WO2015160562A1

WO2015160562A1 - Sulfonation of aromatic polymers in the presence of a polyfluorinated benzene compound as swelling agent

Info

Publication number: WO2015160562A1
Application number: PCT/US2015/024609
Authority: WO
Inventors: Jose A. TREJO O' REILLY; John David Finch; Faith T. LIPFORD
Original assignee: Rohm And Haas Company
Priority date: 2014-04-15
Filing date: 2015-04-07
Publication date: 2015-10-22
Also published as: RO131975A2; DE112015001834T5

Abstract

A method for sulfonating an aromatic polymer by reacting the aromatic polymer with a sulfonating agent in the presence of a polyfluorinated benzene compound.

Description

SULFONATION OF AROMATIC POLYMERS USING FLUORINATED BENZENE COMPOUND AS SWELLING AGENT

FIELD

The invention relates to the sulfonation of aromatic polymers such as crosslinked copolymers of styrene.

INTRODUCTION

Industrially useful ion exchange resins are well known in the art. US2366007 describes the preparation of cation exchange resins based on sulfonated styrene-divinylbenzene copolymers. US2500149 describes an improved sulfonating process using swelling agents to swell the copolymer prior to sulfonation. Various swelling agents are described including: benzene, toluene, xylene, ethylbenzene, isopropylbenzene, chlorobenzene, tetrachloroethane and tetrachloroethylene. US5248435 describes the use of additional swelling agents including:

dichloroethane, dichloropropane, nitrobenzene and nitromethane which are further described in F. Helfferich, Ion Exchange, MacGraw-Hill Book Co. (1962). Over the last few decades, 1,2- dichloroethane or "ethylene dichloride" (EDC) has immerged as one of most common swelling agents. However, more recent environmental and safety concerns have led efforts to eliminate its use. For example, a number of so-called "solvent-less" sulfonation techniques have been developed. See for example: US6228896, US6750259, US6784213 and US2005/0014853. While these solvent-less techniques avoid the use of swelling agents, ion exchange resins made by these techniques suffer from a number of disadvantages including longer sulfonation times, reduced mechanical and osmotic stability and/or undesirable surface characteristics - namely, rough or wrinkled surfaces (see Figures lc-d).

SUMMARY

The present invention includes a method for sulfonating an aromatic polymer by reacting the aromatic polymer with a sulfonating agent in the presence of a polyfluorinated benzene compound. In other embodiments, the method avoids use of EDC or chlorinated swelling agents. In yet another preferred embodiment, the invention results in a cationic exchange resin in particle or "bead" form having a smooth surface.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures la-b are micrographs of AMBERLITE™ 120 Na brand cation exchange resin; Figures lc-d are micrographs of AMBERLITE™ SR1L brand cation exchange resin; both of which are described below. DETAILED DESCRIPTION

The invention includes a method for sulfonating an aromatic polymer. The selection of aromatic polymer is not particularly limited; however, the invention finds particularly utility in the preparation of ion (cationic) exchange resins. The term "ion exchange resin" is intended to broadly describe crosslinked copolymer particles (e.g. beads) which have been chemically treated to attach or form functional groups which have a capacity for ion exchange. The term

"functionalize" refers to processes (e.g. sulfonation) for chemically treating crosslinked copolymer resins to attach ion exchange groups, i.e. "functional groups". The crosslinked copolymer serves as the matrix, (substrate) or polymeric backbone whereas the functional group serves the active site capable of exchanging ions with a surrounding fluid medium. Examples of ion exchange resins along with techniques for their preparation are provided in: US 4,419,245; US 4,564,644; US 4,582,859; US 5,834,524; US 6,251,996; US 6,924,317 and US 2002/0042450. In preferred embodiments, the aromatic polymer comprises crosslinked copolymers of styrene or substituted styrene and a crosslinker such as divinylbenzene. One preferred styrenic co-polymer includes at least 7 molar percent (e.g. 7 to 17 molar percent) of repeating units derived from divinylbenzene. Other applicable monomers are described in more detail below including techniques for their preparation along with the preparation of corresponding cation exchange resins.

