th  - 1988 - 51st ENC Conference

37 IMOLECULAR MOTIONS IN SOLIDS MEASURED FROM 13C
LINEWIDTHS: V. A. Nicely and P. M. Henrichs,* Eastman Kodak
Company, Rochester, NY, 14650.
We have found linewidths of the 13C resonances from solids
to be a sensitive indicator of molecular motions. Often non-motional
contributions to the linewidths obscure the motional linewideth due
to motion in such cases. Fourier transformation of an entire echo
train to give a spectrum broken into spikes (as demonstrated by
Garroway and later by Zilm) is an efficient way to treat spin-echo
results. The shapes of the individual spikes contain the information
about motion. For examples spinning at the magic angle, the spacing
of the echo pulses must be an integral multiple of the rotation
period. Dimethyl sulfone, for which motions are well known, is a
convenient test material. The linewidths are sensitive to both
methyl rotations and reorientation of the_whole molecule. In polymer
below the glass-transition temperature, -~C linewidths reflect the
distribution of correlation times associated with local chain
motions such as ring flips, methyl reorientations, and methylene
oscillations. Results have been obtained from bisphenol-A
polycarbonate, poly(ethylene terephthalate), and poly(ethylene
isophthalate). This method is a useful way to probe motions in
polymers and other materials for which isotopic labelling is not
practical.
38 HIGH RESOLUTION ELECTROPHORETIC NMR (ENMR) OF A MDflWJRE:
Timothy R. Saarinen and Charles S. Johnson, Jr., University of North
Carolina, Dept. of Chem., Chapel Hill, NC 27599-3290
Electrophoretic mobilities have been measured in situ using
pulsed field gradient NMR (PFGNMR). Several components in a mixture
can be studied simultaneously by Fourier transformation of the second
b~if of the spin echo. For a U-tube conficjuration application of an
e!ectl'ic field across the sample results in a cosinusoidal modulation
of spectral peak amplitudes, cos(Kv:t) where K equals the area of the
gradient pulse times the gyrcmagnetic ratio, v is the drift velocity
of the i'th species, and t is the duration of the electric field
pulse. By working at low ionic strengths electric fields of up to 50
V/cm could be applied for i sec before convection was detected by a
change in the amplitude of the HOD peak. The cationic mobilities in
a mixture of tetra-methyl and tetra-ethyl ammonium chloride in D.O
were determined. Application of the technique for studying emu/sions
looks prcnlising.
116