GB1602064A

GB1602064A - Polymer beads

Info

Publication number: GB1602064A
Application number: GB23076/78A
Authority: GB
Original assignee: Rohm and Haas Co
Current assignee: Rohm and Haas Co
Priority date: 1977-06-27
Filing date: 1978-05-26
Publication date: 1981-11-04
Also published as: BR7804015A; IT1111628B; AU3745278A; NL7806892A; BE868487A; AU521552B2; CA1114987A; JPS6414206A; ZA783340B; DE2827475A1; ES471391A1; FR2396027A1; IN149312B; JPS627921B2; IT7868500A0; AR228836A1; JPS5411984A; DE2827475C2; FR2396027B1

Description

(54) POLYMER BEADS (71) We, ROHM AND HAAS COMPANY, a corporation organized under the laws of the State of Delaware, United States of America, of Independence Mall West, Philadelphia, Pennsylvania 19015, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement:- This invention is concerned with the preparation of polymer beads useful as ion exchange beads of superior physical characteristics.

The techniques of preparing crosslinked vinyl copolymers in bead form (as precursors for ion exchange resins) by free-radical catalyzed polymerization of the monomer mixture in aqueous dispersion are well known. The term "crosslinked vinyl copolymer" and the like is used for the sake of brevity herein to signify copolymers of a major proportion, i.e., from 50 up to 99.5 mole percent, preferably 80 to 99% of mono-ethylenically unsaturated monomer, for example, monoethylenically unsaturated aromatic monomer, e.g., styrene, vinyl toluene, vinyl naphthalene, ethyl vinyl benzene, vinyl chlorobenzene and chloromethyl styrene, and esters of acrylic and methacrylic acid e.g., methylacrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, tert-butyl acrylate, ethyl hexyl acrylate, cyclohexyl acrylate, isobornyl acrylate, benzyl acrylate, phenyl acrylate, alkyl phenyl acrylate, ethoxymethyl acrylate, ethoxypropyl acrylate, propoxypropyl acrylate, ethoxyphenyl acrylate, ethoxybenzyl acrylate, ethoxycyclohexyl acrylate, and the corresponding esters of methacrylic acid, with a minor proportion, i.e., of from 0.5 to 50 mole percerit, preferably 1 to 200 of polyethylenically unsaturated monomer having at least two active ethylenically unsaturated groups polymerizable with the aforesaid mono-unsaturated monomer to form a crosslinked, insoluble, infusible copolymer, said polyvinyl compounds being, for example, divinyl benzene, trimethylolpropane trimethacrylate, ethylene glycol dimethylacrylate, divinyl toluene, trivinyl benzene, divinyl chlorobenzene, diallyl phthalate, divinylpyridine, divinylnaphthlene, ethylene glycol diacrylate, neopentyl glycol dimethacrylate, diethylene glycol divinylether, bisphenol-A-dimethacrylate, pentaerythritol tetra- and trimethacrylates, divinylxylene, divinylethylbenzene, divinyl sulfone, divinyl ketone, divinyl sulfide, allyl acrylate, diallyl maleate, diallyl fumarate, diallyl succinate, diallyl carbonate, diallyl malonate, diallyl oxalate, diallyl adipate, diallyl sebacate, divinyl sebacate, diallyl tartrate, diallyl silicate, triallyl tricarballylate, triallyl aconitate, triallyL citrate, triallyl phosphate, N,N'methylenediacrylamide, N,N'-methylene dimethacrylamide, N,N' eth lenediacrylamide, trivinyl naphthalene, polyvinyl anthracenes and the polyallyl and polyvinyl ethers of glycol, glycerol, pentaerythritol, resorcinol and the monothio and dithio derivatives of glycols. The copolymer may also have incorporated therein up to about 5 mole percent of polymerized units of other ethylenically unsaturated monomer which does not affect the basic nature of the resin matrix, for example acrylonitrile and butadiene.

Conventional conditions of polymerization lead to crosslinked vinyl copolymers, which, when converted to ion exchange resins by attachment of functional groups thereto, have certain operational deficiencies resulting from physical weaknesses.