The method involves reacting an aromatic polymer with a sulfonating agent. The selection of sulfonating agent is not particularly limited. Representative sulfonating agents include: sulfuric acid (concentrated, fuming), oleum, sulfur trioxide and chlorosulfonic acid. The reaction conditions are not particularly limited but preferably include heating the reaction mixture, e.g. from 65°C to 200°C, and more preferably 65°C to 140°C. Pressure conditions may vary, e.g. from 0.1 to 1 MPa. The time of reaction is preferably from 1 hour to 6 hours or until the Weight Exchange Capacity of the sulfonated polymer is at least 5 eq/kg, ( i.e. one sulfonic group per aromatic group).

The sulfonation reaction is conducted in the presence of a polyfluorinated benzene compound that serves as a swelling agent. The term "polyfluorinated benzene compound" refers to a benzene moiety substituted with at least two and preferably three or four fluorine atoms. The polyfluorinated benzene compound may be represented by Formula 1.

Formula 1 :

wherein: X is selected from one of: halogen and hydrogen; and Y is selected from one of: halogen, hydrogen and nitro, where the substituents may be positioned at any location on the ring In one subset of embodiments, X is selected from hydrogen, fluorine, bromine or chlorine. In another preferred subset of embodiments, no other substituents (other than hydrogen) are present on the ring. Preferred species include: 1,4-difluorobenzene; 1,2,3-trifluorobenzene; and 1,2,4- trifluorobenzene. In another subset of embodiments, Y is selected from hydrogen, fluorine, bromine, chlorine or nitro. In another preferred subset of embodiments, no substituents other than X are present on the ring. Preferred species include: tetrafluorobenzene (e.g 1,2,4,5- tetrafluorobenzene) and trifluoronitrobenzene (e.g. 3,4,5-trifluoronitrobenzene and 2,3,5- trifluoronitrobenzene). Combinations of swelling agents may be used.

Preferred swelling agents are at least 50% and more preferably at least 75% recoverable after the sulfonation reaction, e.g. the swelling agent can be recovered and reused in subsequent sulfonation reactions. In order to be recoverable, the swelling agent should be stable under the sulfonation reaction conditions (i.e. acidic pH, high temperature) and easily separated from the aromatic polymer after sulfonation. The swelling agent preferably has a boiling point temperature measured at 0.1 MPa (1 bar) of from: 40°C to 180°C, more preferably 70°C to 140°C and even more preferably from 85°C to 120°C; and preferably a melting point temperature measured at 0.1 MPa (1 bar) of from 10°C to -60°C, more preferably from 0°C to -60°C, and still more preferably from -5°C to -20°C. The subject polyfluorinated benzene compounds preferably meet one or more of the preceding properties, and more preferably all of said properties. Thus, the subject method may further include the step of recovering at least 50 wt%, and more preferably at least 75% of the polyfluorinated benzene compound after the sulfonation reaction. Recovery of the polyfluorinated benzene compounds may be accomplished in a manner similar to current techniques used to recover conventional (EDC-type) swelling agents, e.g. vacuum distillation. After recovery, the polyfluorinated benzene compound may be reused in subsequent sulfonation reactions.

When used to prepare cation exchange resins in bead form, the subject method preferably produces a resin having an external exterior surface having a surface roughness comparable to the same resin sulfonated using EDC as a swelling agent. One preferred technique for measuring surface roughness utilizes Confocal Laser Scanning Microscopy (CLSM), with roughness indicated as a "SIOz" value, wherein SIOz is the average difference between the 5 highest and 5 lowest points on the surface relative to the mean plane per sample surface area (e.g. 283 um x 212 um). With reference to the Figures, Figures la-b are micrographs of AMBERLITE™ 120 Na brand cation exchange resin available from The Dow Chemical Company. This resin has a crosslinked, styrene- divinylbenzene copolymer matrix that has been sulfonated with H₂S0₄ using EDC as a swelling agent (solvent). Figures lc-d are micrographs of AMBERLITE™ SR1L brand cation exchange resin also available from The Dow Chemical Company. This resin is substantially similar to AMBERLITE 120 Na; however, this resin was sulfonated using H₂S0₄ without solvent. The surfaces of both cation exchange resins were analyzed with a confocal laser scanning microscope (CLSM) (Keyence VK-9700 microscope application viewer VK-H1V1E with a 50x objective lens and superfine resolution) using a scanning violet laser (408 nm) light source for high resolution confocal surface profiling. Combined with an additional white light source, the system provided simultaneous color, laser intensity, and height information to generate high-resolution images. The CLSM was operated with a 1 nm z resolution and 130 nm spatial resolution providing SEM-like images with a large 7mm through focus range. The surface roughness (SIOz value) of

AMBERLITE™ 120 Na brand cation exchange resin shown in Figures la-b was 4.08 μιη; whereas the SIOz value of AMBERLITE™ SR1L brand cation exchange resin shown in Figures lb-c was 12.01μιη.

