WO1993012167A1 - Seeded porous copolymers and ion-exchange resins prepared therefrom - Google Patents

Abstract

The invention concerns preparation of porous copolymer beads by a seeded polymerization process employing gel copolymer seed particles. The process comprises initially providing a plurality of gel-type copolymer seed particles prepared by polymerization of at least one first monovinylidene monomer and a first cross-linking monomer. A second monomer mixture comprising at least one second monovinylidene monomer, a second cross-linking monomer, and a phase-separating diluent is thereafter imbibed by the seed particles and polymerized therein. The process is characterized by selecting the first monovinylidene monomers such that the phase-separating diluent and second monovinylidene monomers are capable of being imbibed by the seed particles in an amount sufficient to form a porous copolymer. The porous copolymer beads produced have stable polymeric structures and good physical properties that render them useful in preparing ion-exchange resins and polymeric adsorbents.

Description

SEEDED POROUS COPOLYMERS AND ION-EXCHANGE RESINS PREPARED THEREFROM

This invention concerns copolymer beads suitable as a support matrix for ion- exchange resins and polymeric adsorbents. In particular, the invention concerns porous copolymer beads prepared by a seeded polymerization process.

Ion-exchange resins are used by industry to separate chemical species from solutions containing them. Such resins are prepared by substituting various functional groups onto a copolymer bead matrix. The functional groups are capable of associating with the impurities so as to remove them from solution. Ion-exchange resins may be cation-, anion- or chelate-exchange resins, depending on the choice of functional group substituted onto the copolymer bead matrix. The copolymer bead matrix may also be used in preparing polymeric adsorbents, such as those disclosed in U.S. Patent 4,950,332.

The copolymer bead matrix is typically prepared by suspension polymerization of a finely divided organic phase comprising monovinylidene monomers like styrene, polyvinylidene monomers such as divinylbenzene, a free-radical initiator, and, optionally a phase-separating diluent. The copolymer beads produced may be microporous, that is, gellular in character, or macroporous, the result depending upon whether the phase-separating diluent is employed. The term "macroporous" as commonly used in the art means that the copolymer has both macroporesand mesopores. The terms "microporous", "gel" and "macroporous" are well known in the art and generally describe the nature of the copolymer bead porosity.

Microporous or gel copolymer beads have pore sizes on the order of less than 20 Angstroms (A), while macroporous copolymer beads have both mesopores of from 20 A to 500 A and macropores of greater than 500 A. Gel and macroporous copolymer beads, as wel I as thei r preparation, are further discussed in U.S. Patent 4,256,840. Recently, industry has focused on methods of preparing copolymer beads in multi-staged polymerizations, also known as seeded polymerization processes. Such copolymer beads are desirable due to good mechanical strength and osmotic shock resistance. Seeded polymerization processes can also prepare beads of relatively uniform size if the seed particles employed have similar size uniformity. U.S. Patents 4,419,245 and 4,564,644 disclose processes wherein seed particles are suspended in a continuous medium and, thereafter, the seed particles are imbibed and polymerized with additional monomer to form copolymer beads. British Patent 1,151 ,480 discloses a process wherein copolymer beads are prepared from porous seed particles. Other seeded polymerization processes are known- European Patent Application

No.0062088 (October 13, 1982) discloses preparation of gel or macroporous copolymer beads by a seeded polymerization process. However, macroporous copolymer beads made from gel seeds according to this process do not have stable polymeric structures and generally are heterogeneous in.porosity, that is, some discrete portions of the beads are gellular, while other portions are macroporous- Such heterogeneous beads are undesirable due to poor physical strength- European Patent Application No. 0 168622 (January 22, 1986) concerns preparation of macroporous copolymer beads by a seeded polymerization process using macroporous seed particles- This process is limited by its inability to substantially increase the size of the copolymer bead product relative to the size of the seed particles. In conducting a seeded polymerization, it is more advantageous to employ gel ratherthan macroporous seed particles. Gel seed particles, especially those with low levels of crossltnking monomer therein, that is, less than 5 weight percent based on weight of the seed particle, have a substantially better capability for imbibing additional monomers in a subsequent polymerization step. The greater ability to imbibe monomers allows for production of a copolymer bead product having a substantially greater volume, that is, at least about300 percent larger in size, relative to the initial size of the gel seed particle- On the other hand, when macroporous seed particles are employed it is difficultto obtain a significant increase in particle size and the pores of the seed particle are constricted by formation of new polymer. As can be seen, it is desirable to develop a seeded polymerization process for producing porous copolymer beads which is economical and capable of preparing beads having a stable polymeric structure and good physical properties. The resulting porous copolymer beads could then be used to prepare ton-exchange resins and polymeric adsorbents. The above-described objects and advantages are obtained by a process for preparing porous copolymer beads comprising the following steps:

Initially, a plurality of gel-type, copolymer seed particles is provided. The seed particles are prepared by polymerization of a first monomer mixture comprising at least one first monovinylidene monomer and a first cross-linking monomer. The seed particles optionally contain a free radical source therein capable of initiating polymerization of ethylenically unsatu rated monomers.

Thereafter, the seed particles are imbibed with a second monomer mixture comprising a phase-separating diluent, at least one second monovinylidene monomer, a second cross-linking monomer, and a free-radical polymerization initiator. The free-radical initiator is optional for embodiments wherein the seed particles contain a free radical source. The phase-separating diluent and the at least one second monovinylidene monomer are selected so as to have a solubility parameter and dipole moment which are compatible with the solubility parameter and dipole moment of the at least one first monovinylidene monomer such that at least 70 percent by weight of the second monomer mixture is imbibed bythe seed particles.

The imbibed seed copolymer particles are thereafter maintained under suspension polymerizing conditions for a time sufficient to achieve a desired degree of conversion of monomer to copolymer and obtain the porous copolymer beads. Figure 1 is a photomicrograph of a porous copolymer bead prepared in

Example 2.

Figure 2 is a photomicrograph of a conventional macroporous copolymer bead. Figure 3 is a graph which plots the distribution of pore sizes, as a percentage, versus pore diameter in A for the weak-base anion-exchange resin prepared in Example 3. The distribution for a conventional weak-base anion resin is also shown.

