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Article

Heterogeneous Polymer Dynamics Explored Using Static 1H NMR Spectra

Department of Organic Materials Science, Sandia National Laboratories, Albuquerque, NM 87185, USA
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Author to whom correspondence should be addressed.
Int. J. Mol. Sci. 2020, 21(15), 5176; https://doi.org/10.3390/ijms21155176
Received: 17 June 2020 / Revised: 8 July 2020 / Accepted: 8 July 2020 / Published: 22 July 2020
(This article belongs to the Special Issue NMR Characterization of Amorphous and Disordered Materials)
NMR spectroscopy continues to provide important molecular level details of dynamics in different polymer materials, ranging from rubbers to highly crosslinked composites. It has been argued that thermoset polymers containing dynamic and chemical heterogeneities can be fully cured at temperatures well below the final glass transition temperature (Tg). In this paper, we described the use of static solid-state 1H NMR spectroscopy to measure the activation of different chain dynamics as a function of temperature. Near Tg, increasing polymer segmental chain fluctuations lead to dynamic averaging of the local homonuclear proton-proton (1H-1H) dipolar couplings, as reflected in the reduction of the NMR line shape second moment (M2) when motions are faster than the magnitude of the dipolar coupling. In general, for polymer systems, distributions in the dynamic correlation times are commonly expected. To help identify the limitations and pitfalls of M2 analyses, the impact of activation energy or, equivalently, correlation time distributions, on the analysis of 1H NMR M2 temperature variations is explored. It is shown by using normalized reference curves that the distributions in dynamic activation energies can be measured from the M2 temperature behavior. An example of the M2 analysis for a series of thermosetting polymers with systematically varied dynamic heterogeneity is presented and discussed. View Full-Text
Keywords: NMR; polymers; chain dynamics; second moment NMR; polymers; chain dynamics; second moment
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MDPI and ACS Style

Alam, T.M.; Allers, J.P.; Jones, B.H. Heterogeneous Polymer Dynamics Explored Using Static 1H NMR Spectra. Int. J. Mol. Sci. 2020, 21, 5176. https://doi.org/10.3390/ijms21155176

AMA Style

Alam TM, Allers JP, Jones BH. Heterogeneous Polymer Dynamics Explored Using Static 1H NMR Spectra. International Journal of Molecular Sciences. 2020; 21(15):5176. https://doi.org/10.3390/ijms21155176

Chicago/Turabian Style

Alam, Todd M., Joshua P. Allers, and Brad H. Jones 2020. "Heterogeneous Polymer Dynamics Explored Using Static 1H NMR Spectra" International Journal of Molecular Sciences 21, no. 15: 5176. https://doi.org/10.3390/ijms21155176

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