Nuclear Magnetic Resonance Detection of Two Distinctly Different Chains in the Orthorhombic Crystalline Phase of Polyethylenes.
Several com. and noncommercial, high- and low-d. and ultraoriented polyethylene samples, as well as polyethylene samples with inorg. fillers, have been investigated by inversion-recovery cross-polarization magic angle spinning carbon-13 NMR. In all these samples two types of all-trans chains in orthorhombic cryst. domains are detected, which give two overlapping carbon-13 lines with different line widths and different relaxation times. From the NMR relaxation parameters we conclude that one type of the cryst. chains, which composes 60-90% of the cryst. fraction in all samples, can execute at room temp. 180 Deg flips with a frequency in the kilohertz domain. The other cryst. chains are more rigid and probably are found in more perfect structures in which such chain flips do not occur or occur on a much slower time scale. Adding kaolin filler particles to polyethylene enhances the contribution of the more mobile cryst. chains. The presence of the two distinctly different types of cryst. environments is found in all polyethylene samples investigated so far (more than 25 samples).
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