The reactions of 3,3＇-diaminobenzidine with 1,12-dodecanediol in 1 : 1-1:3 molar ratios in the presence of RuCl2(PPh3)(3) catalyst give poly(alkylenebenzimidazole), [-(CH2)(11)-O-(CH2)(11)-Im-/-(CH2)(10)-Im-]n (Im: 5,5＇-dibenzimidazole-2,2 ＇-diyl) (I-a-I-d) in 71-92% yields. The relative ratio between the [(CH2)11-O-(CH2)(11)-Im-] unit (A) and the [-(CH2)(10)-Im-] unit (B) in the polymer chain varies depending on the ratio of the substrates used. The polymer I-a obtained from the 1 : 3 reaction contains these structural units in a 98 : 2 ratio. The polymers are soluble in polar solvents such as DMF (N,N-dimethylformamide), DMSO (dimethyl sulfoxide), and NMP (N-methyl- 2-pyrrolidone) and have molecular weights M-n (M-w) of 4,200-4,800 (4,800-6,500) by GPC (polystyrene standard). The polymerization of the diol and 3,3＇-diaminobenzidine in higher molar ratios leads to partial cross-linking of the resulting polymers I-e and I-f via condensation of imidazole NH group with CH,OH group. Similar reactions of 3,3＇-diaminobenzidine with alpha,omega-diols, HO(CH2)(m) OH (m = 4-10), in a 1 : 3 molar ratio give the polymers containing [-(CH2)(m-1)-O-(CH2) (m-1)-Im-] and [-(CH2) (m-2)-Im-] units with partial cross-linked structures.