Well defined, highly crosslinked nanoparticles and method for making same

Abstract

A method is provided for making nanoparticles, including the steps of: combining a hydrocarbon solvent and an aprotic, polar co-solvent, a mono-vinyl aromatic monomer, polymerization initiator, a solution stabilizer, and a first charge of a cross-linking agent. Subsequently, a second charge of cross-linking agent is added. The nanoparticles have an average diameter of 5 nanometers to about 10,000 nanometers. Spherical nanoparticles are also provided that include a cross-linking agent comprising 30% to 60% by weight of the combined weight of a mono-vinyl aromatic species and the cross-linking agent. The spherical nanoparticles also meet the following equation: 0.90≦( D 1/ D 2)≦1.1 wherein D1 is a first diameter of a nanoparticle and D2 is a second diameter of the nanoparticle, and D1 and D2 intersect at right angles.

It is claimed: 
     
         1 . Spherical cross-linked nanoparticles comprising:
 a core formed from a polymeric seed that includes a mono-vinyl aromatic core species cross-linked with a cross-linking agent, the core having an average diameter of 5 nanometers to 10,000 nanometers;   wherein the mono-vinyl aromatic core species comprises polymeric chains radiating from a center of the core;   wherein the spherical cross-linked nanoparticles meet the following equation:
   0.90≦( D 1 /D 2)≦1.1
 
   wherein D1 is a first diameter of the spherical cross-linked nanoparticles and D2 is a second diameter of the spherical cross-linked nanoparticles, and D1 and D2 intersect at right angles.   
     
     
         2 . The spherical cross-linked nanoparticles of  claim 1 , wherein the polymer chains form a surface of the core and the surface of the core comprises living ends of the polymer chains. 
     
     
         3 . The spherical cross-linked nanoparticles of  claim 2 , further comprising a shell layer bonded to the living ends of the surface, the shell layer comprising a fixed formal charge group. 
     
     
         4 . The spherical cross-linked nanoparticles of  claim 2 , further comprising a shell layer bonded to the living ends of the surface, wherein the shell layer is about 1 nm to about 100 nm in thickness. 
     
     
         5 . The spherical cross-linked nanoparticles of  claim 2 , wherein the surface of the nanoparticle comprises terminated living ends. 
     
     
         6 . The spherical cross-linked nanoparticles of  claim 1 , wherein the cross-linking agent comprises 30% to 60% by weight of the combined weight of the mono-vinyl aromatic species and the cross-linking agent. 
     
     
         7 . Cross-linked nanoparticles comprising:
 a core formed from a polymeric seed that includes a mono-vinyl aromatic core species cross-linked with a cross-linking agent, the core having an average diameter of 5 nanometers to 10,000 nanometers;   wherein the mono-vinyl aromatic core species comprises polymeric chains radiating from a center of the core;   wherein the weight ratio of mono-vinyl monomer species to total cross-linking agent ranges from about 30:70 to about 90:10;   wherein the nanoparticles meet the following equation:
   0.90≦( D 1 /D 2)≦1.1
 
   wherein D1 is a first diameter of the cross-linked nanoparticles and D2 is a second diameter of the spherical cross-linked nanoparticles, and D1 and D2 intersect at right angles.   
     
     
         8 . The spherical cross-linked nanoparticles of  claim 1 , with the proviso that the spherical cross-linked nanoparticles are not made by emulsion polymerization. 
     
     
         9 . The spherical cross-linked nanoparticles of  claim 1 , wherein the nanoparticles are made by the process comprising:
 combining a hydrocarbon solvent and an aprotic, polar co-solvent, a mono-vinyl aromatic monomer, polymerization initiator, a solution stabilizer, and a first charge of a cross-linking agent;   adding a second charge of the cross-linking agent or a charge of another cross-linking agent;   wherein the spherical cross-linked nanoparticles have an average diameter of 5 nanometers to about 10,000 nanometers;   wherein a volume ratio of hydrocarbon solvent to aprotic, polar co-solvent ranges from about 99.9:0.1 to about 70:30.   
     
     
         10 . The spherical cross-linked nanoparticles of  claim 3 , wherein the fixed formal charge group is selected from at least one of the group consisting of: succinic anhydride, imidazole, pyridines, N,N-dimethylaminostyrene, N,N-diethylaminostyrene, pyridine silane, vinyl pyridine and derivates of these, quaternary ammonium compounds, quaternary phosphonium compounds, and quaternary sulfonium compounds. 
     
     
         11 . The spherical cross-linked nanoparticles of  claim 1 , wherein the spherical cross-linked nanoparticles comprise a first group of spherical cross-linked nanoparticles and a second group of spherical cross-linked nanoparticles, wherein the first and second group have a difference in charge of about 50 μC/g or greater. 
     
     
         12 . The spherical cross-linked nanoparticles of  claim 1 , wherein for a given collection of the spherical cross-linked nanoparticles measured by an SEM, 90% to 100% of the nanoparticle group meets the following equation:
   0.90≦( D 1 /D 2)≦1.1
   wherein D1 is a first diameter of the spherical cross-linked nanoparticles and D2 is a second diameter of the spherical cross-linked nanoparticles, and D1 and D2 intersect at right angles.   
     
     
         13 . The spherical cross-linked nanoparticles of  claim 1 , wherein the spherical cross-linked nanoparticles comprise a shell bonded to the core, the shell including polymerized monomers, wherein the core has a higher Tg than the shell. 
     
     
         14 . The cross-linked nanoparticles of  claim 7 , further comprising a shell layer bonded to the surface of the core, the shell layer comprising a fixed formal charge group. 
     
     
         15 . The cross-linked nanoparticles of  claim 14 , wherein the fixed formal charge group is selected from at least one of the group consisting of: succinic anhydride, imidazole, pyridines, N,N-dimethylaminostyrene, N,N-diethylaminostyrene, pyridine silane, vinyl pyridine and derivates of these, quaternary ammonium compounds, quaternary phosphonium compounds, and quaternary sulfonium compounds. 
     
     
         16 . The cross-linked nanoparticles of  claim 7 , wherein the cross-linked nanoparticles comprise a first group of cross-linked nanoparticles and a second group of cross-linked nanoparticles, wherein the first and second group have a difference in charge of about 50 μC/g or greater. 
     
     
         17 . The cross-linked nanoparticles of  claim 7 , wherein for a given collection of the cross-linked nanoparticles measured by an SEM, 90% to 100% of the nanoparticle group meets the following equation:
   0.90≦( D 1 /D 2)≦1.1
   wherein D1 is a first diameter of the cross-linked nanoparticles and D2 is a second diameter of the cross-linked nanoparticles, and D1 and D2 intersect at right angles.   
     
     
         18 . The cross-linked nanoparticles of  claim 7 , wherein the cross-linked nanoparticles comprise a shell bonded to the core, the shell including polymerized monomers, wherein the core has a higher Tg than the shell. 
     
     
         19 . The cross-linked nanoparticles of  claim 16 , wherein the first group of cross-linked nanoparticles has a positive charge and the second group of cross-linked nanoparticles has a negative charge. 
     
     
         20 . The spherical cross-linked nanoparticles of  claim 11 , wherein the first group of spherical cross-linked nanoparticles has a positive charge and the second group of spherical cross-linked nanoparticles has a negative charge.