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

Abstract

NaH promoted deprotonation of the NH group in poly(p-phenylenebenzimidazole) (1) followed by treatment with Br(CH2)12OH 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 1H NMR spectrum of 2 indicates that 90% of the imidazole rings are N-alkylated. Stirring a DMF solution of 2 with α-cyclodextrin (α-CD) leads to inclusion of α-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 α-CD from the side chain is prevented. The 1H NMR spectrum of the side chain polyrotaxane (4) reveals that α-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 α-CD from the side chain.