CA1325310C

CA1325310C - Process for the preparation of monodispersed polymer beads

Info

Publication number: CA1325310C
Application number: CA000565319A
Authority: CA
Inventors: Ernst Bayer; Wolfgang Rapp
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-04-29
Filing date: 1988-04-28
Publication date: 1993-12-14
Anticipated expiration: 2010-12-14
Also published as: DE3855409D1; JPS6479201A; EP0289029A3; EP0289029B1; ATE140239T1; EP0289029A2; DE3714258A1

Abstract

ABSTRACT

The invention concerns a process for the preparation of monodispersed polymer beads, wherein in a first stage a seed polymer is prepared in an organicsolvent and in the presence of an R-X compound, separated and in a second stage an emulsion polymerization is carried out in an aqueous medium in the presence of the seed polymer. The polymer beads obtained in this manner have diameters in the range of 0.5 to 50 µm, and may be used in the immobilizationof proteins and cells, as carriers of catalysts and in peptide synthesis and in chromatography.

Description

~ 1325310 PROCESS FOR THE PREPARATION OP -MONODISPl~RSED POLYMER BEADS
The invention concerns a process for the preparation of monodispersed polymer beads.
;~: S In view Or their extensively inert behavior and their simple manipulation from a technical process standpoint, organic polymer carriers are finding applications at an ever-increasing rate.
In chromatographic processe6, such as ion exchange chromatography, a~finity chromatography and gel permeation chromatography, modified organic carriers are primari1y used. The typical~ grain size distribution is between 5 and 40 ym.
Por organic syntheses, such as nucleotide and peptide syntheses, carrier materials with diameters of 30 to 100 ym are used. Commercial ion exchangers - have in part even larger diameters. ~or ~he immobilization of enzymes, carriers with large surface6, i.e. small grain sizes, are advantageous (for example, lattices with 50-500nm).
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, 3 1 ~

2 6557g-60 All of these carriers usua:Lly are polydlspersed materlals, l.e. materials with a broad graln slze distrlbutlon.
Polymer carrlers wlth a unlform, l.e. monodlspersed graln slze, which generally do not vary by more than +5%, offer clear advan-tages relatlve to polydlspersed systems. As the polymer sphere represents the reactlon space proper, ln the case of a deflned monodlspersed materlal, unlform reactlon spaces are obtalned.
Dlffuslon tlmes and retentlon tlmes are the same ln each polymer bead. Slmllar graln slzes make posslble unlform packlngs ln chromatographic appllcatlons. In additlon to the unlformlty of the polymer partlcles, the graln slze of the carrler plays an lmportant role. The larger the radlus, the lower the rate of ~ -dlffuslon processes ln the polymer, whereby separatlon efflclency ln chromatographlc appllcatlons ls reduced. Furthermore, wlth small dlameters, the avallable surface ls relatlvely larger.
Carrlers wlth a graln slze dlstrlbutlon of 50-1000 ~m may be obtalned readlly wlth respect to process technology by emulslon polymerlzatlon. Carrlers wlth a graln slze of 50-500 ~m, the so-called lattlces, may be obtalned by varlous processes. But -~
the preparatlon of carrlers wlth a graln slze wlthln a range of 0.5-50 ~m, ln partlcular 0.5 to 20 ~m, whlch are of speclal lnter-est ln view of thelr slmple manlpulatlon ln processes, ls dlffl~
cult.
There exlst certaln processes whlch yleld monodlspersed ~;
polymers wlth graln slzes wlthln the range of lnterest. Thus, in -the llterature for example, a process for the preparatlon of poly-styrene polymers ln alcohols wlth graln slzes of 1-5 ~m, ls ' ~.

