix with some degree of processibil-ity. Bjorklund [30] reported the formation of polypyrrole on methylcellulose and studied the kinetics of the in situ polymerization. Likewise, Gregory et al. [31] reported that conductive fabrics can be prepared by the in situ polymerization of either pyrrole or aniline onto textile substrates. The fabrics obtained by this process maintain the mechanical properties of the substrate and have reasonable surface conductivities. In situ polymerization of acetylene within swollen matrices such as polyethylene, polybutadiene, block copolymers of styrene and diene, and ethylene-propylene-diene terpolymers have also been investigated [32,33]. For example, when a stretched polyacetylene-polybutadiene composite prepared by this approach was iodine-doped, it had a conductivity of around 575 S/cm and excellent environmental stability due to the encapsulation of the ICP [34]. Likewise, composites of polypyrrole and polythiophene prepared by in situ polymerization in matrices such as poly(vinyl chloride), poly(vinyl alcohol), poly(vinylidine chloride-( o-trifluoroethylene), and brominated poly(vi-nyl carbazole) have also been reported. The conductivity of these composites can reach up to 60 S/cm when they are doped with appropriate species [10]. 

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