1.2 Synthetic Ion Exchange Resins

Sulfonation of macroporous poly(styrene-co-divinylbenzene) beads: Effect of the proportion of isomers on their cation exchange capacity

“…The transformation of the macroporous polymeric beads into strong cation exchange resins through their sulfonation was accomplished following the usual procedure for the sulfonation [1,[14][15][16][17][18][19][20] of polystyrene beads: the precursor macroporous poly(ST-co-DVB) beads were functionalized to convert them into cation exchange resin in 250-mL, three-necked, round-bottomed glass reactors equipped with mechanical stirrers, reflux condensers, and thermometers. The reactors were loaded with 100 mL of sulphuric acid (95-98%) and heated to 75°C in a polyethylene glycol bath.…”

“…Cation exchange resins are useful in a large number of applications, ranging from the exchange of cations for different purposes in many industrial and laboratory fields [1,2] (substitution, elimination, isolation, separation, recovery and concentration of cations) to their use as catalysts [1][2][3][4][5][6][7]. However, since each of these applications has different characteristics, the best performance in each one of them will only be achieved by using cation exchange resins with properties suited to the application.…”

“…Most cation exchange resins are manufactured from spherical polymeric beads synthesized by the procedure of suspension copolymerization [1,2], using styrene (ST) and divinylbenzene (DVB) as monomers. DVB is a cross-linking agent that provides physical strength to the beads.…”

“…With regard to the degree of functionalization, the transformation of poly(ST-co-DVB) beads into cation exchange resins can be accomplished by several methods, the one most widely used (in the case of strong cation exchange resins) involving the sulfonation of polymeric beads by hot concentrated sulphuric acid [1,[14][15][16][17][18][19][20]. This gives rise to an aromatic electrophilic substitution reaction and sulfonic acid groups are incorporated to the aromatic rings.…”

“…The degree of sulfonation, and hence the exchange capacity, is an important feature of cation exchange resins because in exchange and catalytic operations [21][22][23] their performance depends on this parameter. Cation exchange capacities, which are usually measured [1] through H + / Na + exchange, depend only slightly on the degree of cross-linking of the polymer. Thus, in the case of polystyrene, a mono-sulfonation of each benzene ring in the polymer results in a exchange capacity of about 5.4 meq/(g dry resin in the H + form), whereas, for poly(ST-co-DVB) resins with 50%, w/w, cross-linking, the exchange capacity should decrease to approximately 4.7 meq/g owing to the increase in the molecular weight of the polymeric structural unit.…”