Branched Polymers Made Using Multifunctional Coupling Agents

A process for preparing a branched polymer, the process comprising:

• (i) polymerizing a first monomer comprising at least 90 mole percent of an alkenyl aromatic hydrocarbon, at a temperature from 0° C. to 100° C., to form a polymer block A;
• and adding a second monomer comprising at least 90 mole percent of one or more 1,3-dienes and polymerizing at a temperature from 0° C. to 100° C., to form a polymer block B;
• or
• (ii) polymerizing isoprene at a temperature from 0° C. to 100° C., to form a polymer block C;
• (iii) adding a multifunctional coupling agent of formula (R1O)3Si—Y—Si(OR2)3;
• and
• forming a branched block copolymer having a formula (A-B)m(R1O)3-mSi—Y—Si(R2O)3-n(B-A)n from steps (i) and (iii), or a branched polyisoprene homopolymer having a formula (C)m(R1O)3-mSi—Y—Si(R2O)3-n(C)n from steps (ii) and (iii);
• wherein
• each A block independently comprises at least 90 mole percent of the alkenyl aromatic hydrocarbon, and the one or more A blocks form 8-13 weight percent of the total weight of the branched polymer;
• each B block is independently a poly(1,3-diene) block comprising at least 90 mole percent of one or more 1,3-dienes;
• each C block is a polyisoprene block;
• each A block independently has a weight average molecular weight from 9-15 kg/mol, each B block independently has a weight average molecular weight from 75-150 kg/mol, and each C block independently has a weight average molecular weight from 400-1000 kg/mol;
• R1 and R2 are independently H, or C1-C6 alkyl groups;
• Y is a C2-C8 alkylene group;
• m and n are integers independently having values from 1-3;
• and
• the branched polymer has a coupling efficiency (CE) of at least 40%.