The present-invention may be used to yield ion exchange resins in which the polymer beads have high mechanical strength, high perfect bead count, and resistance to those swelling pressures which are produced within a bead during acid/base cycling (i.e., osmotic shock). Greater mechanical bead strength manifests itself in improved resistance to physical breakdown as a result of external forces such as weight of the resin column bed, high fluid flows and backwashing. Thus, the physically strong ion exchange resins of this invention are especially useful in treating fluid streams at high flow rates, for example in condensate polishing applications in which resins of lesser quality are prone to mechanical breakdown and short life spans.

In our copending Patent Applications 04822/78 and 19793/78 Serial No.

1,602,063 respectively it has been proposed to improve ion exchange resin quality by carrying out the polymerization with oxygen dissolved in and/or swept over the monomer mixture during polymerisation at least until the gel point is reached and/or with a "reaction modifier" in admixture with the monomer mixture in a concentration of from 0.01 millimoles to 20 millimoles per mole of monomer, said modifier being an organic compound containing acetylenic or allylic unsaturation.

The use of one or both of these techniques in the process of the present invention is preferred.

We have now found that a particular group of peroxy catalysts, not heretofore known to have advantages in the manufacture of ion exchange polymers, may be used to produce a polymer which, when functionalized, is substantially and unexpectedly superior to corresponding conventional materials. The catalysts which yield these advantages may be characterized generally as peroxyesters and peroxydicarbonates.

Accordingly, this invention provides a process of preparing hard, crosslinked discrete copolymer beads by the free radical polymerisation in an aqueous dispersion of a monomer mixture comprising 5 to 99.5 mole percent of monoethylenically unsaturated monomer and 0.5 to 50 mole percent of crosslinking monomer having at least two active ethylenically unsaturated groups wherein the polymerisation is conducted in the presence of one or more of certain peroxy catalysts. Useful peroxyesters include the alkyl esters of peroxycarboxylic acids and the alkylene bis(esters) of peroxycarboxylic acids, which peroxyesters fall within the general formula:

wherein R1 is a branched alkyl or 3 to 12 carbon atoms and having a secondary or tertiary carbon linked to the carbonyl group; x is 1 or 2, and when x is 1, R2 is a branched alkyl radical containing a tertiary carbon attached to the oxygen that is:

wherein R', R" and Rt" are independently selected from linear or branched lower alkyl, and when x is 2, R2 is an alkylene or aralkylene, in either case terminating in tertiary carbon atoms attached to the oxygen, that is:

wherein R' and R" are as defined above and R"' is a phenylene or lower alkylene.

The peroxyester catalysts are presently available commercially under the Registered Trade Mark "Lucidol" (Lucidol Division, Pennwalt Corporation) and are recommended for vinyl polymerizations.

Useful peroxydicarbonate catalysts useful in this invention include those having the general formula:

wherein Y and Z may be the same or different and are lower (Cl to C8 preferably Cç to C4) alkyl, cycloalkyl, alkyl-substituted cycloalkyl, or aralkyl groups. Such materials are available commercially from Lucidol Division, Pennwalt Corporation under the Registered Trade Mark "Lupersol", and Noury Chemical Corporation under the Registered Trade Mark "Percadox." A preferred group of peroxyester catalysts includes t-butyl peroxy-2-ethylhexanoate, t-butyl peroxyisobutyrate, t-butyl peroxyneodecanoate, t-amyl peroctoate, and 2,5.dimethyl-2,5-bis(2-ethylhexanoylperoxy)-hexane.

A preferred group of peroxydicarbonate catalysts includes, di(4-tbutylcyclohexyl)peroxydicarbonate, di(sec-butyl)peroxydicarbonate, di(2ethylhexyl)peroxydicarbonate, dicetyl peroxydicarbonate, and dicyclohexyl peroxydicarbonate.

