Ethylene-vinyl acetate copolymer reactivity ratios

The co-monomers such as vinyl acetate, acrylate esters, or carbon monoxide are fed together with ethylene, or introduced by liquid pumps, into the suction of the secondary compressor. The concentration in the feed of the co-monomer which is required to achieve a certain level of the co-monomer in the resulting polymer depends on the reactivity ratios, ri and r2, which are the ratios of rate constants of chain-propagation reactions [5]. The values for the co-monomers used in the high-pressure process are presented in Table 5.1-3. In the case of vinyl acetate, both reactivity ratios are identical and therefore the composition of the copolymer is the same as that of the feed. The concentration of vinyl acetate, for example, in... 

Ethylene-vinyl acetate copolymers can be thought of as modified high pressure polyethylenes. Because of the free-radical polymerization process they have structural characteristics such as short-chain and long-chain branching in addition to the effects due to the incorporation of the vinyl acetate comonomer. Ethylene and vinyl acetate have a reactivity ratio which is close to 1 and as a result EVA copolymers contain vinyl acetate which is homogeneously distributed among the polymer chains. The major effect of the VA on polymer properties is to reduce... 

Some data recently obtained on high pressure ethylene copolymerizations illustrate the quantitative aspects of an ethylene-based Q-e scheme (6). In Figures 3 and 4 copolymer composition curves for the ethylene-vinyl chloride and the ethylene-vinyl acetate copolymerizations are given. The monomer reactivity ratios for these two systems are tabulated in Table III along with Q values and e values for vinyl chloride and vinyl acetate calculated using ethylene as the standard (Q = 1.0 and g = 0). These Q and e values may be compared with those obtained using styrene as the standard. 

As mentioned previously, the Alfrey Priee Q and e values for vinyl acetate are 0.026 and —0.22, respectively [226]. Thus vinyl acetate is rather sluggish in its free-radical copolymerization, with most monomers, particularly olefinic monomers, bearing electron-donating subtitutents. The copolymerization reactivity ratios reflect the reluctance of vinyl acetate to enter into copolymerization with other monomers [270]. Nevertheless, vinyl acetate copolymers with a great many electron-rich as well as electron-poor olefins have been prepared. Especially significant from a commercial point of view are copolymers with ethylene, vinyl chloride, acrylates, methacrylates, fumarates, and maleates. Often, mixtures of three and more comonomers are used in these copolymerizations. 

Copolymers. Vinyl acetate copolymenzes easily with a few monomers, e g, ethylene, vinyl chloride, and vinyl neodecanoate, which have reactivity ratios close to its own. Block copolymers of vinyl acetate with methyl methacrylate, acrylic acid, acrylonitrile, and vinyl pyrrolidinone have been prepared by copolymerization in viscous conditions, with solvents that are poor solvents for the vinyl acetate macroradical,... 

If r, > 1, ethylene tends to self-propagate. If r, < 1, copolymerization is favored. If r, r 1, the monomers have nearly identical reactivities and comonomer incorporation is highly random. This means that the composition of the copolymer will closely reflect the proportions of ethylene and comonomer charged to the reactor. For EVA, the ethylene reactivity ratio and reactivity ratio for vinyl acetate are very close (r, = 0.97 and rj = 1.02), which translates into uniform distribution of VA in the copolymer (10). 

A value of unity (or nearly unity) for the monomer reactivity ratio signifies that the rate of reaction of the growing chain radicals towards each of the monomers is the same, i.e. kn ki2 and 22 — A 2i and the copolymerization is entirely random. In other words, both propagating species and M2 have little or no preference for adding either monomer. The copolymer composition is the same as the comonomer feed with a completely random placement of the two monomers along the copolymer chain. Such behavior is referred to as Bemoullian. Free-radical copolymerization of ethylene and vinyl acetate and that of isoprene and butadiene are examples of such a system, but this is not a common case. Random monomer distributions are obtained more generally in a situation where both types of radicals have exactly the same preference for the same type of monomer as represented by the relationship... 

Limited information exists in the literature, however, on the homo- or copolymerization of vinyl ethylene carbonate, 1 (VEC or 4-ethenyl-l,3-dioxolane-2-one) for the preparation of cyclic carbonate functional polymers. A few comments regarding polymerization of VEC are given in an early patent [9], In the only reported study of the copolymerization behavior of VEC, Asahara, Seno, and Imai described the copolymerization of VEC with vinyl acetate, styrene, and maleic anhydride and determined reactivity ratios [10. Their results indicated that VEC would copolymerize well with vinyl acetate, but in copolymerizations with styrene, little VEC could be incorporated into the copolymer. VEC appeared to copolymerize with maleic anhydride, however the compositions of the copolymers was not reported. Our goal was to further explore the use of VEC in the synthesis of cyclic carbonate functional polymers. 

Various copolymers of ethylene with vinyl acetate are prepared by a free-radical mechanism in emulsion polymerizations. Both reactivity ratios are close to The degree of branching in these... 

Various copolymers of ethylene with vinyl acetate are prepared by free-radical mechanism in emulsion polymerizations. Both reactivity ratios are close to 1.0 [106]. The degree of branching in these copolymers is strongly temperature-dependent [107]. These materials find wide use in such areas as paper coatings and adhesives. In addition, some are hydrolyzed to form copolymers of ethylene with vinyl alcohol. Such resins are available commercially in various ratios of polyethylene to poly(vinyl alcohol), can range from 30% poly(vinyl alcohol) to as high as 70%. 

Ethylene and vinyl acetate (EVA) are copolymerized using a radical initiator (see Chain polymerization). Figure 1 shows the chemical structure of EVA. The reactivity ratios of both monomers are close to unity, so copolymers have a random structure, and can be prepared with composition ranging from almost 0 to almost 100% vinyl acetate (VA). 

In general, bulk polymerization processes have been used to study the copolymerization of A -vinylpyrrolidone with a variety of monomers such as vinyl laurate [31], styrene [32], methyl methacrylate [32], vinyl acetate [32, 33], vinyl chloride [32], crotonaldehyde [34], crotonic acid [35], A -vinylsuccinimide [36], butyl methacrylate [37], N-vinylphthalimide [38], acrylic acid [39], various alkyl acrylates and methacrylates including lauryl methacrylate and stearyl methacrylate [40], and ethylene [41]. Table V lists reactivity ratios of several copolymer systems. 

Where ri > 1 and t2 < 1, the copolymer will always be richer in monomer-1 than in the monomer phase, so that monomer-1 will become depleted in a batch polymerization. The further the reactivity ratios deviate from unity, the greater the deviation between polymer and monomer composition. Systems that exhibit this behavior include methacrylate-acrylate polymerizations, and styrene, methacrylates, or acrylates polymerized with vinyl acetate or ethylene. 

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