Monodisperse submicron polymer particles

Abstract

This invention relates to monodisperse cross-linked polymer particles, comprising particles with a substantially smooth outer surface and an average diameter of less than 1 μm, wherein the particles are solid or porous, and wherein the coefficient of variation (CV) % of the particles, when measured by CPS disk centrifugation analysis, is less than 15%. These monodisperse cross-linked polymer particles may comprise magnetic material and are useful in various application. This invention also relates to monodisperse polymer particles for use as seed particles in the Ugelstad process.

1 . Monodisperse cross-linked polymer particles having the following characteristics:
 a substantially smooth outer surface   a z-average diameter of less than 1 μm   the particles are porous   a coefficient of variation (CV) %, when measured by CPS disk centrifugation analysis, of less than 15%.   
     
     
         2 . The polymer particles of  claim 1 , wherein the polymer particles have a z-average diameter of no more than 900 nm, optionally no more than 700 nm, further optionally no more than 600 nm, still further optionally no more than 500 nm. 
     
     
         3 . The polymer particles of  claim 1  or  claim 2 , wherein the polymer particles have a z-average diameter of at least 200 nm, optionally at least 300 nm, e.g. at least 400 nm. 
     
     
         4 . The polymer particles of any preceding claim, wherein the coefficient of variation (CV) % of the particles, when measured by CPS disc centrifugation analysis, is less than 12%, optionally less than 10%, further optionally less than 5%. 
     
     
         5 . The polymer particles of any preceding claim, wherein the polymer particles constitute a first population of particles and have a swellability of not more than the swellability of a second population of polymer particles, wherein the second population of particles are reference particles produced by a known Ugelstad process and made of a comparable polymer to the first population, wherein the amount of cross-linker monomer used in the suspension polymerisation stage of the known Ugelstad process is >25% by weight of the total weight of monomers used in the suspension polymerisation stage, optionally wherein the first population of polymer particles are polystyrenic particles and the monomers used in the suspension polymerisation stage in the preparation of the reference particles were styrene and, as a crosslinker monomer, divinylbenzene, the divinylbenzene being in an amount of >25% by weight of the total of styrene plus divinylbenzene. 
     
     
         6 . The polymer particles of  claim 5 , wherein the amount of the cross-linker monomer used in said suspension polymerisation stage is 30-60%, optionally 40-50%. 
     
     
         7 . The polymer particles of any preceding claim, wherein the particles have a specific surface area of from 300 to 700 m 2 /g when measured by gas adsorption analysis. 
     
     
         8 . (canceled) 
     
     
         9 . The polymer particles of any of  claims 1  to  6 , further comprising a magnetic material, optionally wherein the magnetic material is a metal oxide or alloy e.g. ferrimagnetic or superparamagnetic iron oxide crystals, further optionally wherein the magnetic material is substantially located in pores of the polymeric material. 
     
     
         10 . The polymer particles of any of  claims 1  to  6 , further comprising a superparamagnetic material, optionally wherein the superparamagnetic material is a metal oxide or alloy, further optionally wherein the superparamagnetic material is substantially located in pores of the polymeric material. 
     
     
         11 . The polymer particles of  claim 10 , wherein the superparamagnetic material comprises a ferrite or coated iron based or iron-nickel alloy nanoparticles, optionally wherein the superparamagnetic material comprises a ferrite selected from magnetite, maghemite, or magnetite or maghemite further optionally where the iron is substituted with up to 5 mol % of Al, Mn, Ni, Cu, Co, Zn, Ca, Ge, Te, Ti or Sn, further optionally wherein the superparamagnetic material comprises magnetite or maghemite in either case substituted with up to 5 mol % manganese. 
     
     
         12 . The polymer particles of any preceding claim, wherein the outer surface further comprises a coating and/or a functional group, optionally wherein the functional group is selected from carboxylic acid, amine, tosyl, epoxy and hydroxyl. 
     
     
         13 . The polymer particles of any preceding claim, wherein the polymer comprises a cross-linked polymer selected from polymers and copolymers of one or more of the following monomeric materials: an acrylic monomer, e.g. methacrylate, and a styrenic monomer, optionally wherein the polymer is polystyrene. 
     
     
         14 . The polymer particles of  claim 10  or  claim 11  which comprise:
 a matrix polymer which is selected from polymers of styrenic monomers and polymers of acrylic monomers and optionally is a polystyrene; 
 magnetic crystals; 
 a polymer coating which is optionally formed from at least one epoxide compound. 
 
