Synthesis of Hyperbranched Polyphenylenes With Controlled Molecular Weight by Suzuki–Miyaura Catalyst‐Transfer Polycondensation

Hyperbranched polyphenylenes with controlled molecular weight and molecular weight distribution were synthesized via Suzuki–Miyaura catalyst‐transfer polycondensation using 3,5‐dibromophenylboronic acid as the monomer and 4‐bromobenzonitrile as the initiator. By employing a commercially available Buchwald palladacycle precatalyst (RuPhos Pd G3) and 4‐bromobenzonitrile initiator, molecular weight can be effectively regulated through the initiator‐to‐AB 2 monomer ratio up to the M/I ratio of 511. The structural analysis by MALDI‐TOF MS spectroscopy suggested that the resulting polymer consists of an initiator‐derived core and bromophenyl repeating units. Inverse‐gated 13 C NMR spectroscopy indicated the preferential oxidative addition of Pd to C–Br bonds in newly added phenyl rings. These results provide mechanistic insight into catalyst‐transfer behavior during branching formation and highlight the potential of this strategy for the controlled synthesis of branched aromatic polymers.