Deuterium quadrupole echo

M.S. Greenfield, A.D. Ronemus, R.L. Void, R.R. Void, P.E. Ellis, T.E. Raidy, Deuterium quadrupole-echo NMR spectroscopy. III. Practical aspects of lineshape calculations for multiaxis rotational processes,. Magn. Reson. 72 (1987) 89—107. 

The solid-state deuterium NMR experiments were performed on surface-adsorbed material from triethoxyaminopropylsilane-rf, (DAPES) and triethoxy-aminobutylsilane-dj (DABES) prepared as described previously [9]. The samples were heated to 90°C at 10 mmHg for 12 h after adsorption. These deuterated coupling agents have been characterized by IR and NMR spectroscopy. The solid-state deuterium NMR spectroscopy was done on a Varian VXR-200 at 30.7 MHz. A quadrupole echo pulse sequence was used with a 2 s interval, 2 /is 90° pulse, 30 ps echo time, 2 MHz sweep width, and, typically, overnight accumulation. 

It is well known that nmr is a powerful means for the study of the dynamics of polymer chains both in solution and in the solid state. The relaxation of 13C nuclei has been extensively employed for this purpose in this and other laboratories. I illustrate here a dilferent and particularly intriguing approach which as yet has seen only very limited application to synthetic polymers. This is deuterium quadrupolar echo spectroscopy, as employed in our laboratory by Dr. Lynn Jelinski and her collaborators (20). The presence of the nuclear electric quadrupole lifts the degeneracy of the two deuterium Zeeman transitions, and in the solid state produces a very broad (ca 200 kHz) powder pattern of transitions which can be interpreted to yield very specific motional information for those carbons labelled with deuterium. In Figure 7 are shown spectra of poly (butylene terephthalate) deuterated on the central carbons of the aliphatic chains ... 

Figure 4. Solid state deuterium NMR spectra of (a) poly (butylene terephthalate) (b) segmented co-polyester containing 0.96 mole fraction of poly (butylene terephthalate) hard segments and (c) segmented copolymer containing 0.87 mole fraction hard segments. (See text for specific deuterium labeling patterns.) All spectra were obtained with the quadrupole echo pulse sequence at 20 °C and 55.26 MHz, using 30 ts at the tj quadrupole echo delay time.

Figure 6. Experimental (a), calculated (b), and difference (c) solid state deuterium NMR spectra for the segmented copolymer with 0.87 mole fraction of hard segments. The spectrum in (a) was obtained at 55.26 MHz and 20 C, using the quadrupole echo pulse sequence. The dashed line in (b) represents the sum calculated for the broad and narrow components in a respective 10 1 ratio. (See text for details of the calculation.) The spectrum in (c) is the difference spectrum obtained by subtracting the spectrum of poly(butylene terephthalate) (Figure 4a) from the segmented copolymer spectrum (Figure 6a).

Figure 7. A plot of the relative intensity of the quadrupole echo deuterium NMR signal versus the echo delay time, t1 for the segmented copolymer containing 0.87 mole fraction hard segments. The line is extrapolated back to zero time.

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