Entering a new level of use for Suzuki cross-coupling: poly(para-phenylene)s with fourth-generation dendrons

Three different synthetic routes to the fourth-generation (G4) macromonomers 4, 6, and 9 for Suzuki polycondensation (SPC) are described and compared in their efficiency. Monomer 9 was selected the best as judged by the number and feasibility of synthetic steps and purification behavior and could be prepared in a 15 g scale. SPC of the monomers 4, 6, and 9 gave the novel poly(para-phenylene)s 17, 18, and 19 with pendant G4 dendrons at every other repeat unit. SPC was optimized for 9 and the diboronic acid ester counterpart 16 which led to polymer 19 with a molecular weight of up to Mn=76,000, Mw=63,9000 (GPC versus polystyrene). High molecular weight is most likely to be obtained for the attempted stoichiometry 9:16 = 1.000:(0.995-1.005).