Gelation-free synthesis of high-molecular-weight hyperbranched aromatic polymers containing silicon by Suzuki–Miyaura polycondensation of tri- or tetra(bromoaryl)silane with arylenediboronate†

Abstract

Suzuki–Miyaura polycondensation of tri- or tetra(bromoarylsilane) with arylenediboronic acid (ester) in the presence of ^tBu₃PPd precatalyst was investigated for the synthesis of silicon-containing hyperbranched aromatic polymers by means of simple A₂ + B_x (x = 3, 4) polycondensation without gelation. The key reaction in this polycondensation, successive substitution of with through intramolecular Pd catalyst transfer on the silyl group and π-face of , was investigated by means of model reactions of with a variety of arylboronates in the presence of at room temperature. The Suzuki–Miyaura reaction of tri(bromophenyl)silane , tri(bromofluorenyl)silane , and tetra(bromophenyl)silane with phenylboronic acid and carbazoleboronate yielded exclusively tri- and tetra-substituted products, even though the bromine sites in were present in excess relative to the boronic acid (ester) sites in . The polycondensation of with phenylenediboronate , fluorenylenediboronate , thienylenediboronate , and carbazolylenediboronate afforded high-molecular-weight silicon-containing aromatic hyperbranched polymers without gelation. The use of instead of resulted in the formation of some polymers with low solubility, but the polycondensations of with phenylenediboronic acid having a branched side chain and with yielded the corresponding high-molecular-weight polymers. In the polycondensation of with , afforded a moderate-molecular-weight polymer (M_n = 7610), whereas yielded polymers with M_n = 64 700–80 700. The UV-vis absorption and emission spectra in solution of the silicon-containing hyperbranched polyphenylenes, obtained by the polycondensation of or with , were similar to those of hyperbranched polyphenylene with no silicon (HBPP), whereas the fluorescence quantum yields were considerably higher (50–53%) than that of HBPP (16%).