Ethylene - Vinyl Acetate Copolymers

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 

TREF of EVA copolymers was first reported by Wild, Ryle, Knobeloch and Peat [9]. They subjected EVA copolymers of VA content of 9, 14 and 18 wt% to TREF analysis and obtained the short-chain branching distribution shown in Fig. 22. Included with the data for EVA was a TREF analysis of an ethylene-ethyl acrylate copolymer (EEA) containing 18 wt% ethyl acrylate. The EVA copolymers exhibit relatively narrow SCB distribution at increasingly higher SCB branch 

Analytical-TREF temperature (°C) at which 50% of the material eluted. 

Kelusky et al. [11] have also applied TREF for EVA copolymer analysis. Their interest was mainly in the use of TREF for blend analysis involving these copolymers. They did, however, evaluate a series of six EVA copolymers in the range of 8 to 24 wt.%, showing how the TREF separation was dependent on the total branching, polyethylene type as well as VA. The resins analysed are listed in Table 4 which includes the analysis of all branches by NMR. The TREF curves (Fig. 23) clearly show the sensitivity of the separation to the total SCB level. 

One aspect of the data obtained for TREF of EVA copolymers is their increasingly distorted and truncated distribution curves for the higher VA copolymers. This behavior is reminiscent of SEC of materials in which the molecular weights exceed the exclusion limits of the column system. Here, it seems likely that it is due to the fact that in the normal operation of the TREF analysis, room temperature represents both the lowest crystallization temperature as well 

The properties of ethylene-vinyl acetate copolymers vary widely vith their ester content. At the lowest levels of vinyl acetate, they have physical properties that are similar to those of low density polyethylene. As the comonomer content increases, the material becomes less crystalline and more elastic. Copolymers made with the highest comonomer levels contain no measurable crystallinity. The resulting products are tough, flexible, and clear. The ester 

EVA is an internally plasticized copolymer used to plasticize or to reduce the amount of plasticizer in polyvinylchloride. A graft copolymer of EVA and PVC is produced (Vmnolit VK 801) containing equal amounts of both polymers. The graft copolymer is either used alone to give an unplasticized article or as a PVC additive. 

The addition of EVA to PVC may be considered either as a modification by a solid plasticizer or as polymer blending. To eliminate plasticizer from certain articles (e g., medical products and toys) this technology is applied fiequently. Membranes are formulated by using combination of PVC and EVA in order to limit amount of a low molecular weight plasticizer such as dioctyl phthalate or dioctyl sebacate.  

Low odor hose was formulated using a combination of PVC, EVA and a low molecular weight plasticizer, such as DOR The formulation shows that only a small amount of DOP was added most likely to accommodate pigments and fillers  

PVC resin BaZn stabihzer Calcium carbonate EVA polymer DOP plasticizer Stearic acid lubricant Titanium dioxide Pigment 

Sometimes plasticizer is deliberately added to a product to make it less sensitive to external plasticizer. This laminating adhesive is used in conjunction with PVC Polyurethane dispersion 17.5 wt% 

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Low-density Medium-density High-density Ultra high-molecular-weight Glass-fiber- reinforced, high-density Ethylene-vinyl acetate copolymer... 

This type of adhesive is generally useful in the temperature range where the material is either leathery or mbbery, ie, between the glass-transition temperature and the melt temperature. Hot-melt adhesives are based on thermoplastic polymers that may be compounded or uncompounded ethylene—vinyl acetate copolymers, paraffin waxes, polypropylene, phenoxy resins, styrene—butadiene copolymers, ethylene—ethyl acrylate copolymers, and low, and low density polypropylene are used in the compounded state polyesters, polyamides, and polyurethanes are used in the mosdy uncompounded state. 

Ethylene vinyl acetate copolymer (EVA) forms a soft, tacky film with good water-vapor barrier but very poor gas-barrier properties. It is widely used as a low temperature initiation and broad-range, heat-sealing medium. The film also serves for lamination to other substrates for heat-sealing purposes. 

