Vinylidene chloride polymers polymerization

Vinylidene Chloride Monoperoxide. When vinyli-dene chloride is stored without a polymerization inhibitor (such as tertiary butyl catechol or other phenol type inhibitors) at a temp of between -40 and +25° in the presence of air or oxygen, the 02 dissolves to form a peroxide compd of undetermined nature which is an extremely violent expl This peroxide seems to act as a polymerization catalyst because its formation is often accompanied by the pptn of a flocculent vinylidene chloride polymer. Since the peroxide is absorbed on the pptd polymer, any separation... 

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. 

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. 

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. 

For disubstituted ethylenes, the presence and type of tacticity depends on the positions of substitution and the identity of the substituents. In the polymerization of a 1,1-disubstituted ethylene, CH2=CRR, stereoisomerism does not exist if the R and R groups are the same (e.g., isobutylene and vinylidene chloride). When R and R are different (e.g., —CH3 and —COOCH3 in methyl methacrylate), stereoisomerism occurs exactly as in the case of a monosubstituted ethylene. The methyl groups can be located all above or all below the plane of the polymer chain (isotactic), alternately above and below (syndiotactic), or randomly (atactic). The presence of the second substituent has no effect on the situation since steric placement of the first substituent automatically fixes that of the second. The second substituent is isotactic if the first is isotactic, syndiotactic if the first substituent is syndiotactic, and atactic if the first is atactic. 

Many other types of polymer have been prepared which exhibit semiconductivity. All obey the equation a = a0exp — E/kT. These include xanthene polymers (109, 110), polymerized phthalocyanines (111, 112), epoxides and polydiketones (86, 113), polypentadienes (114), polydicyanoacetylenes (115), polyvinylferrocene and substituted ferrocene (116, 117, 118, 119), polymeric complexes of tetracyanoethylene and metals (120), poly(vinyl chloride) and poly(vinylidene chloride) (121), polyvinylene and polyphenylene (122) and poly(Schiff s bases) (123, 124). 

POLYVINYLIDENE CHLORIDE. [CAS 9002-86-2J. A stereoregular, thermoplastic polymer is produced by the free-radical chain polymerization of vinylidene chloride (H>C=CCIi) using suspension or emulsion techniques. The monomer lias a bp of 31.6°C and was first synthesized in 1838 by Regnault. who dehydrochlorinated 1,1.2-trichloroethane which he obtained by the chlorination of ethylene. The copolymer product has been produced under various names, including Saran. As shown by the following equation, the product, in production since the late 1930s, is produced by a reaction similar to that used by Regnault nearly a century earlier ... 

The 1,1-disubstitution of chlorine atoms causes steric interactions in the polymer, as is evident from the heat of polymerization (see Table 1) (24). When corrected for the heat of fusion, it is significantly less than the theoretical value of —83.7 kJ/mol (—20 kcal/mol) for the process of converting a double bond to two single bonds. The steric strain apparendy is not important in the addition step, because VDC polymerizes easily. Nor is it sufficient to favor depolymerization the estimated ceiling temperature for poly(vinylidene chloride) (PVDC) is about 400°C. 

Redox initiator systems are normally used in the emulsion polymerization of VDC to develop high rates at low temperatures. Reactions must be carried out below 80° C to prevent degradation of the polymer. Poly(vinylidene chloride) in emulsion is also attacked by aqueous base. Therefore, reactions should be carried out at low pH. 

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... 

Internal plasticizers are synthesized by copolymerization of suitable monomers. Polymeric non-extractable plasticizers, mostly copolymers having substantially lower glass transition temperatures due to the presence of plasticizing ( soft ) segments such as poly(ethylene-co-vinyl acetate) with approximately 45 % vinylacetate content, ethylene-vinyl acetate-carbon monooxide terpolymer, or chlorinated PE, are available for rather special applications in medicinal articles (Meier, 1990). In this case, the performance of the internally plasticized polymers is the principal advantage. However, copolymerization may account for worse mechanical properties. A combination with external plasticizers may provide an optimal balance of properties. For example, food contact products made from poly(vinylidene chloride) should have at most a citrate or sebacate ester based plasticizers content of 5 % and at most 10 % polymeric plasticizers. 

Instruction B. A solution of an ethylene-vinyl acetate copolymer is prepared in a stirrer autoclave in vinyl chloride (vinylidene chloride) while adding azodiisobutyronitrile dissolution takes place at 25° to 30°C. for four hours. A 1% methyl cellulose solution is introduced into the autoclave under pressure, the content is stirred vigorously (400 r.p.m.) at 25 °C. for two hours, and polymerization is effected by temperature increase at the same speed of agitation. After the polymerization is complete, the bead polymer is isolated, washed with large amounts of water, and dried in vacuo at 50°C. 

All the polymers we have discussed are homopolymers, polymers made up of identical monomer units. Many polymeric materials are copolymers, made by polymerizing two or more different monomers together. In many cases, monomers are chosen so that they add selectively in an alternating manner. For example, when a mixture of vinyl chloride and vinylidene chloride (1,1-dichloroethylene) is induced to polymerize, the growing chain preferentially adds the monomer that is not at the end of the chain. This selective reaction gives the alternating copolymer Saran , used as a film for wrapping food. 

All structural effects decreasing the heat of polymerization are cumulated in a-methylstyrene resonance of the double bond with the aromatic ring, —CH3 hyperconjugation stabilizing the monomer, and polymer destabilizing 1,1-disubstitution. The same is true of methacrylic acid and of all its derivatives (AHlc between 54 and 59kJmol-1) and partly even of vinylidene chloride (AHlc = 75.4 kJ mol-1). 

A carbon-halogen bond in the monomer, polymer or solvent is always a centre of transfer reactions. Transfer to monomer controls chain length in polyvinyl chloride so efficiently that the molecular mass of the products is independent of the amount of initiator over a rather wide concentration range [35], Also, vinylidene chloride lowers the polymerization degree of its own polymer by transfer [36]. 

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. 

Steric influences may retard some radical polymerizations and copolymerizations. Double bonds between substituted carbon atoms are relatively inert (unless the substituents are F atoms) and 1,2-substituted ethylenes do not homopolymerize in normal radical reactions. Where there is some tendency of such monomers to enter into polymers, the trans isomer is more reactive. When consideration is restricted to monomers that are doubly substituted on one carbon atom, it is usually assumed that steric effects can be neglected and that the influence of the two substituents is additive. Thus vinylidene chloride is generally more reactive in copolymerizations than is vinyl chloride. 

The occurrence of a homogeneous reaction system is also implicit i n the derivation of the copolymer composition equation. Some polymers, like poly(vinylidene chloride), are insoluble in their own monomer and are not highly swollen by monomer. In emulsion copolymerizations of such reactants the relative concentrations of the comonomers in the polymerizing particles will be influenced by the amounts that can be adsorbed on the surface or absorbed into the interior of these polymerization loci. 

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