Figure 4 is a graph which plots the distribution of pore sizes, as a percentage, versus pore diameter in A forthe sulfonated cation-exchange resin prepared in Example 3. The distribution for a conventional sulfonated cation resin is also shown.

Seeded polymerizations, also known as continuous or semi-continuous staged polymerizations, are generally described in U.S. Patents 4,419,245 and 4,564,644. A seeded polymerization process typically adds monomers in two or more increments, each increment comprising at least 5 percent, and preferably at least 10 percent of the weight of the resulting copolymer beads. 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 an 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 ethylenically unsaturated monomers in the suspending medium and their solubility within the seed particles, the monomers are imbibed by the seed particles and polymerize 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 gel copolymer seed particles employed may be prepared by known suspension polymerization techniques. In general, the seed partirles 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 pps.35-36. The first monomer mixture comprises at least one first monovinylidene monomer, a first cross- linking mono-mer, and 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 50°C to 90°C The suspension is maintained at such temperature until reaching a desired degree of conversion of monomerto copolymer. Other suitable polymerization methods are described in U.S. Patents 4,444,961 ; 4,623,706; and 4,666,673.

The monomers employed herein are addition polymerϊzable ethylenically unsaturated compounds. Such monomers 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 for purposes of illustration-

In Table II on pp.78-81 of Schildknecht are listed diverse kinds of monomers which are suitable in practicing this invention. Of such ethylenicallyunsaturated monomers, of particular interestare water-insoluble monovinylidene monomers including the monovinylidene aromatics such as styrene, vinyl naphthalene, alkylene-substituted styrenes (particularly monoalkyl-substituted styrenes such as vinyltoluene and ethylvinylbenzene) and halo-substituted styrenes, such as bromo- or chlorostyrene and vinylbenzylchloride; other monovinylidene monomers like esters of ι,i-ethylenically unsaturated carboxylic acids, particularly acrylic or methacrylic acid, methyl methacrylate, ethylacrylate; and mixtures of one or more of said monomers. Also suitable are diverse polyvinylidene compounds which may be employed as cross-linking monomers, such as polyvinylidene aromatics like divinylbenzene, dϊvϊnyltoluene,dϊvinylxylene, divinylnaphthalene, trivinyl benzene, divinyldiphenyl ether, divinyldiphenylsulfone, as well as diverse alkylene diacrylates and alkylene dimethacrylates. Preferred cross-linking monomers are divinylbenzene, trivinylbenzene, and ethyl glycol dϊmethacrylate. The monomers used in each polymerization step may be the same or different as those used in other steps.

It is advantageous to select monomers for preparing the seed particles such that the copolymerformed has a sufficiently high glass transition temperature ("T ") to minimize seed particle agglomeration- Preferred seed copolymers are those having a T of 30°C or more.

In practicing the invention, it is also important to employ first monovinylidene monomers in preparing the seed particles which will be compatible with the phase-separating diluent and second monovinylidene monomers, as described hereinafter, employed in subsequent polymerization steps. By "compatible", it is meant thatthe first monovinylidene monomers have a solubility parameter and dipole moment that allow the resulting seed particles to imbibe at least 70 weight percent of the second monomer mixture. Desirably, the first monovinylidene monomers are selected such that at least 80 weight percent, preferably at least 90 weight percent, and more preferably at least 95 weight percent of the second monomer mixture is imbibed. In the most preferred embodiments, substantially all of the second monomer mixture is imbibed by the seed particles. In general, compatible first monovinylidene monomers are selected by matching their solubility parameters and dipole moments with those of the phase-separating diluent and second monovinylidene monomers.

Solubility parameter (also referred to symbolically as "δ" hereinafter) is a measure of the solubility between various polymers and/or solvents and is generally discussed by F. Rodriguez in Principles of Polymer Systems at pp. 18-23 (McGraw-Hill 1970), F. Billmeyer in Textbook of Polymer Science at pps. 151-154 (John Wiley & Sons 1984), and H. Elias in Macromolecules. Vol. 1, at pps. 205-210 (Plenum Press 1977). Solubility parameter values for various solvents and polymers are listed by H. Burrell and B. Immergut in Polymer Handbook (Interscience Publishers 1967) at pps. IV-341 to IV-368. For a given first monovinylidene monomer, compatible phase-separating diluents and second monovinylidene monomers desirably have a solubility parameter within ± 30 percent of the solubility parameter for the first monovinylidene monomer. Preferably, the solubility parameters of the diluent and monomer are within ± 20 percent and most preferably within ± 10 percent of the first monovinylidene monomer's solubility parameter. As used hereinafter, δ values are quoted in terms of (cal/cm³)"², unless stated otherwise.

To match the hydrogen bonding characteristics of the first monovinylidene monomer with that of the phase-separating diluent and second monovinylidene monomer, it is desirable to have their respective dipole moments be within ± 1.0 debyes of each other, preferably within 0.5 debyes, and more preferably within 0.25 debyes. Dipole moments for various compounds are given, for example, in the CRC Handbook of Chemistry and Physics, 71st Ed. (1990) at pps. 9-6 to 9-8 and by Reid et al. in The Properties of Gases and Liquids, 3rd Ed. (McGraw-Hill 1977) at pps. 629-665.

As an example, where a non-polar, aliphatic solvent like hexane, heptane, or iso- octane (which have essentially no dipole moment) is selected as the phase-separating diluent, the first monovinylidene monomer preferably has a solubility parameter of preferably no greater than 9.9, more preferably no greater than 8.6, and most preferably no greater than 8.2. Examples of such preferred aliphatic monomers are tert-butyl styrene (δ of 8.0), isobornyl methacrylate (δ of 8.2), laurylmethacrylate (δ of 8.2), vinyltoluene (δ of 9.2), ethyl vinylstyrene (δ of 8.9), and mixtures thereof. Also suitable are mixtures of such aliphatic monomers with other monovinylidene monomers, such as styrene or alkyl-substituted styrenes, provided thatthe mixture, collectively, has a compatible solubility parameter and dipole moment, as previously described herein.

