Ionomer-polar solvent system

Polyelectrolyte Behavior. Figure 1 shows the characteristic Kc/R vs. c plot of lonomers in polar solvents the reciprocal reduced scattered intensity rises steeply from the intercept at zero polymer concentration, bends over, and becomes nearly horizontal at higher concentration. This type of behavior was reported for some salt-free polyelectrolytes in aqueous solution (23.26), although the reliability of these early measurements is rather poor because of very small scattered intensity from polyelectrolyte/aqueous solution systems. For example, the excess scattered intensity from salt-free sodium poly(methacrylate) in aqueous solution over that of water was only 10 to 100% (2i) - (0.1-1) x 10 °. in ionomer solutions,... 

Lightly sulfonated polystyrene is soluble in mixed solvent systems, such as xylene containing low levels of alcohols, or in moderately polar solvents. In low polarity solvents the viscosity of such ionomer solutions can be substantially higher than polystyrene of comparable molecular weight due to ion pair association at concentrations >1% as shown in Table I. 

Few studies have been conducted heretofore on sulfonated ionomers in solvents which can be considered relatively polar, as defined by a high dielectric constant. A recent study (13) on acrylonitrile-methallyl sulfonate copolymers in dimethyl-formamide is a notable exception. S-PS is readily soluble in a wide variety of solvents, some of them exhibiting rather high values of dielectric constant, such as dimethylformamide (DMF) or dimethylsulfoxide (DMSO). The reduced viscosity-concentration behavior of sulfonated polystyrene is markedly different in polar solvents from that in nonpolar-solvent systems. Typically there is a marked upsweep in reduced viscosity at low polymer concentrations and clearly a manifestation of classic polyelectrolyte behavior. ( 7)... 

Polar solvents such as dimethylformamide, dimethylsulfoxide, and tetrahydrofuran-water mixtures behave differently in that polyelectrolyte behavior is observed at extreme dilution for sulfonate ionomers therefore, the behavior described above does not apply directly to these solvent systems. 

These results confirm the observation that polyelectrolyte aqueous solutions show two separate decay modes in the autocorrelation function and support our contention that ionic polymer systems generally behave similarly in polar solvents [23], To support this, it may be added that similar dynamic scattering behavior was recently reported for another type of ionomer, polyurethane ionomer, dissolved in a polar solvent, dimethylacetamide (e = 38) [92], Finally, it should be stressed that the explanation given above for light scattering (both static and dynamic) behavior of salt-free polyelectrolytes is based on the major role of intermolecular electrostatic interactions in causing characteristic behavior. No intramolecular interactions are explicitly included to explain the behavior. This is in accord with our contention that much of the polyelectrolyte behavior, especially structure-related aspects, is determined by intermolecular interactions [23]. 

Dieterich et al. (1A6) and Taft and Mohar (157) have prepared excellent reviews of urethane ionomers. One of the most Important characteristics of urethane ionomers is the ease with which they form stable water dispersions without the use of emulsifiers (158-16A). These dispersions consist of colloidal two-phase systems that can be readily prepared by adding a solution of the urethane ionomer in polar solvents, such as methyl ethyl ketone or tetrahydrofuran,... 

So far most studies of aggregation behavior have been conducted with low polarity solvents such as THF [4,9,15]. Recently there have been a few reports with nonpolar solvents such as xylene [16-18]. While these systems require low ion contents to form a solution, the ionomer electrical environment is more similar to that found in the solid state (i.e. low dielectric constant). In this work we use static and dynamic light scattering techniques to examine the aggregation behavior of sulfonated polystyrene ionomers in a nonpolar solvent, toluene. 

Several studies (6, 13) of the solution behavior of sulfonate ionomers have provided additional insight on the nature of the ion pair aggregation. The polarity of the solvent environment has been shown to have a major influence on the dilute solution behavior of these polymers. In the course of these studies it has been observed with selected systems that both melt viscosity values and solution behavior can vary according to the history of sulfonate ionomers. This study provides some data and provides one rationale for such differences. 

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