Polymeric Ion-Exchange Fibers

James Economy* and Lourdes Dominguez

University of Illinois, Department of Materials Science, 1304 West Green Street, Urbana, Illinois 61801

Christian L. Mangun

EKOS Materials Corporation, 101 Tomaras Avenue, Savoy, Illinois 61874

This work explores the design of new ion-exchange materials in the form of fibers that yield anumber of important advantages over conventional ion-exchange beads. In this approach, ion-exchange fibers are prepared by (1) coating low-cost glass fiber substrates with an appropriateoligomer, (2) cross-linking, and (3) functionalizing the coating to produce either anionic or cationiccapability. As a result of the thin coatings, the use of solvents prior to both functionalizationand preswelling of the finished product prior to end-use was eliminated, representing a significantsimplification of current synthesis methods. Kinetic experiments showed that the contactefficiencies of these systems were greatly improved over the traditional beads because of thehigher surface-to-volume ratio and shorter diffusion path lengths. This improvement translatedinto an order of magnitude increase in both ion-exchange and regeneration rates. Anotheradvantage is the excellent resistance of the fibers to osmotic shock even after multipleregenerations. Finally, these systems were shown to remove heavy metal contaminants effectivelyto well below part per billion concentrations.

Introduction and Background

Historical Review. Early references to ion-exchangeresins date back to ancient times, particularly in rela-tion to soils and clays. However, two chemists, Thomp-son and Way, were the first to establish the mechanismof the ion-exchange reaction in the 1900s. Treating softcoals with fuming sulfuric acid produced the firstorganic ion exchangers, which were termed carbon-aceous zeolites.1 The first completely organic ion ex-changer was prepared in 1935 by Adams and Holmes.It was synthesized through a condensation polymeri-zation reaction, producing a phenol-formaldehyde cation-exchange resin.2 Later, in 1944, D’Alelio patented thenow well-known and more stable styrene-based cationexchanger.3 Such a system can be used to generate bothcationic and anionic exchange resins. In 1947, McBur-ney contributed to the advancement of anion-exchangeresins with the development of chloromethylation andamination resulting in the desired functionalization. Inthe chloromethylation step, a chloromethyl functionalgroup is introduced into the ethenylbenzene nuclei. Thecopolymer can then be functionalized with various alkylsubstituted aliphatic amines in the amination step.1

Over the past 70 years, a number of importantadvances have been made in the area of ion-exchangesystems of various types, such as inorganic clays,zeolites, and specialized polymeric systems designed forthe “selective” removal of unwanted ions. Ion exchangetoday has a wide variety of important applications inindustries such as pharmaceutical, food processing,chemical synthesis, biomedical, hydrometallurgy, watertreatment, synthetic fiber production, and chromatog-raphy.4 The impetus for work in this field continues togrow as our water resources become reduced and as the

U.S. Environmental Protection Agency (EPA) regula-tions become more stringent. Safe drinking water isbecoming a precious and limited commodity, and inmany communities, it can be obtained only with greateffort and cost because of either scarcity or contamina-tion. Slightly more than half of the U.S. populationreceives its drinking water from groundwater sources,5and water usage has increased steadily during the pastseveral decades. This has resulted in widespread de-clines in water table levels by 40 ft or more.6 Some ofthe contaminants of increasing concern are heavy met-als, pesticides, and toxic chemicals, which have foundtheir way into underground aquifers through anthro-pogenic as well as natural sources. For example, in 1995,more than 270 million lb of toxic waste (cadmium, lead,arsenic, dioxins, etc.) was recycled in fertilizer factoriesand applied at farms.7 These toxic contaminants havethe potential to continue into the food chain throughcrop uptake, as well as percolating into undergroundaquifers as a result of agricultural runoff.

Current State of the Art: Ion-Exchange Beads.Conventional ion-exchange beads (IEBs) consist ofthree-dimensional covalent networks to which ion-exchange groups are bonded. The network preserves thestructural integrity of the material, while the bound ionsprovide either cationic or anionic exchange sites. Forexample, the typical styrene-based matrix is preparedby the suspension polymerization of styrene with vary-ing ratios of divinylbenzene. The beads are then swollenwith organic solvents, either sulfonated or chloromethy-lated, and subsequently aminated to prepare strongcationic or anionic exchange systems, respectively.1,8,9

IEBs are used extensively for the purification anddemineralization of water. Although ion-exchange beadscan be very effective, it should be noted that they havea number of drawbacks. During the functionalizationstage, solvents must be used to facilitate reaction ratesand maintain the spherical form of the beads. Examplesof solvents used include but are not limited to toluene,

* To whom correspondence should be addressed. E-mail:jeconomy@staff.uiuc.edu. Phone: 217-333-9260. Fax: 217-333-2736.