In a preferred embodiment, the cationic exchange resin of the present invention is in bead form with an external exterior surface having a SIOz value of less than 8 μιη, less than 6 μιη, less than 4 μιη and even more preferably less than 3 μιη.

As mentioned above, the aromatic polymers of the present invention are preferably copolymers used in the preparation of ion exchange resins. One preferred type of resin is prepared by a "seeded" polymerization, sometimes also referred to as batch or multi-batch (as generally described in EP 62088A1 and EP 179133A1); and continuous or semi-continuous staged polymerizations (as generally described in US 4,419,245; US 4,564,644; and US 5,244,926). A seeded polymerization process typically adds monomers in two or more increments. Each increment is followed by complete or substantial polymerization of the monomers therein before adding a subsequent increment. A seeded polymerization is advantageously conducted as a suspension polymerization wherein monomers or mixtures of monomers and seed particles are dispersed and polymerized within a continuous suspending medium. In such a process, staged polymerization is readily accomplished by forming an initial suspension of monomers, wholly or partially

polymerizing the monomers to form seed particles, and subsequently adding remaining monomers in one or more increments. Each increment may be added at once or continuously. Due to the insolubility of the monomers in the suspending medium and their solubility within the seed particles, the monomers are imbibed by the seed particles and polymerized therein. Multi-staged

polymerization techniques can vary in the amount and type of monomers employed for each stage as well as the polymerizing conditions employed.

The seed particles employed may be prepared by known suspension polymerization techniques. In general the seed particles may be prepared by forming a suspension of a first monomer mixture in an agitated, continuous suspending medium as described by F. Helfferich in Ion Exchange, (McGraw-Hill 1962) at pp. 35-36. The first monomer mixture comprises: 1) a first monovinylidene monomer, 2) a first crosslinking monomer, and 3) an effective amount of a first free-radical initiator. The suspending medium may contain one or more suspending agents commonly employed in the art. Polymerization is initiated by heating the suspension to a temperature of generally from about 50-90°C. The suspension is maintained at such temperature or optionally increased temperatures of about 90-150° C until reaching a desired degree of conversion of monomer to copolymer. Other suitable polymerization methods are described in US 4,444,961 ; US 4,623,706; US 4,666,673; and US 5,244,926 - each of which is incorporated herein in its entirety.

The monovinylidene aromatic monomers employed herein are well-known and reference is made to Polymer Processes, edited by Calvin E. Schildknecht, published in 1956 by Interscience Publishers, Inc., New York, Chapter III, "Polymerization in Suspension" at pp. 69-109. Table II (pp. 78-81) of Schildknecht lists diverse types of monomers which are suitable in practicing the present invention. Of the monomers listed, styrene and substituted styrene are preferred. The term "substituted styrene" includes substituents of either/or both the vinylidene group and phenyl group of styrene and include: vinyl naphthalene, alpha alkyl substituted styrene (e.g., alpha methyl styrene) alkylene-substituted styrenes (particularly monoalkyl-substituted styrenes such as vinyltoluene and ethylvinylbenzene) and halo-substituted styrenes, such as bromo or chlorostyrene and vinylbenzyl chloride. Additional monomers may be included along with the monovinylidene aromatic monomers, including monovinylidene non-styrenics such as: esters of α,β-ethylenically unsaturated carboxylic acids, particularly acrylic or methacrylic acid, methyl methacrylate, isobornyl- methacrylate, ethylacrylate, and butadiene, ethylene, propylene, acrylonitrile, and vinyl chloride; and mixtures of one or more of said monomers. Preferred monovinylidene monomers include styrene and substituted styrene such as ethylvinylbenzene. The term "monovinylidene monomer" is intended to include homogeneous monomer mixtures and mixtures of different types of monomers, e.g. styrene and isobornylmethacrylate. The seed polymer component preferably comprises a styrenic content greater than 50 molar percent, and more preferably greater than 75, and in some embodiments greater than 95 molar percent (based upon the total molar content). The term "styrenic content" refers to the quantity of monovinylidene monomer units of styrene and/or substituted styrene utilized to form the copolymer. "Substituted styrene" includes substituents of either/or both the vinylidene group and phenyl group of styrene as described above. In preferred embodiments, the first monomer mixture used to form the first polymer component (e.g. seed) comprises at least 75 molar percent, preferably at least 85 molar percent and in some embodiments at least 95 molar percent of styrene.

