Synthesis and properties of new polybenzimidazoles and N‐phenyl polybenzimidazoles with flexibilizing spacers on the polymer backbone

Several new polybenzimidazoles (PBIs) and N ‐phenyl PBIs were synthesized by high temperature solution polycondensation techniques. Three different tetramine hydrochlorides and one N ‐phenyl tetramine hydrochloride were condensed independently with p ‐phenylenedioxydiacetic acid (PDDA), 2,2′‐[isopropylidene bis( p ‐phenyleneoxy)] diacetic acid (bisacid A 2 ) and 2,2′‐[sulfonyl bis( p ‐phenyleneoxy)] diacetic acid (bisacid S) in polyphosphoric acid (PPA) at high temperatures. The polymers were obtained in 55–65% yield with inherent viscosities in the range 0.58–0.96 dL/g. Four model benzimidazoles (MBI) were also synthesized to confirm the formation of polybenzimidazoles. The PBIs and MBIs were characterized by infrared spectroscopy and elemental analysis. The properties of the polymers such as solubility, density, crystallinity, and thermal, thermoxidative, and isothermal stabilities were studied.