I. Schnell, S. Brown, H. Low
Oct 28, 1998
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Journal
Journal of the American Chemical Society
Abstract
A combination of solid-state 1H NMR techniques, namely MAS, CRAMPS, and DQ MAS spectroscopy, is used to investigate the hydrogen-bonding properties of a range of alkyl-substituted benzoxazine dimers in the solid state. These dimers are of interest because they serve as model compounds for a class of recently synthesized polymers, the polybenzoxazines, whose unusual properties, in particular a near-zero shrinkage or volumetric expansion upon curing, have been rationalized in terms of favorable hydrogen-bonding interactions. The enhanced resolution achievable at the only recently available very-fast MAS rotation frequency of 35 kHz coupled with the sensitivity of the 1H chemical shift to the hydrogen-bonding arrangement means that much useful information can be obtained by simple MAS alone. In addition, spectra obtained by using a recently introduced CRAMPS approach, suitable for fast MAS and requiring no special experimental setup, are presented. Comparing the methyl- and ethyl- (and n-propyl-) substituted...