Abstract: This invention discloses a process for synthesizing a styrene-butadiene polymer, which is particularly useful for modifying asphalt to improve force ductility, elastic recovery, toughness and tenacity, by a process which comprises the steps of: (1) continuously charging 1,3-butadiene monomer, an organo lithium compound, a polar modifier and an organic solvent into a first polymerization zone, (2) allowing the 1,3-butadiene monomer to polymerize in said first polymerization zone to a conversion of at least about 90 percent to produce a living polymer solution which is comprised of said organic solvent and living polybutadiene chains having a number average molecular weight which is within the range of about 20,000 to about 60,000, (3) continuously withdrawing said living polymer solution from said first reaction zone, (4) continuously charging styrene monomer, divinyl benzene and the living polymer solution being withdrawn from the first polymerization zone into a second polymerization zone, (5) allowing the s