In operating the process of this invention, the vinyl monomer, crosslinking monomer, and any other optional monomer, may be polymerized in an aqueous dispersion containing the peroxy catalyst (alternatively "free radical initiator") and additionally, if desired, oxygen and/or a "reaction modifier" as disclosed in the copending-applications mentioned above. Generally, from 0.1% to 2.0/o of the peroxy catalyst by weight of the monomer mixture is used. The methods of polymerization in the invention do not generally depart from the well known methods for manufacture of ion exchange polymers and resins.

The polymerization is normally carried out at a temperature from 30"C to 90"C, preferably 45"C to 800C and even more preferably 50"C to 750C. In a preferred embodiment, it is desirable to employ lower temperatures of reaction in the initial stages of polymerization, that is until at least about 50%, preferably at least 75%, of the monomer in the dispersion has reacted. During the final stages of polymerization the temperature is desirably raised 20"C to 300C above the temperature used for the initial stages. It impossible to operate at temperatures 15 to 350C below temperatures normally used in prior art methods. When operating at lower temperatures, e.g., 30"C to 60"C using catalysts of the invention (Percadox type) it may be desirable to employ a second so-called "chaser catalyst" which is active at higher temperatures, e.g., 75-1000C, in order to achieve higher yields of crosslinked vinyl polymer, using for example, from 0.05 to 0.1% based on monomer weight of such initiators as benzoyl peroxide, t-butyl peroctoate and t-butyl peroxyisobutyrate.

The aqueous medium in which the polymerization is conducted in dispersion form will usually contain minor amounts of the conventional suspension additives, that is, dispersants such as xanthan gum (biosynthetic polysaccharide), poly(diallyl dimethyl ammonium chloride), polyacrylic acid (and salts), polyacrylamide, magnesium silicate, and hydrolyzed poly(styrene-maleic anhydride); protective colloids such as carboxymethyl cellulose, hydroxyalkyl cellulose, methyl cellulose, polyvinyl alcohol, gelatin, and alginates; buffering aids such as phosphate and borate salts; and pH control chemicals such as sodium hydroxide and sodium carbonate.

The crosslinked, high-molecular weight copolymers may be recovered from the reactor as hard, discrete beads of particle size 0.02 to 2 mm, average particle size usually being 0.2 to 1 mm. These copolymers may be converted to ion exchange resins by attachment of functional groups thereto by conventional processes, such functional groups including sulfonamide, trialkylamino, tetraalkyl ammonium, carboxyl, carboxylate, sulfonic, sulfonate, hydroxyalkyl ammonium, iminodiacetate, amine oxide and phosphonate. Functionalizing reactions which may be performed on vinyl aromatic copolymers to produce ion exchange resins are exemplified by sulfonation with concentrated sulfuric acid, chlorosulfonation with chlorosulfonic acid followed by amination, reaction with sulfuryl chloride or thionyl chloride followed by amination, and chloromethylation followed by amination. Typical functionalizing reactions on (vinyl) acrylic copolymers include hydrolysis to acrylic acid resins, amidolysis and transesterification. Ion exchange resins may be further delineated by the types: strong acid cation, e.g., containing the groupings sulfonic (7SO3H) or sulfonate (SO3M. where M is usually an alkali metal ion); weak acid cation, e.g., containing the groupings carboxyl (CO2H) or carboxylate (-CO2M, where M is usually an alkali metal ion); strong base anion, e.g., containing the tetra-alkyl ammonium groupings: -NR3X, where R is an alkyl or hydroxy alkyl group and X is usually chloride of hydroxide; and weak base anion, e.g., containing a trialkylamino group, -NR2, where R is an alkyl or hydroxyalkyl group.

The properties of the resins produced by this invention are not evident until the cross-linked copolymers are converted to ion exchange resins by the attachment of functional groups. The physical strength of these ion exchange resins is apparent from their resistance to crushing which is conveniently measured on the Chatillon instrument, as well as by visual inspection before and after use in ion exchange applications. For example, strong acid, styrene-type resins can be produced in accordance with the preferred method of this invention to exhibit Chatillon values of 1000 to 5000 gm, force per bead, as compared with resins derived from copolymers prepared by prior art polymerization methods which conventionally have Chatillon values of 50 to 500 gm/bead. Similarly, strong base styrene-type resins of the invention may exhibit Chatillon values of 500 to 1500 as compared with prior art resins which often have Chatillon values of 25 to 400.

