th  - 1988 - 51st ENC Conference

178 CROSS-POLARIZATION NAS NMR OF 27AI IN =- AND T-ALUMINA.
H. Douglas Morris and Paul D. Ellis
Department of Chemistry
University of South Carolina
Columbia , South Carolina 29208
The NMR characterization of catalyst supports such as T- and ~-
aluminas has been accomplished through the observation of "probe"
molecules absorbed on the surface. This methodology is accurate only for
the sites and site distributions accessible to the probe, we report here
intrinsic observation of surface A1 sites on ~- and y- alumina via
~I CPMAS.- The absence of sub-surface IH allows only surface Br~nsted
site A1 atoms to contribute to the spectra. This observation combined
with cross-polarization to quadrapolar nuclei will allow the surface
characteriza-tion of many catalytic supports which hitherto were
described via probe molecules.
We have been able to clearly distinguish octahedral from tetrahedral
A1 sites. These sites have shown a population distribution dependent on
the degree of surface dehydration. The addition of a weak Lewis base,
pyridine, has shown selective signal enhancement of the T site over the
O h site, which agrees with Majors a~d Ellis, in the a~signment of a
hYgher percentage of T d Lewis sites.
Experimental spectra are presented for different levels of surface
dehydration, and addition of pyridine. Analysis of T I and T b~havior
is presented to describe the spin-dynamics of the surface ;AI-IH
interaction. This work was partially supported by the NSF, grant #CHE86-
11306.
i. Ellis, P. D. and Morris, H. Douglas, submitted to J. Am. Chem. Soc.
2. Majors, P. D. and Ellis, P. D., J. A. C. S., 109, 1648 (1987).
179 I
DYNAMICS OF CHAIN SEGMENTS IN THERMOSKT RESINS* C. G. Fry and
A. C. Lind, McDonnell Douglas Research Laboratories, P. O. Box 516,
St. Louis, Missouri, 631 66
The dynamics of chain segments between crosslinks in thermoset
resins are investigated by use of solid-state deuterium NMR and
molecular modeling techniques. Diamino-alkanes labeled at specific
sites are used as curing agents for the thermoset resins. ~H NMR
spectra obtained at various temperatures are sensitive to the site-
specific motions of the alkane chain. Molecular modeling provides a
powerful technique for interpreting the NMR spectra, and forms a basis
for the modeling of crosslinked polymers in general. The effects of the
mobility of the crosslink points at the chain ends, of the alkane chain
length, and of intermolecular chain interactions on the line shapes will
be discussed.
*This research was conducted under the McDonnell Douglas Independent
Research and Development program.
188