Sulfonated polystyrene ionomer

Li C., Register R.A., and Cooper S.L., Direct observation of ionic aggregates in sulfonated polystyrene ionomers, Polymer, 30, 1227, 1989. 

In this work we used polystyrene-based ionomers.-Since there is no crystallinity in this type of ionomer, only the effect of ionic interactions has been observed. Eisenberg et al. reported that for styrene-methacrylic acid ionomers, the position of the high inflection point in the stress relaxation master curve could be approximately predicted from the classical theory of rubber elasticity, assuming that each ion pah-acts as a crosslink up to ca. 6 mol %. Above 6 mol %, the deviation of data points from the calculated curve is very large. For sulfonated polystyrene ionomers, the inflection point in stress relaxation master curves and the rubbery plateau region in dynamic mechanical data seemed to follow the classical rubber theory at low ion content. Therefore, it is generally concluded that polystyrene-based ionomers with low ion content show a crosslinking effect due to multiplet formation. More... 

Chu, B. Wu, D.Q. Lundberg, R.D. MacKnight, W.J. Small-angle x-ray scattering (SAXS) studies of sulfonated polystyrene ionomers. 1. Anomalous SAXS. Macromolecules 1993, 26, 994. 

Register, R.A. Cooper, S.L. Anomalous small-angle x-ray scattering from a sulfonated polystyrene ionomer. Macromolecules 1988, 21, 1698. 

Li, Y. Peiffer, D.G. Chu, B. Long-range inhomogeneities in sulfonated polystyrene ionomers. 

Kirkmeyer, B.P. Weiss, R.A. Winey, K.I. Spherical and vesicular ionic aggregates in Zn-neutra-lized sulfonated polystyrene ionomers. J. Polym. Sci. B Polym. Phys. 2001, 39, 477. 

A iKitable exception is the recent, application of EXAFS to plasticized Zn sulfonated polystyrene ionomers (73-711. Thi.s technique was used to investigate the effect of various diluents on the local struct.ure of the Zn cation. Plasticizers termed, "non-coordinatirig" (because they do not complex metal cations) - in particular, toluene, acetonitrile, and DOP - were shown to have a minimal influence on the cation s local structure. At most, these cause a slight increase in disorder, but they do not. alter the coordination structure around the cation. These diluents clearly partition themselves into the nonpolar regions of the ionomer. 

Figure 13. Postulated local coordination structure around the zinc atom for Zn sulfonated polystyrene ionomers fully solvated by glycerol. (Reproduced with permission from ref. 73. Copyright 1988 Wiley.)...

Several SANS studies of ionomers have appeared on both deuterium labeled and unlabeled systems(8,12,18-20). The earlier work(14) showed that an ionic peak, similar to that observed by x-rays, could be discerned in some cases, especially when the sample was "decorated" by the incorporation of D20. It was also tentatively concluded(19) that the radius of gyration, R, of the individual chains is not altered when the acid 1s converted to the salt in the case of poly-styrene-methacrylic acid copolymers. Subsequent SANS experiments were performed on sulfonated polystyrene ionomers with up to 8.5% sul-fonation(12). The results of this study indicated that aggregation of the ionic groups is accompanied by considerable chain expansion, which is consistent with the theory of Forsman(ll). 

Cation-Anion and Cation-Cation Interactions in Sulfonated Polystyrene Ionomers... 

The vibrational nodes of the sulfonate group in lightly sulfonated polystyrene ionomers are affected by changes in its local environment. In dry materials, the counterion imposes a strong electrostatic field on the sulfonate anion that polarizes the S-0 dipole and shifts the asymmetric and symmetric vibrations to higher frequencies. The addition of solvent weakens the polarization by the cation and shifts the vibrational frequencies to lower frequencies. These results are explained in terms of a solution shell around the cation. 

Bodycomb J, Hara M. Light scattering study of ionomers in solutions. 5. CONTIN analysis of dynamic scattering data from sulfonated polystyrene ionomer in a polar solvent (dimethylformamide). Macromolecules 1995 28 8190-8196. 

FIG. 5 Viscosity curves for sulfonated polystyrene ionomers (MW = 4.0 X 105 Na salt) with various ion contents in DMF. (From Ref. 49.)... 

Hara M, Wu J, Lee AH. Effect of intia- and intermolecular interactions on solution properties of sulfonated polystyrene ionomers. Macromolecules 1988 21 2214-2218. 

Cooper et al. reported that solid-state 23Na NMR is useful for observing the sodium cation in sulfonated polystyrene ionomers (NaSPS).44 Three NMR peaks were detected, corresponding to isolated ion pairs, aggregated ions and hydrated ions (Fig. 14). The distributions of these three types of sodium cations are systematically influenced by hydration treatment, sulfonation level and neutralization level. Fully dried NaSPS at low ion content shows that the isolated and aggregated sodium ions in NaSPS are available for hydration. As the sulfonation level increases, the fraction of sodium ions held in isolated ion pairs decreases while the fraction of ionic species in the ionic aggregates increases. This coincides with a shift in the peak position of the aggregated sodium ions to low frequency, indicative of increased quadrupolar interactions. 

The melt behavior of sulfonated polystyrene ionomers was studied by Lundberg and coworkers41. As was shown in the case of a sulfonated elastomer30, sulfonation of polystyrene leads to an increase in the melt viscosity (measured at 250 °C) of the SPS upon neutralization, indicating increased association of the sodium poly-(salt). A sudden jump of the melt viscosity occurs at the point of complete neutralization, where a critical concentration of Na polystyrenesulfonate is reached, apparently resulting in a sharp phase separation between the ionic and hydrophobic domains (Figure 5). 

Figure 10.4. Tensile strength and elongation of Na-sulfonated polystyrene ionomer without and with 10% plasticizer (either DOP or glycerol). [Data from Ma X Sauer J A Kara M, J. Polym. Sci. Polym. Phys. Ed., 35, No.8, June 1997, p. 1291-4.]...

Molnar, A., and Eisenberg, A., Miscibility of polyamide-6 with lithium or sodium sulfonated polystyrene ionomers. Macromolecules, 25, 5774-5782 (1992). 

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