Chain Dynamics of Poly(oxyethylene) in Nanotubes of a-Cyclodextrin by Solid-State 2 H NMR a Tom E. Girardeau, Johannes Leisen, Haskell W. Beckham* School of Polymer, Textile and Fiber Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0295, USA Fax: 404-894-9766; E-mail: haskell.beckham@ptfe.gatech.edu Received: March 8, 2005; Accepted: March 18, 2005; DOI: 10.1002/macp.200500095 Keywords: cyclodextrin; dynamics; nanotubes; poly(oxyethylene); solid-state NMR Introduction In addition to the all-carbon varieties, nanotubes have been prepared from an assortment of inorganic materials [1] such as aluminosilicates, [2] and by self-assembly [3] of cyclic peptides [4] or oligosaccharides. [5] The cyclic oligosacchar- ides, better known as cyclodextrins, can self-stack to form channel or tubular structures with outer diameters of 1.4 to 1.7 nm and inner diameters of 0.5 to 1 nm, depending on the constituent cyclodextrin (a, b, or g). [6] Their formation is often templated by a guest that facilitates alignment and hydrogen bonding of adjacent cyclodextrins. Perhaps the most obvious template for a nanotube is a linear polymer, and in fact a number of polymers have been threaded with cyclodextrins to give nanotubular sheaths covering the linear polymer guest. [7–13] However, small molecules can also serve as templates [14–16] and potential-controlled adsorption of cyclodextrins onto Au(111) surfaces also works. [5,17] The resulting products are also referred to as cyclodextrin inclusion complexes, polypseudorotaxanes or, more generally, rotaxanated polymers. Cyclodextrins threaded onto a polymer chain may be covalently linked through their hydroxyl groups [18] to construct what has been referred to as a molecular nano- tube. [19–24] By removing the polymer template, these mo- lecular nanotubes of cyclodextrins can be isolated. Surface modification of these molecular nanotubes is possible and has been reported in one case for increasing their water solubility. [25] Such modifications are important for disper- sing nanotubes in matrices for the construction of hier- archical multicomponent composites. Of course the simplest composite consists of cyclodextrin nanotubes containing linear polymers. Contained within the channels of nanotubes, polymer chains are isolated from other chains and exhibit vastly different dynamics as compared to their dynamics in the bulk. Chain motions Summary: Solid-state 2 H NMR spectroscopy was used to examine the chain dynamics of perdeuterated poly(oxyethyl- ene) (d-POE) inside a-cyclodextrin (a-CD) nanotubes. The nanotubes were prepared by aqueous self-assembly of a-CD onto either low-molecular-weight (1.5 kg/mol) or high- molecular-weight (25.8 kg/mol) monodisperse d-POE. At a given temperature, POE chain segments exhibit faster dy- namics when included inside the CD nanotubes as compared to the bulk. Even at 150 K, when no large-angle dynamics are detected in bulk POE, evidence for chain motions in the nanotube-confined POE is observed. The 2 H line shapes representing this motion were modeled by a discrete 3-site jump using a ln-Gaussian distribution of correlation times. An activation energy of 15  1 kJ/mol was determined and the motion envisioned as gauche defects propagating along the primarily trans chains included within CD nanotubes. As the nanotube length decreased, the jump angle became much less defined and more isotropic motions were observed for POE segments at elevated temperatures (>270 K). Macromol. Chem. Phys. 2005, 206, 998–1005 DOI: 10.1002/macp.200500095 ß 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 998 Full Paper a The publication of this article has been accelerated because of its topical or highly competitive nature.