Formation of Cyclodextrin-Based Polypseudorotaxanes: Solvent Effect and Kinetic Study

Aqueous solutions of β- or γ-cyclodextrin were found to form polypseudorotaxanes upon threading of linear hydrophobic polymers such as poly(propylene glycol) bis-2-aminopropyl ether, H3CCH(NH2)CH2(OCH2CH(CH3))nNH2 (PPG-Am2; MW ≈ 2000; nav ≈ 33), and pluronic 105, HO(CH2CH2O)34(CH2CH(CH3)O)61(CH2CH2O)34H (PLU; MW ≈ 6500). The kinetics of the threading process was determined as a function of the temperature and solvent composition (water, heavy water, and urea). When the water solution of cyclodextrin was added to the polymer's dispersion, a thick solid precipitate was promptly formed, depending on the concentration and temperature. Turbidity measurements allowed us to determine the time necessary for a complete threading of the linear polymer (the “threading time”); this parameter depends on the solution temperature and on the solvent nature. A simple kinetic model provides the activation free energy of the process, and the number of cyclodextrin molecules threaded around a single linear chain. Enthalpy, e...