Vinyl acetate monomer

One remaining possibility that is less costly from an energy point of view but needs to be carefully controlled is to incorporate additives called flow improvers. These materials favor the dispersion of the paraffin crystals and in doing so prevent them from forming the large networks which cause the filter plugging. The conventional flow improvers essentially change the CFPP and pour point, but not the cloud point. They are usually copolymers, produced, for example, from ethylene and vinyl acetate monomers ... 

Polyvinylpyrrohdinone/vinyl acetate copolymer (PVP/VA) was developed as an improved, less hygroscopic version of PVP. The monomer ratios control the stiffness and the resistance to humidity however, too high a vinyl acetate monomer content requires another solvent in addition to water to completely solubilize it. 

Poly(vinyl alcohol) used to manufacture the poly(vinyl acetal)s is made from poly(vinyl acetate) homopolymer (see Vinyl polymers, vinyl alcohol polymers Vinyl POLYMERS, vinyl acetate polymers). Hydrolysis of poly(vinyl acetate) homopolymer produces a polyol with predominandy 1,3-glycol units. The polyol also contains up to 2 wt % 1,2-glycol units that come from head-to-head bonding during the polymeri2ation of vinyl acetate monomer. Poly(vinyl acetate) hydrolysis is seldom complete, and for some appHcations, not desired. For example, commercial PVF resins may contain up to 13 wt % unhydroly2ed poly(vinyl acetate). Residual vinyl acetate units on the polymer help improve resin solubiHty and processibiHty (15). On the other hand, the poly(vinyl alcohol) preferred for commercial PVB resins has less than 3 wt % residual poly(vinyl acetate) units on the polymer chain. 

Mechanisms. Because of its considerable industrial importance as well as its intrinsic interest, emulsion polymerization of vinyl acetate in the presence of surfactants has been extensively studied (75—77). The Smith-Ewart theory, which describes emulsion polymerization of monomers such as styrene, does not apply to vinyl acetate. Reasons for this are the substantial water solubiUty of vinyl acetate monomer, and the different reactivities of the vinyl acetate and styrene radicals the chain transfer to monomer is much higher for vinyl acetate. The kinetics of the polymerization of vinyl acetate has been studied and mechanisms have been proposed (78—82). 

Chain transfer also occurs to the emulsifying agents, leading to their permanent iacorporation iato the product. Chain transfer to aldehydes, which may be formed as a result of the hydrolysis of the vinyl acetate monomer, tends to lower the molecular weight and slow the polymerisation rate because of the lower activity of the radical that is formed. Thus, the presence of acetaldehyde condensates as a poly(vinyl alcohol) impurity strongly retards polymerisation (91). Some of the initiators such as lauryl peroxide are also chain-transfer agents and lower the molecular weight of the product. 

Partially hydrolyzed poly(vinyl alcohol) grades are preferred because they have a hydrophobic /hydrophilic balance that make them uniquely suited for emulsion polymerization. The compatibUity of the residual acetate units with the poly(vinyl acetate) latex particles partly explains the observed stabilization effect. The amount of PVA employed is normally 4—10% on the weight of vinyl acetate monomer. The viscosity of the resulting latex increases with increasing molecular weight and decreasing hydrolysis of the PVA (318). 

Acetic acid is a versatile reagent. It is an important esterifying agent for the manufacture of cellulose acetate (for acetate fibers and lacquers), vinyl acetate monomer, and ethyl and butyl acetates. Acetic acid is used to produce pharmaceuticals, insecticides, and dyes. It is also a precursor for chloroacetic acid and acetic anhydride. The 1994 U.S. production of acetic acid was approximately 4 billion pounds. 

Reactive species can be generated prior to monomer exposure (preirradiation grafting), during contact with monomer, or, after the polymer surface has been saturated with monomer and isolated (postirradiation grafting). The radiation-induced (y-ray and EB) graft copolymerization of AA and vinyl acetate monomer onto PE surface has been reported [170]. The grafted sheets show excellent bonding with an epoxy adhesive and enhanced adhesion with aluminum. 

The commercial process for the production of vinyl acetate monomer (VAM) has evolved over the years. In the 1930s, Wacker developed a process based upon the gas-phase conversion of acetylene and acetic acid over a zinc acetate carbon-supported catalyst. This chemistry and process eventually gave way in the late 1960s to a more economically favorable gas-phase conversion of ethylene and acetic acid over a palladium-based silica-supported catalyst. Today, most of the world s vinyl acetate is derived from the ethylene-based process. The end uses of vinyl acetate are diverse and range from die protective laminate film used in automotive safety glass to polymer-based paints and adhesives. 

Chloromethyl methyl ether 0.0018 Vinyl acetate monomer 0.26... 

Abbreviations HCL Hydrochloric Acid ABS Acrylonitrile Butadiene Styrene PVC Polyvinyl Chloride VAM Vinyl Acetate Monomer... 

U.S. Industrial Chemicals Co., VINYL ACETATE MONOMERS HANDBOOK. National Distillers and Chemical Corporation, New Yoric, NY (1978). 

Maltoni C, Ciliherti A, Lefemine G, et ah Results of a long-term experimental study on the carcinogenicity of vinyl acetate monomer in mice. Ann NY Acad Set 837 209-38, 1997... 

Soon afterwards, however, Wacker Qiemie developed methods for the large scale production of vinyl acetate monomer (VAM) and also overcame S3mthetic limitations in the production of PVAc from VAM [5, 6]. The resulting polymer PVAc was soon found to be suitable for use both as a binder and as a major component in adhesives. 

Acetic Anhydride vinyl Acetate Monomer Cellulose Acetate i Ethyl Acetate Butyl Acetate Isnpropanol... 

As with monomer reactivities it is seen that the order of radical reactivities is essentially the same irrespective of the monomer used as reference. The order of substituents in enhancing radical reactivity is the opposite of their order in enhancing monomer reactivity. A substituent that increases monomer reactivity does so because it stabilizes and decreases the reactivity of the corresponding radical. A consideration of Table 6-4 shows that the effect of a substituent on radical reactivity is considerably larger than its effect on monomer reactivity. Thus vinyl acetate radical is about 100-1000 times more reactive than styrene radical toward a given monomer, while styrene monomer is only 50-100 times more reactive than vinyl acetate monomer toward a given radical. A comparison of the self-propagation rate constants (kv) for vinyl acetate and styrene shows that these two effects very nearly compensate each other. The kp for vinyl acetate is only 16 times that of styrene (Table 3-11). 

In particular, EVA waxes refer generally to oligomeric polymer compounds. They are prepared by the copolymerization of ethylene monomers and vinyl acetate monomers in the same way as the high molecular weight types. 

Figure 5.6 The vinyl acetate monomer plant (Luyben and Tyreus 1998). The reactor-separator process core is highlighted.

Luyben, M. L. and Tyreus, B. D. (1998). An industrial design/control study for the vinyl acetate monomer process. Comput. Chem. Eng., 22(7-8), 867-877. 

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