Controlled synthesis of unsubstituted high molecular weight poly(para-phenylene) via Suzuki polycondensation-thermal aromatization methodology†
Suzuki polycondensation-thermal aromatization methodology was developed as a versatile new route to structurally regular, unsubstituted high molecular weight poly(para-phenylene) (PPP). The utility of this methodology was demonstrated by synthesizing PPP from both cis- and trans-precursor prepolymers 1a–b. The structure of precursor prepolymers containing exclusively 1,4-repeating units with the hydroxyphenyl group at the chain end was determined by two-dimensional NMR spectroscopy. Pyrolysis of trans-poly(para-phenylene) precursor 1b resulted in complete aromatization to PPP containing an average of 110 phenylene units in the polymer chain. The thermal conversion of precursor polymers to polyphenylene is a straightforward process leading to pristine PPP without significant chain degradation as confirmed by solid-state NMR and TGA analysis. The characterization of PPP by solid-state NMR, UV-vis absorption, fluorescence emission and IR spectroscopy, TGA, and conductivity measurements exhibits significant features for electronic and photoelectronic application, such as broadened absorption, high thermal stability, and typical conducting properties.