Ionomers ethylene

Ethylene ionomers consist of copolymers of ethylene and an organic acid, such as methacrylic acid, the acid moieties of vhich have been neutrali2ed to form a metal salt. The metal salts from neighboring chains tend to form clusters, such as the one shown schematically in Fig. 18.3. The net result is the overall structure shown in Fig. 18.2 g), in which the ionic clusters form weak crosslinks between adjacent chains. lonomers also contain short and long chain branches, which are similar to those foimd in low density polyethylene. 

We make polyethylene resins using two basic types of chain grosvth reaction free radical polymerization and coordination catalysis. We use free radical polymerization to make low density polyethylene, ethylene-vinyl ester copolymers, and the ethylene-acrylic acid copolymer precursors for ethylene ionomers. We employ coordination catalysts to make high density polyethylene, linear low density polyethylene, and very lo v density polyethylene. 

Ethylene-acrylic acid copolymers are converted to ethylene ionomers in a separate, post-polymerization reaction. 

Elastomeric ionomers based on the sulfonation of chlorinated PE were introduced by DuPont during the early 1950s. Curing of these materials with various metal oxides gives rise to a combination of ionic and covalent crosslinks and these elastomers are commercially available under the trade name Hypalon. 

Ethylene-carbon monoxide polymers offer superior performance as high-strength fibres for aramide tyre cord, but at a significantly lower cost. Their structure is more compatible with rubber than steel, polyester, or PA tyre reinforcements. 

The purpose of the present chapter is to overview recent applications of NMR to the structure and ionic aggregates of ionomers, in particular the ethylene ionomers. It is expected that more NMR studies on ionomers will be activated by this review. 

In this section, the metal-cationic salts of copoly(ethylene-methacrylic acid) are called the ethylene ionomers. This ethylene ionomer is one of the well-known commercial ionomers, marketed under the trade name Surlyn by DuPont. Many ethylene ionomers have crystalline and amorphous phases of ethylene chain units as well as polyethylene. Therefore, there is a three-phase structure, with crystalline, amorphous, and ionic aggregate phases this is a unique characteristic of ethylene ionomers compared with other ionomers. Although the ionic aggregate structure of the ethylene ionomer has not been fully established, its structural model is represented5 as shown in Fig. 1. In ethylene ionomers, therefore, it is necessary that some physical properties should be considered by correlating to not only the ionic aggregates but also the crystalline phases. 

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New lonomer Types. There is a continuing interest in new ionomers within the academic community, since novel and unexpected phenomena are frequently being discovered. However, there are still many unanswered questions with respect to the ethylene ionomers, especially the influence of ionic bonding on crystalline stmcture. Continued study of these interesting polymers will close the gaps in knowledge of this area of polymer science. 

Itaconic acid is a specialty monomer that affords performance advantages to certain polymeric coatings (qv) (see Polyesters, unsaturated). Emulsion stabihty, flow properties of the formulated coating, and adhesion to substrates are improved by the acid. Acrylonitrile fibers with low levels of the acid comonomer exhibit improved dye receptivity which allows mote efficient dyeing to deeper shades (see Acrylonitrile polymers Fibers, acrylic) (10,11). Itaconic acid has also been incorporated in PAN precursors of carbon and graphite fibers (qv) and into ethylene ionomers (qv) (12). 

The crystallinity levels in ethylene ionomers are generally low due to their high levels of branching and the clustering of the metal salts. At high temperatures, the clusters dissociate and the individual chains can move independently in the molten state, permitting them to be molded. When the ionomer is cooled dusters reform, crosslinking the chains... 

Polyacrylic acid and polymcthacrylic acid and their sodium salts are water-soluble. Copolymers with small amounts of methacrylic add and ethylene (ionomers), are moldable transparent resins. 

Copolymers of methacrylic add and ethylene termed as ethylene ionomers have been used as the base polymer for binding alkali, alkaline earth and transition metal ions. Organic amines such as n-hexylamine, hexamethylene tetraamine, 2,2,6,6-tetramethyM-hydroxy piperazine, ethylene diamine and polymeric diamines such as silicone diamine, polyether diamine and polymeric diamines such as silicone diamine, polyether diamine and polyamide oligomers considerably enhance the complex formation characteristics of Zn(II) ethylene ionomers thereby enhancing the physico-chemical properties [13]. 

Corresponding model studies in which DAA-saturated laminate films as well as DAA-saturated mono films were heated under the cooking conditions confirmed the suspected dehydration reaction of DAA by the ethylene ionomer. This gave an logical explanation for the mechanism of formation for the 4-methyl-4-mercaptopentane-2-one off-odor (Fig. 13-5). 

Kuwabara, K. Horii, F. Solid-state NMR analyses of the crystalline-noncrystalline structure and its thermal changes for ethylene ionomers. J. Polym. Sci. B Polym. Phys. 2002, 40, 1142. 

Ion clusters are commonly observed in the ionized forms of the perfluorinated membranes. The size of the clusters appears to be larger for sulfonate than for carboxylate membranes." " The size increases in the order Na, and Cs" and decreases with increasing number of functional groups per chain and with increasing temperature.As in the case of ethylene ionomers, the perfluorinated carboxylic acid membranes do not form ion clusters, at least in the dry state." The electrostatic interaction may be too weak to form ionic clusters. These observations are expected according to the Eisenberg theory (see Section II.2). 

Next, an attempt was made to clarify the effect of crystalline phase on the mechanical properties of ethylene ionomer. Dynamic mechanical measurements... 

Fig. 2. DSC thermograms of the zinc salt of ethylene ionomers after ageing at room temperature for a long time (heating rate lO°C/min). These ethylene ionomers are copoly(ethylene-methacrylic acid) with an acid content of 0.054 and various degrees of neutralization (E-0.054MAA-xZn) x = 0, 0.20, 0.60, and 0.90.

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