Where a relatively polar solvent like sec-butanol (δ of 11.1 and dipole moment of 1.70 debyes) is employed, suitable first monovinylidene monomers are also polar in nature, such as acrylonitrile (δ of 10.6 and dipole moment of 1.70 debyes). By "polar", it is meant that the particular monovinylidene monomer has a solubility parameter advantageously greater than 9.9- Similarly, mixtures of such polar monomers with other monovinylidene monomers are suitable, provided thatthe mixture, collectively, has a compatible solubility parameter and dϊpole moment, as previously described. Other suitable combinations of first monovinylidene monomers with phase- separating diluents and second monovinylidene monomers will become apparent to those skilled in the art upon reading the disclosure herein.

The proportion of cross-linking monomer in the gel copolymer seed particles should be sufficient to renderthe particles insoluble in subsequent polymerization steps (and also on conversion to an ion-exchange resin), yet still allowfor adequate imbibition of the phase-separating diluentand monomers of the second monomer mixture. Generally, a suitable amount of cross-linking monomer in the seed particles is minor, that is, desirably from 0-01 to 5 weight percent, preferably from 0.1 to 2.5 weight percent, and most preferably from 0-2 to 1.5 weight percent based on total weight of monomers in the seed particles, with the balance comprising the first monovinylidene monomer.

Phase-separating diluents useful in conducting the invention are those which are a solvent for the monomers employed, but are non-sol vents for the resulting copolymer. As such, the copolymer precipitates from the monomer phase as it is formed. Suitable phase- separating diluents are organic solvents which are substantially inert with respect to the suspending medium, monomers, and resulting copolymer. Generally, organic solvents having boiling points of at least 60°C are suitable and include aromatic hydrocarbons, aliphatic hydrocarbons, halogenated hydrocarbons, and aliphatic alcohols. Examples of suitable diluents are hexane, heptane, iso-octane (2,2,4-trimethylpentane), benzene, toluene, xylene, tert-amyl alcohol, n-butanol, sec-butanol, 2-ethylhexanol, and decanol. Other phase- separating diluents are described in U.S. Patents 4,224,415 and 3,176,482. The choice of diluent will depend on the particular monomers being polymerized as previously discussed. The amount of diluent used can also vary depending on the type and proportion of monomers employed, but generally an adequate amount will be from 20 to 50 weight percent, based on total weight of the second monomer mixture. 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" refersto 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 20 to 95 weight percent ofthefirstmonomer mixture, based on weight of the monomers therein, be converted to copolymer, and more preferably from 50 to 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 5 polymerization stages.

The free-radical initiator may be any one or a combination of conventional initiators for generating free-radicals in the polymerization of ethylenicaliy unsaturated monomers. Representative initiators are UV radiation and chemical initiators, such as azo- compounds like azobisisobutyronitrile; and peroxygen compounds such as benzoyl peroxide, t- 10 butyl peroctoate, t-butylperbenzoate and isopropylpercarbonate. Other suitable initiators are mentioned in U.S. Patents 4,192,921 ; 4,246,386; and 4,283,499. 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 5 monomers being polymerized. Generally, an amount of from 0.02 to 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, preferably water. Generally, the suspending medium is 20 employed in an amount from 30 to 70, and preferably from 35 to 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, methylcelluloses, and 25 carboxymethylmethylcellulose. Other suitable suspending agents are disclosed in U.S. Patent 4,419,245. The amount of suspending agent used can vary widely dependi ng on the monomers and suspending agents employed.

The seed particles may be of any convenient size. In general, the seed particles desirably have a volume average particle diameter of from 75 to 1000 microns, preferably from 30 150to 800 microns, and more preferably from 200 to 600 microns. Volume average particle diameter may be determined by a commercially available instrument designed to make such measurement, such as a Criterion Model PC-320 Particle Size Analyzer available from the HIAC- Royco Company. Volume average particle diameter may also be determined by screen analysis, such as ASTM D-2187-74, using appropriate screen sizes. 35. Porous copolymer beads may be prepared by providing a plurality of the gel seed particles and, thereafter, adding the second monomer mixture (which contains diluent) such thatthe mixture is imbibed by the seed particles and polymerization conducted therein. This step is preferably conducted as a batch-seeded process or as an insitu batch-seeded process, as described hereinafter. The second monomer mixture may also be added intermittently or continuously under polymerizing conditions, such as in U.S. Patent 4,564,644 previously discussed. .

In the so-called batch-seeded process, gel seed particles comprising from 10 to 40 weight percent of the porous copolymer bead product 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 priorto 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 bytheseed 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. The second monomer mixture desirably contains from 3 to 25, preferably from 5 to 20 weight percent of cross-linking monomer based on total weight of monomers in the second monomer mixture, with the balance being the second monovinylidene monomer.

In an insitu batch-seeded process, gel seed particles comprising from 10to 40 weight percent of the porous copolymer bead productare initially formed by suspension polymerization of the first monomer mixture. The gel 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 insitu within a single reactor. A second monomer mixture isthen added to the suspended seed particles, imbibed thereby, and polymerized. The second monomer mixture may be added under polymerizing conditions, but is preferably added to the suspending medium under conditions such that substantially no polymerization occurs until the mixture is substantially fully imbibed bytheseed particles. The composition of the second monomer mixture corresponds to the description previously given for the batch-seeded embodiment.

Preferred second monovinylidene monomers include monovinylidene aromatics, particularly styrene, ora mixture of styrene with a monoalkyl- or halo-substituted styrene, and vinylbenzylchloride; esters of α,β-ethylenically unsaturated carboxylic acids, particularly methyl methacrylate or methacrylonitrile; and mixtures thereof. Such monomers are preferred due to their commercial availability and relatively low cost.

Conditions employed to polymerize ethylenically unsaturated monomers are well known in the art. Generally, the monomers are maintained at a temperature of from 50°Cto 90°C fora time sufficient to obtain a desired degree of conversion. Typically, an intermediate temperature of from 60°C to 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 porous copolymer beads may be recovered from the suspending medium by conventional methods.

