Vinylidene chloride polymers stabilization

Other Polymers. Various other polymers frequently require stabilization against thermal or thermo-oxidative degradation. Poly(vinylidene chloride) is stabilized by epoxides and sodium pyrophosphate. 

Use Plasticizer-stabilizer for vinylidene chloride polymers, synthetic rubbers and cellulosic lacquers, insecticides. 

Stabilization of Vinylidene Chloride Polymers by Comonomer Incorporation xi... 

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 Copolymer Foams. Low density, fine-celled VDC copolymer foams can be made by extmsion of a mixture of vinylidene chloride copolymer and a blowing agent at 120—150°C (190). The formulation must contain heat stabilizers, and the extmsion equipment must be made of noncatalytic metals to prevent accelerated decomposition of the polymer. The low melt viscosity of the VDC copolymer formulation limits the size of the foam sheet that can be extmded. 

Impact of Chain-End Structure, Basic Comonomer Incorporation and Pendant Structure on the Stability of Vinylidene Chloride Barrier Polymers... 

Both methyl acrylate and butyl acrylate have been used to prepare vinylidene chloride copolymers with sufficient stability to permit thermal processing. The presence of alkyl acrylate units in the polymer mainchain limits the size of vinylidene chloride sequences and thus the propagation of degradative dehydrochlorination. More importantly it lowers the melt... 

Limited studies suggest that the nature of the initiator, azo versus peroxide, used for the preparation of vinylidene chloride copolymers has little influence on the stability of the resulting polymers. The nature of the comonomer incorporated, methyl versus butyl acrylate, also seems to have little impact on the stability of the copolymers generated. The incorporation of isomeric butyl acrylate esters into vinylidene chloride copolymers also displays little impact on the stability of the resulting polymer, beyond that obtained by incorporation of any comonomer, independent of butyl structure. 

Adding plasticizer, like dioctyl phthalate, is generally accomplished by mechanical methods. Permanent or chemical plasticization can be done by copolymerization of VCM with monomers such as vinyl acetate, vinylidene chloride, methyl acrylate, or methyl rhethacrylate. Comonomer levels vary from 5-40%. The purpose of the co-polymers, of course, is to change the properties such as softening point, thermal stability, flexibility, tensile strength, and solubility. 

The AH value for vinyl chloride is lowered relative to that for ethylene because of increased steric strain in the polymer and increased resonance stabilization of the monomer. However, it is not clear why AH for vinylidene chloride is not lower than that for vinyl chloride. The abnormally high AH for tetrafluoroethylene is difficult to understand. A possible explanation may involve increased stabilization of the polymer due to the presence of intermolecular association (dipole interaction). 

Heat stabilizers protect polymers from the chemical degrading effects of heat or uv irradiation. These additives include a wide variety of chemical substances, ranging from purely organic chemicals to metallic soaps to complex organometallic compounds. By far the most common polymer requiring the use of heat stabilizers is poly(vinyl chloride) (PVC). However, copolymers of PVC, chlorinated poly(vinyl chloride) (CPVC), poly(vinylidene chloride) (PVDC), and chlorinated polyethylene (CPE), also benefit from this technology. Without the use of heat stabilizers, PVC could not be the widely used polymer that it is, with worldwide production of nearly 16 million metric tons in 1991 alone (see VlNYL polymers). 

Inherently Stable Structure. Inherent stability of the polymer structure includes resins such as unplasticized poly (vinyl chloride) containing about 56% chlorine which is self-extinguishing and poly(vinylidene) chloride. 

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... 

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). 

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