Kumada-Tamao Catalyst-Transfer Condensation Polymerization of AB2 Monomer: Synthesis of Well-Defined Hyperbranched Poly(thienylene-phenylene)

Abstract

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.