How the monomer concentration of polymerization influences various properties of polybenzimidazole: A case study with poly(4,4'-diphenylether-5,5'- bibenzimidazole)

Abstract

In this work, a series of poly(4,4'-diphenylether-5,5'-bibenzimidazole)s (OPBIs) were synthesized from 4,4'-oxybis(benzoic acid) and 3,3',4,4'- tetraaminobiphenyl through the variation of the initial monomer concentration with a solution polycondensation technique in a poly(phosphoric acid) medium. The resulting polymers were characterized by various techniques such as infrared (IR), nuclear magnetic resonance, dynamic mechanical analysis (DMA), and thermogravimetric analysis. The initial monomer concentration in the polymerization mixture played an important role in controlling the molecular weight of the resulting polymers. A temperature-dependent IR study showed that the free movement of the ANH group of the imidazole ring was blocked by the absorbed moisture. The DMA study showed that the glass-transition temperature (Tg) varied with the molecular weight, and the presence of the ether linkage in the OPBI polymer backbone had a significant influence on T g. A high-molecular-weight OPBI polymer tended to form a supramolecular organization, which influenced the thermal characteristic of the polymer. Photophysical studies demonstrated the fluorescent characteristics of the OPBI polymers in both solid and solution states. © 2008 Wiley Periodicals, Inc.