Cross-linked ion-exchange resins

Figure 26-1 Structures of styrene-divinylbenzene cross-linked ion-exchange resins...

The real swelling behavior of cross-linked ion-exchange resins immersed in electrolyte solutions of varying concentrations denote that these systems can be considered as a charged... 

Thus a reliable experimental approach to the evaluation of the intrinsic pfC values of highly swollen, weakly acidic (basic) gels and more rigidly cross-linked ion-exchange resins has been demonstrated fully in this study. It is the successful culmination of earlier studies in this direction by Nagasawa (12), Katchalsky (13), and Michaeli (14). 

Only trends in ion-exchange selectivity were predicted by this approach when it was used to examine the interpretive quality of the Gibbs Donnan model for analysis of the ion-exchange phenomenon in flexible, cross-linked ion-exchange resins... 

N. Lakshminarayanaiah, Measurement of electrical conductivity of cross-linked ion-exchange resins by d.c. method, J. Polym. Sci., 1960, 46, 529-531. 

Macroporous resin stationary phase material formed from cross linked ion exchange resins that have pores of molecular size, 100-500 A across, and large surface areas. 

Poly(acrylic acid) and poly(methacrylic acid) have found use in a variety of applications. A widespread use is for thickening polymer latices for textile finishes and paints. Other uses are as suspending agents for inorganic pigments, flocculants in metal ore recovery, textile sizes and (cross-linked) ion exchange resins. 

Tjlatek and Marinsky (13) first suggested that a zeolite may be con-A sidered a highly cross-linked ion exchanger and that a relationship of the type introduced by Gregor (7, 8) and Glueckauf (6) for organic resins also may apply for the zeolite namely... 

Polyelectrolyte (cross-linked) Ion-exchange Ion-exchange resins Sulfonated polystyrene aminated polystyrene... 

The reactions are catalyzed by tertiary amines, quaternary ammonium salts, metal salts, and basic ion-exchange resins. The products are difficult to purify and generally contain low concentrations of acryhc acid and some diester which should be kept to a minimum since its presence leads to product instabihty and to polymer cross-linking. 

The organic and aqueous phases are prepared in separate tanks before transferring to the reaction ketde. In the manufacture of a styrenic copolymer, predeterrnined amounts of styrene (1) and divinylbenzene (2) are mixed together in the organic phase tank. Styrene is the principal constituent, and is usually about 90—95 wt % of the formulation. The other 5—10% is DVB. It is required to link chains of linear polystyrene together as polymerization proceeds. DVB is referred to as a cross-linker. Without it, functionalized polystyrene would be much too soluble to perform as an ion-exchange resin. Ethylene—methacrylate [97-90-5] and to a lesser degree trivinylbenzene [1322-23-2] are occasionally used as substitutes for DVB. 

Substituted Phenols. Phenol itself is used in the largest volume, but substituted phenols are used for specialty resins (Table 2). Substituted phenols are typically alkylated phenols made from phenol and a corresponding a-olefin with acid catalysts (13). Acidic catalysis is frequendy in the form of an ion-exchange resin (lER) and the reaction proceeds preferentially in the para position. For example, in the production of /-butylphenol using isobutylene, the product is >95% para-substituted. The incorporation of alkyl phenols into the resin reduces reactivity, hardness, cross-link density, and color formation, but increases solubiHty in nonpolar solvents, dexibiHty, and compatibiHty with natural oils. 

Divinylbenzene copolymers with styrene are produced extensively as supports for the active sites of ion-exchange resins and in biochemical synthesis. About 1—10 wt % divinylbenzene is used, depending on the required rigidity of the cross-linked gel, and the polymerization is carried out as a suspension of the monomer-phase droplets in water, usually as a batch process. Several studies have been reported on the reaction kinetics (200,201). 

Nature of ion exchange resin. The absorption of ions will depend upon the nature of the functional groups in the resin. It will also depend upon the degree of cross-linking as the degree of cross-linking is increased, resins become more selective towards ions of different sizes (the volume of the ion is assumed to include the water of hydration) the ion with the smaller hydrated volume will usually be absorbed preferentially. 

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