Hydrocarbon resins (qv) are prepared by copolymerization of vinyltoluene, styrene, and a-methylstyrene in the presence of a Eriedel-Crafts catalyst (AlCl ). These resins are compatible with wax and ethylene—vinyl acetate copolymer (197). 

Organic peroxides are used in the polymer industry as thermal sources of free radicals. They are used primarily to initiate the polymerisation and copolymerisation of vinyl and diene monomers, eg, ethylene, vinyl chloride, styrene, acryUc acid and esters, methacrylic acid and esters, vinyl acetate, acrylonitrile, and butadiene (see Initiators). They ate also used to cute or cross-link resins, eg, unsaturated polyester—styrene blends, thermoplastics such as polyethylene, elastomers such as ethylene—propylene copolymers and terpolymers and ethylene—vinyl acetate copolymer, and mbbets such as siUcone mbbet and styrene-butadiene mbbet. 

Fig. 10. Preparation and morphology of toughened PVC (a) secondary PVC grain (50—250 flm) (b) modified PVC with coherent primary grain (ca 1 -lm) (220). CPE = chlorinated polyethylene EVA = ethylene—vinyl acetate copolymers ABS = acrylonitrile—butadiene—styrene MBS = methyl...

Pubhcations on curing polymers with TAIC include TEE—propylene copolymer (135), TEE—propylene—perfluoroaHyl ether (136), ethylene—chlorotrifluoroethylene copolymers (137), polyethylene (138), ethylene—vinyl acetate copolymers (139), polybutadienes (140), PVC (141), polyamide (142), polyester (143), poly(ethylene terephthalate) (144), sdoxane elastomers (145), maleimide polymers (146), and polyimide esters (147). 

Substituted amides (not of the alkanolamide variety) are sold to diverse low volume markets. They have some utility ki polymers such as polyethylene, ethylene-vinyl acetate copolymers, acryUc polymers, PVC, polyamides, and polyesters. They have been found effective as pharmaceutical processkig aids, defoamers (qv), antimicrobials, pesticides, kisect repellents, dispersion stabilizers, and corrosion inhibitors. 

Rosin, modified rosins, and derivatives are used in hot-melt adhesives. They are based primarily on ethylene—vinyl acetate copolymers. The rosin derivative is used in approximately a 1 1 1 concentration with the polymer and a wax. The resin provides specific adhesion to the substrates and reduces the viscosity at elevated temperatures, allowing the adhesive to be appHed as a molten material. 

Materials are also blended with VDC copolymers to improve toughness (211—214). VinyHdene chloride copolymer blended with ethylene—vinyl acetate copolymers improves toughness and lowers heat-seal temperatures (215,216). Adhesion of a VDC copolymer coating to polyester can be achieved by blending the copolymer with a linear polyester resin (217). 

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. 

The low vinyl acetate ethylene—vinyl acetate copolymers, ie, those containing 10—40 wt % vinyl acetate, are made by processes similar to those used to make low density polyethylene for which pressures are usually > 103 MPa (15,000 psi). A medium, ie, 45 wt % vinyl acetate copolymer with mbber-like properties is made by solution polymerisation in /-butyl alcohol at 34.5 MPa (5000 psi). The 70—95 wt % vinyl acetate emulsion copolymers are made in emulsion processes under ethylene pressures of 2.07—10.4 MPa (300—1500 psi). 

Ce = cellulosics, EVA = ethylene-vinyl acetate copolymers, F = foods, GAS = gasoline, LUB = lubricants, PA = polyamides, PES = polyesters,... 

Polymers ndResins. / fZ-Butyl peroxyneopentanoate and other peroxyesters of neopentanoic acid can be used as free-radical initiators for the polymeri2ation of vinyl chloride [75-01-4] (38) or of ethylene [74-85-1]. These peresters have also been used in the preparation of ethylene—vinyl acetate copolymers [24937-78-8] (39), modified polyester granules (40), graft polymers of arninoalkyl acrylates with vinyl chloride resins (41), and copolymers of A/-vinyl-pyrrohdinone [88-12-0] and vinyl acetate [108-05-4] (42). They can also be used as curing agents for unsaturated polyesters (43). 