The following examples, which are for illustration only, give some preferred embodiments of the invention in which t-butyl peroctoate used is in fact t-butyl peroxy 2-ethyl hexanoate.

Example 1 The polymerization reactor is two liter, three neck, round bottom flask equipped with a two blade paddle stirrer, thermometer, condenser, heating mantle with temperature controller and provision for sweeping with an inert gas. Into this reactor is charged a monomer mixture consisting of 500.4 g styrene and 85.6 g divinylbenzene,and 1.9 g t-butyl peroctoate. The head space is swept with nitrogen and the aqueous phase is then added: 510 g water, 20.1 g poly(diallyldimethyl ammonium chloride) dispersant, 1.6 g of gelatin protective colloid, 0.88 g boric acid, and sufficient 5-O/O sodium hydroxide solution to maintain pH- between 10.0 and 10.5. The stirrer is started and the reaction mixture is heated from room temperature to 750C over 45 minutes and held at this temperature for 4.0 hours.

Thereafter, the polymerization is concluded by holding the reaction mixture at 95"C for 1 hour. The copolymer beads are separated, washed und prepared for functionalization.

In this and the following examples strong acid resins were prepared from the copolymer by means of the following alternative procedures.

Sulfonation A A portion of the copolymer beads as prepared above (110 g) is added to 600 g of 95% H2SO4 is a one liter flask equipped with stirrer, condenser, dropping funnel, thermometer, caustic scrubber and heating means. Thirty nine grams of ethylene dichloride (bead swelling agent) are added, and the suspension is heated from 30"C to 1300C over a three hour period. This is followed by a hydration procedure in which water is added to quench the product. The sulfonated product is then washed to remove residual acid. The physical properties of the strong acid resin product are set forth in Table I, hereinafter.

Sulfonation B A portion of the copolymer beads as prepared in Example I above (50 g) is added to 315 g of 94% H2SO4 in a one liter flask equipped with stirrer, condenser, dropping funnel, thermometer, caustic scrubber, and heating means. Thirty grams of ethylene dichloride (bead swelling agent) are added, and the suspension is heated to 60--650C where it is held for one hour. The mixture is then heated to 115"C and held there for 4 hours. This is followed by a hydration step in which water is added to quench the product. The sulfonated product is then washed to remove residual acid.

Of the first eighteen specific examples herein, in Examples 1,2, 4--7, and 1 1- 18 the copolymer products were functionalized by Sulfonation method "A", and in the remaining Examples by sulfonation method "B".

Example 2 Using the procedure set forth in Example 1, a copolymer ion exchange resin precursor was prepared from identical starting materials in identical amounts. The properties of the product, after sulfonation are as given below in Table I.

Example 3 Following the procedure of Example 1, 254.5 g of styrene, 42.4 grams of divinylbenzene, 3.0 g methyl acrylate, and 1.5 g t-butyl peroctoate were charged to the reactor. The aqueous phase consisted of 270 g H2O, 10.0 g poly(diallyl dimethyl ammonium chloride), 0.8 g of gelatin protective colloid, 0.45 g boric acid and 50 4, NaOH solution to maintain the pH between 10.0 and 10.5. The reaction mixture was heated to 75 C for 2.7 hours, then 95 C for an additional hour. The product was washed and sulfonated. The properties of the resin are given below in Table I.