~ .~ .: ~ .; , 132~31~
2a 65579-60 descrlbe~. These monodlspersed carrlers contaln functional groups, but are not cross-llnked. Their fleld of appllcatlon ls therefore restrlcted to medla whlch do not dlssolve polystyrene.
The mechanlcal stablllty of the polymer matrlx whlch ls not cross-llnked ls low.
EP-A-003 905 publlshed September 5, 1979 agaln descrlbes a process for the preparatlon of a monodlspersed carrler materlal.
In thls process, lnltlally a dlsperslon of polymer partlcles ln water ls prepared by polymerlzing a monomer ln the presence of a compound that has a very low solublllty ln water, or by lettlng thls low water solubillty materlal dlffuse ln the polymer obtalned from the monomer. It ls necessary for thls purpose to lntroduce thls low wat.er solublllty substance in the reaction mlxture in as fine a dlstributlon as posslble.
In a second stage, whlch ls agaln carried out ln an aqueous medlum, partlally water soluble monomers are caused to dlffuse lnto the polymer partlcles, whereupon the mlxture obtalned ~-ln thls manner ls polymerlzed. The process descrlbed E ::

3 132531~

in the aforecited European application is highly complex, particularly in view of the first stage, and frequently i6 not reproducible.
It is therefore the object of the present invention to provide a process for the preparation of monodispersed polymer beads making possible the 5 production of polymer beads with diameters within a range of 0.5 to 50 ~Im, in a simple and reliable manner.
The process also makes it further possible to prepare polymer beads with variable properties. For example, it should be possible to produce polymer beads with an arbitrary porosity, cross-linked or not cross-linked, and with or 10 without functional groups.
It has now been discovered that this object may be attained by preparing a seed polymer in an organic solvent in the presence of certain organic compounds.
The invention thus concerns a process for the preparation of monodispersed 15 polymer beads with a diameter in a range of 0.5 to 50 ,um, characterized in that:
In a first stage a polymer seed is prepared, by polymerizing a monomer yielding a monodispersed seed polymer in an organic solvent or a mixture of solvents, in the presence of triphenylmethane or a compound of the f /r;m~la 20 R-X, wherein R signifies a saturated or unsaturated, linear or branched radical with more than 6 carbon atoms and X stands for a hydrogen or halogen atom or a hydroxy group, a Cl-C6 alkoxy group, an amino group, a Cl-C6 alkyl-amino group, a di-Cl-C6 alkylamino group, a phenyl group or a phenyl group sub6tltuted by a Cl-C4 alky1 group, a hydroxy group optionally 25 polyoxyethylenated, a Cl-C4 alkoxy group, an amino group or a sulfonic acid group, in the presence of a polymerization initiator, and separating the seed polymer obtained; and In a second stage an emulsion polymerization is carried out by polymerizing a monomer in the presence of the seed polymer, an emulsifier, a polymerization 30 initiator and optionally a cross-linking agent in an aqueous medium.
According to the invention, the seed polymer is prepared in the first stage in an organic solvent producing a monodispersed seed. This solvent preferably i8 an alcohol, particularly a linear or branched Cl-C6 alcohol, and preferably a Cl-C4 alcohol, such as methanol, ethanol or t-butanol. The organic solvent 3'i may consist of an individual solvent or a mixture of several solvents.
. - , . .

~4~ 132~310 The organic solvent may also be used in a mixture with another solvent that does not lead to the formation of a monodispersed seed. This other solvent serves to modify the solution behavior. By the addition of such different solvents, the particle size of the seed polymer formed may be controlled. By using such a different solvent, seed polymers with a larger particle diameter are obtained.The proportion of the other solvent generally amounts to 20% by volume, preferably 5 to 15% by volume.
Suitable solvents that may be added to a solvent to produce a monodispersed seed polymer, in particular, are hydrocarbons, such as pentane and hexane;
10 aromatic hydrocarbons, such as toluene, o-, m- and p-xylene; chlorinated hydro-carbons, such as methylene chloride and chloroform; ketones, such as acetone and methylethylketone; esters, such as ethyl acetate; and ethers, such as tetra-hydrofuran and dioxan. Water may also be added, particularly if alcohols are used, provided the mixture remains homogeneous. Generally, a maximum of 15 10% by volume of water may bé added as a function of the type of the organic solvent, the R-X compound, and of the monomer.
As a further component for the preparation of the seed polymer, a compound of the formula R-X is added. Here, R stands for a saturated or unsaturated, linear or branched alkyl radical with more than 6 carbon atoms and X signifies 20 a hydrogen or halogen atom (in particular a chlorine or bromine atom), a hydroxy or Cl-C6 alkoxy group, an amino Cl-C6 alkylamino group or a di-Cl-C6 alkyl-amino group, a phenyl group or a phenyl group substituted by a Cl-C4 alkyl group, a hydroxy group optionally polyoxyethylenated, a Cl-C4 alkoxy group, an amino group or a sulfonic acid group.
Preferably, a compound of the formula R-X, wherein R is a saturated, preferably linear alkyl radical with 7 to 20 carbon atoms, in particular 9 to 18 carbon atoms, i6 used. Examples of such R radicals are the linear Cg-, Clo-, C12-J Cl 4~~ C16- and C18- alkyl radicals. But mixtures of such radicals may also be 30 present.
Preferably, in the R-X formula, X stands for a halogen atom (in particular a chlorine atom) or a hydroxy, amino, phenyl or substituted phenyl group. In a particularly preferred manner, X signifies a halogen atom or a phenyl group.
Examples of particularly preferred R-X compounds are nonylbenzene 35 or dodecylchloride. The use of triphenylmethane is also preferred, because , . ' '', ' ' ' ' ' i.

