A novel crown ether stopping group for side chain polyrotaxane. Preparation of side chain polybenzimidazole rotaxane containing alkyl side chain ended by crown ether-ONa group

NaH promoted deprotonation of the NH group in poly(p-phenylenebenzimidazole) (1) followed by treatment with Br(CH2)(12)OH causes substitution of the NH hydrogen of 1 to give N-alkylated polymer (2) having a -CH2ONa group at the end of the side chain. The H-1 NMR spectrum of 2 indicates that 90% of the imidazole rings are N-alkylated. Stirring a DMF solution of 2 with alpha-cyclodextrin (alpha-CD) leads to inclusion of alpha-CD onto the N-alkyl side chain, and subsequent addition of 15-crown 5-ether (15C5) causes complex formation of the -ONa group with 15C5. Because of the formation of the bulky 15C5-ONa end group, dethreading of alpha-CD from the side chain is prevented. The 1H NMR spectrum of the side chain polyrotaxane (4) reveals that alpha-CD is incorporated in 57% of the side chain and that all the ONa groups form the complex with 15C5. GPC and DSC profiles of 4 support formation of the side chain polyrotaxane. Treatment of 4 with H2O causes detaching of 15C5 and dethreading of alpha-CD from the side chain.