Identification and quantitative analysis of the intermediate phase in a linear high‐density polyethylene

Abstract

The observation of chain conformation and mobility in polyethylene by solid‐state 13C magic angle spinning (MAS) nuclear magnetic resonance (NMR) permits unambiguous identification and quantitative analysis of an intermediate phase. The carbon‐carbon bonds in the intermediate phase adopt, on the average, an all‐trans conformation and are more mobile than in the crystalline state (room temperature rate of reorientation ≈ 107 Hz). Comparisons of crystallinities by differential scanning calorimetry, wide‐angle x‐ray diffraction, and NMR support the high orientation of the intermediate phase and suggest a lower heat of fusion than for the crystals. Results from 13C spin‐lattice relaxation and 1H spin diffusion show that the mass fractions are ≈ 20% and the domain sizes ≈ 36 Å. Both change with crystallization and annealing conditions. © 1994 John Wiley & Sons, Inc.

Variable-temperature study of a gel-spun ultra-high molecular-mass polyethylene fiber by solid state NMR

“…The current NMR method on the determinations of mass fractions of the alltrans components (including the orthorhombic and the intermediate phases) and the amorphous phase have been documented [9,10]. The method involves curve fitting of two peaks (one all-trans peak at 33.0 ppm and one amorphous peak at 31.2 ppm) for each variable contact time of the cross-polarization and magic-angle-spinning spectra.…”

“…In addition, a quantitative method has also been established for the determination of the mass fractions of the crystalline, the intermediate, and the amorphous phases in melt-crystallized polyethylenes [9]. Initial success of applying such a concept and quantitative method at ambient temperature for the structure-property study of PE fibers has been noted [8,10].…”

“…The operational definition of the intermediate phase by solid state NMR, DSC, and wide angle X-ray diffraction (WAXD) have been introduced by examining the chain conformation and mobility [9]. It could be shown by solid state t3c NMR that the intermediate phase is a region in which the carbon--carbon bonds adopt, on the average, all-trans conformation and are more mobile than 0368 ~6619615 5.00 John Wiley & Sons, Limited 9 1996 Akad~miai Kiad6, Budapest Chichester those in the crystalline state.…”

Phase Structures of Nascent Polyethylene Powder Studied by Wideline Proton NMR

“…However, the NMR crystallinity is much higher than DSC crystallinity, generally the difference between these two techniques is 10%-20%, as can be seen in Table 2 and Figure 2. It is well accepted that crystallinity obtained from WAXD can be much higher than from DSC, 14,15 because an intermediate region existed between the crystalline and amorphous phases, and this intermediate phase also possesses diffraction intensity within the WAXD peaks chosen while giving comparatively less contribution to heat of fusion, thus yielding a higher apparent crystallinity than DSC. As for the agreement between X NMR and X WAXD , similar results were reported for annealed samples by 1 H line shape analysis 3 and 13 C NMR.…”

Thermodynamics and kinetics of crystallization of flexible molecules

“…This difference has also been detected by a discrepancy between X-ray and DSC crystallinity. 87 The size of this intermediate phase was estimated to be about 4.0 nm for melt crystallized samples.…”