Example 4 Following the procedure of g ethyl Example 1, 491.7 g of styrene, 85.5 g of divinylbenzene, 8.8 g methyl acrylate, 0.51 g methylcyclopentadiene dimer, and 1.90 g t-butylperoctoate were charged to the reactor. The aqueous phase consisted of 510.0 g H2O, 20.1 g of poly(diallyl dimethyl ammonium chloride), 1.6 g of gelatin protective colloid, 0.83 g boric acid and 50% NaOH solution to maintain the pH between 10.0 and 10.5. The reaction mixture was heated to 750C for 4 hours and then 95 C for an additional hour. The product was washed and sulfonated. The properties of the resin are given below in Table I.

Example 5 Following the procedure of Example 1, 491.7 grams of styrene, 85.5 grams of divinylbenzene, 8.8 g of methyl acrylate, 0.59 g methylcyclopentadiene dimer, and 1.90 g of t-butylperoctoate were charged to the reactor. The aqueous phase consisted of 510.0 g of H2O, 20.1 g poly(diallyl dimethylammonium chloride), 1.6 g gelatin protective colloid, 0.88 g boric acid and sufficient 50% NaOH solution to maintain the pH between 10.0 and 10.5. The reaction mixture was heated to 750C for 4 hours and 95 C for an additional hour. The product was washed and sulfonated. The properties of the resin are given below in Table I.

Example 6 Following the procedure of Example 5, using the same organic and aqueous phases, a resin was prepared having the properties set forth in Table I.

Example 7 Following the procedure of Example 1, but including the reaction modifier a- methylstyrene dimer (0.59 g) and the initiator t-butyl peroctoate (1.9 g) a resin was prepared having the properties set forth in Table I.

Example 8 Following the procedure of Example 1, but including 3.0 g methyl acrylate, 1.5 g t-butyl peroctoate, and 0.3 g cycloheptatriene (reaction modifier), a resin was prepared having the properties set forth in Table I.

Example 9 Following the general procedure of Example 1, but including 3.0 g methyl acrylate, 1.5 g t-butyl peroctoate and 0.3 g norbornene (reaction modifier) a resin was prepared having the properties set forth in Table I.

Example 10 Following the general procedure of Example 1, but including 3.0 g methyl acrylate, 1.5 g t-butyl peroctoate and 0.3 g dicyclopentadiene (reaction modifier) a resin was prepared having the properties set forth in Table I.

Example 11 Following the general procedure of Example 1, but additionally including 8.8 g methyl acrylate and 0.29 g methylcyclopentadiene dimer (reaction modifier) and using 2.64 g di - (4 - t - butylcyclohexyl) - peroxydicarbonate (Percadox 16) as the initiator a resin was prepared having the properties set forth in Table I. A blanket of 8% O2 in N2 was swept over the reaction mixture for 30 minutes. Also 0.59 sodium nitrite was used in the aqueous phase to prevent polymerization therein (also in Examples 12 and 13 which follow).

Example 12 Following the general procedure of Example 1, but additionally including 8.8 g methyl acrylate and 0.29 g methylcyclopentadiene dimer, and using 2.64 g di - (4 t - butylcyclohexyl) - peroxydicarbonate as the initiator in the organic phase a resin was prepared. The initial polymerization was conducted at 57% for seven hours after which the temperature was raised to 95% for 1 hour. The properties of the resin were as shown in Table I.

Example 13 Following the general procedure of Example 1, but additionally using 8.8 g methyl acrylate and using 2.64 g di - (4 - t - butylcyclohexyl) - peroxydicarbonate as the initiator (but no reaction modifier) and a reaction temperature of 56"C for seven hours and 75"C for two hours, a resin was prepared having the properties set forth in Table I.

Example 14 Following the general procedure of Example 1, but using 1.9 g of 2,5 dimethyl - 2,5 - bis(2 - ethylhexanoylperoxy) - hexane as the initiator and a reaction temperature of 70"C for 4 hours followed by 90"C for 1 hour, a resin was prepared having the properties set forth in Table I.

Example 15 Following the general procedure of Example 1, but using 1.12 g t-butyl peroxyneodecanate as the initiator an initial reaction temperature of 53-54"C for 4.5 hours and 70"C for I hour thereafter, a resin was prepared having the properties set forth in Table I.

The following examples illustrate the prior art method of preparation and products resulting therefrom.

