Processable N‐Substituted Polybenzimidazole; Direct Synthesis

Abstract

In this work, the preparations of N‐phenyl substituted polybenzimidazoles by direct polycondensation between N‐phenyl substituted aromatic tetramine, 4,6‐di(N‐phenylamine)‐1,3‐diaminebenzene, and dicarboxylic acids in Eaton's reagent are reported. It is shown that the factors of concentration and temperature are very important for synthesis of soluble linear polymer structures. The high temperatures promote strong crosslinking reactions resulting in insoluble gel fraction. Only decreasing the reaction temperature to 90 °C it is possible to obtained soluble polymer of high molecular weights with inherent viscosity of 1.6 dL/g. Although the FTIR and 1H NMR analyses demonstrated incomplete cyclization of thus obtained polymers, but they are readily soluble in organic solvents and the good quality films were prepared by solution casting. In order to complete the cyclization films were undergone by thermal treatment at 320 °C during 1 h. The N‐phenyl substituted polybenzimidazoles demonstrated good thermal and mechanical properties, which were compared to their analog unsubstituted polybenzimidazoles obtained from 1,2,4,5‐Benzenetetramine tetra‐hydrochloride using similar synthetic conditions.

Fluorinated Polybenzimidazole as a Novel Precursor for Carbon Molecular Sieve Membranes with Enhanced Gas Separation Properties

“…Such a difference may be explained by a closer chain packing in PBI-6F than the packing in fluorinated polyimides due to a strong intermolecular interaction between the imidazole rings. Although PBI-6F has higher fractional free volume than Celazole or OPBI, the fractional free volume reported for the polyimides generally is larger. , As discussed above, the small shoulder noted in the PBI-6F X-ray diffractogram (Figure ) corresponds to an interplanar distance of 3.54 Å, which indicates the existence of areas with very compact chain packing. The gas molecules sorbed in the polymer matrix reside within a volume formed by locally ordered chain segments …”

“…The shoulder at the high 2θ angle side of this diffractogram corresponds to a distance of 3.54 Å. Such tight packing is caused by strong intermolecular hydrogen bonding formed by the N–H groups of the imidazole rings. , The X-ray analysis of CMSM-600 shows a broad band corresponding to 3.73 Å, that could be assigned to a d -spacing of the (002) plane of graphite at 3.35 Å. It is also possible to distinguish an amorphous peak at 2.02 Å corresponding to the (100) plane of graphite. ,,, It was also possible to notice a little shoulder at the very small 2θ angle in the diffractogram corresponding to a distance of 14.5 Å that could be associated with the formation of micropores due to decomposition of the CF 3 groups.…”

“…Several strategies have been employed to overcome these drawbacks, such as using ether bridges, blending with other better processable polymers, thermal rearrangement of soluble precursors, and N-substituted modifications of already synthesized polymers or during the synthesis. − Generally, all of them allowed enhancement of gas permeability of the modified PBIs, but the improvements were not very impressive, particularly, in comparison with the synthetic efforts made. All these disadvantages limit the application and research on PBI membranes, and only a few studies have been published on the PBI-based CMSMs. − All of them dealt with commercially available Celazole (poly­[2,2′-( m -phenylene)-5,5′-bisbenzimidazole]) and OPBI (poly­[2,2′-( p -oxydiphenylene)-5,5′-bibenzimidazole]).…”

Effect of the Acid Medium on the Synthesis of Polybenzimidazoles Using Eaton’s Reagent

“…The N-phenyl substituted tetraamine, 4,6-di(N-phenylamine)-1,3-diaminebenzene (Ph-BET), was prepared as reported elsewhere [33]. N-phenyl substituted polybenzimidazole (Ph-CF 3 PBI) was obtained using this Ph-BET (100 mg, 0.344 mmol) and HFA diacid (135 mg, 0.344 mmol) in 1.86 mL of modified ER and nitrobenzene 50/50 (v/v).…”

“…The method particularly works well for monomers considered unsuitable for the synthesis of PBIs in ER under standard conditions or requiring a very long reaction time. However, the application of these conditions for the synthesis of N-substituted PBIs resulted in either low molecular weight polymers or gels [33]. Meanwhile, the introduction of bulky substitutes in the backbone chain is one of the principal strategies to lose the chain packing and, therefore, to gain some additional free volume in the polymer [34].…”