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methylene chloride, perchloroethylene, carbon tetra-chloride, ether, and dioxane.1,8 These toxic solvents alsoimpart strong odors or tastes that remain in the finishedproduct. The beads are very susceptible to fracture andbreakage due to osmotic shock and must be kept wet atall times (Figure 1a). In addition, the beads frequentlyrequire costly service containment systems (because theprevailing shape of the final product is generally limitedto small particles) and the added expense of EPA-required disposal of spent beads. More importantly,there are a number of major needs with respect toenvironmental pollution, where greatly improved ion-exchange materials are required. These needs includematerials with better contact efficiencies, capabilitiesfor rapid regeneration, much longer service lifetimes,and selectivities to the removal of specific ions (such asheavy metals to acceptable levels of less than 1 ppb).

Polymeric Ion-Exchange Fibers

The concept of developing ion-exchange materials inthe form of fibers was first reported by Economy et al.30 years ago.10 Fibrous ion-exchange materials haveseveral advantages over the conventional ion-exchangeunits. These advantages include the ability to befabricated in the form of felts or fabrics where thecontact efficiency is greatly improved. A fibrous formeliminates the need for currently used retainers suchas canisters, screens, etc. Thus, the concept of designingcationic and anionic exchange materials by coating glassfiber substrates with a polymeric ion-exchange resinwas developed.11

Important parallels can be drawn from recent workon a family of activated carbon coatings prepared on aglass fiber substrate.12,13 In earlier work, issues ofenvironmental concern were addressed with the devel-opment of improved activated carbon fibers (ACFs) withtailored pore sizes and pore surface chemistries.14-16

These systems established that activated carbon coatedon glass fiber substrates could be produced more cost-effectively than commercially available ACFs. This wasthe consequence of using much lower-cost startingmaterials and a simplified synthesis route. It was shownthat such systems were far more efficient in removingtrace contaminants (such as benzene, toluene, ethyl-benzene, xylene) to below the part per billion range thangranular activated carbon.17 In addition, the carbon-coated fibers displayed a 7-fold improvement in ratesof adsorption and desorption. This essentially nullifiedthe disadvantage of having a glass core, which tendedto decrease the total overall capacity.

More recently, research was undertaken to extendmany of the above concepts to the design of polymericbased ion-exchange fibers (IEFs) for the removal ofundesirable aqueous contaminants.

Application of IEFs. Ion-exchange materials coatedon glass fiber substrates should demonstrate a numberof advantages over the conventional ion-exchange beads.These include simplification of the overall synthesisprocedures, including more efficient functionalizationand elimination of toxic solvents. Other benefits includethe ability to be easily fabricated in the form of felts,papers, or fabrics that will improve media contactefficiency. This will enhance the rates of both reactionand regeneration. In addition, physical and mechanicalrequirements of strength and dimensional stabilityshould be achieved by the use of glass fiber sub-strates.11,18

The research outlined in this paper has applicationto the cleaning of waters contaminated with toxic metalions from the metal plating industry; tap water thatcontains excessive lead and copper owing to corrosionof premises plumbing; waters that contain excessiveconcentrations of species such as arsenic, mercury, andfluoride; and treated drinking water that containsexcessive concentrations of the suspected carcinogenbromate. There is a need for new materials that canselectively and cost-effectively remove such contami-nants from the matrix of other benign substances.

Polymeric Cationic Exchange Fibers. In thisapproach, cationic exchange fibers were prepared by (1)coating glass fiber substrates with a polystyrene/divi-nylbenzene oligomer with loadings in the range of 30-60%, (2) curing, and (3) sulfonating. Through improvedpolymerization techniques, the use of solvents prior tofunctionalization and end-use was eliminated, thusgreatly simplifying the overall preparation procedure(Figure 2).11 The use of relatively thin coatings on glassfiber substrates appeared to ensure longer life byeliminating long-term fatigue and cracking caused byresidual strains and swelling of the beads (Figure 1b).By lowering the oligomerization temperature to 80 °Cand slowing the gelation period (coating at room tem-perature), the effects of shrinkage forces that canproduce internal strains were minimized. In 1952,Wheaton established that the change in volume that thecross-linked beads undergo during sulfonation in con-centrated sulfuric acid is 20%.8 In addition, styreneundergoes approximately 14% shrinkage in going from

Figure 1. SEM images of (a) Purolite cationic exchange beaddisplaying the effect of osmotic shock and (b) ion-exchange fibers.

