A continuous, liquid phase method for producing a polymer having a predetermined number of conjugated diene units per molecule in which (a) a first monomer stream is contacted with an organo-lithium compound, in a manner to intimately mix increments of monomer, containing the predetermined number of moles of conjugated diene, with each mole of organo-lithium and continuously mix and move the mixture through a first, elongated reaction zone to react the predetermined number of moles of conjugated diene with one mole of organo-lithium, (b) mixing the effluent from (a) with an alkyl-substituted aromatic hydrocarbon, an organo-alkali metal of potassium, rubidium or cesium and a tertiary amine to form a complex-initiator of the aromatic hydrocarbon, the alkali metal and the amine, (c) mixing the effluent from (b) with a second stream of monomer, in a manner to intimately mix increments of monomer, containing the predetermined number of moles of conjugated diene, with each mole of complex-initiator and continuously mix and move the mixture through a second, elongated reaction zone and (d) mixing the effluent of (c) to produce to form a polymer comprising the predetermined number of conjugated diene units and the aromatic hydrocarbon. Preferably, a portion of the effluent from (d), containing complex-initiator, is cooled and recycled to (c) to cool the reaction and supply complex-initiator.