In this paper, we report the full resonance assignments in the olefinic region of the 600
MHz 1H NMR spectra of a typical ethene/1-octene copolymer (4.0 mol % of octene units) produced with
a metallocene catalyst at high temperature, and of an ethene homopolymer prepared under similar
conditions for comparison. The assignments were based on a thorough analysis of 1D (1H, 1H{1H}, 13C)
spectra and of 2D 1H−1H (COSY, TOCSY) and 1H−13C (HSQC, DEPT-HSQC) maps. Thirteen different
olefinic structures were identified, and their formation explained in terms of plausible mechanistic paths
associated with the high polymerization temperature. The fraction of internal chain unsaturations
traceable to allylic activation turned out to be comparable to that of terminal ones in both samples. Despite
its complexity, the said spectral region is now amenable to deconvolution and full simulation in terms of
known and recognizable patterns, and usable for fast (possibly on-line) measurements of chain
unsaturation degree, as well as for catalyst “fingerprinting” studies.
Several commercial and noncommercial, high- and low-density and ultraoriented polyethylene samples, as well as polyethylene samples with inorganic fillers, have been investigated by inversion-recovery cross-polarization magic angle spinning carbon-13 nuclear magnetic resonance (NMR). In all these samples two types of all-trans chains in orthorhombic crystalline 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 crystalline chains, which composes 60-90% of the crystalline fraction in all samples, can execute at room temperature 180 degrees flips with a frequency in the kilohertz domain. The other crystalline 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 kaoline filler particles to polyethylene enhances the contribution of the more mobile crystalline chains. The presence of the two distinctly different types of crystalline environments is found in all polyethylene samples investigated so far (more than 25 samples).
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