Temperature variations of NMR second moments for drawn tapes based on polypropylene and polyethylene

Uhrin, J.; Murín, J.; Ševčovič, L.; Chodák, Ivan

doi:10.1002/1521-3900(200106)170:1<123::aid-masy123>3.0.co;2-e

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“…Static (non-spinning) NMR line shapes are broadened by homonuclear and heteronuclear dipolar couplings between different nuclei, quadrupolar couplings (for spin I > ½), chemical shielding anisotropy, or chemical shift dispersions, thus providing a handle to probe local structures and dynamics. For example, 7 Li, 23 Na, 31 P, and 133 Cs NMR M 2 results have been reported for glasses in analyses of structures and ion dynamics [ 8 , 9 , 10 , 11 , 12 ], as well as 1 H NMR M 2 studies of dynamics, miscibility, and chain orientations in polymers [ 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ]. While static NMR is hampered by low spectral resolution, it does benefit from being sensitive to local motions on the order of the line width and can be employed over very wide temperatures ranges.…”

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confidence: 99%

Heterogeneous Polymer Dynamics Explored Using Static 1H NMR Spectra

Alam

Allers

Jones

2020

IJMS

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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.

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