Thermoresponsive Behavior of Cationic Polyrotaxane Composed of Multiple Pentaethylenehexamine-grafted α-Cyclodextrins Threaded on Poly(propylene oxide)-Poly(ethylene oxide)-Poly(propylene oxide) Triblock Copolymer

This paper reports the synthesis and the studies of the thermoresponsive behavior of a new cationic polyrotaxane consisting of multiple pentaethylenehexamine-grafted alpha-cyclodextrin (PEHA-grafted-alpha-CD) rings threaded on a poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide) (PPO-PEO-PPO) triblock copolymer. The PEHA-grafted alpha-CD rings were threaded and embedded in the PEO block of the block copolymer, forming a hydrophilic polyrotaxane domain, while the two PPO blocks flank the cationic polyrotaxane domain. The cationic polyrotaxane was found to form thermosensitive micelles in aqueous solution. The thermosensitive micellization phenomena were studied using H-1 and fluorescence spectra. The critical micellization temperatures of the cationic polyrotaxane micelles at various concentrations were determined using a fluorescence probe technique. On the basis of the closed association model, the standard free energy (Delta G degrees), enthalpy (Delta H degrees) and entropy (Delta S degrees) of micellization were calculated, and then the entropy change was confirmed to be the driving force for the micellization.