', ~

-5~ ~32531~ -the seed polymer may be handled in an especially slmple manner if this compound is employed.
The use of compounds of the R-X formula, wherein R is an unsaturated radical, is advantageous when it is desired to prepare cross-linked monodispersed polymer beads.
The monorners used in the first stage of the preparation of the seed polymer very generally may consist of vinyl monomers. However, two or more polymers may also be used, so that a copolymer is obtained. Preferably, styrene or functionalized styrene, for example, styrene functionalized with chormethyl, sulfonic acid or amino groups, is employed. Additional suitable monomers are acrylic acid derivatives, such as acrylic acid, acrylamide, acrylonitrile and the corresponding methacrylic acid derivatives, and the like. The seed polymer is prepared in the presence of a polymerization initiator, which is one of the compounds customarily used in tbis field. Suitable examples are azoisobutyronitrile (AIBN) and peroxides, such as benzoylhydroperoxide and benzoylperoxide.
The usual auxiliary substances may further be used in the preparation of the seed polymer, for example, protective colloids, such as polyvinylpyrrolidone (molecular weight approximately 1,000,000) and polyvinylalcohol.
The proportion of the monomer and the R-X compound depends upon the type of these components and on the solvent used. Generally, however, the ratio of the monomer to the R-X compound is within a range of 1:0.1 to 1:3.
The quantity of the solvent is generally chosen so that about 10 to 20%
by weight of the monomer is contained in the solvent.
The temperature for the preparation of the seed polymer is chosen generally as a function of the solvent. It is generally between 50 to 1 00C, preferably 60 to 90C. The reaction time may amount to up to 48 h and is preferably between 24 to 48 h.
A monodispersed seed polymer with a particle size between 0.5 to 10 llm, -~
preferably I to 5 llm, is obtained in this manner. It is also possible to control the particle size by the quantity of the R-X formula. The higher the proportion of this compound, the larger the particle size of the seed polymer.
- The seed polymer obtained in this manner is separated and isolated in a conventional manner, for example, by centrifuging. -In the second stage of the process according to the inventlon, emulsion : , -6- 132531~

