Vinylidene chloride, polymerization

The stability of vinylidene chloride copolymers generated using different polymerization initiators has also been examined. The two common types of initiators for radical polymerization are azo compounds and peroxides. A common azo initiator is azoisobutronitrile or AIBN. The initiation of vinylidene chloride polymerization using AIBN is illustrated in scheme 3. 

Scheme 3. Initiation of Vinylidene Chloride Polymerization Using AIBN as Initiator.

Vinylidene chloride polymerizes by both ionic and free-radical reactions. Processes based on the latter are far more common (23). Vinylidene chloride is of average reactivity when compared with other unsaturated monomers. The chlorine substituents stabilize radicals in the intermediate state of an addition reaction. Because they are also strongly electron-withdrawing, they polarize the double bond, making it susceptible to anionic attack. For the same reason, a carbonium ion intermediate is not favored. 

Of the three isomers of dichloroethylene, only the asymmetrically substituted vinylidene chloride polymerizes eatily. The polymerization of the monomer can be achieved either under pressure at 30-60 C or better, in... 

Dispersion polymerizations can be carried out either in bulk or in the presence of a solvent. Dispersion bulk polymerizations are industrially utilized to polymerize vinyl chloride, acrylonitrile, and vinylidene chloride. Polymerizations requiring the presence of a solvent are those whose monomer is solid in the polymerization conditions a solvent that favors phase separation can also be useful for example, styrene and methyl methacrylate are polymerized in dispersion in the presence of an alcohol inducing phase separation. When an adequate suspending agent (hydrox-ypropylcellulose, etc.) is added in the reaction medium, dispersion polymerization affords particles of imiform size (about 3-30 pm). 

POLYSTEP A-15-30K surfactant, vinylidene chloride polymerization POLYSTEP A-18 surfactant, vitamin E Soiimate E... 

Polymeric vinylidene chloride generally produced by free radical polymerization of CH2 = CCl2. Homopolymers and copolymers are used. A thermoplastic used in moulding, coatings and fibres. The polymers have high thermal stability and low permeability to gases, and are self extinguishing. 

Vinylidene chloride -10 (Dichloroethylene-1,1) CH2 CCl2 458 5.6-11.4 1.3 T T J. J 37 Colourless volatile liquid Polymerizes unless inhibited Decomposes at 457°C... 

Group of plastics whose resins are derived from the polymerization of vinylidene chloride or the copolymerization of vinylidene chloride and other unsaturated compounds. 

Problem 31.4 Vinylidene chloride, H2C=CCl2. does not polymerize in isotactic, svndiotactic, and atactic forms. Explain. 

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. 

Vinylidene Chloride CH2=CC12. Monomer forms unstable peroxides by autooxidation therefore, no oxidg agents or w Air Vap Monomer In Air 7.0 to 16.0% > Ambient > Ambient Inhibitor—Methyl Ether of Hy droquino ne (100 ppm) Transport store under. inert gas in a cool, dry place. No sparks -18.0 570 Self-polymerizing, easily copolymerizes with with Acrylates Styrene. Polymerization catalyzed by light or w... 

In addition, Bamford, Jenkins and coworkers (19) previously reported on the behavior of occluded radicals in the heterogeneous polymerizations of acrylonitrile, methyl acrylate, methyl methacrylate and vinylidene chloride. From their electron spin resonance studies, they concluded that the degree of occlusion was ... 

Polymerizations conducted in nonaqueous media in which the polymer is insoluble also display the characteristics of emulsion polymerization. When either vinyl acetate or methyl methacrylate is polymerized in a poor solvent for the polymer, for example, the rate accelerates as the polymerization progresses. This acceleration, which has been called the gel effect,probably is associated with the precipitation of minute droplets of polymer highly swollen with monomer. These droplets may provide polymerization loci in which a single chain radical may be isolated from all others. A similar heterophase polymerization is observed even in the polymerization of the pure monomer in those cases in which the polymer is insoluble in its own monomer. Vinyl chloride, vinylidene chloride, acrylonitrile, and methacryloni-trile polymerize with precipitation of the polymer in a finely divided dispersion as rapidly as it is formed. The reaction rate increases as these polymer particles are generated. In the case of vinyl chloride ... 

The observed heat of polymerization of vinylidene chloride includes whatever heat is evolved on crystallization of the polymer. The magnitude of this heat is not known, but it may have increased the observed —AHp as much as 1 or 2 kcal. per mole. 

Saran Wrap used in food packing is made by polymerizing a mixture in which the vinylidene chloride predominates. 

Some chemicals are susceptible to peroxide formation in the presence of air [10, 56]. Table 2.15 shows a list of structures that can form peroxides. The peroxide formation is normally a slow process. However, highly unstable peroxide products can be formed which can cause an explosion. Some of the chemicals whose structures are shown form explosive peroxides even without a significant concentration (e.g., isopropyl ether, divinyl acetylene, vinylidene chloride, potassium metal, sodium amide). Other substances form a hazardous peroxide on concentration, such as diethyl ether, tetrahydrofuran, and vinyl ethers, or on initiation of a polymerization (e.g., methyl acrylate and styrene) [66]. 

Regnault polymerized vinylidene chloride (PVDC) using sunlight. 

PVC materials are often defined to contain 50% or more vinyl chloride units by weight. PVC is generally a mixture of a number of additives and often other units, such as ethylene, propylene, vinylidene chloride, and vinyl acetate. Structurally similar products, but with differing properties, are made from the chlorination of PE but almost all PVC is made from the polymerization of vinyl chloride. Typical homopolymers are about 400-1000 units long. 

What will be the composition of copolymers produced in the first part of the polymerization of equimolar quantities of vinylidene chloride and vinyl chloride ... 

The effect of pressure on polymerization, although not extensively studied, is important from the practical viewpoint since several monomers are polymerized at pressures above atmospheric. Pressure affects polymerization through changes in concentrations, rate constants, and equilibrium constants [Ogo, 1984 Weale, 1974 Zutty and Burkhart, 1962], The commercial polymerizations of most gaseous monomers (e.g., vinyl chloride, vinylidene chloride, tetrafluoroethylene, vinyl fluoride) are carried out at very moderate pressures of about 5-10 MPa (1 MPa = 145 psi), where the primary effect is one of increased... 

Talamini, G. andE. Peggion, Polymerization of Vinyl Chloride and Vinylidene Chloride, Chap. 5 in Vinyl Polymerization, Vol. 1, Part I, G. E. Ham, ed., Marcel Dekker, New York, 1967. 

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