Styrene ionomers

Styrene-divinylbenzene resins, 23 353 Styrene-DVB copolymers, 14 388 Styrene ionomers, 14 466, 481 properties of, 14 470-473 Styrene liquid, 23 347 Styrene-maleic anhydride (SMA) copolymers, 23 391 copolymer, 10 207 Styrene manufacture, 24 259 Styrene manufacturing, 23 326, 334-345 development of high selectivity catalyst for, 23 339... 

Preliminary results were described for a carboxylate styrene ionomer plasticized by the nonpolar oligoner 8-S (29). Although... 

Undervacuum Stress Relaxation Studies. The stress relaxation behavior of the Nafion system presents some unusual characteristics. The relaxation master curves of the precursor, as well as of Nafion in its acid and salt forms, are very broad and are characterized by a wide distribution of relaxation times. The individual stress relaxation curves and the master curves for the precursor (45), Nafion acid and Nafion-K (46), are shown in Figures 14, 15 and 16 with the reference temperatures Indicated in the captions. Time-temperature superposition of stress relaxation data appears to be valid in the precursor and in the dry Nafion acid, at least over the time scale of the experiments. In the case of Nafion-K, time-temperature superposition is not valid, because it leads to a breakdown at low temperatures, which is reestablished at high temperatures (above ISO C). Similar behavior was also observed for a low molecular weight (5x10 ) styrene ionomer. The addition of small amounts of water to the Nafion acid can lead to a breakdown in the time-temperature superposition. The Influence of crystallinity and of strong ionic interaction will be discussed in the section on underwater stress relaxation studies. 

The Eisenberg theory indicates that at low ion concentration, as the distance between multiplets increases, the interaction between multiplets is expected to decrease to the point where the elastic forces become too large to be overcome below that concentration clustering would not be expected. This is consistent with the experimental findings. This theory has been applied well to both ethylene and styrene ionomers which contain carboxylate groups. Hash-imoto et have recently shown that the Eisenberg theory... 

For example, in the case of sulfonated styrene ionomers (34), the peak height of primary transition is much higher than that of secondary transition below the critical concentration, while the hight of secondary transition peak exceeds that of primary transition peak above the critical concentration. 

Figure 3. The individual stress relaxation curves and master curve reduced to the a glass transition temperature for Nafion acid, compared with those of polystyrene and two styrene ionomers reduced to their glass transition temperatures (31).

The samples were synthesized by the same techniques as those used for the styrene ionomers (12). The protonated styrene-methacrylic acid copolymers were prepared by thermal initiation. The polymerization took place in sealed glass tubes in the bulk at 80 °C after several freeze-thaw cycles. A conversion of 10% was obtained after 19 hr. The polymer was precipitated in methanol and neutralized in a benzene-methanol solution. A similar procedure was used for the deuterated samples except that the unreacted deuterated styrene monomer was evaporated prior to the precipitation. The mixing of the deuterated and protonated styrene copolymers was performed in a benzene solution by stirring for 1 hr. The benzene used as the solvent contained a minimum amount of methanol necessary to dissolve the ionomer (approximately 5-10% for the samples of high ion content). The samples were freeze-dried, then dried further at 60°-80°C under vacuum, and finally compression-molded at Tg - - 30°C. 

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...

Polystyrene-based ionomers have no crystalline phase in a host polymer matrix. Figure 13 shows a schematic model of the styrene ionomer (compare with Fig. 1). One of the characteristics of styrene ionomers is that, in addition to the ionic aggregates, there are also some isolated ion pairs distributed throughout the polystyrene matrix, which do not contribute to the crosslinking of the polystyrene chains. 

J.-C. Lim, J.-K. Park and H.-Y. Song, FTIR investigation of ion-dipole interaction in styrene ionomer/poly(ethylene oxide) blends, J. Polym. Sci., Polym. Phys. Ed., 1994, 32, 29-35. 

Plasticization of poly(styrene-b-isobutylene-b-styrene) ionomer by 2-ethylhexyl-p-dimethylaminobenzoate causes a decrease in the glass transition temperature, Tg, as the amount of plasticizer increases (Figure 11.12). This lowering of the Tg indicates that there is a slight plasticization of the non-ionic polystyrene phase. A much larger shift is observed in temperature at which tan5 = 3. This indicates a prefererrtial plasticization of the ionic clusters. 

Fig. 1 Glass transition and density vs. ionic comonomer content for styrene ionomers.

Fig. 2 Mol % ions in multiplets or clusters vs total mol % of ionic comonomer in the styrene ionomers (from dielectric data).

Fig. 3 Glass transition and density vs mol % ions in clusters for the styrene ionomers.

Fig. 5 Young s Modulus (10 sec) vs T-Tg for the styrene ionomers (dotted lines) and the ethyl acrylate ionomers (solid lines) for various ion contents.

A recent investigation gives some insights into one aspect of the kinetics of cluster formation, both above and below Tg. In a study of the expansion coefficients of the styrene ionomers as a function of ion contentit was.found that the equilibrium values were independent of ion content. However, whenever the sample had been allowed to remain at room temperature for a few hours after cooling from above Tg, and subsequently heated again above the glass transition temperature, the first run yielded a value of the liquid expansion coefficient ca 25% lower than that... 

Pioneering work in the area of ionomer blends has been undertaken by Eisenberg and co-workers, studying ion-pair interactions as a means of obtaining miscibility in blends of urethanes and styrene ionomers. In blends of copoly(styrene/sodium methacrylate) with urethanes containing quaternary ammonium salts in the hard segments, ion-pair/ion-pair interactions induce miscibility, lon-pair/dipole interactions, by contrast, do not yield miscible blends. The properties of the resulting ionomer blends have also been reported. Such blends are clearly of interest in the development of new polymeric materials. 

Shim, S.-Y., and Weiss, R. A. (2005). Sulfonated poly(ethylene-ran-styrene) ionomers. Polym. Int. 54, 1220. 

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