Sodium salt ethylene ionomers

Sodium ionomers are commercially recognized as the most effective nucleating agents for PET compounds. The typical use rate of sodium ionomer-based nucleating agents is 3-4 wt%. The sodium salt of poly(ethylene-co-methacrylic acid) is a particularly effective nucleating agent for PET. 

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. 

Fig. 5. Observed and calculated curves of SAXS profiles by a modified hard-sphere model for the sodium salt of ethylene ionomers. These ethylene ionomers are copoly(ethylene-methacrylic acid) with an acid content of 0.054 and various degrees of neutralization (E-0.054MAA-xNa) circles are observed data (A), O x = 0.82, (B), 3 0.73, (C), C 0.55, and (D), 0.44.

Fig. 9. 13C CP/MAS NMR spectra of zinc and sodium salt ethylene ionomers (E-0.054MAA-Zn and E-0.054MAA-Na) with degrees of neutralization of 20, 60 and 90% in the carbonyl carbon region at room temperature.

Figure 10 shows the 23Na MAS NMR spectra of some sodium salt ethylene ionomers at room temperature. A broad peak at about —10 to 12 ppm is clearly observed for all samples. The 23Na NMR spectra of the styrene ionomers have been reported44 (details are given in the next section, see Fig. 14). Peaks are observed at about 7, 0, and -12 to -23 ppm, which are assigned to isolated ion pairs, hydrated ions and aggregated ions respectively. The sodium cations in ethylene ionomers, therefore, are almost in ionic aggregates. The isolated ion pairs...

Fig. 11. 23Na MAS NMR spectra of the sodium salt of ethylene ionomer with a degree of neutralization of 0.9 (E-0.054MAA-0.9Na) at various temperatures.

Copolymers of ethylene and methacrylic acid are the basis of interesting materials which have been called ionomers. These are prepared by copolymerizing ethylene with 1—10% methacrylic acid using a high pressure process. The polymer is then treated with a metal derivative such as sodium methoxide and some of the carboxy groups are converted to the sodium salt. The product may be represented as follows ... 

Ionomers are made in a two-stage process. In the first step, we copolymerize ethylene with small amounts of an organic acid containing a vinyl group, such as acrylic or methacrylic acid, in a high pressure reactor. In the second step, we neutralize the acid comonomers to form metal salts. We can create ionomers with a variety of metal salts, including sodium, calcium, and zinc. 

Ionomer. Ionomer is the generic name for polymers based on sodium or zinc salts of ethylene-methacrylic acid copolymers in which interchain ionic bonding, occurring randomly between the long-chain polymer molecules, produces solid-state properties. 

EMA ionomers (see Figure 4.30) are speciality thermoplastics copolymerized from ethylene and a small fraction of methacrylic acid, which is then transformed into the salt of sodium, zinc, lithium or another metal randomly distributed along the backbone. The backbone is identical to that of the polyolefins but the pendant groups are different, with a polar and ionic character. 

Typically, carboxylate ionomers are prepared by direct copolymerization of acrylic or methacrylic acid with ethylene, styrene or similar comonomers by free radical copolymerization (65). More recently, a number of copolymerizations involving sulfonated monomers have been described. For example, Weiss et al. (66-69) prepared ionomers by a free-radical, emulsion copolymerization of sodium sulfonated styrene with butadiene or styrene. Similarly, Allen et al. (70) copolymerized n-butyl acrylate with salts of sulfonated styrene. The ionomers prepared by this route, however, were reported to be "blocky" with regard to the incorporation of the sulfonated styrene monomer. Salamone et al. (71-76) prepared ionomers based on the copolymerization of a neutral monomer, such as styrene, methyl methacrylate, or n-butyl acrylate, with a cationic-anionic monomer pair, 3-methacrylamidopropyl-trimethylammonium 2-acrylamlde-2-methylpropane sulfonate. 

Ionomers of practical interest have been prepared by two synthetic routes (a) copolymerization of a low level of functionalized monomer with an olefinically unsaturated monomer or (b) direct functionalization of a preformed polymer. Typically, carboxyl containing ionomers are obtained by direct copolymerization of acrylic or methacrylic acid with ethylene, styrene and similar comonomers by free radical copoly-merization. Rees (22) has described the preparation of a number of such copolymers. The resulting copolymer is generally available as the free acid which can be neutralized to the degree desired with metal hydroxides, acetates and similar salts. Recently, Weiss et al.(23-26) have described the preparation of sulfonated ionomers by copolymerization of sodium styrene sulfonate with butadiene or styrene. 

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