Separation of Components in Crystalline and Amorphous Regions of Polyethylene by Solid State Carbon-13 Nmr Spectroscopy

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Abstract
The cross-polarization (CP) technique1–2, combined with magic angle sample spinning (MAS)3,4 and high power decoupling5, usually provides high resolution spectra of solids2,6–8. These high resolution 13C NMR spectra are in many cases sufficiently detailed to characterize the system9–17 In the case of polyethylene (PE), it was shown that distinct conformations in the crystalline regions lead to a narrow crystalline resonance and the non-crystalline regions appear as a broad shoulder on the upfield side. 14 Since it is often difficult to obtain detailed information from unresolved spectra, it is either desirable to resolve these peaks or isolate one resonance peak from another by alteration of the measurement. We report here the identification of different components in each of the crystalline and amorphous regions. This result is based on differences in the strength of the I3C-lH dipolar interactions, and these components are characterized by different dipolar dephasing time decay constants (TDD).