Selective measurement of heteronuclear 1H-13C dipolar couplings in motionally heterogeneous semicrystalline polymer systems.

J. Brus, M. Urbanová 

¹⁾ Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovsky Sq. 2, 162 06 Prague 6, Czech Republic,

J. Phys. Chem. A 109(23), 5050 (2005).

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 H 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.