polymerization is carried out, using the seed polymer obtained. Polymerization takes place in an aqueous rnedium with the addition of an emulsifier and a polymerization initiator. The usual emulsifiers employed in this field are used,for example, an alkylsulfonic acid, such as hexadecanesulfonic acid or the produc~
with the commercial designation of K-30 (C12-Cl4 sulfonic acid) of BASP.
The polymerization initiator, which must be soluble in oil, again may be one of the compounds customarily employed in this field, for example, a compoundcited relative to the first stage.
The monomer to be used here generally is a polymerizable vinyl compound, which may be difunctional (for cross-linking). Preferably, these are monomers described in connection with the first stage. The monomers used in the first and the second stage may be identical or different.
Por the preparation of cross-linked polymer beads, in the second stage a cross-linking agent is also used. For the purpose, conventional cross-linking agents, such as divinylbenzene, bifunctional acrylic compounds, and the like, may be employed, but cross-linking may also be effected by applying functionalized monomers. A preferred functionalized monomer is chloromethylated styrene. Cross-linking is effected by the addition of a Priedel-Crafts catalyst, such as aluminum chloride.
In order to vary the structure of the monodispersed polymer beads, in the second stage, an inert compound that does not polymerize, may be added.
This inert component must be such that it diffuses into the seed polymer and may be removed after the completion of the polymerization by suitable measures, such as washing, evaporation by heating or in a vacuum, and the like.
If, as the Inert component a solvent of the polymer (seed polymer) is used, microporous polymer beads are obtained. If, on the other hand, an inert component is used that is not a solvent of the polymer, macroporous polymer beads are obtained.
Suitable inert components are higher aliphatic, cyclic or aromatic hydro-carbons, such as heptane, octane, cyclohexane, benzene, toluene, o-, m-, p-xylene, ethylbenzene and the like; higher alcohols, such as hexanol, heptanol, octanol, decanol and the like; cyclic alcohols, such as cyclohexanol and the like, chlorinated hydrocarbons, such as dichloromethane and chloroform and the like. The inert component may be added indlvidually or in a mixture. The selection of a suitable solvent is a function of the polymer. By choosing an ,~,. " - , . :. ,.: . , - " , . . " . . ., ., ,, . ,", -,~ . - . . .

-7- 13253~0 appropriate solvent or a suitable mixture of solvents, it is therefore possible to vary the solvent properties of the inert component and, as such, the porosityof the polymer beads as desired. In this manner, polymer beads with a pore size of about 5 R to approximately 3000 R may be produced.
For the emulsion polymerization of the second stage, the seed polymer is used in quantities of 1 to 20% by weight, preferably, 1-15% by weight, relative to the quantity of the monomer.
Cross-linking agents are used in a proportion relative to the quantity of the monomer of 0.1 to 60% by weight, depending on the degree of cross-linking 10 desired. Advantageously, 60% divinylbenzene in ethylvinylbenzene is used.
The components introduced Into the aqueous medium diffuse into the seed polymer. The seed polymer particles are thus present in a swollen state in the monomer. Polymerization then takes place in the seed polymer particles.
Polymerization is carried out at a temperature up to a maximum of 100C, 15 preferably at 60 to 90C. The time of the polymerization generally varies up to 48 h and is preferably between 24 and 48 h.
The process according to the invention thus yields in a simple manner monodispersed polymer beads with a particle diameter of 0.5 to 50 llm, preferably 1 to 20 llm and particularly preferably from I to 10 ym. The polymer particles 20 may be cross-linked or not cross-linked. Their porosi~y may be varied by the conditions of the process. -The polymer beads that may be obtained by the process of the invention -therefore have a wide field of applicarion. They may be used in particular for the immobilization of proteins (enzymes) and cells (for whole cells), as carriers 25 of catalysts (biocatalysts, organic or inorganic catalysts) or as carriers in peptide synthesis. I~or peptide synthesis in particular, polymer beads forming a gel are used, i.e., lightly cross-linked polymer beads with a degree of cross-linking of I to 510, preferably I to 2%.
The monodispersed polymer beads according to the invention are especially -30 suitable for use in chromatography. They are employed specifically in high pressure liquid chromatography (HPLC~, ion exchange chromatography and exclusion chromatography.
In the drawings: ~ -E7ig. I shows a HPLC chromatogram obtained with polymer beads according 35 to the invention as the s~ationary phase.

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.
:

-8- 132~310 Fig. 2 shows an HPLC chromatogram obtained with commercially available polymer beads as the stationary phase.
Pig. 3 shows another HPLC chromatogram obtained with polymer beads according to the invention as the stationary phase.
The following examples are intended to explain the invention without limiting it.

In 480 ml ethanol, 384 azoisobutyronitrile (AIBN) and 2.4 g polyvinylpyrro-lidinone (PVP) are dissolved. To the solution, 30 ml styrene and 30 ml dodecyl-10 chloride are added. The polymerization temperature i6 60C. After a reaction time of 24 h, a monodispersed polystyrene latex with a grain size of 1.8 ym, containing about 12% dodecylchloride, is obtained.
Solids content: I ml polystyrene/10 ml solution - 635 mg latex.