Comparative Example 16 Following the general procedure of Example 1, using 2.20 grams of benzoyl peroxide (initiator) an initial reaction temperature of 75"C for 4 hours and a final temperature of 950C for 1 hour, a resin was prepared having the properties set forth in Table I.

Comparative Examples 17 and 18 Example 16 was repeated twice and the products resulting had properties set forth in Table I.

The resins produced according to the foregoing examples were tested to determine the percentage whole bead count (%WB) percentage perfect bead count (%PB) the crushing strength of the beads (Chatillon test method) and the % reduction of the perfect bead count after repeated cycling in acid and base solutions (on accelerated usage test). All tests were conducted on the resin after sulfonation.

TABLE I Physical Properties of Resins % Reduction Example Chatillon in PB After No. %WB %PB g./bead Cycling 1 98 98 1110 6 2 98 92 1100 - 3 99 95 1520 5* 4 100 98 1610 6 5 99 97 1065 3 6 100 97 915 7 99 97 914 2 8 99 98 1810 3* 9 99 95 1450 2* 10 99 98 1900 8* 11 97 98 1770 12 98 98 1400 0 13 98 84 1170 14 100 96 695 15 98 87 900 16 99 90 325 49 17 99 91 335 52 18 97 78 515 39 *50 cycles with 1N HCI and 1N NaOH, all others have 100 cycles with 1N HCI and 0.5N NaOH Weak and strong base resins having improved properties may also be prepared in accordance with the present invention, substituting the well known methods for post-functionalizing the copolymer resin to produce weak or strong anion exchange groups for the sulfonation method shown above. A preferred method known in the art for functionalizing with anion exchange groups involves chloromethylation followed by amination.

Examples 19-20 Two styrene/divinylbenzene strong base resins were prepared following the general procedure of Example 1 for the copolymer, and using conventional chloromethylation/amination procedures to functionalize the copolymer. The copolymer of Example 19 utilized terpinolene as a reaction modifier and 2,6 dimethyl - 2,4,6 - octatriene was utilized for Example 20. Both copolymers utilized t-butyl peroctoate as the initiator. A control sample of a commercial strong base resin produced without reaction modifier and using a conventional prior art initiator was produced for comparative purposes. The properties of the resins produced are set forth in Table II.

TABLE II Properties of Strong Base Resins Example Chatillion No. %WB %PB g./bead 19 100 98 610 20 100 99 750 Control (commercial strong base resin) 100 94 140 As used herein and in the appended claims the avid/base cycling test is conducted with 1 normal HCI and 0.5 normal NaOH at room temperature for 100 cycles, at approximately two cycles per hour.

WHAT WE CLAIM IS: 1. A process of preparing hard, cross-linked discrete copolymer beads by the free-radical polymerisation in an aqueous dispersion of a monomer mixture comprising 50 to 99.5 mole percent of monoethylenically unsaturated monomer and 0.5 to 50 mole percent of cross-linking monomer having at least two active ethylenically unsaturated groups, wherein the polymerisation is conducted in the presence of one or more peroxy catalysts of the formula:

wherein Rl is a branched alkyl of 3 to 12 carbon atoms and having a secondary or tertiary carbon linked to the carbonyl group and x is 1 or 2 and when x is 1, R2 is a branched alkyl radical containing a tertiary carbon attached to the oxygen, and when x is 2, R2 is an alkylene or aralkylene group, in either case terminating in tertiary carbon atoms attached to the oxygen; or of the formula:

wherein Y and Z are the same or different and are lower alkyl, cycloalkyl, alkylsubstituted cycloalkyl or aralkyl groups.

