Introduction of a Long Alkyl Side Chain to Poly(benzimidazole)s. N-Alkylation of the Imidazole Ring and Synthesis of Novel Side Chain Polyrotaxanes

Abstract

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(CH 2 ) 8 −] n ( 2a ), and [{−Im(CH 2 ) 11 O(CH 2 ) 11 } 0.91 {Im(CH 2 ) 10 −} 0.09 ] n ( 3a ) followed by addition of Br(CH 2 ) 12 O(C O)CH 2 CPh 3 causes substitution of the NH hydrogen of the parent polymer with the (CH 2 ) 12 OCOCH 2 CPh 3 group. The produced respective poly(benzimidazole) derivatives, 1b, 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. 1 H 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-β-cyclodextrin (TMe-β-CD), the reaction gives a new type of polymer ( 1c, 2c, and 3c, respectively), side chain polyrotaxanes. TMe-β-CD is incorporated in 21% and 57% of the side chains of 1c and 2c, while every side chain of 3c threads through two TMe-β-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 .