Para‐ordered polybenzimidazole

Abstract

A series of novel AB monomers such as 2‐[p‐carboxyphenyl]‐5,6‐diaminobenzimidazole hydrochloride have been synthesized. In addition, a new aromatic monomer, 1,3‐diamino‐4,6‐bis(p‐toluenesulfonamido)benzene has been prepared in high purity and substituted for 1,2,4,5‐tetraaminobenzene in a polymerization with terephthalic acid. Homopolymerization of the AB monomers, and polycondensation of monomer with terephthalic acid in polyphosphoric acid, produced the rod‐like para‐oriented polymer, poly[1,7‐dihydrobenzo(1,2‐d: 4,5‐d)diimidazole‐2,6‐diyl‐1,4‐phenylene]. The yellow polymer was completely soluble in methanesulfonic acid (MSA) and PPA, exhibiting intrinsic viscosities as high as 5 dl/g in MSA, and a blue opalescence in solution. Polymerization at temperatures above 225°C caused crystallization and subsequent precipitation to occur. Polymer thus obtained was completely insoluble in MSA and possessed a high degree of crystallinity as demonstrated by x‐ray analysis.

High-temperature fuel cell membranes based on mechanically stable para-ordered polybenzimidazole prepared by direct casting

“…The wholly parastructured pPBI exhibits superior mechanical properties, including a high degree of tensile strength and unusually high stiffness, compared with the meta-structured mPBI [17,18]. Thus, pPBI might sustain its mechanical strength with a higher acid doping level.…”

“…One possible reason for the improved mechanical strength of pPBI membranes at doping levels greater than 5 mol H 3 PO 4 is the increased viscosity (or molecular weight); the inherent viscosity values for mPBI and pPBI are 2.45 and 3.22 dL g −1 , respectively. The stiffer backbone structure of pPBI due to its wholly paraordered molecular orientation may also improve the mechanical stability [18].…”

Synthesis of Poly (2,2′‐(1,4‐phenylene) 5,5′‐bibenzimidazole) (para‐PBI) and Phosphoric Acid Doped Membrane for Fuel Cells

“…polymers. Subsequent development work sponsored by the US Air Force Materials Lab [17,18] resulted in para-oriented PBI polymers with high I.V., although in some instances the polymerisations required almost five weeks of heating during the polymerisation due to the lengthy dissolution time for terephthalic acid (TA) in PPA. The low solubility of TA in PPA, approximately 0.0006 g in 1 g of PPA (86 wt.-% P 2 O 5 ) at 140°C, and its effects on the polymerisation of rigid-rod polymers were reported in elegant work by So et al [19][20][21] Thus, it appears that the low solubility of TA and the para-oriented PBIs limited the development of appropriate synthetic conditions for the preparation of high molecular weight polymers.…”

High temperature proton exchange membranes based on polybenzimidazoles for fuel cells

“…Compared with the meta-PBI, the para structure of the polymer showed superior tensile strength and stiffness [90], however, the glass transition temperature was lowered by 59 • C [57], indicating the enhanced flexibility of the polymer chain due to introduction of the p-phenylene linkage in the backbone. The synthesis is done by using para-terephthalic acid (TPA) instead of meta-isophthalic acid (IPA).…”