Vinyl acetate from ethylene

Liquid- and vapor-phase processes have been described the latter appear to be advantageous. Supported cadmium, zinc, or mercury salts are used as catalysts. In 1963 it was estimated that 85% of U.S. vinyl acetate capacity was based on acetylene, but it has been completely replaced since about 1982 by newer technology using oxidative addition of acetic acid to ethylene (2) (see Vinyl polymers). In western Europe production of vinyl acetate from acetylene stiU remains a significant commercial route. 

Natural mbber comes generally from southeast Asia. Synthetic mbbers are produced from monomers obtained from the cracking and refining of petroleum (qv). The most common monomers are styrene, butadiene, isobutylene, isoprene, ethylene, propylene, and acrylonitrile. There are numerous others for specialty elastomers which include acryUcs, chlorosulfonated polyethylene, chlorinated polyethylene, epichlorohydrin, ethylene—acryUc, ethylene octene mbber, ethylene—propylene mbber, fluoroelastomers, polynorbomene, polysulftdes, siUcone, thermoplastic elastomers, urethanes, and ethylene—vinyl acetate. 

The nmr spectmm of PVAc iu carbon tetrachloride solution at 110°C shows absorptions at 4.86 5 (pentad) of the methine proton 1.78 5 (triad) of the methylene group and 1.98 5, 1.96 5, and 1.94 5, which are the resonances of the acetate methyls iu isotactic, heterotactic, and syndiotactic triads, respectively. Poly(vinyl acetate) produced by normal free-radical polymerization is completely atactic and noncrystalline. The nmr spectra of ethylene vinyl acetate copolymers have also been obtained (33). The ir spectra of the copolymers of vinyl acetate differ from that of the homopolymer depending on the identity of the comonomers and their proportion. 

Ethylene-vinyl acetate copolymers have been available for several years from Bayer (Levapren 450) and these contain about 45% of vinyl acetate units. As with EPM these rubbers cannot be cured with accelerated sulphur systems but by peroxides. 

In addition to the above materials a number of copolymers containing vinyl acetate have been marketed. Ethylene-vinyl acetate (EVA) copolymers are discussed in Chapter 11 and vinyl chloride-vinyl acetate copolymers in Chapter 12. On the other hand, the commercial ethylene-vinyl alcohol copolymers, although derived from EVA, are considered briefly in this chapter since in weight terms the ethylene component is usually the minor one. 

These adhesives differ from normal hot-melt adhesives, such as the standard ethylene vinyl acetate hot melts. Standard hot-melt adhesives like EVA have no curing mechanism. They are heated above the crystalline melting point and applied as a low-viscosity liquid in the same manner as is the curing hot melt. The bond is closed in the same manner and strength is developed upon crystallization. 

Like vinyl acetate from ethylene, allyl acetate is produced by the vapor-phase oxyacylation of propylene. The catalyzed reaction occurs at approximately 180°C and 4 atmospheres over a Pd/KOAc catalyst ... 

FIGURE 4.2 Transmission electron microscopic (TEM) image of ethylene-vinyl acetate (EVA)-expanded graphite (EG) (4 wt%) nanocomposites. (From George, J.J. and Bhowmick, A.K., J. Mater. Sci., 43, 702, 2008. Courtesy of Springer.)... 

Chattopadhyay S., Chaki T.K., and Bhowmick A.K., New thermoplastic elastomers from poly(ethyle-neoctene) (engage), poly(ethylene-vinyl acetate) and low-density polyethylene by electron beam technology structural characterization and mechanical properties. Rubber Chem. TechnoL, 74, 815, 2001. Roy Choudhury N. and Dutta N.K., Thermoplastic elastomeric natural rubber-polypropylene blends with reference to interaction between the components. Advances in Polymer Blends and Alloys Technology, Vol. 5 (K. Finlayson, ed.), Technomic Publishers, Pensylvania, 1994, 161. 

