Molecular vinyl acetate monomer process

PAN, a synthetic fiber, is a polymer of acrylonitrile monomers. Worldwide, 2.73 million tons of PAN are produced per year, of which over 98% are processed as filament yarn serving as material in the textile industry (Tauber et al., 2000). PAN usually has a molecular weight of 55,000-70,000 g mol and is most commonly a copolymer produced by radical polymerization from acrylonitrile, 5-10 mol% vinyl acetate (or similar nonionic comonomers) to disrupt the regularity and crystallinity, and ionic comonomers, such as sulfuric or sulfonic acid salts. PAN is a hydrophobic polymer that affects the processability of the fibers. The surface is not easily wetted. 

A major drawback of conventional microemulsion polymerization is the high surfactant-to-monomer ratio usually needed to form the initial microemulsion. Surfactant can be used more efficiently in semi-continuous or fed polymerization processes. Several polymerization cycles can be run in a short period of time by stepwise addition of new monomer. After each cycle of monomer addition, most of the surfactant is still available to stabilize the growing hydro-phobic polymer particles, or to forms microemulsion again when a polar monomer is used. For instance, in the polymerization of vinyl acetate (VA) by a semi-continuous microemulsion process [21], latexes with a high polymer content of about 30 wt% were obtained at relatively low AOT concentrations of about 1 wt%. Moreover, their particle sizes and molecular weights were much smaller than those obtained by conventional emulsion polymerization. 

High-Temperature Application. Vinyl Acetate Distribution in Copoly (ethylene-vinyl acetate). In the characterization of polymers, molecular distribution and composition are two critical parameters. Every physical property and processing change of the material can be related to these two parameters. With copolymers, IR spectroscopy can be used for determination of the distribution of one or both monomers within the molecular weight distribution. 

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 commercially 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 processed at much lower temperatures and are useful in the manufacture of gramophone records and flooring compositions. 

The fact that the decrease in molecular weight in the photodegradation of polymethylvinylketone does not continue at the same rate throughout the irradiation has been ascribed to the occurrence of a competing reaction that opposes the main chain scission process. This is assumed to be the formation of new polymer—polymer linkages by mutual recombination of macro-radicals resulting from the addition of CHj or CH3—CO to unsaturated chain ends formed in the Norrish type II reaction [55]. Evidence for the presence of such macro-radicals is found in the production of graft copolymers when solutions of polymethylvinylketone in various monomers (acrylonitrile, methyl methacrylate, vinyl acetate) are irradiated [57]. 

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