Molecular motion of polycarbonate included in γ-cyclodextrin

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 1...

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Bibliographic Details
Published in:Journal of polymer science. Part B, Polymer physics Polymer physics, 2007-06, Vol.45 (11), p.1271-1282
Main Authors: Paik, Younkee, Poliks, Barbara, Rusa, Cristian C., Tonelli, Alan E., Schaefer, Jacob
Format: Article
Language:English
Subjects:
Applied sciences
chain packing
dipolar echo
dipolar recoupling
Exact sciences and technology
inclusion compound
molecular dynamics
NMR
Organic polymers
phenyl-ring flip
Physicochemistry of polymers
polycarbonates
Properties and characterization
relaxation
Structure, morphology and analysis
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Summary: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
ISSN:0887-6266
1099-0488
DOI:10.1002/polb.21112