Progress in the Synthesis of Poly(2,7-Fluorene-alt-1,4-Phenylene), PFP, via Suzuki Coupling.

Four different palladium catalysts were evaluated in order to optimize the conditions in the Suzuki coupling protocol with 1,4-diphenylboronic acid and 9,9-bis(6'-bromohexyl)-2,7-dibromofluorene. The commercially available catalysts [Pd(PPh3)(4)], (1); [Pd(PPh3)2Cl(2)], (2); [PdCl2(dppe)], (3) and [PdCl2(dppf)]center dot CH2Cl2, (4) were chosen. Palladium catalysts 1-4 have been previously used Successfully I'll polymerization. K2CO3 was used as base in the presence of the adequate solvent mixture. Poly[9,9-bis(6'-bromohexylfluoren-2,7-diyl)-alt-co-(benzen-1,4-diyl)], PFPBr2, was obtained and selected as model to study the polymerization degree. Calibration curves of fluorene were used to perform a real estimation of the molecular weights of the polymers, and also typical polydispersity Values were measured. Polymer conversion was determined using coupled size exclusion chromatography-evaporative light scattering detector (SEC-ELSD). The (Z)-Pd(II) catalyst, (4), which contains the electron acceptor ligand dppf, showed the fastest conversion rate at low reaction times, followed closely by catalyst (2), (E)-Pd(II), which presents a conventional PPh3 ligand. The typical Pd(0) catalyst, (1), with phospane ligands, was slower than others and this process needed almost 12 h to convert the monomers in real polymer. Taken together, all these results provide new insights into the polymerization mechanism using different Pd(II) and Pd(0) catalysts, which seem to behave differently when different ligands are used.