The porous copolymer beads obtained desirably have a volume average particle diameter of from 95 to 1700 μm, and preferably from 190 to 1350 μm. Bead size is determined primarily by the size of the seed particles employed and a swelling ratio, as this term is described hereinafter. The porous copolymer beads advantageously have substantially increased weight

(and also volume) in comparison to the weight of the seed particles from which they are made As used herein, the term "swelling ratio" refers to this result and is a number determined by dividing the weight of the product porous beads by the weight of the seed particles employed. Desirably, the swelling ratio achieved in producing the porous copolymer bead product is from 1.5 to 10, preferably from 2 to 6, and more preferably from 3 to 5.

With respect to porosity, the porous copolymer beads have an average pore size which is generally smaller in comparison to conventional macroporous copolymer beads. The porous copolymer beads also have a pore size distribution which is generally narrower than a typical macroporous copolymer. Thus, the term "porous copolymer" used herein refers to the relatively small pores and narrow pore size distribution of beads prepared according to the invention, when compared to conventional macroporous copolymer beads prepared in a single stage (non-seeded), suspension polymerization. The porous copolymer beads advantageously have a treated bulk density of from 0.2 to 0.6 g/cm³ and a specific surface area of from 2 to 75 m /g as determined by BET nitrogen adsorption techniques. The beads advantageously have a porosity value of from 0.1 to 2.5 cm³/g. Pore size and pore size distributions are illustrated, for example, by Figs. 1-4 discussed hereinafter.

If desired, the porous copolymer beads may be converted to ion-exchange resins by functionalizing them with ion-exchange functional groups. Techniques for converting copolymer beads to anion-, cation-, and chelate-exchange resins are known. In preparing anion- and chelate-exchange resins from poly(vinylaromatic) copolymer beads, such as cross-linked polystyrene beads, the beads are first haloalkyiated, preferably halomethylated, and most preferably chloromethylated, and the anion- or chelate- exchange groups are subsequently substituted onto the haloalkyiated copolymer.

Methods for haloalkylating copolymer beads and attaching anion-exchange or chelating groups are described in U.S. Patents 2,642,417; 2,960,480; 2,597,492; 2,597,493; 3,311,602; 2,632,000; 2,632,001; and 2,992,544. In general, the copolymer beads are haloalkyiated by first swelling the copolymer with a haloalkylating agent, such as bromomethylmethylether, chloromethylmethylether, or a mixture of formaldehyde and hydrochloric acid, and thereafter reacting the copolymer with the haloalkylating agent in the presence of a Friedel-Crafts catalyst.

- Anion- or chelate-exchange resins may be prepared from the haloalkyiated beads by contact with an amine compound capable of replacing the halogen of the haloalkyl group with an amine-based functional group. Suitable compounds and methods for preparing such resins are also illustrated in the patents discussed in the preceding paragraph. Weak-base anion resins may be prepared by contacting the haloalkyiated copolymer beads with ammonia, a primary amine, a secondary amine, or polyamines like ethylene diamine or propylene diamine. Commonly employed primary and secondary amines include methylamine, ethylamine, butylamine, cydohexylamine, dimethylamine, and diethylamine. Strong-base anion resins may be prepared by contact with tertiary amines, such astrimethylamine, triethylamine, dϊmethylisopropanolamine, orethylmethylpropylamine. Chelate resins may be prepared, for example, by contacting the haloalkyiated copolymer beads with an aminopyridine compound, such as a 2-picolylamine. Chelate-exchange resins may also be prepared by contacting the haloalkyiated copolymer beads with a primary amine to initially convert the copolymer beadsto a weak-base anion-exchange resin, followed by contact with a carboxyl-containing compound, like chloroacetic acid, as described in U.S. Patent 2,888,441.

Aminatϊon typically comprises contacting the haloalkyiated copolymer beads with about a stoichiometric amount ofthe amine compound at a temperature of from 25°Cto 150°C for at least one hour.

Cation-exchange resins may be prepared from the copolymer beads using methods illustrated by U.S. Patents 3,266,007; 2,500,149; 2,631,127; 2,664,801 ; and 2,764,564. In general, strong acid resins are prepared by reacting the copolymer with a sulfonating agent such as sulfuric acid, chlorosulfonic acid, or sulfur trioxide. Contact with the sulfonating agent can be conducted neat, or with a swelling agent. Contact may be conducted at temperatures from 0°Cto 150°C-

The resulting cation-exchange resin may be converted to a desired metal salt form by contact with an aqueous solution of a salt or base containing the desired metal counterion. For example, the resin can be converted to its calcium form by contact with a CaCl₂ or Ca(OH)₂ solution- The resin can be converted to otherforms in like manner using suitable water-soluble salts of the desired metal.

The following examples illustrate the invention and should not be construed to limitthe scope of the appended claims. All parts and percentages are by weight and all temperatures are in degrees Celsius (°C), unless stated otherwise. Example 1

This example concerns preparation of porous copolymer beads by seeded polymerization of gel copolymer seeds containing equal parts of styrene and isobornylmethacrylate. The example also concerns preparation of anion-exchange resins from the porous copolymer beads. Seed Preparation

In a 4 liter polymerization kettle, a first monomer mixture containing 464 grams of styrene, 464 grams of isobornylmethacrylate, 0.84 grams of a commercially available 55.7 percent divinylbenzene solution (the balance being essentially ethyivinyl-benzene), and as free-radical polymerization initiators, 0.46 grams of t-butyl perbenzoate and 1.86 grams of a 50 percent solution of t-butyl peroctoate, was suspended in a continuous aqueous suspending medium. The divinylbenzene solution employed is commercially available from The Dow Chemical Company and the isobornylmethacrylate employed is available from Rohm & Haas Company. The aqueous suspending medium consisted of 2.5 grams of a 60 percent aqueous solution of sodium dichromate as a latex inhibitor, 375 grams of a 1 percent aqueous carboxymethylmethylcellulose (CMMC) solution, and 873 grams of water.