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monomer to polymer.19 These shrinkage forces duringpolymerization can result in internal strains that arefrozen into the molecule and are strong enough torupture the material during the early curing stage. Aslow gelation period tends to minimize this effect byallowing the gel to accommodate itself to those shrink-age forces with a minimum of strain frozen into thepolymer mass.20 In the spherical cationic beads, theosmotic pressures can be strong enough to destroy theresinous structure and have been calculated to be 143atm for a 10% cross-linked resin.21

The sulfonation process can be carried out withsulfuric acid, sulfur trioxide, oleum, chlorosulfonic acid,or mixtures thereof.22 Achieving close molecular contactbetween aromatic sites and the sulfonating agent be-comes problematic for the beads, as the surface of thepolymer must swell before the next layer can be exposedto the reagent.8 It follows that uniformity of sulfonationmight not occur throughout the copolymer. Typically,swelling agents are used to access the bead core andachieve higher levels of functionalization. Fortunately,the ease of sulfonation with thin resin coatings elimi-nates this problem by circumventing the need forsolvents while still attaining homogeneous distributionsof exchange groups.

Cation-Exchange Properties. A range of cation-exchange capacities (CECs) was achieved as a functionof the sulfonation time and temperature, with values

reaching as high as 5 mequiv/g based on resin loading(see Figure 3). This is comparable to the best CECvalues for the commercial beads. However, kineticexperiments showed that the contact efficiencies of thenew systems were greatly improved over those of thetraditional beads because of the greater surface/volumeratio associated with the film morphology and theshorter diffusion lengths. This translated into an orderof magnitude increase in the ion-exchange rate, asillustrated by Figure 4. (Two concentrations of sodiumchloride were evaluated.) The rate of exchange alsoincreased when the ion concentration was higher. Thesolution closely in contact with the resin was rapidlydepleted of ions by proton exchange from the resin.Further exchange was delayed until more ions from thebulk solution could diffuse into the surface film. Diffu-sion was easier with increasing ionic concentration inbulk solution, making the exchange faster. This sup-ports the view that at low concentrations, the rate iscontrolled by “film” diffusion and, at higher concentra-tions, the rate is controlled by “particle” diffusion. Inaddition, the usefulness of the ion-exchange processresides in the ability to regenerate quickly with no lossin capacity. The IEF were successfully regenerated for10 cycles with no observable changes in capacity orstability. (A corresponding improvement in the rate ofregeneration was also observed.)

Although water softening is an important commercialuse for ion-exchange materials, a much more seriousconcern is the removal of toxic inorganics such as heavy

Figure 2. Comparison of the synthetic steps required for ion-exchange bead versus fiber.

Figure 3. Capacities of cationic exchange fibers resulting fromvarious sulfonation treatments.

Figure 4. Batch rates of exchange at two saline concentrations,illustrating a 10-fold increase in reaction rates for the IEF.

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metals that remain in wastewaters from the platingindustry, tap water that contains excessive lead andcopper owing to corrosion, well water that containsspecies such as arsenic, etc. Recent dynamic modetesting of IEF filters (Table 1) with lead and mercuryhas demonstrated the superiority of the fibrous sub-strate over the beads. In the high-concentration (150ppm lead) regime, the beads’ breakthrough point isevident at 50 ppm (see Figure 5) and then graduallyincreases. In comparison, the cationic fiber filter wascapable of decreasing the lead concentration to ap-proximately 5 ppb. Thus, the fiber form greatly outper-formed the cationic beads and, even at this elevatedconcentration, was able to achieve values below thecurrent EPA maximum containment level (MCL) of 15ppb. The fiber retains this low effluent concentrationuntil a relatively sharp breakthrough occurs, which isindicative of a short mass transfer zone and fast reactionkinetics. The increased surface-to-volume ratio of thefibers is the apparent reason behind these contrastingresults. After regeneration, these same filters were thentested with a 9.6 ppm lead influent concentration, andthe breakpoint dropped to 1.8 ppm for the beads and 1ppb for the ion-exchange fibers, over a 1000-fold differ-ence (Figure 6).