     
     
         15 - 23 . (canceled) 
     
     
         24 . Monodisperse particles of any preceding claim which have a silica coating. 
     
     
         25 . Monodisperse particles of any preceding claim, wherein the polymer particles do not comprise methylene bridged phenyl groups. 
     
     
         26 - 32 . (canceled) 
     
     
         33 . A process for the preparation of monodisperse particles for use as Ugelstad seed particles, the process comprising an emulsion polymerisation process comprising:
 forming an aqueous dispersion comprising a vinylic monomer and a water soluble polymerisation initiator; and   agitating until the commencement of particle nucleation;   
       characterised in that:
 the aqueous dispersion comprises a surfactant and a chain transfer agent is added after the commencement of particle nucleation, such that the polymerisation forms monodisperse seed particles having a z-average diameter of from 50 nm to 200 nm and, when measured by gel permeation chromatography, the polymer has a mean weight average molecular weight of more than 1,000 and less than 70,000. 
 
     
     
         34 . The process of  claim 33 , wherein the surfactant is present below its critical micelle concentration. 
     
     
         35 . The process of  claim 33 , wherein the surfactant is present in a concentration of not more than 2.5 g/L, optionally not more than 2 g/L, further optionally not more than 1.7 g/L, still further optionally not more than 1.5 g/L. 
     
     
         36 . (canceled) 
     
     
         37 . The process of any of  claims 33  to  35 , wherein the surfactant is sodium dodecyl sulfate. 
     
     
         38 . (canceled) 
     
     
         39 . The process of any of  claims 33  to  37  or  claim 37 , wherein the vinylic monomer is an acrylic monomer, a styrene monomer or a methacrylate monomer, optionally wherein the monomer comprises styrene. 
     
     
         40 . The process of any of  claims 33  to  35 , or  claim 37  or  claim 39 , wherein the chain transfer agent comprises a haloalkane, optionally bromotrichloromethane. 
     
     
         41 . The process of any of  claims 33  to  35  or  claim 37  or  claims 39  to  40 , wherein the chain transfer agent comprises an alkymercaptan, optionally butyl mercaptan, isooctyl 3-mercaptopropionate or octylmercaptan. 
     
     
         42 . The process of any of  claims 33  to  35  or  claim 37  or  claims 39  to  41 , wherein the addition of chain transfer agent starts about 5 to 15 minutes after the commencement of visible particle nucleation, optionally about 10 minutes after the commencement of visible particle nucleation. 
     
     
         43 - 46 . (canceled) 
     
     
         47 . The process of any of  claims 33  to  35  or  claim 37  or  claims 39  to  42 , further comprising subjecting the monodisperse seed particles to an Ugelstad process wherein the percentage by weight of cross-linker monomer included in the total monomer used in the suspension polymerisation stage of the Ugelstad process (the final polymerisation stage where there are plural polymerisation stages) is >25% wt cross-linker, to form submicron monodisperse particles and a z-average diameter of less than 1 μm, optionally wherein the submicron monodisperse particles are porous particles having a smooth outer surface, e.g. wherein the submicron monodisperse particles have a specific surface area of from 300 to 700 m 2 /g when measured by gas adsorption analysis. 
     
     
         48 . The process of  claim 47 , wherein the Ugelstad process comprises:
 (i) forming an aqueous dispersion comprising
 the monodisperse seed particles, 
 finely divided droplets comprising an organic compound of molecular weight below 5,000 and water solubility at 25° C. of less than 10 −2  g/L, and 
 an organic solvent in which the organic compound is soluble, the organic solvent being optional when the polymer forming the seed particles has an average molecular weight which corresponds to up to 50 monomer units; 
   (ii) allowing the organic compound to diffuse into the monodisperse seed particles, causing the seed particles to become activated;   (iii) removing the organic solvent, where present from inside the seed particles, and contacting the activated seed particle with an aqueous vehicle containing a monomer that is at least 10 times more soluble in water than the organic compound, and a crosslinker;   (iv) allowing the monomer to diffuse into the activated seed particles to form an aqueous dispersion of swollen seed particles; and   (v) initiating polymerisation of the monomer in the swollen seed particles.   
     
     
         49 - 70 . (canceled)