Simple NMR Experiments Reveal the Influence of Chain Length and Chain Architecture on the Crystalline/Amorphous Interface in Polyethylenes

Abstract

The distribution of polyethylene (PE) chain segments between the crystalline, noncrystalline, and interfacial morphological regions is an old question that continues to intrigue the polymer science community. Simple solid state NMR experiments described here reveal that even in the case of linear PE, four distinct chain components may be resolved and reliably quantified. The amounts of rigid crystalline chains in all-trans conformations, amorphous chains with increased equilibrium gauche conformer content undergoing essentially isotropic reorientation, mobile all-trans chains (termed mobile trans), and less mobile noncrystalline chains (termed constrained amorphous) can be quantified by simple 13C NMR experiments on solid polymer samples. A version of the EASY background suppression pulse sequence [Jaeger and Hemmann Solid State Nucl. Magn. Reson. 2014, 57–58, 22], modified to eliminate transient Overhauser effects, is used to obtain all of the data in a single experimental acquisition. Using a broad rang...