| Abstract
| - We studied the mechanism of the chain-growth polymerization of 2-bromo-5-chloromagnesio-3-hexylthiophene (1) with Ni(dppp)Cl2 [dppp = 1,3-bis(diphenylphosphino)propane], in which head-to-tailpoly(3-hexylthiophene) (HT-P3HT) with a low polydispersity is obtained and the Mn is controlled by thefeed ratio of the monomer to the Ni catalyst. Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectra showed that the HT-P3HT uniformly had a hydrogen atom at one end of each moleculeand a bromine atom at the other. The reaction of the polymer with aryl Grignard reagent gave HT-P3HTwith aryl groups at both ends, which indicates that the H-end was derived from the propagating Ni complex.The degree of polymerization and the absolute molecular weight of the polymer could be evaluated fromthe 1H NMR spectra of the Ar/Ar-ended HT-P3HT, and it was found that one Ni catalyst molecule formsone polymer chain. Furthermore, by reaction of 1 with 50 mol % Ni(dppp)Cl2, the chain initiator was foundto be a bithiophene−Ni complex, formed by a coupling reaction of 1 followed by insertion of the Ni(0)catalyst into the C−Br bond of the dimer. On the basis of these results, we propose that this chain-growthpolymerization involves the coupling reaction of 1 with the polymer via the Ni catalyst, which is transferredintramolecularly to the terminal C−Br bond of the elongated molecule. We call this mechanism “catalyst-transfer polycondensation”.
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