2. Aprocess as claimed in Claim 1 wherein the polymerisation is conducted at a temperature of 30 to 90"C.

3. A process as claimed in Claim 2 wherein the polymerisation is conducted at a temperature of 45 to 800 C.

4. A process as claimed in Claim 3 wherein the polymerisation is conducted at a temperature of 50 to 75"C.

5. A process as claimed in any preceding claim wherein the peroxy catalyst is tbutyl peroxy 2-ethylhexanoate, t-butyl peroxyneodecanoate, 2,5-dimethyl - 2,5

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

Weak and strong base resins having improved properties may also be prepared in accordance with the present invention, substituting the well known methods for post-functionalizing the copolymer resin to produce weak or strong anion exchange groups for the sulfonation method shown above. A preferred method known in the art for functionalizing with anion exchange groups involves chloromethylation followed by amination.

Examples 19-20 Two styrene/divinylbenzene strong base resins were prepared following the general procedure of Example 1 for the copolymer, and using conventional chloromethylation/amination procedures to functionalize the copolymer. The copolymer of Example 19 utilized terpinolene as a reaction modifier and 2,6 dimethyl - 2,4,6 - octatriene was utilized for Example 20. Both copolymers utilized t-butyl peroctoate as the initiator. A control sample of a commercial strong base resin produced without reaction modifier and using a conventional prior art initiator was produced for comparative purposes. The properties of the resins produced are set forth in Table II.

TABLE II Properties of Strong Base Resins Example Chatillion No. %WB %PB g./bead

19 100 98 610

20 100 99 750 Control (commercial strong base resin) 100 94 140 As used herein and in the appended claims the avid/base cycling test is conducted with 1 normal HCI and 0.5 normal NaOH at room temperature for 100 cycles, at approximately two cycles per hour.

WHAT WE CLAIM IS: 1. A process of preparing hard, cross-linked discrete copolymer beads by the free-radical polymerisation in an aqueous dispersion of a monomer mixture comprising 50 to 99.5 mole percent of monoethylenically unsaturated monomer and 0.5 to 50 mole percent of cross-linking monomer having at least two active ethylenically unsaturated groups, wherein the polymerisation is conducted in the presence of one or more peroxy catalysts of the formula:

wherein Rl is a branched alkyl of 3 to 12 carbon atoms and having a secondary or tertiary carbon linked to the carbonyl group and x is 1 or 2 and when x is 1, R2 is a branched alkyl radical containing a tertiary carbon attached to the oxygen, and when x is 2, R2 is an alkylene or aralkylene group, in either case terminating in tertiary carbon atoms attached to the oxygen; or of the formula:

wherein Y and Z are the same or different and are lower alkyl, cycloalkyl, alkylsubstituted cycloalkyl or aralkyl groups.
2. Aprocess as claimed in Claim 1 wherein the polymerisation is conducted at a temperature of 30 to 90"C.
3. A process as claimed in Claim 2 wherein the polymerisation is conducted at a temperature of 45 to 800 C.
4. A process as claimed in Claim 3 wherein the polymerisation is conducted at a temperature of 50 to 75"C.
5. A process as claimed in any preceding claim wherein the peroxy catalyst is tbutyl peroxy 2-ethylhexanoate, t-butyl peroxyneodecanoate, 2,5-dimethyl - 2,5

bis(2 - ethylhexanoylperoxy) - hexane, di(4 - t butylcyclohexyl)peroxydicarbonate and/or dicyclohexyl peroxydicarbonate.
6. A process as claimed in any preceding claim wherein the polymerisation is conducted with oxygen in contact with and/or dissolved in the monomer mixture at least until the polymerisation reaches the gel point.
7. A process as claimed in any preceding claim wherein the polymerisation is conducted with a polymerisation modifier in admixture with the monomer mixture in a concentration of from 0.01 to 20 millimoles per mole of monomer, said modifier being an organic compound containing acetylenic of allylic unsaturation.
8. A process as claimed in claim I substantially as described in any one of the foregoing Examples 1 to 15, 19 and 20.
9. A process as claimed in any preceding claim which includes the further step or reacting the beads formed by the polymerisation to add ion exchange functional groups thereto.
10. Hard cross-linked discrete copolymer beads whenever made by a process as claimed in any of claims 1 to 8.
11. Ion exchange beads whenever produced by a process as claimed in Claim 9.