In 24 ml ethanol, 12.2 mg AIBN and 120 mg PVP are dissolved. 1.5 ml styrene and 2.4 ml dodecylchloride are added and heated to 60C. After 16 h, another solution of 2 ml styrene and 50 mg AIBN in 2 ml ethanol is added. After another 5 h of reaction time, 50 mg PVP in 5 ml ethanol are added and polymerized for another 24 h. A monodispersed polystyrene with a grain size 20 of 2.5 llm is obtained. The seed polymer contains 12% dodecylchloride.

10 ml of the seed solution prepared in Example 2 are centrifuged for 20 min at 2000 rpm and the organic phase decanted. To the residue an aqueous emul3ion of 250 mg alkylsulfonic acid, 0.4 ml divinylbenzene, 3 ml chloromethyl-25 styrene, 17 ml styrene and 250 mg BPO (benzoylperoxide) in 180 ml water, are added. The mixture is agitated at 120 rpm for 24 h at room temperature and subsequently for another 48 h at 72C. The monodispersed copolymers obtained in this manner have a diameter of 7.8 ym and a chlorine content of 4~ = 1.14 meq Cl/g.
30 EXAMP~E 4 250 mg emulsifier (alkylsulfonic acid) are dissolved in 165 ml water and 3.3 ml chloromethylstyrene, 4 ml divinylbenzene, 14.5 ml styrene and 250 mg BPO are emulsified therein. From 30 ml of a solution of the latex prepared in Example 1, the solids are separated as in Example 3, and mixed with the 35 aqueous emulsion of the monomers.

9 1 32~31 ~

The mixture is agitated for 18 h at room temperature at 100 rpm and then the temperature is raised to 72C. After 48 h, a monodispersed product with a chlorine content of 4.47% = 1.27 meq Cl/g is obtained. The grain size is 4.2 ~m.

In 48 ml ethanol, 38.4 g AIBN and 240 mg PVP are dissolved. 3 ml styrene and 3 ml nonylbenzene are added, flushed with argon and heated in 24 h to 72C.
The monodispersed polystyrene latex has a grain size of 2 ,um.

Prom 10 ml of the seed solution prepared in Example 5, the polymer component is obtained by centrifuging. An emulsion is prepared, which contains 16 ml water, 110 mg alkylsulfonic acid, 8.5 ml styrene, 2.6 ml divinylbenzene/-ethylvinylbenzene, 2.2 ml chloromethylstyrene and 160 mg BPO. The seed -;
polymer is mixed with the monomer emulsion, agitated for 24 h at room 15 temperature and heated under an inert gas to 75C. After a reaction time of 48 h a monodispersed carrier with a grain size of 5.9 ym is obtained. The chlorine content is 1.25 meq/g.

A monomer emulsion is prepared, containing 83 mg BPO, 1.1 ml chloro-20 methylstyrene, 1.3 ml divinylbenzene/ethylvinylbenzene, 4.2 ml styrene, 8.3 ml water and 83 mg alkylsulfonic acid. Further processing is similar to Example 6. A monodispersed carrier with a grain size of 4.5 llm is obtained. Chlorine content: 1.26 meq/g. -In 100 ml methanol, 500 mg PVP and 80 mg AIBN are dissolved. To the solution, 6.25 ml styrene and 6.25 ml dodecyibenzene are added, flushed with argon and heated under agitation at 48 h to 62C. A monodispersed latex with a grain size of 2.5 l1m is obtained. The latex contains 46% dodecylbenzene. -The latex is isolated by centrifuging and mixed with a monomer emulsion 30 of 940 mg emulslfier K-30, 62.5 ml water, 10.8 ml divinylbenzene/ethylvinyl-benzene (60/40), 48.2 ml styrene and 800 mg benzoylperoxide. The ~ emulsion is homogenized in an ultrasonic bath. Diffusion is effected for 2 h at room temperature, the temperature raised to 80C and this temperature maintained -for 48 h. Polystyrene beads with a grain size of 8.5 ym are obtained in this -35 manner.

