A method for performing a one-batch synthesis of a blend of nanoparticles and liquid polymer includes polymerizing a first monomer and optionally a second monomer in a hydrocarbon solvent to form the liquid polymer. The polymerization is terminated before completion with a quenching agent. Then a charge of polymerization initiator, and a mixture of multiple-vinyl aromatic monomer and mono-vinyl aromatic monomer are added. This causes further polymerization whereby nanoparticles are formed in situ having a core including the multiple-vinyl aromatic monomer, and a shell including the first monomer or the first monomer and the second monomer. Liquid polymer/nanoparticle blends resulting from the method and rubber compositions incorporating the blends are also disclosed.