Process for the preparation of monodisperse polymer particles

1. A process for the preparation of monodisperse polymer particles comprising:

1) preparing monodisperse swellable seed particles by emulsion polymerization, wherein an anionic surfactant is employed as emulsifier under substantially oxygen-free conditions;

wherein said seed particles are non-oligomeric:

(a1) contacting said non-oligomeric seed particles with an aqueous dispersion comprising an organic compound with a molecular weight below 5000 Dalton and a water solubility at 25° C. of less than 10 −2 g/L; the anionic surfactant; and optionally an organic solvent in which said organic compound is soluble;

(b1) allowing said organic compound to diffuse into said non-oligomeric seed particles; and

(c1) contacting the aqueous dispersion of non-oligomeric seed particles with a monomer which is at least ten times more water soluble than said organic compound; or

wherein said seed particles are oligomeric:

(a2) contacting said oligomeric seed particles with an aqueous dispersion comprising the anionic surfactant; and

(b2) contacting the aqueous dispersion of oligomeric seed particles with a monomer;

2) if required adding a water-soluble steric stabilizer, if required adding a porogen, and if required adding a polymerization initiator; and

3) initiating polymerization of said monomer in an aqueous dispersion containing a steric stabilizer in continuous phase.

2. A process of claim 1 wherein in step 1) the oxygen content of the aqueous phase is between 0 and 5 ppm or is between 0 and 3 ppm.

3. A process of claim 2 wherein the oxygen content is between 0 and 2 ppm or between 0 and 1 ppm.

4. A process of claim 1 wherein said monomer comprises at least 30% by weight divinyl benzene.

5. A process of claim 1 wherein said organic compound is dioctanoyl peroxide.

6. A process of claim 1 , wherein the organic compound is a polymerization initiator.

7. A process of claim 1 wherein the monomer is an amino-functionalized monomer and a polymerization initiator is added after said seed particles have been swollen, wherein the organic compound is not a polymerization initiator.

8. A process of claim 7 , wherein two or more monomers are used and at least one monomer is an amino functionalized monomer.

9. A process of claim 7 wherein the organic compound which is not a polymerization initiator is dioctyladipate.

10. A process of claim 7 wherein said polymerization initiator is 2,2′-azobis-(2-methylbutyronitrile).

11. A process of claim 1 wherein the resulting monodisperse polymer particles are further swollen and polymerized to obtain larger particles.

12. A process of claim 1 wherein the swollen particles produced have sizes from 1 to 25 μm and polyvinylpyrrolidone is the steric stabilizer.

13. A process of claim 1 wherein the swollen particles produced have sizes above 15 μm and cellulose ether is the steric stabilizer.

14. A process of claim 1 wherein the swollen particles produced have a mode diameter from 5 to 15 μm and cellulose ether is the steric stabilizer.

15. A process of claim 1 wherein the swollen particles have particle sizes below 5 μm, preferably below 2 μm, and said anionic surfactant is a C 8-16 alkyl sulphate or sulphonate, preferably a dodecyl sulphate.

16. A process of claim 1 wherein said anionic surfactant is sodium dodecyl sulphate.

17. A process of claim 1 wherein said monodisperse polymer particles are subsequently coated, impregnated or derivatised.

18. A process of claim 1 wherein said swellable seed particles have a mode particle diameter in the range of 0.2 to 1 μm.