Kumada-Tamao Catalyst-Transfer Condensation Polymerization of AB₂ Monomer: Synthesis of Well-Defined Hyperbranched...

The synthesis of well-defined hyperbranched aromatic polymer by Kumada-Tamao catalyst-transfer condensation polymerization of AB₂ monomer is investigated. Grignard monomer 2 is generated by treatment of 2-(3,5-dibromophenyl)-3-hexyl-5-iodothiophene (1) with 1.0 equivalent of isopropylmagnesium chloride in THF at 0 °C for 1 h and subsequently polymerized with Ni(dppe)Cl₂ at room temperature for 1 h. The molecular weight of the obtained polymer increases linearly up to ≈30 000 in proportion to the ratio of [consumed 2] /[Ni(dppe)Cl₂]₀ and in proportion to the conversion of 2, while a narrow molecular weight distribution is maintained (M_w/M_n ≤ 1.12). The matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrum shows almost a single series of peaks due to polymer with hydrogen at one end and bromine at the other, as in the case of Kumada-Tamao catalyst transfer condensation polymerization of AB monomers. The degree of branching (DB) of the obtained polymers is 0.70-0.75, irrespective of the degree of polymerization. These results indicate that the polymerization of 2 proceeds in a chain-growth polymerization manner through the intramolecular catalyst transfer mechanism, affording hyperbranched polymer with higher DB than the theoretical DB value of 0.5 in conventional polycondensation of AB₂ monomers.