Although current matrix diffusional systems are most suitable for small-molecule compounds, it has been demonstrated (84) that soHd hydrophobic polymers allow dispersed powdered macromolecules of nearly any size, for example, ethylene—vinyl acetate copolymers containing dispersed polypeptides, to be released for periods exceeding 100 days. 

Poly(ethylene-i (9-vinyl alcohol) is made by saponification of ethylene—vinyl acetate copolymers. The properties of these materials depend on the amount of vinyl alcohol present in the copolymer. High vinyl alcohol content results in more hydrophilic materials possessing higher densities, stiffness, and moduh. They are used commercially as barrier resins for packaging. Important producers include Du Pont and EVALCA (74) (see Barrier polymers). 

A further class of ethylene-vinyl acetate copolymer exists where the vinyl acetate content is of the order of 3 mole %. These materials are best considered as a modification of low-density polyethylene, where the low-cost comonomer introduces additional irregularity into the structure, reducing crystallinity and increasing flexibility, softness and, in the case of film, surface gloss. They have extensive clearance as non-toxic materials. 

A substantial part of the market for the ethylene-vinyl acetate copolymer is for hot melt adhesives. In injection moulding the material has largely been used in place of plasticised PVC or vulcanised rubber. Amongst applications are turntable mats, base pads for small items of office equipment and power tools, buttons, car door protector strips and for other parts where a soft product of good appearance is required. Cellular cross-linked EVA is used in shoe parts. 

Ethylene-ethyl acrylate copolymers are very similar to the ethylene-vinyl acetate copolymers. The former materials are considered to have higher abrasion resistance and heat resistance whilst the EVA have been considered to be tougher and of greater clarity. 

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. 

Among the different pressure sensitive adhesives, acrylates are unique because they are one of the few materials that can be synthesized to be inherently tacky. Indeed, polyvinylethers, some amorphous polyolefins, and some ethylene-vinyl acetate copolymers are the only other polymers that share this unique property. Because of the access to a wide range of commercial monomers, their relatively low cost, and their ease of polymerization, acrylates have become the dominant single component pressure sensitive adhesive materials used in the industry. Other PSAs, such as those based on natural rubber or synthetic block copolymers with rubbery midblock require compounding of the elastomer with low molecular weight additives such as tackifiers, oils, and/or plasticizers. The absence of these low molecular weight additives can have some desirable advantages, such as ... 

Several authors have discussed the ion exchange potentials and membrane properties of grafted cellulose [135,136]. Radiation grafting of anionic and cationic monomers to impart ion exchange properties to polymer films and other structures is rather promising. Thus, grafting of acrylamide and acrylic acid onto polyethylene, polyethylene/ethylene vinyl acetate copolymer as a blend [98], and waste rubber powder [137,138], allows... 

The molecules join together to form a long chain-like molecule which may contain many thousands of ethylene units. Such a molecule is referred to as a polymer, in this case polyethylene, whilst in this context ethylene is referred to as a monomer. Styrene, propylene, vinyl chloride, vinyl acetate and methyl methacrylate are other examples of monomers which can polymerise in this way. Sometimes two monomers may be reacted together so that residues of both are to be found in the same chain. Such materials are known as copolymers and are exemplified by ethylene-vinyl acetate copolymers and styrene-acrylonitrile copolymers. 

It has been found that, for a fixed mineral filler content, the viscosity of PMF-based composites increases when the coat is made of polyethylene [164, 209, 293], poly(vinyl chloride) [316] and polypropylene [326, 327], The picture was different, however, for composites based on the ethylene/vinyl acetate copolymer to which kaolin with grafted poly (vinyl acetate) was added [336]. Addition of PMF with a minimum quantity of grafted polymer results in a sharp drop of flowability (rise of viscosity), in comparison to addition of unmodified filler but with a further increase of the quantity of grafted polymer the flow gradually increases and, depending on the kaolin content and quantity of grafted polymer, may even become higher than in specimens with unmodified filler, for equal concentrations. 

Zone 2 acetal, ABS, chlorinated polyether, ethyl cellulose, ethylene-vinyl acetate copolymer, furan, ionomer, phe-... 

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