Molecular motion of polycarbonate included in γ‐cyclodextrin |
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Authors: | Younkee Paik Barbara Poliks Cristian C. Rusa Alan E. Tonelli Jacob Schaefer |
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Affiliation: | 1. Department of Chemistry, Washington University, St. Louis, Missouri 63130;2. Department of Physics, Binghamton University, Binghamton, New York 13902;3. Fiber and Polymer Science Program, North Carolina State University, Raleigh, North Carolina 27695;4. Department of Chemistry, Washington University, St. Louis, Missouri 63130Department of Chemistry, Washington University, St. Louis, Missouri 63130 |
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Abstract: | Molecular motions of single polycarbonate (PC) chains threaded into crystalline γ‐cyclodextrin (γ‐CD) channels were examined using solid‐state 13C NMR and molecular dynamics simulations. The location of PC within the channels was confirmed by spin diffusion from a PC 13C label to natural‐abundance 13C of the γ‐CD. Rotor‐encoded longitudinal magnetization (RELM) (under 7‐kHz magic‐angle sample‐spinning conditions) was combined with multiple‐pulse 1H‐1H dipolar decoupling to detect large‐amplitude phenyl‐ring motion in both bulk PC and polycarbonate γ‐cyclodextrin inclusion compound (PC‐γ‐CD). The RELM results indicate that the phenyl rings in PC‐γ‐CD undergo 180° flips faster than 10 kHz just as in bulk PC. The molecular dynamics simulations show that the frequency of the phenyl‐ring flips depends on the cooperative motions of PC atoms and neighboring atoms of the γ‐CD channel. The distribution of protonated aromatic‐carbon laboratory and rotating‐frame 13C spin‐lattice relaxation rates for bulk PC and PC‐γ‐CD are similar but not identical. The distributions for both systems arise from site heterogeneities. For bulk PC, the heterogeneity is attributed to variations in local chain packing, and for PC‐γ‐CD the heterogeneity arises from variations in the location of the PC phenyl rings in the γ‐CD channel. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1271–1282, 2007 |
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Keywords: | chain packing dipolar echo dipolar recoupling inclusion compound molecular dynamics NMR phenyl‐ring flip polycarbonates relaxation |
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