After charging the kettle, agitation was initiated to size the first monomer mixture into droplets. The kettle was then sealed, nitrogen purged, and maintained at a temperature of 70°Cfor 15 hours with agitation. Thereafter, the kettle was maintained at a temperature of 110°C for another 4 hours to complete the reaction. The resulting seed particles were recovered from the reactor, washed thoroughly with water, and dried at room temperature. The seed particles had a divinylbenzene content of 0.05 percent based on the total weight of the copolymer beads.

The seed particles had the following particle size distribution as determined by screen analysis:

Particle Diameter (urn) Weight Percent greater than 841 0.2 841 to 707 0

707 to 595 0.2

595 to 500 0.4

500 to 420 2.8

420 to 354 40.9 354 to 297 24.9

297 to 250 9.1

250 to 177 12.6 less than 177 8.9

Bead Preparation A lOO gram portion ofthe seed particles corresponding to the 420 to 354 μm particle size range described above was used hereinafter. The seed particles were placed in a bottle and a second monomer mixture consisting of 455 grams of styrene, 95 grams of the divinylbenzene solution previously described, 450 grams of commercial grade iso-octane (essentially 2,2,4-trimethylpentane) and as free-radical polymerization initiators, 1.63 grams of the 50 percent solution of t-butyl peroctoate solution and 1.09 grams of t-butyl perbenzoate, was added in sequential steps as described hereinafter.

An initial charge of 248 grams of styrene, 52 grams ofthe divinylbenzene solution, and the t-butyl peroctoate solution and t-butyl perbenzoate was added to the bottle. Thereafter, the bottle was placed on a bottle roller and rolled until essentially all ofthe initial charge was imbibed bythe seed particles. A second charge was then added consisting of 207 grams of styrene, 43 grams of the divinylbenzene solution, and 250 grams of iso-octane and again rolled on the bottle roller until essentially all ofthe second charge was imbibed. Thereafter, another 200 grams of iso-octane was added to the bottle and imbibed bythe seed particles in the same fashion.

The imbibed seed particles were then placed into the polymerization kettle and dispersed into a continuous aqueous suspending medium consisting of 2.5 grams of a 60 percentaqueous sodium dichromate solution, 223 grams of a 1 percent aqueous carboxymethyl methylcellulose (CMMC) solution, and 775 grams of water. The kettle was sealed, nitrogen purged,and maintained at a temperature of 80°Cfor 15 hours with agitation. Thereafter, the kettle was maintained at a temperature of 110°Cfor an additional five hours to complete the reaction. The resulting porous copolymer beads were recovered from the kettle, washed, and steam distilled to remove residual iso-octane. The beads were washed a final time with water and air dried. The porous copolymer beads appeared essentially uniform in size and were opaque.

The porous copolymer beads were measured to determine various physical properties. The properties are:

Treated Bulk Density 0.323 gram/cm³ Porosity 1.074 cmVgram

Average Pore Radius 320 A

Specific Surface Area 28.4 mVgram

Treated bulkdeπsity was determined by taking a portion ofthe copolymer beads and swelling them in an excess of toluene to expand the copolymer structure. The swollen copolymer beads were then thoroughly washed by three successive batch-type washes with methanol and finally allowed to dry in air overnight. A portion ofthe copolymer beads of known weight was then treated with a powdered, silicon dioxide antistatic agent and placed into a graduated cylinder. The graduated cylinder was tapped until a constant volume for the beads was measured. Treated bulk density is the weight of the beads divided by their volume. Porosity was determined from the treated bulk density data using standard calculations employed in the art.

Average pore radius and specific surface area ofthe treated copolymer were determined by well-known BET nitrogen adsorption analysis. Anion-Exchanqe Resin Preparation

The porous copolymer beads were converted to both strong-base and weak-base anion-exchange resins by conventional methods. A 75 gram portion ofthe copolymer beads was chloromethylated by placing the beads and 920 milliliters (ml) of chloromethylmethyl- ether into a 1 liter glass reactor. The reactor was equipped with a paddle agitator, heating jacket, addition funnel, and a reflux condenser. The copolymer beads were allowed to swell for 45 minutes and, thereafter, 37.5 grams of ferric chloride as a catalyst was added. The reactor contents were then maintained at a temperature of 53°Cfor 3 hours. The resulting chloromethylated beads were washed thoroughly with methanol and then recovered from the reactor.

A 15 gram portion of the methanol-damp, chloromethylated beads was converted to a strong-base anion resin by placing them with an excess amount of a non- halogenated swelling solvent in a glass bottle. The chloromethylated beads were allowed to swell for 30 minutes. A 60 ml portion of a 40 percent aqueous trimethylamine solution was added and the bottle contents reacted at room temperature overnight. The resulting strong- base resin was washed with water, then with an excess amount of a 5 weight percent aqueous hydrochloric acid solution, and finally with water to a neutral pH.

The strong-base resin was measured to determine various physical and chemical properties. The resin beads had a dry weight capacity of 3.80 meq/g, a water retention capacity in the chloride form of 64.3 percent, a wet volume capacity of 0.88 meq/ml, and an average particle diameter of 1084 μm.

Water retention capacity was determined by swelling a weighed amount of resin with water, removing excess water and weighing the fully swollen resin. The resin was then dried on a moisture balance until a constant weight was obtained. Water retention capacity is the ratio of water imbibed to the total combined weight of the resin plus imbibed water.

Average particle diameter was determined by a photographing the resin beads at a known magnification. The diameters of a statistically significant population of beads, such as at least 30 beads, were determined by measuring individual beads on the photograph and then adjusting for the magnification used. An average diameter was calculated from the adjusted bead diameters.

Dry weight capacity and wet volume capacity were determined by standard analytical techniques.

The remaining portion of the methanol-damp, chloromethylated beads was converted to a weak-base resin by placing it with 400 grams of water, 18 ml of a 50 weight percent aqueous sodium hydroxide solution, and 112 grams of a 40 weight percent aqueous dimethylamine solution into a Paar bomb reactor. The reactor was sealed and the contents maintained at 90°C for 4 hours. The resulting weak-base resin beads were recovered from the reactor and sequentially washed with a first water wash, a 5 weight percent aqueous hydrochloric acid solution, a second water wash, a 5 weight percent aqueous sodium hydroxide solution, and finally with a third water wash to a neutral pH.

