Broad-line H NMR

To elucidate the phase structure in detail it is necessary to characterize the molecular chain conformation and dynamics in each phase. However, it is rather difficult to obtain such molecular information, particularly of the noncrystalline component, because it is substantially amorphous. In early research in this field, broad-line H NMR analysis showed that linear polyethylene crystallized from the melt comprises three components with different molecular mobilities solid, liquid-like and intermediate molecular mobility [13-16]. The solid component was attributed to molecules in the crystalline region, the liquid component to... 

Molecular Weight Dependence of Phase Structure. Similar line shape analysis was performed for samples with molecular weight over a very wide range that had been crystallized from the melt. In some samples, an additional crystalline line appears at 34.4 ppm which can be assigned to trans-trans methylene sequences in a monoclinic crystal form. Therefore the spectrum was analyzed in terms of four Lorentzian functions with different peak positions and line widths i.e. for two crystalline and two noncrystalline lines. Reasonable curve fitting was also obtained in these cases. The results are plotted by solid circles on the data of the broad-line H NMR in Fig. 3. The mass fractions of the crystalline, amorphous phases and the crystalline-amorphous interphase are in good accord with those of the broad, narrow, and intermediate components from the broad-line NMR analysis. 

Our broad-line XH NMR analysis showed that this type of sample generally consists of the phase structure of lamellar crystallites and noncrystalline overlayer with a negligible amount of the noncrystalline amorphous phase [16,62]. In broad-line H NMR spectra of solution-grown linear polyethylene samples, a narrow component that suggests the existence of a liquid-like amorphous phase is hardly recognized. In Table 2, the three-component analysis of the broad-line XH NMR spectra of linear polyethylene samples with different molecular weights that were crystallized isothermally from 0.08% toluene solution at 85 °C for 24 hours under a nitrogen atmosphere is summarized. 

As can be seen, for both samples the crystalline mass fraction (orthorhombic plus monoclinic) agrees well with that estimated from the density measurements and broad-line H NMR analysis. The thicknesses of the interphases are 3.8 and... 

Fig. 2. a 60 MHz broad-line H NMR spectrum of bulk polyethylene at 20 °C. b Two-component analyses, dotted line straight line decomposition [45] dashed line symmetrical decomposition [46,47]... 

Fig. 3. Mass fractions of crystalline, rubbery, and crystalline-amorphous interfacial phases of bulk polyethylene as a function of molecular weight Mv O data by broad-line H NMR analysis. data by high-resolution NMR analysis...

Generally the sweep width of broad-line NMR is about 10 to 10 Hz, while that of high-resolution NMR is about 10 Hz at 36.4 MHz for a proton. But the H NMR spectra of the mesophase for Kureha pitch (Figure 8) and ethylene tar pitch (Figure 9) were swept over 2.5 x 10" Hz. Thus the sweep width of the H NMR spectrum for the carbonaceous mesophase is intermediate between those of broad-line H NMR... 

FIG. 4 Broad line H NMR spectrum of solid polyethylene and its components obtained by digital decomposition (a) absorption lineshape and (b) derivative lineshape. Solid curves, experimental dash-dot, crystalline short dashes, partially ordered long dashes, amorphous phase. (Adapted from Ref. 10.)... 

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