Eaton’s reagent in polybenzimidazole synthesis

Abstract

The polycondensations of 3,3′-diaminobenzidine with two acids, 4,4′-oxybis(benzoic acid) and hexafluoroisopropylidene bis(benzoic acid), were conducted in Eaton’s reagent at the unusually high temperature of 180°C and under microwave irradiation at 90°C. Both protocols resulted in soluble polybenzimidazoles, OPBI and CF3PBI, of high molecular weights in very short reaction times. The synthesized polybenzimidazoles exhibited high thermostability and excellent mechanical properties. The influence of the reaction conditions on the polymer structure and molecular weights was studied. The “microwave effect” was demonstrated by comparison of the polycondensations conducted under microwave irradiation and conventional heating.

Processable N‐Substituted Polybenzimidazole; Direct Synthesis

“…For the unsubstituted tetraamine, the reaction worked better in the high temperature regime, affording soluble polymer with minimum amount of the insoluble fraction. The same tendency was previously observed for DAB tetraamine . Meanwhile, N ‐phenyl di‐substituted tetraamine was much more prone to crosslinking at high temperature, and the use of low temperatures was the optimal regime for formation of soluble polymer in ER.…”

“…The FTIR spectrum of the gel fraction obtained at 180 °C in a longer reaction time (Figure (b) B) shows intensive band around 1700 cm −1 , that rather indicates the presence of carboxyl groups. The presence of this band in the insoluble fraction of PBIs obtained in ER was previously noted by our group and was attributed to the possible acylation reactions as a side process in ER …”

“…The main data is given in Table . Recently, we reported the synthesis of PBIs based on DAB tetraamine with the two same acids, OBBA and HFA, in ER but using unusually high temperature of 180 °C . Such high temperature allowed to reduce significantly the reaction time and obtain high molecular weight PBIs soluble in organic solvents.…”

“…The data on these two polymers, OPBI and CF 3 PBI, obtained at 180 °C using DAB/ER of 7/93 (w/w) that is equal of 4 mL of ER per 1 mmol DAB, are also presented in Table as references. Additionally, it was shown that applying such high temperature in ER permitted to reduce the percentage of the insoluble gel fraction formed during the synthesis . Therefore, the initial idea was to try the same reaction condition for synthesis of N ‐Ph substituted PBIs.…”

“…After 2.5 h at this temperature quantitative conversion and soluble fraction of polymer with much high molecular weights were obtained (PBI‐4), while the amount of gel was negligible. Further heating at 180 °C resulted in visible destruction of ER …”