Effect of Reaction Parameters on the Molecular Weights of Polymers Formed in a Suzuki Polycondensation

A comprehensive investigation was undertaken in order to determine the effect of different reaction parameters on the molecular weights of polymers formed in a Suzuki polycondensation. In particular, we studied how the choice of solvent, base, ligand cocatalyst, palladium source, and monomers could affect the molecular weights. For these particular polymerizations, the best solvent and base were found to be CH2Cl2 and aqueous 3 m K3PO4, respectively. More interestingly, we determined that tri(o-tolyl)phosphine far surpassed not only the traditional triphenylphospine ligand cocatalyst, but also the more-recently developed hindered, electron-rich ligands that have yielded impressive results in small-molecule Suzuki coupling reactions. Molecular weights were also found to depend upon the source of palladium, with bis[tri[o-tolyl]phosphine]palladium(0) providing the best overall catalyst system. Finally, contrary to earlier reports, we found no advantage to replacing the more readily accessible bromide monomers with the corresponding iodides, and that pinacol boronic esters were inferior to the more traditional 1,3-propanediol boronic ester monomers. In sum, the work performed here shows that under optimized conditions, molecular weights on the order of 10(5) g/mol can be readily achieved with a Suzuki polycondensation.