Semi-continuous process for making star-block copolymers

Claim 1

A semi-continuous process for preparing star-block copolymers of a monovinyl aromatic compound and a conjugated diene in an inert hydrocarbon solvent using an anionic initiator consisting essentially of: a. charging a first reactor with the solvent and all of the initiator and heating to 70° to 85° C. followed by the addition of, in 3 equal portions, over a period of from 6 to 15 minutes, all of the monovinyl aromatic compound while maintaining the reactor at polymerization temperature to insure complete polymerization of the monovinyl aromatic compound to form blocks of formula A--Li where A is a block of polyvinyl aromatic compound; b. transferring the contents to a second reactor and charging all of the conjugated diene in 3 equal portions over a period of 27 to 55 minutes while maintaining said second reactor at a temperature of from 65° to 80° C. to insure complete polymerization of the diene to form chains of formula A-B-Li where B is a block of polydiene; c. transferring the contents of said second reactor to a third reactor and charging 0.6 to 3.5 parts by weight of coupling agent per 100 parts by weight of total monomer and allowing to couple at 70°-80° C. for 30 to 60 minutes to form star-block copolymer having formula (A--B) m --X where A and B are block segments, as above, m is an integer between 3 and 20, and X is the radical of a polyfunctional coupling agent; d. transferring the contents of said third reactor to a fourth reactor, terminating the polymerization by the addition of methanol, adding stabilizers and recovering the polymer by extrusion into polymer pellets; and e. repeating steps a-d as soon as each reactor is emptied into the succeeding reactor.