Examples of suitable crosslinking monomers (i.e., polyvinylidene compounds) include polyvinylidene aromatics such as divinylbenzene, divinyltoluene, divinylxylene, divinylnaphthalene, trivinylbenzene, divinyldiphenylsulfone, as well as diverse alkylene diacrylates and alkylene dimethacrylates. Preferred crosslinking monomers are divinylbenzene, trivinylbenzene, and ethylene glycol dimethacrylate. The terms "crosslinking agent," "crosslinker" and "crosslinking monomer" are used herein as synonyms and are intended to include both a single species of crosslinking agent along with combinations of different types of crosslinking agents. The proportion of crosslinking monomer in the copolymer seed particles is preferably sufficient to render the particles insoluble in subsequent polymerization steps (and also on conversion to an ion-exchange resin), yet still allow for adequate imbibition of an optional phase-separating diluent and monomers of the second monomer mixture. In some embodiments, no crosslinking monomer will be used. Generally, a suitable amount of crosslinking monomer in the seed particles is minor, i.e., desirably from about 0.01 to about 12 molar percent based on total moles of monomers in the first monomer mixture used to prepare the seed particles. In a preferred embodiment, the first polymer component (e.g. seed) is derived from polymerization of a first monomer mixture comprising at least 85 molar percent of styrene (or substituted styrene such as ethylvinylbenzene) and from 0.01 to about 10 molar percent of divinylbenzene.

Polymerization of the first monomer mixture may be conducted to a point short of substantially complete conversion of the monomers to copolymer or alternatively, to substantially complete conversion. If incomplete conversion is desired, the resulting partially polymerized seed particles advantageously contain a free -radical source therein capable of initiating further polymerization in subsequent polymerization stages. The term "free-radical source" refers to the presence of free -radicals, a residual amount of free -radical initiator or both, which is capable of inducing further polymerization of ethylenically unsaturated monomers. In such an embodiment of the invention, it is preferable that from about 20 to about 95 weight percent of the first monomer mixture, based on weight of the monomers therein, be converted to copolymer and more preferably from about 50 to about 90 weight percent. Due to the presence of the free radical source, the use of a free-radical initiator in a subsequent polymerization stage would be optional. For embodiments where conversion of the first monomer mixture is substantially complete, it may be necessary to use a free-radical initiator in subsequent polymerization stages.

The free-radical initiator may be any one or a combination of conventional initiators for generating free radicals in the polymerization of ethylenically unsaturated monomers.

Representative initiators are UV radiation and chemical initiators, such as azo-compounds including azobisisobutylronitrile; and peroxygen compounds such as benzoyl peroxide, t-butylperoctoate, t- butylperbenzoate and isopropylpercarbonate. Other suitable initiators are mentioned in US 4,192,921; US 4,246,386; and US 4,283,499 - each of which is incorporated in its entirety. The free-radical initiators are employed in amounts sufficient to induce polymerization of the monomers in a particular monomer mixture. The amount will vary as those skilled in the art can appreciate and will depend generally on the type of initiators employed, as well as the type and proportion of monomers being polymerized. Generally, an amount of from about 0.02 to about 2 weight percent is adequate, based on total weight of the monomer mixture.

The first monomer mixture used to prepare the seed particles is advantageously suspended within an agitated suspending medium comprising a liquid that is substantially immiscible with the monomers, (e.g. preferably water). Generally, the suspending medium is employed in an amount from about 30 to about 70 and preferably from about 35 to about 50 weight percent based on total weight of the monomer mixture and suspending medium. Various suspending agents are conventionally employed to assist with maintaining a relatively uniform suspension of monomer droplets within the suspending medium. Illustrative suspending agents are gelatin, polyvinyl alcohol, magnesium hydroxide, hydroxyethylcellulose, methylhydroxyethylcellulose methylcellulose, and carboxymethyl methylcellulose. Other suitable suspending agents are disclosed in US 4,419,245. The amount of suspending agent used can vary widely depending on the monomers and suspending agents employed. Latex inhibitors such as sodium dichromate may be used to minimize latex formation.

