Polystyrene conventional sulfonated resins

Both the normal and expanded forms of Nafion exhibit the expected order of selectivities of alkali metal ions for a sulfonate ion exchanger. Perhaps the most interesting feature of these values is their large spread compared to conventional sulfonate resins. For example, a 16% cross-linked polystyrene sulfonate has metal ion-hydrogen ion selectivity coefficients equal to 0.680 (Li+), 1.61 (Na+), 3.06 (K+), 3.14 (Rb+), and 3.17 (Cs+) (12). The selectivity coefficients of Ag+ and Tl+ for Nafion are lower than those of polystyrene sulfonate resins of... 

More recently, Biswas and Chatteijee have prepared polystyrene electro-philically substituted with phthalic anhydride pyromellitic diianhydride tri-mellitic anhydride and 1,2,3,4-tetrahydrophthalic anhydride by Friedel-Crafts reaction. These anhydride-modified polystyrenes have further been converted into sulfonic acid resins by conventional sulfonation reaction. The thermal stabilities of these modified polymers are comparatively better than that of unmodified polystyrene. Ion-exchange capacities also compare favourably with the polystyrene-based commercial resins. 

Figu re 10.4 Modified conventional sulfonated polystyrene resins. 

In a similar way, Mizota et al. grafted polymer chains functionalized with sulfonic sites over a polystyrene-type polymer. As observed above, the flexibility of the polymer chains allowed better accessibility of the catalytic sites and this solid acid catalyst was ten times more active than the conventionally used cross-linked resin in the hydrolysis of sucrose (Scheme 2) [27]. 

The use of solid acid catalysts, consisting of polysiloxanes bearing alkylsulfonic acid groups, is described, in organic synthesis and in technical applications. Although sulfonated polysiloxanes have been reported in the literature and have been found to show excellent activities in comparison to conventional polystyrene based cation exchange resins, no large scale technical use has become known thus far. 

Partial sulfonation under mild conditions has been reported to improve the activity and selectivity for some processes [66-69], Thus, for the esterification of dodecanoic acid with 3-phenylpropan-l-ol in water, sulfonated polystyrene resins with low substitution degrees gave better results than those with higher loadings [69], It was suggested that conventional acidic ion exchange resins are too... 

Figure 16.2 Dependence of the time of saturation of 50% functional groups with (C4H9)4N ions on the resin water uptake for the sulfonates prepared by crosslinking (1-3) linear polystyrene with (1) 1,4-bis(chloromethyl diphenyl), (2) p-xylylene dichloride, and (3) monochlorodimethyl ether (4) styrene-1 % DVB copolymer crosslinked with 1,4-chloromethyl diphenyl (5) sulfonates based on conventional styrene-DVB copolymers numbers denote the degree of crosslinking. (After [371].)...

It follows from the above that sulfonated hypercrosslinked polystyrene resins taken in the form should be able to eliminate trace metal cations from concentrated mineral acids much more efficiently than conventional cation exchanger [377], which could be exploited in the preparation of high-purity acids. 

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