Diene polymers having reduced hysteresis and improved raw viscosity incorporating primary partial coupling and fused-ring polynuclear aromatic terminators

A method for preparing a diene polymer or copolymer having improved raw viscosity and adapted to form elastomer compositions having reduced hysteresis properties comprising the steps in sequence of:

• (a) preparing a living diene polymer or copolymer containing active organoalkali or organoalkaline earth metal terminals by anionically polymerizing a conjugated diene monomer or mixture of a conjugated dene monomer and vinyl aromatic hydrocarbon monomer in a hydrocarbon solvent using an organoalkali metal or organoalkaline earth metal initiator;
• (b) coupling from about 10 to about 70 percent by weight of the living diene polymer or copolymer chains by reacting the organoalkali or organoalkaline earth metal terminals thereof with from about 0.1 to about 0.7 equivalents of a tin polyhalide, based on the number of halogen atoms in said tin polyhalide, per mole of said living diene polymer or copolymer chains, said tin polyhalide having the general formula R.sub.a SnX.sub.b, wherein R is selected from the group consisting of alkyl, alkenyl, cycloalkyl and aryl groups, X is a halogen atom, a is an integer of 0-2 and b is an integer of 2-4;
• and
• (c) terminating the remaining living diene polymer or copolymer chains by reacting the organoalkali or organoalkaline earth metal terminals thereof with from about 0.3 to about 100 moles of a fused-ring polynuclear aromatic compound capable of reacting with no more than 1 mole of living polymer per mole of said fused-ring polynuclear aromatic compound.