The seed particles may be of any convenient size. In general, the seed particles desirably have a volume average particle diameter of from about 75 to about 1000 microns, preferably from about 150 to about 800 microns, and more preferably from about 200 to about 600 microns. The distribution of the particle diameters may be Gaussian or uniform (e.g. at least 90 volume percent of the particles have a particle diameter from about 0.9 to about 1.1 times the volume average particle diameter).

As previously described, copolymer particles may be prepared by providing a plurality of the seed particles and thereafter, adding a second monomer mixture such that the mixture is imbibed by the seed particles and polymerization is conducted therein. This step is preferably conducted as a batch-seeded process or as an in situ batch-seeded process, as described below. The second monomer mixture may also be added intermittently or continuously under polymerizing conditions, such as described in US 4,564,644.

In the so-called "batch-seeded" process, seed particles comprising from about 10 to about 50 weight percent of the copolymer are preferably suspended within a continuous suspending medium. A second monomer mixture containing a free radical initiator is then added to the suspended seed particles, imbibed thereby, and then polymerized. Although less preferred, the seed particles can be imbibed with the second monomer mixture prior to being suspended in the continuous suspending medium. The second monomer mixture may be added in one amount or in stages. The second monomer mixture is preferably imbibed by the seed particles under conditions such that

substantially no polymerization occurs until the mixture is substantially fully imbibed by the seed particles. The time required to substantially imbibe the monomers will vary depending on the copolymer seed composition and the monomers imbibed therein. However, the extent of imbibition can generally be determined by microscopic examination of the seed particles, or suspending media, seed particles and monomer droplets. The second monomer mixture desirably contains from about 0.5 to about 25 molar percent, preferably from about 2 to about 17 molar percent and more preferably 2.5 to about 8.5 molar percent of crosslinking monomer based on total weight of monomers in the second monomer mixture with the balance comprising a monovinylidene monomer; wherein the selection of crosslinking monomer and monovinylidene monomer are the same as those described above with reference to the preparation of the first monomer mixture, (i.e. seed preparation). As with the seed preparation, the preferred monovinylidene monomer includes styrene and/or a substituted styrene. In a preferred embodiment, the second polymer component (i.e. second monomer mixture, or "imbibed" polymer component) has a styrenic content greater than 50 molar percent, and more preferably at least 75 molar percent (based upon the total molar content of the second monomer mixture). In a preferred embodiment, the second polymer component is derived from polymerization of a second monomer mixture comprising at least 75 molar percent of styrene (and/or substituted styrene such as ethylvinylbenzene) and from about 1 to 20 molar percent divinylbenzene.

In an in-situ batch-seeded process, seed particles comprising from about 10 to about 80 weight percent of the IPN copolymer product are initially formed by suspension polymerization of the first monomer mixture. The seed particles can have a free -radical source therein as previously described, which is capable of initiating further polymerization. Optionally, a polymerization initiator can be added with the second monomer mixture where the seed particles do not contain an adequate free radical source or where additional initiator is desired. In this embodiment, seed preparation and subsequent polymerization stages are conducted in-situ within a single reactor. A second monomer mixture is then added to the suspended seed particles, imbibed thereby, and polymerized. The second monomer mixture may be added under polymerizing conditions, but alternatively may be added to the suspending medium under conditions such that substantially no polymerization occurs until the mixture is substantially fully imbibed by the seed particles. The composition of the second monomer mixture preferably corresponds to the description previously given for the batch-seeded embodiment.

Conditions employed to polymerize ethylenically unsaturated monomers are well known in the art. Generally, the monomers are maintained at a temperature of from about 50 - 150°C for a time sufficient to obtain a desired degree of conversion. Typically, an intermediate temperature of from about 60 - 80°C is maintained until conversion of monomer to copolymer is substantially complete and thereafter the temperature is increased to complete the reaction. The resulting copolymer particles may be recovered from the suspending medium by conventional methods.

