Effect of Initiators on the Kumada Catalyst-Transfer Polycondensation Reaction

An investigation for the initiation of a chain-growth polymerization, Kumada catalyst-transfer polycondensation, for the synthesis of poly(3-hexylthiophene) is described. A novel method for the generation of an active catalyst/initiator complex was developed utilizing the inexpensive, air stable Ni(PPh3)2Cl2 precursor to generate the active Ni(PPh3)4 catalyst in situ. Poly(3-hexylthiophene) polymerization reactions were carried out using aryl halides with various substituents on the phenyl ring as external initiators, and it was found that the type of the functional group present on the initiator plays a crucial role in the polymerization. The new method provided a more efficient way to initiate polymerization yielding polymers with higher regioregularity, larger molecular weight, and lower polydispersity than the previously reported methods.