Suzuki-Miyaura catalyst-transfer condensation polymerization of triphenylamine AB2 monomer and one-pot synthesis of linear-hyperbranched diblock copolymers

Suzuki-Miyaura catalyst-transfer condensation polymerization (CTCP) of 4-bis(4-bromophenyl)aminophenylboronic acid pinacol ester (pinBTPABr₂) was investigated. The model reaction of tris(4-bromophenyl)amine (TPABr₃) with phenylboronic acid in the presence of ^tBu₃PPd or AmPhos Pd precatalyst afforded exclusively a triphenyl-substituted product, indicating that the Pd catalyst underwent intramolecular catalyst transfer on TPABr₃. The polymerization of pinBTPABr₂ with ^tBu₃P-ligated tolyl-Pd-Br initiator (ini. A) proceeded in a chain-polymerization manner, affording hyperbranched poly(triphenylamine)s (PTPA) with well-defined molecular weight and low dispersity at [pinBTPABr₂]₀/[ini. A]₀ feed ratios up to 30; however, at the feed ratio of 30, a part of PTPA precipitated during the polymerization. Since pinBTPABr₂ underwent Suzuki-Miyaura CTCP, we next investigated the synthesis of block copolymers of linear π-conjugated polymer and PTPA in one pot by means of successive Suzuki-Miyaura CTCP of AB monomer (fluorene, phenylene, and thiophene) and pinBTPABr₂. When ini. A was used, the GPC elution curves of the block copolymers showed shoulders. However, when AmPhos-ligated tolyl-Pd-Br initiator (ini. B) was used, no shoulder was seen, and the GPC traces showed monomodal peaks. The composition of the block copolymers was in good agreement with the feed ratio of the two monomers to ini. B.