Synthesis and solubility of poly(N‐methylbenzimidazole) and poly(N‐ethylbenzimidazole): control of degree of alkylation

In this paper, synthesis of poly(N‐methylbenzimidazole) (PNMBI) and poly(N‐ethylbenzimidazole) (PNEBI) with various alkylation degrees was achieved by adding enough LiH and controlling the amount of substituting reactant. The degree of substituted methyl or ethyl was determined by elemental analysis. Changes in infrared spectroscopy due to nature and degree of substitution can clearly be found. With the modification of PBI, the solubility of PNMBI and PNEBI is improved significantly. There is no significant change of chemical structure of PNMBI after 0.5 h thermal treatment in both N2 and air at a temperature lower than 250 °C. Compared with PBI, the methanol permeability of PNMBI and PNEBI is a little higher but still of the same order of magnitude.