For the mercury kinetic experiments at a startingconcentration of 98 ppm, the beads’ breakthrough pointwas observed at 45 ppm, and the fibers’ breakthroughpoint was observed at 0.4 ppm (see Figure 7). At a 7.2ppm influent concentration, the two systems droppedto 3.5 and 0.2 ppm respectively (see Figure 8). Finally,at a starting concentration of 0.75 ppm, the beads’breakthrough point dropped to 0.33 ppm, and the ion-

exchange fibers’ dropped to <0.56 ppb (see Figure 9).The cationic beads lowest achievable mercury effluentconcentration was well above the EPA’s MCL of 2 ppb,whereas the fibers only achieved this goal with thelowest influent concentration. As can be seen from the

Table 1. Characteristics of Cationic Filters for Breakthrough Experiments

filter typedegree of

crosslinking (%)resinwt %

dry resinweight (g)

filter dimensions(diameter × length)

capacity(mequiv/g of resin)

C-100H beads 5 100 1.51 1.3 cm × 5.2 cm 5.0cationic fibers 8 57 1.80 2.54 cm × 3.4 cm 4.0

Figure 5. Dynamic-mode kinetics of cationic fibers versus beadsat 150 ppm lead influent concentration.

Figure 6. Dynamic-mode kinetics of cationic fibers versus beadsat 9.6 ppm lead influent concentration.

Figure 7. Dynamic-mode kinetics of cationic fibers versus beadsat 98 ppm mercury influent concentration.

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experimental results, the ion-exchange fibers providedmuch better removal efficiencies. (It should be pointedout, however, that the cumulative effluent volume wasadjusted for dry resin weight. Thus, addition of the inertglass substrate weight would cause a shift in the curveto shorter breakthrough times but would have no effecton the magnitude of effluent concentration.) Often,costly chelating resins must be employed to achieveheavy metal removal in the part per billion range. It isevident from this study that the IEFs were capable of

achieving this goal at relatively low cost using the well-known sulfonic chemical structure.

Polymeric Anionic Exchange Fibers. In this sec-tion, the preparation and characterization of anionicexchange fibers is described. Commercial anion-ex-change beads are synthesized through suspension po-lymerization of a styrene-divinylbenzene matrix. Thisis followed by chloromethylation using highly carcino-genic chloromethyl methyl ether with aluminum chlo-ride as the catalyst to chloromethylate the copolymer.22

This is a critical and demanding step that must becarefully executed to minimize undesirable side reac-tions such as secondary cross-linking through methylenegroup bridging, also thought to affect ion-exchangecapacity and increase material fragility.1 After purifica-tion of the chloromethylated copolymer, the bead mustbe swollen in a suitable solvent such as dioxan, bu-tanone, tetrahydorfuran, or benzene to allow for auniform amination reaction and to help reduce theeffects of osmotic shock.23,24 As with the cationic sys-tems, there are also concerns regarding leachables, aswell as the added expense of solvent handling anddisposal.

Our work in this area depended on developing a muchsimpler synthetic route than that traditionally used foranion-exchange beads. This involved the use of com-mercially available chloromethyl styrene, which permit-ted direct polymerization and cross-linking to formvinylbenzyl chloride (VBC) copolymer coated on a glassfiber substrate. This eliminated the need for chlorom-ethyl methyl ether and toxic solvents for swelling. Theamination reaction of the fibrous form required 4 h. (Thequaternization reaction of the commercial beads with7.5% divinylbenzene concentration requires 7 days at 0°C using anhydrous amines24.)

The resin-coated fiber samples were cured at 95-125°C overnight. In a manner similar to that employed withcationic systems, a heat treatment was used to promotean annealing effect, thus minimizing the effects ofshrinkage forces that can produce internal strains asthe copolymer solidifies. The nonwoven glass fibersubstrate was coated with 40-80 wt % of oligomerizedresin. However, a range of 50-60% resin weight gainwas preferred to minimize bridging and retain flexibilityin the substrate. The VBC copolymer fibers weresubsequently functionalized with trimethylamine atroom temperature for 4 h without organic solvents viaa second-order nucleophilic aliphatic substitution reac-tion (SN2). After amination, an additional 5-10% weightgain was observed depending on the extent of reactionand degree of cross-linking. The degree of functionalitywas analyzed and determined to be in the range of 4.0-4.5 mequiv/g of resin through mercurimetric titration.