- The weak-base resin was measured to determine various physical and chemical properties. The properties measured are summarized as follows: Weak-base capacity 0.93 meq/ml

Salt-splitting capacity 0.15 meq/ml

Dry weight capacity 4.35 meq/gram

Water retention capacity (OH^" form) 58.6 percent

Shrink swell (%) 15 percent Crush Strength 325 ± 60 grams/bead

Average Particle Diameter 967 μm

Weak-base capacity, salt-splitting capacity, and dry weight capacity were determined by standard analytical techniques well known in the art. Water retention capacity and average particle diameter were determined bythe procedures previously described. Shrink swell was determined by placing a portion of the resin in its free base form in a graduated cylinder-filled with water. The graduated cylinder was tapped until the volume ofthe resin remained at a constant value. Thereafter, the resin was converted to its acid form by contact with a dilute aqueous hydrochloric acid solution and a final water wash. The volume ofthe resin, in its acid form, was determined in the same manner. Shrink/swell, as a percentage, is calculated by:

where: af sthe volume ofthe resin in its acid form; ' and

V I.D is the volume ofthe resin in its free base form. Crush Strength was determined by taking a statistically representative sample of at least 30 beads from a given sample of resin or copolymer beads, and determining the force, in grams, needed to fracture each bead using a Chatillon Scale, Model DPP-1 KG, available from J. Chatillon & Sons Company. Crush strength is reported as the average of he force measurements obtained for the 30 beads. Example 2

This example concerns preparation of porous copolymer beads from seed particles prepared from t-butylstyrene. The procedure of Example 1 was substantially repeated, except where indicated otherwise. The resulting porous copolymer beads were also converted to a cation-exchange resin, rather than an anion-exchange resin. Seed Preparation

The kettle was charged with a monomer mixture consisting of 1160 grams of t- butylstyrene, 4.2 grams ofthe divinylbenzene solution, and as free-radical polymerization initiators, 0.58 grams of t-butyl perbenzoate and 2.32 grams ofthe t-butyl peroctoate solution The monomer mixture was suspended in an aqueous medium consisting of 3.75 grams of the sodium dichromate solution, 4.7 grams of CMMC, and 1560 grams of water. The monomer mixture was polymerized as in Example 1 to yield cross-linked seed particles having a divinylbenzene content of 0.2 weight percent based on the total weight ofthe seed particles. The seed particles had the following particle size distribution as determined by screen analysis: Particle Diameter (urn) Weight Percent

841 to 707 1.0

707 to 595 27.6

595 to 500 41.7 500 to 420. 10.2

420 to 354 9.0

354 to 297 4.2

297 to 250 2.2 less than 250 4.0 Bead Preparation

A 176 gram portion of the seed particles corresponding to the 595 to 500 μm particle size range of the above-described distribution was used for this example. The seed particles were placed in the kettle along with a second monomer mixture consisting of 433 grams of styrene, 247 grams of the divinylbenzene solution previously described, 320 grams of iso-octane, 1.81 grams of the t-butyl peroctoate solution, 0.60 grams of t-butyl perbenzoate, and 932 grams of water. The seed particles were allowed to imbibe the second monomer mixture for 30 minutes. At this point, a small sample of the imbibed seed particles was obtained from the reactor. The seed particles were examined under a microscope which indicated thatthe monomer had been substantially imbibed and thatthe seed particles were separated. Thereafter, 1.5 grams of the sodium dichromate solution and 241 grams of the 1 percent aqueous CMMC solution was added to the kettle. The second monomer mixture was polymerized as in Example 1.

The resulting copolymer beads were opaque in appearance and had a slightly irregular surface. The beads were essentially uniform in size with a volume average particle diameter of 1043 μm. There were no copolymer beads of substantially reduced size present that would indicate poor imbibition of the second monomer mixture.

The porous copolymer beads were measured to determine physical properties. The beads had a treated bulk density of 0.539 g/cm³ and a porosity of 0.267 cm³/g. The treated beads had an average pore radius of 103 A and a specific surface area of 13.5 m²/g as measured by BET analysis.

The porosity of the porous copolymer beads is illustrated by Figure 1 which is a scanning electron photomicrograph taken of a bead cross-section at 20.800X magnification. The porous copolymer beads had a relatively "fine" porosity, i.e., the pore sizes are fairly uniform and somewhat smaller in comparison to a conventional (non-seeded) macroporous copolymer as depicted by Figure 2. Figure 2 is a scanning electron photomicrograph taken at a magnification of 20,600X. Cation-Exchange Resin Preparation The porous copolymer beads were converted to a cation-exchange resin by conventional sulfonation. A 50 gram portion ofthe copolymer beads was allowed to swell for 30 minutes with an excess of a halogenated swelling solventand concentrated 99 weight percent sulfuric acid. The swollen copolymer beads were then heated to a temperature of 100°C which was maintained for2 hours. The resulting sulfonated beads were hydrated gradually by rinsing them with successive washes of increasingly dilute aqueous sulfuric acid solutions and finally with water to aneutral pH. The washed beads were converted to resin in the calcium form by contact with an excess of a saturated calcium hydroxide solution. Thereafter, the resin beads were thoroughly washed with waterto a neutral pH. The cation-exchange resin was measured to determine various physical and chemical properties- The resin beads had a dry weight capacity of 4.82 meq/g, a water retention capacity in the calcium form of 53 percent, a volume average particle diameter of 1266 μm, and a crush strength of 315 g/bead. With respectto osmotic shock resistance, the percentage of whole perfect beads (WPB) was 97 percent after 10 cycles of successive washes as follows: 1) 8N sodium hydroxide, 2) water, 3) 8N hydrochloric acid, and 4) water. Example 3

This example concerns preparation of porous copolymer beads from seed particles prepared with a mixture of iauryfmethacrylate and isobornylmethacrylate. The procedure of Example 1 was substantially repeated, exceptwhere indicated otherwise. The resulting porous copolymer beads were converted to an anion-exchange resin as in Example 1 and also to a sulfonated cation-exchange resin as in Example 2. Seed Preparation

