Patent ID: 7009000

Claim:
A method for preparing a radial styrenic block copolymer having a general formulas: (AB) n X wherein: (i) A is a styrenic block, (ii) B is a dienic block, (iii) X is a residue of a diester coupling agent, (iv) n is the number styrenic block copolymer arms bonded to the residue of a diester coupling agent, (v) the molecular weight of the styreniec block copolymer arm (AB) is from about 2000 dalton to about 300,000 daltons, and (vi) the weight percentage of the polymer wherein n is at least 5 is less than about 8 percent, comprising: (a) contacting styrenic and dienic monomers with an anionic polymerization initiator which is an organo-substituted alkali metal compound in a suitable solvent to form a living polymer cement; (b) adding from about 0.01 to about 1.5 equivalents of a metal alkyl compound per equivalent of living polymer chain ends to the cement, during or after polymerization, wherein the alkyl groups of the metal alkyl compound are chosen so that they will not exchange with the living polymer chain ends and the metal alkyl compound is selected from the group consisting of aluminum, zinc and magnesium alkyls having from 1 to 20 carbon atoms per alkyl substituent; and (c) adding a diester coupling agent to the cement under reaction conditions sufficient to couple the living polymer; and wherein the weight percentage of the polymer so formed having n=5 + is less than about 8 percent.