Initial regeneration studies were conducted employinga high-stress method where the samples were vacuum-dried, weighed, and rehydrated before being cycledagain. This method allowed for a step-by-step observa-tion of weight loss after each cycle and for osmotic forcesto take their toll. This technique showed minimal weightlosses in the fibers through five cycles. In addition, whenthe samples were placed in a column and cycled for over20 runs, the column showed no signs of degradation.Thus, the physical stability of the fibers was substanti-ated, and it was observed that these systems demon-strated excellent resistance to osmotic shock.

Removal of Arsenate. An area of special interestfor us was the removal of arsenate ion from drinking

Figure 8. Dynamic-mode kinetics of cationic fibers versus beadsat 7.2 ppm mercury influent concentration.

Figure 9. Dynamic-mode kinetics of cationic fibers versus beadsat 0.75 ppm mercury influent concentration.

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water using the anionic fibers. The U.S. EPA recentlyproposed a rule that will lower the existing standardfor arsenic in drinking water from 50 to 10 ppb,generating a great deal of urgency for improved materi-als for arsenic removal. The IEF filter was testedagainst a commercial product, Purolite A-400 Type Istrongly basic anionic beads (sample information givenin Table 2). Partial breakthrough experiments were runfor the three arsenate (As5+) influent concentrations of100, 10, and 2 ppm. All filters were degassed prior totesting, and experiments were performed at a constant100 mL/min flow rate. In the high-concentration (100ppm arsenate, pH 3.1) regime, the beads’ initial break-through point is evident at 15 ppm (see Figure 10)compared to the much lower effluent concentration of<0.1 ppm for the anionic fibers, followed by a gradualincrease. This is due to the better contact efficiency andfaster reaction rates of the fibers as compared to thebeads. Even though the beads have the advantage ofgreater equilibrium capacity, this value is not realizedunder these conditions, resulting in poorer performance.(As mentioned before, the results were normalized fordry resin weight, and in this case, the overall resi-dence time was much greater for the fibers over thebeads, thus contributing to their better removal efficien-cies.) After regeneration, these same filters were thentested for a 10 ppm arsenate influent concentration.Again, an immediate breakthrough was noted for thebeads at 1 ppm compared to an even lower effluentconcentration of <0.01 ppm for the fibers (data notshown for brevity). Finally, in the low-concentrationregime of 2 ppm influent arsenate, the commercialproduct performance once again was unable to match

that of the IEF filter. The bead displayed an initialbreakthrough point of 330 ppb, whereas the fiber formachieved negligible effluent concentrations below 1 ppb.The fibrous ion exchanger’s performance under dynamicmode conditions is indicative of a highly effective systemthat makes complete use of its ion-exchange sites andwould have lower associated energy costs due to easeof regeneration.

Summary

The application of coatings on glass fiber substratesappears to provide a far more versatile route for thesynthesis of a wide range of novel ion-exchange andchelating systems. The ion-exchange fibers discussedhere have resulted in a number of significant benefitsover the commercially available beads such as order ofmagnitude faster rates of exchange and regeneration,the uncomplicated nature of the processing technique(including elimination of solvents), improved mechanicalproperties (reduction of osmotic shock, as was observedwith beads), and design versatility provided by thefibrous form. Experimental breakthroughs on lead andarsenic showed the removal of these heavy metals tobelow part per billion levels, indicating the potential ofthese fibers to cost-effectively remove a wide range ofother toxic contaminants.

Literature Cited

(1) Dorfner, K. Ion Exchangers; Walter de Gruyter: Berlin,1991.

(2) Rodrigues, A. E. Ion Exchange: Science & Technology;Martinus Nijhoff Publishers: Dordrecht, The Netherlands, 1986.

(3) D’Alelio, G. F. Production of Synthetic Polymeric Composi-tions Comprising Sulfonated Polymerizates of Polyvinyl ArylCompounds and Treatment of Liquid Media Therewith. U.S.Patent 2,366,007, 1944.

(4) Kirk-Othmer. Encyclopedia of Chemical Technology; JohnWiley & Sons: New York, 1981.