The polymerization kettle was charged with a monomer mixture consisting of 232 grams of laurytmethacrylate, 928 grams of isobornylmethacrylate, 4.2 grams ofthe divinylbenzene solution, and as free-radical polymerization initiators, 0.58 grams of t-butyl perbenzoate and 2.32 grams ofthe t-butyl peroctoate solution. The monomer mixture was suspended in an aqueous medium consisting of 2.5 grams ofthe aqueous sodium dichromate solution, 360 grams ofthe 1 percent aqueous CMMCsolution, and 840 grams of water. The monomer mixture was polymerized as in Example 1 to yield cross-linked seed particles having a divinylbenzene content of 0.2 weight percent based on the total weight of the seed particles. The seed particles had the following particle size distribution as determined by screen analysis: Particle Diameter (urn) Weight Percent greater than 420 1.2

420 to 354 2.6

354 to 297 14.9 297 to 250 22.5

250 to 177 33.3 less than 177 25.5

Cation-Exchange Resin Preparation

A 160 gram portion of the seed particles having diameters from 297 to 177 μm was used for this portion ofthe example. The seed particles were placed in the kettie along with 775 grams of water and 0.26 grams of a 30 percent aqueous sodium laurylsulfate sol ution. A second monomer mixture consisting of 346 grams of styrene, 198 grams of the divinylbenzene solution previously described, 256 grams of iso-octane, 1.45 grams of the t- butyl peroctoate solution, and 0.48 grams of t-butyl perbenzoate was added at a constant rate to the kettle over a 2.5 hour period. The seed particles were allowed to imbibe the second monomer mixture for an additional 45 minutes. Thereafter, 2.5 grams of the sodium dichromate solution and 223 grams of the 1 percent aqueous CMMC solution was added to the kettle. The second monomer mixture was polymerized as in Example 1. The resulting porous copolymer beads were somewhat opaque. All other procedures were substantially similar to those of Example 1. The porous copolymer beads had a treated bulk density of 0.611 g/cm³ and a porosity of 0.175 cm³/g.

The porous copolymer beads were then converted to a sulfonated cation- exchange resin by substantially following the procedure of Example 2. The sulfonated cation- exchange resin had a dry weight capacity of 4.92 meq/g, a water retention capacity in the calcium form of 50.4 percent, a volume average particle diameter of 480 μm, and a crush strength of 59 g/bead. With respect to osmotic shock resistance, the number of WPB was 99 percent. Anion-Exchanqe Resin Preparation

A 75 gram portion of the seed particles having diameters from 297 to 177 μm was used in this portion of the example. The seed particles were placed in the kettie along with 364 grams of water and 0.12 grams of a 30 percent aqueous sodium laurylsulfate solution. A second monomer mixture consisting of 218 grams of styrene, 37 grams of the divinylbenzene solution previously described, 120 grams of Soltrol 10 (a mixture of isoparafinic solvents) available from the Phillips 66 Company, 0.68 grams of the t-butyl peroctoate solution, and 0.23 grams of t-butyl perbenzoate was added at a constant rate to the kettle over a 20-minute period. The seed particles were allowed to imbibe the second monomer mixture for 6.5 hours. Thereafter, 1.2 grams of the sodium dichromate solution, 1 gram of Antifoam B available from the Dow Corning Company, and 105 grams of the 1 percent aqueous CMMC solution were added to the kettle. The seed particles and second monomer mixture were polymerized as in Example 1- The resulting porous copolymer beads appeared opaque. All other procedures were substantially similarto those of Example 1. The beads were not analyzed to determine treated bulk density, porosity, average pore diameter, or specificsurface area. A 75 gram portion ofthe porous copolymer beads was converted to a strong-base anion-exchange resin by substantially repeating the procedure of Example 1. The strong-base anion-exchange resin had a dry weight capacity of 4.85 meq/g, a water retention capacity in the chloride form of 48.3 percent, and a volume average particle diameter of 677 μm. The beads had a Chatillon crush strength of 171 grams bead and an osmoticshock resistance of 100 10 percent WPB.

The remaining portion, about 140 grams, ofthe porous copolymer beads was converted to a weak-base anion-exchange resin by substantially repeating the procedure of Example 1. After chloromethylation, the beads were placed into the Paar bomb reactor with 32 grams of water, 35.5 grams of a 50 weight percent aqueous sodium hydroxide solution, and 15 143 grams ofthe dimethylamine solution. All remaining procedures were substantially similar to those of Example 1.

The resulting weak-base resin had the following properties: Weak-base capacity 1.60 meq/ml

Salt-splitting capacity 0.08 meq/ml 0 Dry weightcapacity 4.39 meq/g

Water retention capacity (Cl^" form) 41.6 percent

Shrink/swell (percent) 20.5 percent

Crush Strength 797 g/bead

Volume Average Particle Diameter 556 μm 5 Osmotic Shock Resistance 100 percent WPB

Non-Treated Bulk Density 0.66 g/cm³

The pore size distribution (as determined by size exclusion chromatography) of the weak-base anion-exchange resin prepared by this example isshown in Figure 3. The figure also compares the pore size distribution ofthe present weak-base anion resin with that of a 0 conventional macroporous weak-base anion resin. The distributions showthatthe resin ofthe present invention has a greater proportion of pores with a size below about 140 A or less compared to the conventional resin.

Figure 4 shows the pore size distribution ofthe sulfonated cation resin prepared by this example and compares it with that of a conventional sulfonated cation resin. Similarly, the distributions of Figure 4show thatthe cation resin ofthe present invention has a greater proportion of pores with a size below about 140 A or less compared to the conventional resin.

In Figures 3 and 4, the distribution coefficient is a number which indicates the portion (as a percentage) of pores in a bead which have a given pore diameter. For example in Figure 3, the curve associated with the weak-base resin of the invention indicates that approximately 52 percent of the pores in a bead have a diameter greater than or equal to 51 A. Example 4 .

