Divinylbenzene-cross-linked polystyrene sulfonated

Mg2" " > Ca2" " > Sr2" " > Ba2" " which is the inverse order of exchange selectivities. The spread in selectivities for the alkaline earth ion series is much smaller compared to that of the alkali metal ions however. The values for the normal form of Nafion in Table II are similar to those of a 4% divinylbenzene cross-linked polystyrene sulfonate resin Mg2" ", 2.23 Ca2" ", 3.14 Sr2" ", 3.56 Ba2" ", 5.66 (12). Resins of 8% and 16% cross-linking have a much larger spread than do these values thus the enhancement in... 

Typical examples of covalently cross-linked networks are a styrene-divinylbenzene copolymers swollen in an organic solvent and ion-exchange resins made from cross-linked polystyrene sulfonate, poly(/ -aminostyrene), or 2-hydroxyethyl methacrylate-ethylene glycol dimethacrylate copolymer swollen in water, which is the typical material used for soft contact lenses. Table 1 gives a classification of gels. 

The resins are prepared first by copolymerizing styrene (ST) and divinylbenzene (DVB), resulting in a cross-linked polystyrene. Usually, they are produced in the form of spherical beads. These beads are sulfonated with sulfuric acid for anionic resins and methylated with chloromethyl ether followed by quatemization with trimethylamine for cationic resins. Two types of resins exist gel and microporous. The microporous beads are used to remove ionic substances quickly while the gel-type beads are used for sustaining drug release over a long period of time. 

FIGURE 19.3 Schematic of a cation resin bead showing the polystyrene chains with sulfonic groups, the divinylbenzene cross-links, and the active sulfonic groups where the ion exchange occurs. Because the void spaces between the polymer chains and crosslinks contain water, the effective ion-exchange surface area of the bead is not limited to its outside diameter. 

Sevenich and Fritz [9] published a comprehensive study of metal cation selectivity with resins of a more modern type. The studies were made on a column packed with a 12% cross-linked polystyrene-divinylbenzene resin 12-15 mm in diameter and with an exchange capacity of 6.1 pequiv/g. The resins were prepared by rapid sulfonation so that the sulfonic acid groups are concentrated on the outer perimeter of the resin beads [10]. 

The heterogeneous sulfonation of a cross-linked polystyrene, prepared by polymerizing a styrene-divinylbenzene mixture in an aqueous suspension, is the basis for production of strong-acid cation-exchange resins34. Even a superficial treatment of resins of this type would be beyond the scope of the present chapter, and interested readers should consult special treatises on the subject3 5a. Their application as a tool in analytical chemistry is treated elsewhere3515. 

Humidity sensors using cross-linked styrene-sulfonate have been developed by Pope [41] using this mechanism. Cross-linked copolymers prepared from styrene-sulfonate are fabricated on polystyrene substrates furnished with Ag electrodes. This sensor responds to water vapor at temperatures below 100 °C and rinsing the element is enough to restore the sensor characteristics in case of contamination. A similar sensor which consists of polystyrene-sulfonate containing 4-10% divinylbenzene, has been developed by Musa [42]. This sensor exhibits extremely low hysteresis, 3% r.h., but the long term stability is poor. 

Sulfonation of the cross-linked polystyrene Insoluble polystyrene cross-linked with divinylbenzene can easily be converted by sulfonation to a usable ion exchanger. For this purpose a mixture of 0.2 g of silver sulfate and 150 mL of concentrated sulfuric acid are heated to 80-90 °C in a 500 mL three-necked flask fitted with stirrer, reflux condenser and thermometer. 20 g of the polymer of styrene and divinylbenzene are then introduced with stirring the temperature rises spontaneously to 100-105 °C. The mixture is maintained at 100 °C for 3 h, then cooled to room temperature and allowed to stand for some hours. Next the contents of the flask are poured into a conical flask that contains about 500 mL of 50% sulfuric acid. After cooling, the mixture is diluted with distilled water, and the gold-brown eolored beads are filtered off on a sintered glass filter and washed carefully with water. 

The sulfonated cross-linked polystyrene resins have been by far the most popular materials for the separation of inorganic species, including the actinides. Typical of these is Dowex-50. This resin is usually specified as "X 4" or "X 12," etc., which means 4% or 12%, etc. divinylbenzene was added to the styrene in the... 

