Selective measurement of heteronuclear 1H-13C dipolar couplings in motionally heterogeneous semicrystalline polymer systems |
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Authors: | Brus Jiri Urbanova Martina |
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Institution: | Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovsky sq. 2, 162 06 Prague 6, Czech Republic. brus@imc.cas.cz |
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Abstract: | A pulse sequence for the selective recoupling of heteronuclear dipolar interactions in mobile amorphous phase of powdered semicrystalline polymers is described. 1H-13C dipolar interactions are selectively measured by PISEMA-type sequence. Selection of 13C magnetization originating from amorphous phase is achieved by a train of saturation pulses followed by a short delay and a direct excitation pulse on 13C spins. The development of undesired net 13C magnetization during the recoupling sequence is prevented by the efficient "reverse" 13C --> 1H cross-polarization. The efficacy of the 2D method to measure 1H-13C dipolar couplings selectively for mobile components is demonstrated on powdered crystalline L-alanine, semicrystalline polyethylene, and nanocomposite polyamide-6/montmorillonite. |
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