Proton magnetic resonance studies of the phase structure of bulk‐crystallized linear polyethylene

Abstract

Abstract The broad‐line proton NMR spectra of melt‐crystallized samples of polyethylene covering a very wide range in molecular weight have been analyzed in terms of contributions from three components: (1) a crystalline region with crystals of orthorhombic form; (2) a noncrystalline region with liquid‐like character which produces a Lorentzian contribution to the spectrum; and (3) an intermediate region in which the rotation of methylene groups about C—C bonds is partly hindered. The relative mass fractions as well as the character of these components depend greatly on the molecular weight. Samples of low molecular weight (e.g., ⩽30,000) are predominantly composed of lamellar crystalline regions with a minor amount of interfacial regions and no liquid‐like interzonal regions. As the molecular weight increases beyond 45,000, an interzonal region with a liquid‐like character associated with a higher molecular mobility is produced. Above a molecular weight of 100,000, this liquid‐like character becomes pronounced with an increase in molecular mobility in the interfacial region.