NaH promoted deprotonation of the NH group in poly(benzimidazole)s, (-ImC(6)H(4)-)(n) (1a, Im=5,5’-dibenzimidazole-2,2’-diyl), [-Im(CH2)(8)-](n) (2a), and [{-Im(CH2)(11)O(CH2)(11)}0.91{Im(CH2)(10)-}0.09](n) (3a) followed by addition of Br(CH2)(12)O(C=O)CH2CPh3 causes substitution of the NH hydrogen of the parent polymer with the (CH2)(12)OCOCH2CPh3 group. The produced respective poly(benzimidazole) derivatives, Ib, 2b, and 3b, contain the N-alkylated imidazole group with a high content (85-91%) in the main chain and show high solubility in organic solvents. H-1 NMR spectra of 1b-3b reveal that 91, 91, and 85% of the respective imidazole rings are N-alkylated. When the same reaction is carried out in the presence of trimethyl-beta-cyclodextrin (TMe-beta-CD), the reaction gives a new type of polymer (Ic, 2c, and 3c, respectively), side chain polyrotaxanes. TMe-beta-CD is incorporated in 21% and 57% of the side chains of Ic and 2c, while every side chain of 3c threads through two TMe-beta-CDs. A GPC trace of 3c supports the formation of the polyrotaxane. Polyrotaxanes 1c-3c also show considerably higher solubility in organic solvents than the parent polymers 1a-3a.