Neutral Nickel(II) methyl catalysts with (κ<sup>2</sup>-<i>N,O</i>) salicylaldiminato ligands show high activities towards linear high molecular weight polyethylene. Their tolerance of polar compounds can be used for a unique structure forming principle: Water-soluble types of these catalyst are capable of producing polyethylene starting from a homogenous aqueous surfactant solution. By this aqueous catalytic polymerization, polyethylene can be obtained in the unusual morphology of nanoscale single crystals. They are characterized by an exceptionally high degree of order thought to arise from the particular formation process: the growing chain is deposited on the crystal growth front, leaving no opportunity for entanglements or other disorder. Isotope labelling of the catalyst and monitoring of the reaction in a custom-made pressure reactor reveal that under appropriate conditions single chain nanocrystals are formed. To generate such particles with uniform lateral crystal sizes, full control of the catalytic crystal growth process is necessary. This requires novel catalysts stable over the entire aqueous polymerization experiment. In turn, a mechanistic picture of the relevant deactivation reaction is necessary. We will present our ongoing studies employing advanced catalysts and careful process design to produce nanoscale dispersions of ultra-high-molecular-weight polyethylene, and to control uniform nanocrystal sizes and shapes.

Single chain polyethylene nanocrystals

253rd National Meeting (2017)

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