th  - 1988 - 51st ENC Conference

PHOSPHATE PLASTICIZER DYNAMICS IN GLASSY POLYMER BLENDS BY 3~F~ CSA
-- LINESHAPES: Paul T. Inglefield*, Alan A. Jones, Ajoy K. Roy and
I 78 IBonnie J. Cauley (Department of Chemistry, Clark University,
Worcester, MA 01610) and Roger P. Kambour (Polymer Physics and Engineering, General
Electric Company, Research and Development Center, Schenectady, NY 12301)
The ability of 3tp CSA lineshape collapse to critically determine subtle details of
the microscopic dynamics in the solid state is presented. The particular example of
the motion of phosphorus containing diluents in solid polymer blends is considered.
No sub-glass transition mechanical loss peaks are observed in 50:50 blends of poly
(2,6-dimethyl-1,4-phenylene oxide) and polystyrene. However if organic phosphate,
)lasticizing diluents (e.g. trioctyl phosphate) are added, the modulus is lowered and
a broad low temperature loss peak appears. Non-spinning 3Xp lineshapes were observed
and clearly indicate the onset of plasticizer motion in the glass. An axially symme-
tric lineshape at low temperature evolves to a narrow line below the glass transition.
At intermediate temperatures a superficially bimodal lineshape is observed indicative
of a broad distribution of correlation times. The plasticizer motion appears to be
isotropic in nature and detailed quantification of the dynamics is possible. The dy-
namics of different phosphate diluents correlates with the glass transition of the
pure diluent and it is postulated that the plasticizer motion is responsible for the
low temperature mechanical relaxation.
7 9 I NON UNIFORM SAMPLING IN NMR EXPERIMENTS
Y. Manassen and G. Navon*, School of Chemistry, Tel Aviv University,
Ramat Aviv, Tel Aviv 69978, Israel.
In many NMR experiments the resonance frequencies and the
linewidths are known a-priory and only the peak intensities are sought.
This includes spectroscopic imaging experiments and 2-D NMR experiments
(such as COSY and NOESY), where the possible frequencies of the peaks
and their approximate linewidths can be obtained from the 1-D spectrum.
It is shown here that a significant improvement in sensitivity can be
obtained in such cases by collecting the data in a non-uniform manner
instead of constant dwell times. It is further shown how the error in the
intensity calculation can be estimated, and how this can be used to select
the sampling times so that the the sensitivity is maximized. The increase
in sensitivity is particularly pronounced in cases with small number of
peaks and in cases where the distribution of the peaks in the spectrum is
non-uniform. Our simulation experiments indicate that the calculated
amplitudes are not very sensitive to errors in the linewidths.
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