NR, styrene-butadiene mbber (SBR), polybutadiene rubber, nitrile mbber, acrylic copolymer, ethylene-vinyl acetate (EVA) copolymer, and A-B-A type block copolymer with conjugated dienes have been used to prepare pressure-sensitive adhesives by EB radiation [116-126]. It is not necessary to heat up the sample to join the elastomeric joints. This has only been possible due to cross-linking procedure by EB irradiation [127]. Polyfunctional acrylates, tackifier resin, and other additives have also been used to improve adhesive properties. Sasaki et al. [128] have studied the EB radiation-curable pressure-sensitive adhesives from dimer acid-based polyester urethane diacrylate with various methacrylate monomers. Acrylamide has been polymerized in the intercalation space of montmorillonite using an EB. The polymerization condition has been studied using a statistical method. The product shows a good water adsorption and retention capacity [129]. 

FIGURE 31.2 Plots of crystalline melting point, heat of fusion and percent crystallinity of ethylene-vinyl acetate (EVA) samples versus (a) radiation dose (b) trimethylolpropane trimethacrylate (TMPTMA) level from differential scanning calorimetry (DSC) studies. (From Datta, S.K., Bhowmick, A.K., Chaki, T.K., Majali, A.B., and Deshpande, R.S., Polymer, 37, 45, 1996. With permission.)... 

FIGURE 31.15 Variation of percent heat shrinkage and amnesia rating with radiation doses of low-density polyethylene/ethylene-vinyl acetate (LDPE/EVA) film from 50 50 blend without ditrimethylol propane tetra-crylate (DTMPTA). (From Chattopadhyay, S., Chaki, T.K., and Bhowmick, A.K., Radiat. Phys. Chem., 59, 501, 2000. With permission.)... 

Chattopadhyay, S., Chaki, T.K., Bhowmick, A.K., Gao, G.J.P., and Bandyopadhyay, S., Structural characterization of electron-beam crosslinked thermoplastic elastomeric films from blends of polyethylene and ethylene-vinyl acetate copolymers, J. Appl. Polym. Sci., 81, 1936, 2001. 

Wheeler, R. G. Friel, P. G., Release of Drugs From IUD s Using an Ethylene / Vinyl Acetate Matrix, International Fertility Research Program, Research Triangle Park, NC, 1982. 

The hormone-releasing devices have a closer resemblance to standard methods of sustained release because they involve the release of a steroid compound by diffusion [198,199]. The Progestasert, a reservoir system, is shown in Fig. 16. Progesterone, the active ingredient, is dispersed in the inner reservoir, surrounded by an ethylene/vinyl acetate copolymer membrane. The release of progesterone from this system is maintained almost constant for 1 year. The effects of release are local, with none of the systematic side effects observed with orally administered contraceptives [200-207]. 

We can incorporate short chain branches into polymers by copolymerizing two or more comonomers. When we apply this method to addition copolymers, the branch is derived from a monomer that contains a terminal vinyl group that can be incorporated into the growing chain. The most common family of this type is the linear low density polyethylenes, which incorporate 1-butene, 1-hexene, or 1-octene to yield ethyl, butyl, or hexyl branches, respectively. Other common examples include ethylene-vinyl acetate and ethylene-acrylic acid copolymers. Figure 5.10 shows examples of these branches. 

The two-step degradation of commercial ethylene-vinyl acetate (EVA) copolymers has been investigated using TGA coupled with FTIR detection of the pyrolytic products evolved [48]. Acetic acid was evolved from the first... 

Bayer-Hoechst A gas-phase process for making vinyl acetate from ethylene and acetic acid, using a supported palladium catalyst. Developed jointly by Bayer and Hoechst. In 1991, nearly 2 million tonnes per year of vinyl acetate were made by this process. 

Hoechst-Uhde (2) A variation of the Wacker process, which makes vinyl acetate from ethylene and acetic acid. The catalyst is an aqueous solution of palladium and copper chlorides. 

An energy transfer immunosensor described for IgG measurement exploits controlled release of donor and acceptor from ethylene-vinyl acetate copolymer plugs positioned in opposite ends of a cylindrical reaction chamber (Figure 14.19).(122) Fluorescein-antibody donor and Texas Red-antigen-IgG acceptor are continuously released from the polymeric plugs. The reagents diffuse to the center of the cylindrical reaction chamber, where a perpendicular top-mounted optical fiber delivers the excit-... 

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