A. Maus, C. Hertlein, K. Saalwächter.
A Robust Proton NMR Method to Investigate
Hard/Soft Ratios, Crystallinity, and Component Mobility in Polymers.
Macromol. Chem. Phys. 207, 1150–1158 (2006).
An improved proton NMR method for the realtime measurement of the hard/soft
ratio or the crystallinity, and the mobile-fraction dynamics, in phase-separated
or semicrystalline polymers is presented. It avoids some difficulties associated
with earlier approaches and can be applied on high- as well as inexpensive
low-field instrumentation. A pulsed mixed magic-sandwich echo is shown to
provide near-quantitative refocusing of the rigid contribution to the initial
part of the free induction decay. This essentially removes the need to account
for signal loss during the receiver dead time, and the method should thus be
useful for a variety of applications where the magnetization distribution over
differently mobile fractions is to be determined. The overall decay of the
mobile signal of a semicrystalline polymer was found to exhibit a significant
field dependence, such that the apparent transverse relaxation function of the
amorphous part is in a real-time experiment best characterized by a subsequent
Carr–Purcell–Meiboom– Gill pulse train. It is demonstrated to be mainly
influenced by mobility, while instrumental effects play a minor role. The
mobility of the amorphous fraction depends not only on the overall
crystallinity, but also on the crystallization conditions, thus on the