Direct synthesis of cyclodextrin-rotaxanated poly(ethylene glycol)s and their self-diffusion behavior in dilute solution

Poly[(ethylene glycol)-rotaxa-(alpha-cyclodextrin)]s, (PEG-rotaxa-alphaCD)s, were prepared by a direct route from commercially available poly(ethylene glycol)s (PEG) with molecular weights from 1.5 to 20 kg/mol. The rotaxanated structure was verified by diffusion-ordered 2D NMR spectroscopy (DOSY). The self-diffusion coefficients for PEG-rotaxa-alphaCD and PEG in dilute DMSO-d(6) scale with their respective molecular weights as DPEG-rotaxa-alphaCD similar to M-n(-0.60+/-0.05) and D-PEG similar to M-n(-0.55+/-0.03). With increasing temperature, the hydrodynamic radius of the PEG-rotaxa-alphaCD increases by the same slope as the unthreaded PEG backbone. These polyrotaxanes, in which up to 70% of the backbone is covered with cyclodextrins, behave as random coils in good solvents.