Catalyst-transfer polycondensation for the synthesis of poly(p-phenylene) with controlled molecular weight and low polydispersity.

To examine whether catalyst-transfer polycondensation, which affords well-defined polythiophenes, has generality for other conjugated polymers, the synthesis of poly(p-phenylene) (PPP) with various Ni catalysts was investigated. Monomer 1, 1-bromo-4-chloromagnesio-2,5-dihexyloxybenzene, was polymerized with Ni(dppe)Cl2 in the presence of equimolar LiCl to give PPP with a narrow polydispersity. The number-average molecular weight (Mn) of PPP thus obtained increased in proportion to the conversion of 1, indicating that this polymerization also proceeded in a chain-growth polymerization manner. Furthermore, the molecular weight of PPP was controlled by the feed ratio of 1 to the Ni catalyst up to at least Mn = 30000.