Hairy polymeric nanoparticles
This invention discloses a process for synthesizing a hairy polymer particle which comprises the steps of (1) polymerizing a vinyl aromatic monomer by emulsion polymerization in an aqueous medium to produce core particles, (2) recovering the core particles from the aqueous medium, (3) dispersing the core particles in an organic solvent, (4) adding an organo-lithium compound to the dried core particles in the organic solvent to produce the hairless core initiator, and (5) utilizing the hairless core initiator to initiate the anionic polymerization of a conjugated diolefin monomer in an organic solvent to produce a solution of the hairy polymer particles. The hairy polymer nanoparticles can then be recovered from the organic solvent. These hairy polymer particles are comprised of (1) a core which is comprised of a polymer of a vinyl aromatic monomer and (2) hairs which are polymer chains of a conjugated diolefin monomer, wherein the hairs are covalently bonded to the core. The core is typically spherical in shape, has a diameter of less than 1000 nm, and is comprised of a crosslinked polymer of a vinyl aromatic monomer. The hairy polymer particles of this invention are useful as fillers in rubber compositions used in making articles of manufacture, such as tires, hoses, power transmission belts, windshield wiper blades, and the like.
1. A process for synthesizing a hairless core initiator which comprises the steps of (1) polymerizing a vinyl aromatic monomer by emulsion polymerization in an aqueous medium to produce core particles, (2) recovering the core particles from the aqueous medium, (3) dispersing the core particles in an organic solvent, and (4) adding an organo-lithium compound to the core particles in the organic solvent to produce the hairless core initiator.
2. A process as specified in claim 1 wherein the core particles are recovered from the aqueous medium by displacing the aqueous medium with a liquid solvent that is soluble in water and organic hydrocarbon solvents, and subsequently displacing the liquid solvent that is soluble in water and organic solvents with an organic solvent.
3. A process as specified in claim 1 which further comprises drying the core particles recovered in step (2) and subsequently dispersing the dried core particles in the organic solvent in step (3).
4. A process as specified in claim 1 wherein divinylbenzene is copolymerized with styrene in step (1) to produce the core particle.
5. A process as specified in claim 1 wherein the core particles are dried after being recovered from the aqueous medium.
6. A process as specified in claim 1 wherein the vinyl aromatic monomer contains from 8 to 20 carbon atoms.
7. A process as specified in claim 1 wherein the vinyl aromatic monomer contains from 8 to 14 carbon atoms.
8. A process as specified in claim 1 wherein the vinyl aromatic monomer is styrene.
9. A process as specified in claim 1 wherein the vinyl aromatic monomer is α-methylstyrene.
10. A process as specified in claim 1 wherein the organo-lithium compound is of the formula R(Li) x , wherein R represents a hydrocarbyl radical that contains from 1 to 20 carbon atoms.
11. A process as specified in claim 10 wherein the hydrocarbyl radical contains from 1 to 4 carbon atoms.
12. A process as specified in claim 1 wherein the organo-lithium compound is selected from the group consisting of ethyllithium, n-propyllithium, isopropyllithium, n-butyllithium, isobutyllithium, t-butyllithium, n-butyllithium, sec-butyllithium, tert-butyllithium, phenyllithium, p-tolyllithium, 4-phenylbutyl lithium, 4-butylcyclohexyl lithium, and 4-cyclohexylbutyl lithium.
13. A process as specified in claim 2 wherein the liquid solvent is selected from the group consisting of acetone, ethanol, and isopropyl alcohol.
14. A process as specified in claim 3 wherein the core particles are dried by heating the core particles in a stream of warm dry air.
15. A process as specified in claim 14 wherein the emulsion polymerization of the vinyl aromatic monomer in the aqueous medium to produce the core particles is initiated with a free radical initiator.
16. A process as specified in claim 1 wherein the vinyl aromatic monomer is copolymerized with a crosslinking monomer to produce the core particles.
17. A process as specified in claim 16 wherein the crosslinking monomer is present at a level which is within the range of 10 percent to 30 percent, based upon the weight of the core particles.
18. A process as specified in claim 14 wherein the organo-lithium compound is n-butyllithium.
19. A process as specified in claim 13 wherein the organic solvent is an aliphatic hydrocarbon.
20. A process as specified in claim 16 wherein the crosslinking monomer is selected from the group consisting of divinyl benzene and diisopropenylbenzene.