Vinylidene chloride, copolymers with acrylonitrile

Incorporation of a comonomer reduces crystallinity and the crystalline melting point, permitting processing at lower temperatures or imparting solubility in organic solvents. Vinyl chloride and methyl acrylate are commonly used as comonomers for extrudable resins, typically in amounts from 6 to 28%. Vinylidene chloride copolymers with methyl acrylate and methyl methacrylate are commonly used for latex (water-based) coatings. Copolymers with acrylonitrile, methacryloni-trile, and methyl methacrylate are common for solvent-based coatings. All commercially available PVDC resins are copolymers. 

On account of its low thermal stability, polyfvinylidene chloride) is seldom used in paints. Vinylidene chloride copolymers with vinyl chloride, acrylonitrile, or acrylates are mainly employed. These heat-sealable copolymers are efficient gas barriers and have an outstanding resistance to chemicals. They are marketed as solid resins and dispersions. Vinylidene chloride copolymers are mainly used for coating foodpackaging foils. They are also important in paint coatings where good chemical resistance is required. 

Saran The names Saran and Saran Wrap are tradenames for vinylidene chloride copolymer produced by Dow Chemical Co. They represent a series of vinylidene chloride copolymers with vinyl chloride or acrylonitrile. The vinyl chloride copolymers are best known. Other copolymers with vinyl acetate, allyl esters, unsaturated ethers, acrylates, methacrylates, and styrene have appeared but have not achieved significant commercial interest. 

Copolymers of acrylonitrile and vinylidene chloride have been used for many years to produce films of low gas permeability, often as a coating on another material. Styrene-acrylonitrile with styrene as the predominant free monomer (SAN polymers) has also been available for a long time. In the 1970s materials were produced which aimed to provide a compromise between the very low gas permeability of poly(vinylidene chloride) and poly(acrylonitrile) with the processability of polystyrene or SAN polymers (discussed more fully in Chapter 16). These became known as nitrile resins. 

Poly(vinylidene chloride-co-acrylonitrile) is widely used as a latex coating for cellophane, polyethylene and paper. Since this copolymer is soluble in organic solvents, it is also used as a solution coating. Tile resistance to vapor permeability and the ease of printing on polyethylene and cellophane is increased by coating with this vinylidene chloride copolymer. 

The principal solution to fabrication difficulties is copolymerization. Three types of comonomers are commercially important vinyl chloride acrylates, including alkyl acrylates and alkylmethacrylates and acrylonitrile. When extrusion is the method of fabrication, other solutions include formulation with plasticizers, stabilizers, and extmsion aids plus applying improved extrusion techniques. The literature on vinylidene chloride copolymers through 1972 has been reviewed (1). 

A number of copolymers of vinylidene chloride are used in practice. Copolymers with acrylonitrile are used in low flammability fibers (modacrylic fibers). These fibers begin to lose weight when heated at 285-308° C due to dehydrohalogenation [41] but do not ignite easily. A tercopolymer butadiene-styrene-vinylidene chloride is used in fabrics industry and in paper industry. Other copolymers include PVC/PVDC, used for fibers and for films with low permeability to gases and water vapors (barrier films), etc. 

Four polymers with different surface compositions were used in this study—polystyrene (PS), poly(methyl methacrylate) (PMMA), polyacrylamide (PAM), and a poly(vinylidene chloride) (PVeC) copolymer (containing 20% polyacrylonitrile). Polystyrene has essentially a hydrocarbon surface, whereas the surfaces of poly (methyl methacrylate) and polyacrylamide contain ester and amide groups, respectively. The surface of the poly(vinylidene chloride) copolymer on the other hand will contain a relatively large number of chlorine atoms. The presence of acrylonitrile in the poly(vinylidene chloride) copolymer improved the solubility characteristics of the polymer for the purposes of this study, but did not appreciably alter, its critical surface tension of wetting. Values of y of these polymers ranged from 30 to 33 dynes per cm. for polystyrene to approximately 40 dynes per cm. for the poly(vinylidene chloride) copolymer. No attempt was made to determine e crystallinity of the polymer samples, or to correlate crystallinity with adsorption of the fluorocarbon additives. 

Zhang and Prud homme estimated values of the binary interaction parameters for PCL with vinylidene chloride copolymers known as Saran, that is with copolymers of vinylidene chloride with, separately, vinyl chloride, acrylonitrile or vinyl acetate [74]. Interaction parameters were estimated from melting point depressions. Values obtained were found to be composition-dependent and are... 

Many synthetic latices exist (16-18). They contain butadiene and styrene copolymers (elastomeric), styrene-butadiene copolymers (resinous), butadiene and acrylonitrile copolymers, butadiene with styrene and acrylonitrile, chloro-prene copolymers, methacrylate and acrylate ester copolymers, vinyl acetate copolymers, vinyl and vinylidene chloride copolymers, ethylene copolymers, fluori-nated copolymers, acrylamide copolymers, styrene-acrolein copolymers, and pyrrole and pyrrole copolymers. Many of these latices also have carboxylated versions. 

