Sodium ionomers

In addition to time-related effects, the soUd-state physical properties are also affected by adsorbed water, which functions as a plasticizer. Water pickup is affected by the nature of the cation, with sodium ionomers absorbing about 10 times the level of the zinc equivalent (6) under the same conditions. Drying must be carried out at temperatures below 100°C and is therefore a slow process. In commercial practice, ionomers are suppUed dry, and techniques have been developed to minimize moisture absorption during processing. 

Melt Viscosity. As shown in Tables 2 and 3, the melt viscosity of an acid copolymer increases dramatically as the fraction of neutralization is increased. The relationship for sodium ionomers is shown in Figure 4 (6). Melt viscosities for a series of sodium ionomers derived from an ethylene—3.5 mol % methacrylic acid polymer show that the increase is most pronounced at low shear rates and that the ionomers become increasingly non-Newtonian with increasing neutralization (9). The activation energy for viscous flow has been reported to be somewhat higher in ionomers than in related acidic... 

Fig. 4. lonomer melt iadex reduction vs percent neutralization for sodium ionomers. A, 10 wt % methacrylic acid B, 15 wt % methacrylic acid (6). 

A process based on saponification of ethylene—acrylate ester copolymers has been practiced commercially in Japan (29). The saponification naturally produces fully neutralized polymer, and it is then necessary to acidify in order to obtain a pardy neutralized, melt-processible product. Technology is described to convert the sodium ionomer produced by this process to the zinc type by soaking pellets in zinc acetate solution, followed by drying (29). 

A direct method for obtaining a sodium ionomer by polymerizing a mixture of ethylene, sodium methacrylate, and methacrylic acid has been described (30). 

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. 

Figure 14.15 Mechanism of PET nucleation by sodium ionomers. A particular advantage of such compounds is that they provide active nucleation sites without molecular chain scission...

Differences in spectra obtained at different measurement temperatures were also used to aid in the determination of the structure of calcium and sodium ionomers 215). 

The tin II product shows four peaks (from DSC data)-at 60, 85, 115 and 350 C. The tin IV product shows only two peaks at 85 and 370 C. The sodium ionomer shows peaks at 60, 95, 130 and beginning at 450 C. The pre-ionomer shows peaks at about 40, 90 and 430 C. In all cases, the highest transition appears to coincide with a loss in weight observed in the TGA and the lowest (approximately) corresponds to the softening temperature observed with the Fisher-Johns apparatus. It is believed that the lowest temperature corresponds to movement in the ethylene units and that the additional peaks may correspond to more complex movements involving the carboxylate moieties. 

In addition to time-related effects, the solid-state physical properties are also affected hy adsorbed water, which functions as a plasticizer. Water pickup is affected by the nature of the cation, with sodium ionomers... 

However, due to the slow rate of crystallization, PET has not been used in injection molding applications until recently [Burke and Newcombe, 1982 Hecht and Ford, 1985]. Through the use of specific types of nucleators (e.g., sodium stearate, sodium ionomers) and other crystalliza-... 

The experimental protocol of our studies involved the exposure of fresh healthy platelet-rich plasma (PRP) of young males to 9 pure synthetic polymers, namely polyethylene, ethylene-butylene copolymer, ethylene-propylene copolymer, ethylene-ethylacrylate copolymer, ethylene-vinylacetate copolymer, ethylene-methylmethacrylate sodium ionomer, nylon 12, polyurethane, and tetrafluoroethylene-hexafluoropro-pylene copolymer ( Figure-1). Polymer pellets tested have been especially synthesized under clean conditions and were substances of known composition, free of plasticizers and... 

Ethylene-methylmethacrylate sodium ionomer (Random copolymer)... 

R. K. Shah, R. K. Krishnaswamy, S. Takahashi, and D. R. Paul. Blown films of nanocomposites prepared from low density polyethylene and a sodium ionomer of poly(ethylene-co-methacrylic acid). Polymer, 47 (2006),... 

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