Synthesis and processing of poly(p-phenylene) via the phosphoric acid-catalyzed pyrolysis of a stereoregular precursor polymer: a characterization study

Flexible, free-standing films of high molecular weight, structurally regular poly(p-phenylene) (PPP) were prepared via the thermal conversion of a stereoregular precursor polymer using o-phosphoric acid as an aromatization catalyst. Approximately 83–90 wt.% of the resulting polymetaphosphoric acid formed during pyrolysis can be removed from the as-synthesized PPP films by washing in dilute aqueous HCl. The small amount of residual polymetaphosphoric acid left in the free-standing films acts as a plasticizer by imparting a degree of flexibility to the otherwise brittle polymer. The resulting PPP films are amorphous by X-ray diffraction. Infrared and UV-Vis-NIR analyses of the films are consistent with high molecular weight, completely 1,4-linked polyphenylene chains. The washed PPP films exhibit remarkable thermal and thermal oxidative stability. They also can be doped by 98% H2SO4 to form air-stable conducting complexes that can be subsequently undoped by diluting the acid with water.