This example concerns preparation of porous copolymer beads by seeded polymerization of gel copolymer seeds prepared from vinyltoluene. The procedure followed was substantially similar to that of Example 1 , except as otherwise indicated. Seed Preparation

A first monomer mixture consisting of 1 160 grams of vinyltoluene available from The Dow Chemical Company, 4.2 grams of the divinylbenzene solution, and as free-radical polymerization initiators, 0.58 grams of t-butyl perbenzoate and 2.32 grams of a 50 percent solution of t-butyl peroctoate, was added to the kettle and suspended in an aqueous medium. The aqueous medium consisted of 3.75 grams of the 60 percent aqueous solution of sodium dichromate as a latex inhibitor, 375 grams of the 1 percent aqueous carboxymethylmethyl¬ cellulose (CMMC) solution, and 875 grams of water. The monomer mixture was polymerized as in Example 1. The resulting seed particles had a divinylbenzene content of 0.2 percent based on the weight ofthe monomer. The kettle contained some popcorn polymer (a waste product) which was removed by screening out particles larger than 707 μm.

The seed particles obtained had the following particle size distribution as determined by a screen analysis: Particle Diameter (μm) Weight Percent

707 to 595 1.8

595 to 500 25.3

500 to 420 31.0

420 to 354 24.6 354 to 297 8.3

297 to 250 3.3 less than 250 5.7

Bead Preparation

A 200 gram portion ofthe seed particles corresponding to the 595 to 354 μm particle size range ofthe above-described distribution was used in this example. The seed particles were placed in the kettle along with 932 grams of water. A second monomer mixture consisting of 346 grams of styrene, 198 grams of the divinylbenzene solution previously described, 256 grams of iso-octane, 1.45 grams ofthe t-butyl peroctoate solution, and 0.48 grams of t-butyl perbenzoate was added gradually to the kettle over a 30-minute period. The seed particles were then allowed to imbibe the second monomer mixture for 6 hours.

Thereafter, 1.5 grams of the sodium dichromate solution and 241 grams ofthe 1 percent CMMC solution were added. The seed particles and second monomer mixture were polymerized as in Example 1 and measured to determine physical properties. The porous copolymer beads had a treated bulk density of 0.593 g/cm³ and a porosity of 0.158 cmVg.

-The porous copolymer beads were converted to a sulfonated cation-exchange resin by substantially following the procedure of Example 2. The resin had a dry weight capacity of 4.76 meq g, a water retention capacity in the calcium form of 49.2 percent, a volume average particle diameter of 962 μm, and a crush strength of 570 g/bead. With respect to osmoticshock resistance, the number of WPB was 99 percent.

Claims

WHAT IS CLAIMED IS:

1. A process for making porous copolymer beads comprising:

(a) providing a plurality of gel-type, copolymer seed particles prepared by polymerization of a first monomer mixture comprising at least one first monovinylidene monomer and a first cross-linking monomer, the seed particles optionally containing a free- radical source therein capable of initiating polymerization of ethylenically unsaturated monomers;

(b) imbibing the seed particles with a second monomer mixture comprising a phase-separating diluent, at least one second monovinylidene monomer, a second cross-linking monomer, and a free-radical initiator, the free-radical initiator being optional where the seed particles contain the free radical source, the phase-separating diluent and second monovinylidene monomer having a solubility parameter and dipole moment which are compatible with the corresponding solubility parameter and dipole moment of the at least one first monovinylidene monomer such that at least 70 percent by weight of the second monomer mixture is imbibed bythe seed particles; and

(c) maintaining the imbibed seed particles under suspension polymerizing conditions for a time sufficient to polymerize the second monomer mixture to a desired degree of conversion and obtain porous copolymer beads.

2. The process of Claim 1 wherein the seed particles are prepared by insitu suspension polymerization of a first monomer mixture comprising the at least one first monovinylidene monomer and the first cross-linking monomer within a continuous suspending medium.

3. The process of Claim 2 wherein conversion ofthe at least one first monovinylidene monomer and the first cross-linking monomer is from 50 to 90 percent based on total weight of the monomers in the first monomer mixture.

4. The process of Claim 1 wherein step (a) further comprises suspending the seed particles within a continuous suspending medium.

5. The process of Claims 1 to 4 wherein the at leastone first monovinylidene monomer is selected from t-butylstyrene, vinyltoluene, ethylvinyl benzene, laurylmethacrylate, or isobornylmethacrylate.

6. The process of Claims 1 to 5 wherein the first cross-linking monomer is divinylbenzene, trivinylbenzene, ethylene glycol dimethacrylate, or mixtures thereof.

7. The process of Claims 1 to 6 wherein the seed particles comprise from 95 to 99.99 weight percent of the at leastone first monovinylidene monomer and from 0.01 to 5 weight percent of the first cross-linking monomer based on total weight of the monomers.

8. The process of Claims 1 to 7 wherein the at least one second monovinylidene monomer is selected from styrene, alkyl-substituted styrenes, or vinylbenzylchloride and the cross-linking monomer is divinylbenzene.

9. The process of Claims 1 to 8 wherein the second monomer mixture has from 75 to 97 weight percent of the at least one second monovinylidene monomer and from 3 to 25 weight percent ofthe second cross-linking monomer, based on total weight of monomers in the second monomer mixture.

10. The process of Claim 5 wherein the phase-separating diluent is selected from hexane, heptane, or iso-octane.

11. The process of Claim 1 wherein the solubility parameters ofthe phase- separating diluent and the at least one second monovinylidene monomer are within ± 10 percent of the solubility parameter for the at leastone first monovinylidene monomer.

12. The process of Claim 1 wherein the dipole moments ofthe phase-separating diluentand the at-Ieastone second monovinylidene monomer are within ± 0.25 debyes of the dipole moment forthe at leastone first monovinylidene monomer.

13. The process of Claim 10 wherein the phase-separating diluent is present in an amount from 20 to 50 weight percent based on total weight of the second monomer mixture.

14. The process of Claims 1 to 13 further comprising: (d) functionalizing the porous copolymer beads with ion-exchange functional groups to obtain an ion-exchange resin.

15. A porous copolymer bead prepared bythe process of Claims 1 to 13.

16. An ion-exchange resin prepared bythe process of Claim 14.