The water-soluble catalyst precursor [[(2,4,6-(3,5-(CF3)2C6H3)3-C6H2)-N═C(H)-(3-(9-anthryl)-2-O-C6H3)-κ(2)-N,O]Ni(CH3)(TPPTS)] (TPPTS = tri(sodiumphenylsulfonate)phosphine) polymerizes ethylene to aqueous dispersions of highly ordered nanoscale crystals (crystallinity χ(DSC) ≥ 90%) of strictly linear polyethylene (<0.7 methyl-branches/1000 carbon atoms, Mn = 4.2 × 10(5) g mol(-1)). SAXS in combination with cryo-TEM confirms this unusually high degree of order (χ(SAXS) = 82%) and shows the nanoparticles to possess a very thin amorphous layer on the crystalline lamella, just sufficient to accommodate a loop, but likely no entanglements. This ideal chain-folded structure is corroborated by annealing studies on the aqueous-dispersed nanoparticles, which show that the chain can move through the crystal as evidenced by lamella thickening without disturbing the crystalline order as concluded from an unaltered low thickness of the amorphous layers. These ideal chain-folded polyethylene nanocrystals arise from the crystallization in the confined environment of a nanoparticle and a deposition of the growing polymer chain on the crystal growth front as the chain is formed by the catalyst.

The crystallization and the mechanical properties of polyethylene, which is one of the most important commodity polymers, are influenced by the crystalline α-relaxation. This process originates from the diffusive chain transport through the crystallites as mediated by local 180°flips. Recent studies have stressed the relevance of the chain folding morphology on the chain diffusion, but its relation to the rate of jumps of the individual repeat units has not yet been addressed. In this study, we compare samples with very different morphology, including nanocrystals as a unique new model system, and use proton low-field and carbon-13 high-field solid-state NMR spectroscopy to determine the rate of local jumps and the largescale crystalline−amorphous diffusion coefficient, respectively. We find that samples with tight folds (reactor powders and nanocrystals) display on average lower activation energies of the local jumps. Nanocrystals stand out in that they feature a significantly broader distribution of local jump rates, which we attribute to the location of stems in the finite nanocrystal. Our results for the crystalline−amorphous long-range diffusion are at partial variance with previous findings in that samples with tight folds do not generally exhibit the fastest diffusion, and we discuss the related ambiguities. Our data suggest that the higher chain mobility in the amorphous domain of melt-crystallized samples has an accelerating effect on intracrystalline chain dynamics at high temperatures but is accompanied by a more progressive slowdown at low temperatures due to cooperativity effects.

The novel neutral κ2-N,O-salicylaldiminato Ni(II) complex, [κ2-N,O-{2,6-(3′,5′-R2C6H3)2C6H3-NC(H)-(3,5-I2-2-O-C6H2)}NiCH3(pyridine)] (1a-pyr, R = NO2), with four nitro substituents on the N-terphenyl motif is a catalyst precursor for ethylene polymerization to yield linear higher molecular weight polyethylene (e.g., M n 2.1 × 105 g mol–1 and only 2 methyl branches per 1000 carbon atoms). A comparison with other known catalyst precursors at various polymerization conditions shows that the catalytic properties in terms of linearity and molecular weight are similar to the fluorinated catalyst precursor with R = CF3, showing that the latter is not singular, but rather suppression of chain transfer and branch formation by β-hydride elimination can also be brought about by nonfluorinated electron-withdrawing remote substituents.

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Polymer crystals are metastable and exhibit morphological changes when being annealed. To observe morphological changes on molecular scales we started from small nanometer-sized crystals of highly fold ed long-chain polymers. Micron-sized stripes consisting of monolayers or stacks of several layers of flat-on oriented polyethylene nanocrystals were generated via evaporative dewetting from an aqueous dispersion. We followed the morphological changes in time and at progressive ly hi gher annealing temperatures by determining the topography and viscoelastic properties of such assemblies of nanocryst als using atomic force microscopy. Due to smallness and high surface-to-volume ratio of the nanocrystals, already at 75 °e, i. e. about 60 degrees below the nominal melting point, the lateral size of the crystal coarsened. Intriguingly, this occurred without a noticeable reduction in the number of folds per polymer chain. Starting at around 110°C, chain folds were progressively removed leading to crystal thickening. At higher temperatures, but still below the melti ng point , prol onged anll eali ng allowed for surface diffusion of molten polymers on th e initially bare substrate, leading eventually to the disappearance of crystals. We compared these results to the behavior of the same nanocrystals annealed in an aqueous dispersion and to bulk samples .