(5) Office of Ground Water & Drinking Water, EnvironmentalProtection Agency. Where Does My Drinking Water Come From?(Web page). Accessed at http://www.epa.gov/safewater/wot/where-does.html, January, 2002.

(6) Council on Environmental Quality. The Twenty-FourthAnnual Report of the Council on Environmental Quality (Webpage). Accessed at http://ceq.eh.doe.gov/reports/1993/chap2.htm,January, 2002.

(7) Hansen, D. J. Waste Recycled into Fertilizer ContainsToxics. Chem. Eng. News 1998, 79 (13), 29.

(8) Wheaton, R. M.; Harrington, D. F. Preparation of CationExchange Resins of High Physical Stability. Ind. Eng. Chem. 1952,44, 1796.

(9) Pepper, K. W. Sulphonated Cross-linked Polystyrene: AMonofunctional Cation-Exchange Resin. J. Appl. Chem. 1951, 1,124.

(10) Economy, J.; Wohrer, L. C.; Frechette, F. J. Ion ExchangeFiber. IR-100 Award for Outstanding Technical Developments inAmerican Industry, Sep 1972.

(11) Dominguez, L.; Benak, K.; Economy, J. Design of HighEfficiency Polymeric Cationic Exchange Fibers. Polym. Adv.Technol. 2001, 12, 197.

(12) Yue, Z.; Mangun, C. L.; Economy, J. Preparation of FibrousPorous Materials by Chemical Activation: (1) ZnCl2 Activation ofPolymer-Coated Fibers. Carbon 2002, 40 (8), 1181.

(13) Benak, K.; Dominguez, L.; Economy, J.; Mangun, C.; Yue,Z. Control of Organic/Inorganic Contaminants Utilizing Tailored

Table 2. Characteristics of Anionic Filters for Breakthrough Experiments

filter typeDVB content

(%)dry resinweight (g)

columni.d. (cm)

columnlength (cm)

resinwt %

capacity(mequiv/g of resin)

A-400 beads 8 2.11 0.4 7.5 100 3.3anionic fibers 11 1.14 2.7 2.3 58 4.0

Figure 10. Breakthrough results at high arsenate concentration.

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ACFs. Presented at the Annual AWWA Conference, Denver, CO,Jun 11-15, 2000.

(14) Mangun, C. L.; Benak, K. R.; Daley, M. A.; Economy, J.Oxidation of Activated Carbon Fibers: Effect on Pore Size, SurfaceChemistry, and Adsorption Properties. Chem. Mater. 1999, 11,3476.

(15) Mangun, C. L.; DeBarr, J. A.; Economy, J. Adsorption ofsulfur dioxide on ammonia-treated activated carbon fibers. Carbon2001, 39 (11), 1689.

(16) Economy, J.; Mangun, C. Design of New Materials forEnvironmental Control. Macromol. Symp. 1999, 143, 75.

(17) Yue, Z.; Mangun, C.; Economy, J.; Kemme, P.; Cropek D.;Maloney, S. Removal of chemical contaminants from water tobelow USEPA MCL using fiber glass supported activated carbonfilters. Environ. Sci. Technol. 2001, 35, 2844.

(18) Dominguez, L.; Benak, K.; Economy, J. Polymeric IonExchange Fibers. U.S. patent pending.

(19) Odian, G. Principles of Polymerization; John Wiley &Sons: New York, 1991.

(20) Boundy, R. H. Styrene. Its Polymers, Copolymers, andDerivatives; Reinhold Publishing Corporation: New York, 1952.

(21) Harland, C. E. Ion ExchangesTheory and Practice; TheRoyal Society of Chemistry: Cambridge, U.K., 1994.

(22) Bauman, W. C.; Wheaton, R. M. Method of SulfonatingInsoluble Aromatic Materials. U.S. Patent 2,733,231, 1956.

(23) Giffin, J. D. Chloromethylation of Polystyrene. Ind. Eng.Chem. 1952, 44 (11), 2686.

(24) Pepper, K. W.; Paisley H. M.; Young, M. A. Properties ofIon-Exchange Resins in Relation to Their Structure. Part VI.Anion-Exchange Resins Derived from Styrene-DivinylbenzneCopolymers. J. Appl. Chem. 1953, 4097.

Received for review June 21, 2002Revised manuscript received August 28, 2002

Accepted August 30, 2002

IE0204641

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