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.