Sulfonated PS ionomers

Some additional information obtained because of the use of ionomers should be stressed. This is the observation that even ionomers with very small ion content produce characteristic polyelectrolyte behavior. For example, it was shown that sulfonated PS ionomers having only 0.9 mol% ion... 

Dynamic light scattering experiments were conducted for sulfonated PS ionomers in DMF [87]. CONTIN analysis of the decay rate generally indicates the existence of two decay modes. Both modes have a q2 dependence and therefore are diffusive processes. This is similar to that observed for salt-free polyelectrolytes in aqueous solution [76-79],... 

FIG. 10 Spectrum of decay rate, T, normalized by q2, of dynamic light scattering data, analyzed by CONTIN (6 = 90°), for sulfonated PS ionomer in DMF at different ionomer concentrations. (From Ref. 87.)... 

Here the counterion binding of ionomer nonaqueous (polar) solutions is described. Figure 12 shows conductance data for a sulfonated PS ionomer in DMF. For comparison, conductance data for comparable small salts, sodium styrenesulfonate, which has a similar structure to the ionic repeat units of sulfonated PS ionomers, is also shown [29], A significant drop in conductance is clearly noted for the ionomer solution as compared with the simple salt. This is due to counterion binding, as discussed above for polyelectrolyte nonaqueous solutions. 

FIG. 12 Equivalent conductance for sulfonated PS ionomer (ion content 3.0 mol%) (closed circles) and sodium styrenesulfonate (open circles) in DMF. (From Ref. 29.)... 

Another characteristic viscosity behavior of polyelectrolyte solution, viz., the effect of added salts, has been reported for ionomer solutions [55]. The reduced viscosity of sulfonated PS (Li salt) in DMF increases markedly with decreasing polymer concentration in the absence of added salt, LiCl. However, as the concentration of LiCl increases, the reduced viscosity significantly decreases, then a maximum appears in the viscosity curve, and finally straight lines are obtained. The last behavior is characteristic of neutral polymer solutions. Table 3 summarizes ionomer nonaqueous solutions whose viscosity behavior has been reported. Those results have demonstrated that the viscosity behavior of random ionomers is basically similar to that of polyelectrolyte aqueous solutions. 

Immiscible polyolefin impact modifiers have been compatibilized with PPE/PS blends by employing polyolefin sulfonate ionomers and including PS sulfonate ionomer in the blend (Table 5.54). In these compositions, the polyolefin ionomer can crosslink with PS ionomer. The latter is miscible with PS, which in turn is miscible with PPE. Simple ionomers have been used [Golba and Seeger, 1986 Campbell et al, 1986]. In similar blends, a masked ionomer, such as a polyolefin phosphonate ester, could also be used [Brown and McFay, 1986]. The masked ionomer is melt processable but generates a polyolefin phosphonate ionomer in situ during extrusion with zinc stearate. The polyolefin phosphonate ionomer can crosslink with PS sulfonate ionomer that is miscible with PS which in turn is miscible with PPE. 

Tg measurements have been performed on many other polymers and copolymers including phenol bark resins [71], PS [72-74], p-nitrobenzene substituted polymethacrylates [75], PC [76], polyimines [77], polyurethanes (PU) [78], Novolac resins [71], polyisoprene, polybutadiene, polychloroprene, nitrile rubber, ethylene-propylene-diene terpolymer and butyl rubber [79], bisphenol-A epoxy diacrylate-trimethylolpropane triacrylate [80], mono and dipolyphosphazenes [81], polyethylene glycol-polylactic acid entrapment polymers [82], polyether nitrile copolymers [83], polyacrylate-polyoxyethylene grafts [84], Novolak type thermosets [71], polyester carbonates [85], polyethylene naphthalene, 2,6, dicarboxylate [86], PET-polyethylene 2,6-naphthalone carboxylate blends [87], a-phenyl substituted aromatic-aliphatic polyamides [88], sodium acrylate-methyl methacrylate multiblock copolymers [89], telechelic sulfonate polyester ionomers [90], aromatic polyamides [91], polyimides [91], 4,4"-bis(4-oxyphenoxy)benzophenone diglycidyl ether - 3,4 epoxycyclohexyl methyl 3,4 epoxy cyclohexane carboxylate blends [92], PET [93], polyhydroxybutyrate [94], polyetherimides [95], macrocyclic aromatic disulfide oligomers [96], acrylics [97], PU urea elastomers [97], glass reinforced epoxy resin composites [98], PVOH [99], polymethyl methacrylate-N-phenyl maleimide, styrene copolymers [100], chiral... 

For almost ten years the properties of ionomer solutions have been studied and lightly sulfonated polystyrene (S-PS) was chosen as the model compound. The properties of S-PS ionomer solutions in polar and nonpolar solvents, which are briefly reviewed, were associated with polyelectrolyte and ionomer behavior respectively. In both cases, structural models have been proposed to explain the rheological and scattering data. A similar study on perfluorinated ionomer solutions is then presented and compared in order to define some general ionomer behavior. 

Weiss et al. [75] have synthesized Na and Zn salt of sulfonated styrene(ethylene-co-butylene)-styrene triblock ionomer. The starting material is a hydrogenated triblock copolymer of styrene and butadiene with a rubber mid-block and PS end-blocks. After hydrogenation, the mid-block is converted to a random copolymer of ethylene and butylene. Ethyl sulfonate is used to sulfonate the block copolymer in 1,2-dichloroethane solution at 50°C using the procedure developed by Makowski et al. [76]. The sulfonic acid form of the functionalized polymer is recovered by steam stripping. The neutralization reaction is carried out in toluene-methanol solution using the appropriate metal hydroxide or acetate. 

Studies on the dilute solution behavior of sulfonated ionomers have shown these polymers to exhibit unusual viscosity behavior in solvents of low polarity. These results have been interpreted as arising from strong ion pair associations in low polarity diluents. Solvents of higher polarity, such as dimethyl sulfoxide and dimethyl formamide induce classic polyelectrolyte behavior in sulfonate ionomers even at very low sulfonate levels. To a first approximation these two behaviors, ion pair interactions or polyelectrolyte behavior, are a consequence of solvent polarity. Intramolecular association of Lightly Sulfonated Polystyrene (S-PS) results in a reduced viscosity for the ionomer less than that of polystyrene precursor at low polymer levels. Inter-association enhances the reduced viscosity of the ionomer at higher polymer concentrations. Isolation of the intra- and inter-associated species of S-PS has been attempted (via freeze drying). A comparison of selected properties reveals significant differences for these two conformations. 

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