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132~31~

In 100 ml ethanol, 500 mg PVP and 80 mg AIBN are dissolved. The solution is mixed with 7.2 ml styrene and 6.25 ml stearylalcohol, flushed with argon and polymerized for 48 h at 75C. The latex has a grain size of 1 ~m.
The latex is then treated as in Example 8 and polystyrene beads with a grain size of 2.5 llm are obtained.

In 100 ml t-butanol, 500 mg PVP and 80 mg AIBN are dissolved. The solution is mixed with 6.25 ml styrene and 3.3 g triphenylmethane, flushed with argon and heated under agitation to 77C. The monodispersed latex has a diameter of 1.5 llm.
The latex is treated as in Example 9 and polystyrene beads with a grain size of 4.8 llm are obtained.

.. .. _ To a solution of 100 ml t-butanol, 500 mg PVP and 80 mg AIBN, 12.5 ml dodecylbenzene and 6.25 ml styrene are added. After flushing with argon, the mixture is heated to 75C and the temperature maintained for 48 h. The seed has a grain size of 4 ym and a dodecylbenzene content of 50%.
The latex is then treated as in Example 9 and polystyrene beads with a -20 grain size of 9.2 ym are obtained.

. . .
To a solution of 25 ml ethanol, Z0 mg AIBN, 125 mg polyvinyl alcohol (PVA), 5 ml THF and 1.56 ml styrene are added. The mixture is heated to 70C
for 40 h and a 5 ym latex is obtained.
25 E~XAl~PLE 13 To a solution consisting of 60 ml ethanol, 6.4 ml water, 300 mg PVP and ~ -48 mg AIBN, 7.5 ml styrene and the same quantity of dodecylchloride are added.
The mixture is heated to 74C for 48 h. A latex of 750 nm is produced in this manner.
The latex is treated as in Example 9 and polystyrene beads with a grain size of 2.2 llm are obtained.

600 ml ethanol are mixed with 3 g PVP and 480 mg AIBN. To the clear solution, 75 ml dodecylchloride and 75 ml styrene are added. The mixture is 35 heated to 72C for 48 h.

The grain size of the monodispersed latex is 2.2 llm.
EXAMPLE l5 Prom 120 ml of the latex suspension described in Example 14, the poly-styrene latex is separated by centrifuge 19.9 g latex).
The seed latex is mixed with a finely divided emulsion consisting of 160 ml water, 2.2 g alkylsulfonic acid (K-30), l6 ml divinylbenzene/ethylvinylbenzene (60/40), 64 ml styrene, 80 ml heptane and l g BPO. The emulsion is produced by ultrasonic treatment.
Diffusion is effected for 30 min at room temperature under agitation, the suspension is diluted with 600 ml water, flushed with argon and heated to 80C for 45 h.
A microporous, cross-linked polymer with a grain size of 5.5 llm is obtained.
EXAMPLE l6 A seed latex is prepared as in Example l5. The seed latex is mixed with a finely divided emulsion, consisting of l60 ml water, 2 g alltylsulfonic acid (K-30), 128 ml divinylbenzene/ethylvinylbenzene (60/40), 32 ml styrene and 2.0 g benzoylperoxide. The emulsion is produced by ultrasonic treatment.
Diffusion is effected in 45 min at room temperature, the suspension diluted with 600 ml water, flushed with argon and heated to 80C for 45 h. A
homogeneously cross-linked polymer with a grain size of 4.5 ~Im is obtained.
EXAMPLE l7 In the following experiments, polymer beads obtained according to the invention (MOPS 33/4; polystyrene/40% divinylbenzene; prepared according to ~xample 16) are used as the stationary phase in HPLC chromatography. As a comparison, two commercial products are also used as the stationary phase, i.e. ACT-I (commercial product of the Interaction Co.; polystyrene modified with Clg-alkyl) and PRP (commercial polystyrene-reverse phase). The phases were used under the following conditions:

30 Mobile phase: acetonitrile/water 85/15 Grain size: 4.5 ym Column: 60 x 4.5 Plow: l ml/min and 2 ml/min, respectively Pressure: 32 bar -, : ~ ' -12- 132~i3:10 ACP-l an_PRP
Mobile phase: 85~/o methanol Flow: 6 cm/min Column: 125 x 4.6 Detection was effected in all cases at 254 nm.
The following product mixture was separated.
N,N-diethylaniline 2 N,N-dimethylaniline 3 N-methylaniline 4 aniline The chromatograms obtained are compiled in Flg. 1 and Fig. 2. It is seen that the phases according to the invention (Fig. 1) have a significantly higher separation efficiency, as in spite of an appreciably shorter column they yleld good separation. In addition, the use of the phases according to the invention 15 clearly improves the peak symmetry, while the phases of the state of the art show pronounced tailing.
Flg. 3 shows a chromatogram obtained with the use of the same phase according to the invention in the separation of the following product mixture:
toluene 2 ethylbenzene -~
3 propylbenzene -4 butylbenzene

Claims

1. A process for preparing monodispersed polymer beads having a diameter of 0.5 to 50 µm, comprising, in a first stage, preparing a seed polymer by polymerizing a monomer in at least one organic solvent, yielding a monodispersed seed, in the presence of a polymerization initiator and triphenylmethane or a compound having the formula R-X, wherein R is a saturated or unsaturated, linear or branched aliphatic radical with more than 6 carbon atoms, and X is selected from the group consisting of a hydrogen or halogen atom, a hydroxy group, a C1-C6 alkoxy group, an amino group, a C1-C6 alkylamino group, a di-C1-C6 alkylamino group, a phenyl group or a phenyl group optionally substituted with a C1-C4 alkyl group, an optionally polyoxyethylenated hydroxy group, a C1-C4 alkoxy group, an amino group or a sulfonic acid group;
separating the seed polymer obtained; and in a second stage, emulsion polymerizing a monomer in the presence of the seed polymer, an emulsifier and a polymerization initiator, in an aqueous medium.

2. A process according to claim 1, wherein an alcohol is used as the organic solvent.

3. A process according to claim 2 wherein the alcohol is a C1-C4 alcohol.

4. A process according to claim 3, wherein the alcohol is methanol, ethanol or t-butanol.

5. A process according to any one of claims 1 to 4, wherein the organic solvent is used in a mixture with water, tetrahydrofuran or dioxan.

6. A process according to claim 1, wherein, in the first stage, an R-X compound is used.

7. A process according to claim 6 wherein R is a C7-C20 alkyl radical.

8. A process according to claim 7 wherein R is a C9-C18 alkyl radical.

9. A process according to claim 6, wherein X is selected from the group consisting of a halogen atom or a phenyl group.

10. A process according to claim 6, wherein the R-X compound is nonylbenzene or dodecylchloride.

11. A process according to any one of claims 1 to 4 or 6 to 10, wherein cross-linking agents, which may be the same or different, are present in both the first stage and the second stage.

12. A process according to any one of claims 1 to 4 or 6 to 10 wherein said second stage is effected in contact with a cross-linking agent.

13. A process according to claim 12 wherein the cross-linking agent is divinylbenzene, a bifunctional acrylic compound or functionalized styrene or a mixture thereof.

14. A process according to claim 13, wherein the functionalized styrene is chloromethylated styrene.

15. A process according to claim 1, wherein, in the second stage an inert, nonpolymerizing compound is added.

16. Monodispersed polymer beads obtained by a process according to any one of claims 1 to 4, 6 to 10, or 13 to 15.

17. Monodispersed polymer beads obtained by a process according to claim 5.

18. Monodispersed polymer beads obtained by a process according to claim 11.

19. Monodispersed polymer beads obtained by a process according to claim 12.

20. A use of monodispersed polymer beads according to claim 16 as a carrier in the immobillzation of a protein or cell, a carrier for a catalyst, in peptide synthesis or in chromatography.

21. A use of monodispersed polymer beads according to claim 17, 18 or 19 as a carrier in the immobilization of a protein or cell, a carrier for a catalyst, in peptide synthesis or in chromatography.