Vinylidenic comonomers

The synthetic approach to optically active polymers based on the copolymerization of prochiral carbazole containing monomers with easily available optically active vinyl or vinylidenic comonomers is by far the most convenient route to a large variety of optically active polymers. Accordingly, N-vinylcarbazole and spaced-carbazole containing vinyl monomers 11-14 have been copolymerized with different optically active monomers 15-20. 

Vinyhdene chloride copolymers are available as resins for extmsion, latices for coating, and resins for solvent coating. Comonomer levels range from 5 to 20 wt %. Common comonomers are vinyl chloride, acrylonitrile, and alkyl acrylates. The permeability of the polymer is a function of type and amount of comonomer. As the comonomer fraction of these semicrystalline copolymers is increased, the melting temperature decreases and the permeability increases. The permeability of vinylidene chloride homopolymer has not been measured. 

In addition to homopolymers of varying molecular and particle structure, copolymers are also available commercially in which vinyl chloride is the principal monomer. Comonomers used eommercially include vinyl acetate, vinylidene chloride, propylene, acrylonitrile, vinyl isobutyl ether, and maleic, fumaric and acrylic esters. Of these the first three only are of importance to the plastics industry. The main function of introducing comonomer is to reduce the regularity of the polymer structure and thus lower the interchain forces. The polymers may therefore be proeessed at much lower temperatures and are useful in the manufacture of gramophone records and flooring compositions. 

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

In this instance the thermal stability of vinylidene chloride /alkyl acrylate copolymers in which the alkyl groups are isomeric butyl units has been examined by thermogravimetry. The butyl ester comonomers incorporated are shown below (scheme 7). 

Scheme 7. Structures of Butyl Ester Comonomers Incorporated Into Vinylidene Chloride Polymers.

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. 

Uses Synthetic fibers and adhesives chemical intermediate in vinylidene fluoride synthesis production of poly(vinyl dichloroethylene) and LLl trichloroethane comonomer for food packaging, coating resins, and modacrylic fibers. 

Copolymers of vinyl chloride and vinylidene chloride are widely used (Equation 6.60). Two extremes are employed. The lesser known has a high vinyl chloride content compared with the vinylidene chloride comonomer. These copolymers are more easily dissolved and have greater flexibility. The most widely known copolymer has about 90% vinylidene chloride and 10% vinyl chloride and is known as Saran. This copolymer has low permeability to gases and vapors and is transparent. Films are sold as Saran Wrap. 

Fibers with more than 85% acrylonitrile units are called acrylic fibers but those containing 35%-85% acrylonitrile units are referred to as modacrylic fibers. The remainder of the modacrylic fibers are derived from comonomers, such as vinyl chloride or vinylidene chloride, that are specifically added to improve flame resistance. 

Fluorocarbon elastomers represent the largest group of fluoroelastomers. They have carbon-to-carbon linkages in the polymer backbone and a varied amount of fluorine in the molecule. In general, they may consist of several types of monomers poly-vinylidene fluoride (VDF), hexafluoropropylene (HFP), trifluorochloroethylene (CTFE), polytetrafluoroethylene (TFE), perfluoromethylvinyl ether (PMVE), ethylene or propylene.212 Other types may contain other comonomers, e.g., 1,2,3,3,3-pentafluropropylene instead of HFP.213 Fluorocarbon elastomers exhibit good chemical and thermal stability and good resistance to oxidation. 

By chemical agents, indirect grafting on Nylon in liquid phase is frequently referred to in the bibliography. The most common reagent is air (144) or ozone, under controlled conditions, in order to avoid deterioration on the mechanical properties of the fiber, which is then immersed in the monomer. Hence, styrene (145-149), vinylidene chloride (146), vinyl acetate (146), acrylic and methacrylic acids (149), methyl methacrylate (146), acrylonitrile (146,148,149), 2-methyl-5-vinylpyridine (149) were successfully employed as grafting comonomers. 

Because of the intractability of poly(vinylidene chloride), these studies have used copolymers containing various comonomers however, the results are believed to be indicative of the interactions with vinylidene chloride units and not primarily those of the comonomer. 

Monomers such as vinyl acetate or vinylidene chloride may be copolymerized with vinyl chloride, Up to 15% of the comonomer may be employed. Vinyl acetate increases die solubility, film formation and adhesion. Processing or forming temperatures are generally lowered. Chemical resistance and tensile strength decrease with increasing amount of vinyl acetate. 

Copolymerization. Vinyl chloride can be copolymerized with a variety of monomers. Vinyl acetate, the most important commercial comonomer, is used to reduce crystallinity, winch aids fusion and allows lower processing temperatures. Copolymers are used in flooring and coatings. This copolymer sometimes contains maleic add or vinyl alcohol (hydrolyzed from the poly(vinyl acetate ) to improve the coating s adhesion to other materials, including metals, Copolymers with vinylidene chloride are used as barrier films and coatings. Copolymers of vinyl chlonde with acrylic esters in latex from are used as film formers in paint, nonwoven fabric binders, adhesives, and coatings. Copolymers with olefins improve thermal stability and melt flow, but at some loss of heat-deflection temperature,... 

Vinylidene chloride polymers are more impermeable to a wider variety of gases and liquids than other polymers. For example, commercial copolymers are available with oxygen permeabilities of 0.03 nmol/m s-GPa. This is a consequence of the combination of high density and high crystallinity in the polymer. An increase m either tends to reduce permeability. Permeability is affected by the kind and amounts of comonomer as well as crystallinity. A more polar comonomer, e.g., an AN comonomer, increases the water-vapor transmission more than VC when other factors are constant. All VDC copolymers, are very impel meable to... 

Raw-gum fluorocarbon elastomers are transparent to translucent with molecular weights from approximately 5000 (e.g., VITON LM with waxy consistency) to over 200,000. The most common range of molecular weights for commercial products is 100,000 to 200,000. Polymers with molecular weights over 200,000 (e.g., Kel-F products) are very tough and difficult to process. Elastomers prepared with vinylidene fluoride as comonomer are soluble in certain ketones and esters, copolymers of IFF and propylene in halogenated solvents perfluorinated elastomers are practically insoluble.16... 

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). 

The maximum rates of crystallization of the more common crystalline copolymers occur at 80—120°C. In many cases, these copolymers have broad composition distributions containing both fractions of high VDC content that crystallize rapidly and other fractions that do not crystallize at all. Poly(vinylidene chloride) probably crystallizes at a maximum rate at 140—150°C, but the process is difficult to follow because of severe polymer degradation. The copolymers may remain amorphous for a considerable period of time if quenched to room temperature. The induction time before the onset of crystallization depends on both the type and amount of comonomer PVDC crystallizes within minutes at 25°C. 

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. 

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