Facile synthesis of hyperbranched poly(p-phenyleneethynylene-alt-m-phenyleneethynylene) with narrow dispersity and high branching degree by sonogashira polymerization of an AB2 monomer

An AB(2) monomer PhBr2-C C-Ph-C CH containing one acetylene group and two bromide groups was efficiently synthesized by a strategy based on the different reactivity between aromatic iodide and bromide in Sonogashira reaction. The Sonogashira polymerization of PhBr2-C C-Ph-C CH was investigated to get hyperbranched poly(p-phenyleneethynylene-alt-m-phenyleneethynylene) (hb-PMPE) in terms of the effects of monomer addition method, core molecule with different functionality, and ratio of [monomer]/[core molecule]. The results showed that narrow dispersities (D) (D: 1.23 similar to 1.50) were obtained by slow monomer addition and with core molecule. Bifunctional core molecule induced narrower dispersity than monofunctional core molecule. The molecular weight of hb-PMPE increased with increasing ratio of [monomer]/[core molecule], however, a negative deviation from calculated value was observed. The dispersity slightly increased with increasing [monomer]/[core molecule]. When the ratio of [monomer]/[core molecule] was below 50/1, monomodal distribution was observed; whereas when the ratio increased to 70/1, bimodal distribution was obtained. All the polymers showed degrees of branching (DBs) around 0.6. The hb-PMPEs showed one major absorption band with (max) around 330 nm, and emission band with (max) around 390 nm. All the polymers showed relative quantum yields (phi(r)) above 0.5 in dilute THF solution. (c) 2017 Wiley Periodicals, Inc.