Additionally to the procedures described earlier, improvements for thermostabilization is copolymerisation of vinyl chloride with suitable monomers. A great number of monomers were investigated to optimize the properties of resins. But only vinyl acetate, vinylidene chloride, ethylene, propylene, acrylonitrile, acrylic acid esters, and maleic acid esters, respectively, are of interest commercially [305,436,437]. The copolymerization was carried out in emulsion, suspension, and solution in connection with water- or oil-soluble initiators, as mentioned elsewhere. Another possibility for modifying PVC is grafting of VC on suitable polymers [305,438], blends of PVC with butadiene/styrene and butadiene/ methacryl acid esters copolymers [433], and polymer-analogous reactions on the macromolecule [439,440] (e.g., chlorination of PVC). 

Laser Raman spectroscopy has been proposed as a useful technique for probing the microstructure of copolymers. Good correlations were found between the concentrations of some isolated, dyad, triad and tetrad comonomer sequences in vinyl chloride/vinylidene chloride copolymers and certain scattering intensities [99]. The positions and intensities of particular absorption bands have also been correlated with chain microstructure in an infrared study of ethylene/vinyl chloride copolymers, previously characterised by C-NMR analysis [100]. More recently, FTIR spectra have been analysed for monad, dyad and triad monomer sequence-distribution dependencies in random styrene/acrylonitrile copolymers [101]. Changes in peak intensities from normalised spectra were correlated with microstructure probabilities assignments were given if there existed a linear relationship between peak intensity and the number fraction of a microstructure. 

PVC is also copolymerised with other monomers such as vinyl acetate, vinylidene chloride propylene and acrylonitrile. Copolymerisation with vinyl acetate tends to soften the polymer to the point that plasticiser addition may be unnecessary. For low temperature applications, plasticiser addition may still be desirable and in this form the copolymer is used in the fabrication of refrigerator trays. 

By copolymerising the vinylidene chloride with about 10-15% of vinyl chloride, processable polymers may be obtained which are used in the manufacture of filaments and films. These copolymers have been marketed by the Dow Company since 1940 under the trade name Saran. Vinylidene chloride-acrylonitrile copolymers for use as coatings of low moisture permeability are also marketed (Saran, Viclan). Vinylidene chloride-vinyl chloride copolymers in which the vinylidene chloride is the minor component (2-20%) were mentioned in Chapter 12. 

Copolymers of vinylidene chloride with 5-50% acrylonitrile were investigated by IG Farben during World War II and found to be promising for cast films. Early patents by ICC and Dow indicated that the copolymers were rigid, transparent and with a high impact strength. 

Poly(vinylidene chloride) (XLII) and its copolymers with vinyl chloride, acrylonitrile, and acrylates, usually produced by the suspension or emulsion process, are useful as oil, fat, oxygen, and moisture-resistant packaging films (Saran wrap), containers, coatings, tank liners, and monofilaments in drapery fabrics and industrial filter cloths. 

Vinylidene chloride is used principally in copolymers with vinyl chloride, acrylonitrile and other monomers for packaging materials, adhesives and synthetic fibres (Lewis, 1993). 

Trier (34) described one bulked paper as being loaded with microspheres of a copolymer of vinylidene chloride and acrylonitrile. Such polymers are known to split off hydrochloric acid. While this may have occurred in oven aging, the pH of the sample did not drop below 7 so acid degradation does not seem to have been involved. On the other hand, the paper did degrade rapidly in the humid oven, and this was very well corrected by the KI treatment. From the evidence in the literature peroxides and, through the catalysts, free radicals appear to be at work, which the KI corrected. This is an application that recalls its use in oxygen-alkaline pulping and in the prevention of the peroxide defects in microfilm. 

The first two modacrylic fibers ever introduced in the United States were Dynel (by Union Carbide) in 1949 and Verel (by Tennessee Eastman) in 1956. The former was a copolymer of 60 percent vinyl chloride and 40 percent acrylonitrile, and the latter was said to be a 50-50 copolymer of vinylidene chloride and acrylonitrile with perhaps a third component graft-copolymerized onto the primary material to secure dyeability. SEF and its version for wigs, Elura , were introduced by Monsanto Fibers in 1972. A few foreign manufacturers are making modacrylic fibers, but the only modacrylic fiber currently in production in the United States is SEF . 

Copolymers of acrylonitrile and methyl methacrylate (115) and terpolymers of acrylonitrile, styrene, and methyl methacrylate (116,117) are used as barrier polymers. Acrylonitrile copolymers and multipolymers containing butyl acrylate (118—121), ethyl acrylate (122), 2-etliylliexyl acrylate (118,121,123,124), liydroxyethyl acrylate (120), vinyl acetate (119,125), vinyl ethers (125,126), and vinylidene chloride (121,122,127—129) are also used in barrier films, laminates, and coatings. Environmentally degradable polymers useful in packaging are prepared from polymerization of acrylonitrile with styrene and methyl vinyl ketone (130). Table 5 gives the structures, formulas, and CAS Registry Numbers for several comonomers of acrylonitrile. 

Inverse gas chromatography, IGC, has been used to study water sorption of two poly (vinylidene chloride-vinyl chloride) and poly (vinylidene chloride-acrylonitrile) copolymers, at temperatures between 20 and 50°C and low water uptakes. It was found that the specific retention volume of water increases with decreasing amount of water injected, increases dramatically with decreasing temperature and strongly depends on the type of copolymer. Thermodynamic parameters of sorption namely free energy, entropy, enthalpy of sorption and activity coefficient were calculated. 

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