Two-dimensional 13C NMR of highly oriented polyethylene

Abstract

The two‐dimensional NMR procedure of separated local field spectroscopy [J. S. Waugh, Proc. Natl. Acad. Sci. USA 73, 1394 (1976)] is applied to fibers of highly oriented polyethylene. The 1H decoupled 13C chemical shift spectrum of the fiber oriented parallel to the external magnetic field is a single line, while a distinctive powder pattern results from the perpendicular orientation that is in excellent agreement with calculations. The 13C–1H dipolar splitting is 45 kHz at σ33 and nonexistent at σ22 consistent with perfectly aligned methylene groups with C–H bond length of 1.10 a.u. The splitting at σ11 is somewhat reduced from the predicted value; this finding, along with the temperature invariance of parameters, is discussed in terms of the molecular disorder and motion of the polymer.