Results from a series of degradation tests on grafted polystyrene sulfonic acid (g-PSSA) membranes have shown that thinner membranes have higher degradation rates than thicker ones (Gubler et al. 2005). Divinylbenzene cross-linked membranes have higher durability than non-cross-linked membranes owing to their lower gas crossover rate. 

One of the earliest proton exchange membranes was based on sulfonated polystyrene where divinylbenzene was used as a cross-linking unit for extra stability. Developed by General Electric, this membrane (21) was cheap and easy to manufacture, and it was used for fuel cells in the Gemini space pro-gram.i However, due to the sensitivity of the benzylic hydrogen to radical attack, lifetimes for these membranes under FC operating conditions were quite low. Thus, little work has been carried out on these systems since their inception. 

Ainberlyst-type catalysts were as active as and more selective than the best homogeneous catalyst, II2SO4. Amberlyst 15 and 3G are macroreticular type polystyrene sulfonic acid resins partially cross-linked with divinylbenzene. The absence of the N—benzyl product when solid acid catalysts were employed suggests the possibility that the reaction could be carried out in a single step. It is also expected to provide all the aforementioned advantages of solid catalysts over liquid catalysts. 

The ion movement can be controlled by ion exchange or ion transfer membranes, thin sheets of cross-linked organic polymers with ion exchange properties—for example, sulfonated polystyrene-divinylbenzene polymers. Both cation-permeable and anion-permeable membranes are available and have been described (3, 9). To achieve demineralization, these membranes are spaced alternately between a cathode and an anode which introduce direct current. The compartment between each pair of membranes is filled with a saline water. The resulting ion motion is controlled by the membranes, so that one set of compartments—for example, the even-numbered compartments—lose ions and the odd-numbered compartments gain ions. The product from the ion-losing cells is collected and comprises electrically demineralized water. 

We are interested in the application of polymers as adsorbents, ion exchangers, fuel cells, and permeable materials. In this regard, the first resins with some of these properties were obtained by D Aleleio in 1944 based on the copolymerization of styrene and divinylbenzene. Unfunctionalized polystyrene resins cross-linked with divinylbenzene (Amberlite) are widely applied as adsorbents [191,192], In addition, the polystyrene-divinylbenzene resins functionalized with sulfuric acid (sulfonation) to create negatively charged sulfonic sites are applied as cation exchangers, and treated by chloromethylation followed by animation produce anionic resins [193,194],... 

Stationary Phase Use prepacked macroreticular polystyrene sulfonate divinylbenzene cation-exchange resin (2% to 8% cross-linked, 8- to 25-ptm particle size), preferably in the calcium or silver form. Examples of acceptable resins are Bio-Rad Aminex HPX-87C, or equivalent, for separating DPi-DP4 saccharides, and Aminex HPX-42C and HPX-42A, or equivalent, for separating DP1-DP7 saccharides. Maintain the column at 85° during operation. 

IR-1 (V4). The Dp values for Dowex 50, a typical sulfonated polystyrene resin, have been shown by Boyd and Soldano (B7) to depend greatly upon the extent of cross-linking as determined by the divinylbenzene (DVB) content of the resin. For 8% DVB, the Dp values are similar to Amberlite IR-1. For 12% DVB, the usual commercial grade, self-diffusion... 

R.H. Wiley and E. Reich, The peroxide-induced degradation of sulfonated polystyrenes cross-linked with m- and / -divinylbenzene, J. Polym. Sci., Polym. Chem. Ed., 1968, 6,3174-3176. 

Ioti exchange membranes are primarily produced in large amounts for electrodialysis in aqueous media, e.g., for seawater desalination. They are typically made of polystyrene, cross-linked with divinylbenzene, as a base polymer. Sulfonic acid groups are introduced as fixed ions for CEM and quaternary ammonium groups for AEM. These materials may be of limited stability in combination with organic compounds due to increased swelling or even chemical attack, particularly at elevated temperatures. Simple AEMs of this type will be destroyed in alkaline media, i.e., they cannot work for longer time as OH conductor. However, many membranes made from newly developed materials are also available. Different manufacturers should be contacted to identify suitable membranes for a particular task. 

---