The copolymer particles of the present invention are preferably prepared by suspension polymerization of a finely divided organic phase comprising monovinylidene monomers such as styrene, crosslinking monomers such as divinylbenzene, a free-radical initiator and, optionally, a phase-separating diluent. The crosslinked copolymer may be macroporous or gel-type. The terms "gel-type" and "macroporous" are well-known in the art and generally describe the nature of the copolymer particle porosity. The term "macroporous" as commonly used in the art means that the copolymer has both macropores and mesopores. The terms "microporous," "gellular," "gel" and "gel-type" are synonyms that describe copolymer particles having pore sizes less than about 20 Angstroms A , while macroporous copolymer particles have both mesopores of from about 20 A to about 500 A and macropores of greater than about 500 A . Gel-type and macroporous copolymer particles, as well as their preparation are further described in US4256840 and US5244926. The copolymer particles preferably have a bead structure with a median particle diameter from 200 to 800 microns. The crosslinked copolymer particles may have a Gaussian particle size distribution but preferably have a relatively uniform particle size distribution, i.e. "monodisperse" that is, at least 90 volume percent of the beads have a particle diameter from about 0.9 to about 1.1 times the volume average particle diameter.

EXAMPLES

A series of commercially available styrene copolymers (poly(styrene-co-ethylbenzene - co divinylbenzene) prepared with different levels of divinylbenzene where sulfonated using a variety of swelling agents according to the following procedure: The 50 grams of copolymer were charged into a 1 liter glass reactor with 250 g of sulfuric acid (96%) and different levels of different swelling agent, depending upon the degree of crosslinking of the copolymer (see Table 1). The mixture was agitated at 100 rpm and temperature was maintained at 40°C for 1 hour. After the first hour the temperature was increased to sulfonation hold temperature and hold time as function of the amount of crosslinker (divinylbenzene) used to prepare the copolymer. Prior to the hydration step, the swelling solvent was recovered by distillation.

Table 1 :

The samples where then hydrated by addition of acid at different concentrations while the acid was removed from the reactor with overall decrease of the acid concentration. The sulfuric acid cuts used for the hydration were 70 wt%, 50 wt%, 25 wt%, and 12 wt%. Excess deionized water was used at the last step of acid hydration until the pH of the reactor was approximately 3. The resin was Buchner dried. Moisture Hold Capacity (MHC), Volume Capacity (VC), Weight Capacity (WC) and Perfect Bead (PB) where calculated as described below. The swelling agent was recovered by distillation and condensation and is reported as a percent of the initial charge for the reaction.

Moisture Hold Capacity (MHC) was measured by wetting a specific volume of resin and removing the excess water with a Buchner funnel. After removal of excess water, the weight of the moist resin was recorded. The resin was then oven dried at 105°C for 12 hours and the dry weight was recorded. The MHC was calculated from equation 1. Equation 1 :

MHC (%) = 100 * [1 - (W_DAVM)]

where:

MHC = Moisture Hold Capacity, reported as a percent

W_D = Weight of dry resin (grams)

W_M = Weight of water removed during drying

Additional characteristics of a collection of resin beads were assessed as follows. The Volume Capacity (Vol. Cap.) was measured by measuring a volume of resin in acid form. Protons of acid form of the copolymer were eluted with Na, and quantity of proton was determined by titration with NaOH. Volume Capacity was calculated from equation 2.

Equation 2:

VC(eq/L) = 10 * (V_NaoH - V_bi_ank, NaOH) *N_N3OH / V_M Weight Capacity (W.Cap.) was measured by dry basis of resin calculated from equation 3.

Equation 3:

W.Cap. (eq/kg) = 10 * ((V_NaoH(mi) -V_bi_ank, NaOH (ml) ) N (eq/L) / W_moist(g) * (l-MHC( ) / 100) where:

VC = Volume Capacity(Vol. Cap.) (equivalents per liter (eq/L))

V_NaoH = Volume used of NaOH solution for neutralization (milliliter) Biank,NaOH = Volume used of NaOH solution for neutralization a blank sample (ml) N_NaoH = concentration of NaOH used for titration (eq/L)

W_moi_st = W_m = weight of the water present in the moist resin

V_M = Volume of moist resin (ml)

"10" is used in equation 3 for the case of a 100 ml sample for the titration from 1 ,000 ml eluant for cation exchange on the resin.

