Anionic dispersion polymerization process to make random copolymer rubber

A process for producing a copolymer by anionic dispersion polymerization comprising:

• adding to a first polymerization reactor:
• a first monomer charge comprising a first conjugated diene monomer and optionally a first vinyl aromatic monomer;
• organolithium polymerization initiator;
• and a non-aqueous dispersing medium,
• wherein the first monomer charge is polymerized to form a first block of a dispersing agent, the first block being soluble in the non-aqueous dispersing medium, and
• wherein at least 8% to 20% by wt of total monomer is provided by the first monomer charge, the total monomer being the sum of all monomer charges;
• and
• adding to a second polymerization reactor:
• the first block, the non-aqueous dispersing medium, a second monomer charge comprising a second vinyl aromatic monomer and a second conjugated diene monomer;
• and organolithium polymerization initiator,
• wherein the second monomer charge is polymerized to form the copolymer, the copolymer being the polymerized reaction product of at least 30% to 90% by weight of the second vinyl aromatic monomer, based on a total weight of the copolymer, and at least 10% to 70% by weight of the second conjugated diene monomer, based on the total weight of the copolymer, and
• wherein the second polymerization reactor produces an outlet stream comprising the copolymer and a second block of the dispersing agent, the second block being insoluble in the non-aqueous dispersing medium and linked with the first block to form the dispersing agent, and
• wherein the dispersing agent disperses the copolymer in the non-aqueous dispersing medium,
• adding coupling agent into the outlet stream, wherein the coupling agent attaches to the copolymer to increase the Mooney viscosity of the copolymer, wherein the coupling agent comprises a non-organometallic aromatic triester coupling agent.