Further characteristics of the copolymer beads were assessed as follows. The Perfect Bead (PB) was defined by no fragments, no cracks, and no major flaws as observed by optical microscopic method. The Whole Bead (WB) was defined as beads that are complete with no parts missing from its structure as a complete sphere.

The Perfect Bead also includes the bead cluster (agglomerate) content. A minimum of 100 beads are located in the microscope field for observation and in 4 quadrants of the Petri dish. WB and PB are reported from equations 4 and 5. Equation 4:

^WBquadrant = ^{100 x} (1 ^{" N}Fragmented / ^NTotal)

Equation 5:

^PBquadrant = 100 x ( 1 - N_Irnp_erfect / N_Total) WB and PB are calculated from the 4 different quadrants using equations 6 and 7. Equation 6:

WB_average = (WB i + WB₂ + WB₃ + WB₄) / 4

Equation 7:

PBaverage = (PB 1 + PB₂ + PB₃ + PB₄) / 4

Comparative Examples 1 to 10: Sulfonation of styrene copolymers (10 wt DVB) using non4ialogenated swelling agents. Note the dramatic difference in recovered swelling agent.

Table 2:

Comparative Examples 11-20: Sulfonation of styrene copolymers using chlorinated swelling agents.

Comparative Examples 11-13 were prepared using a styrene copolymer comprising 2 wt

DVB, whereas Comparative Examples 14-20 included 10 wt DVB. Sulfonation conditions were as described above. Table 3:

NA = copolymer broke into small particles which did not allow for measurement. Examples 1 to 7 and comparative examples 21 to 26: Sulfonation using various fluorinated benzene compounds as swelling agents. Note swelling agent recoveries and Perfect Bead values.

Table 4:

Sulfonation of styrene copolymers using various swelling agents. The copolymer (10 wt DVB) and sulfonation conditions were as described above. Surface roughness determined by CSLM method (SIOz value reported below).

Table 5:

Commercial cationic exchange resins obtained from The Dow Chemical Company. Surface roughness determined by CSLM method (SIOz value reported below).

Table 6:

Claims

1. A method for sulfonating an aromatic polymer by reacting the aromatic polymer with a sulfonating agent in the presence of a polyfluorinated benzene compound.

2. The method of claim 1 wherein the polyfluorinated benzene compound comprises a benzene ring substituted with at least two fluorine atoms.

3. The method of claim 1 wherein the polyfluorinated benzene compound comprises a benzene ring substituted with at least three fluorine atoms.

4. The method of claim 1 wherein the polyfluorinated benzene compound is represented by:

wherein: X is selected from one of: halogen and hydrogen; and Y is selected from one of: halogen, hydrogen and nitro.

5. The method of claim 1 wherein the polyfluorinated benzene compound comprises a polyfluorinated benzene compound selected from at least one of: 1,4-difluorbenzene; 1,2,3- trifluorbenzene; 1,2,4-trifluorbenzene; 1,2,4,5-tetrafluorobenzene; 3,4,5-trifluoronitrobenzene and 2,3,5-trifluoronitrobenzene.

6. The method of claim 1 wherein the polyfluorinated benzene compound is characterized by having a boiling temperature measured at 100 kPa (1 bar) of from: 40°C to 180°C and a melting temperature measured at 100 kPa (1 bar) of from 10°C to -60°C.

7. The method of claim 1 wherein: i) the sulfonating agent comprises at least one of: sulfuric acid, oleum, sulfur trioxide and chlorosulfonic acid; ii) the aromatic polymer comprises a crosslinked copolymer of styrene and divinylbenzene; and iii) the reaction is conducted at a temperature of from 65 °C to 150°C.

8. The method of claim 7 wherein the aromatic polymer comprises at least 7 mole percent of repeating units are derived from divinylbenzene.

9. The method of claim 1 wherein the aromatic polymer comprises a cationic exchange resin.

10. The method of claim 9 wherein the cationic exchange resin is in bead form with an external exterior surface having a SIOz value of less than 8 μιη.

11. The method of claim 9 wherein the cationic exchange resin is in bead form with an external exterior surface having a SIOz value of less than 6 μιη.

12. The method of claim 1 wherein at least 40 wt of the polyfluorinated benzene compound is recovered after the reaction.