Tailoring Mono-, Bi-, and Trimodal Molar Mass Distributions and All-Hydrocarbon Composites by Ethylene Polymerization on Bis(imino)pyridine Chromium(III) Supported on Ultrathin Gibbsite Single Crystal Nanoplatelets

Multimodal molar mass distributions (MWD) of high-density polyethylene (HDPE) were tailored either by reactor cascade technology using a chain transfer agent or by multisite polymerization catalysis combining different single-site catalysts on the same support in a single reactor. Herein, 2,6-bis-[1-(2,6dimethylphenylimino)ethyl]pyridine chromium(III) (CrBIP) is supported on methylaluminoxane (MAO)-tethered ultrathin yAl(OH)3 (gibbsite) single crystal nanoplatelets to produce reactor blends of HDPE wax and higher molar mass HDPE in a single reactor without adding either a second catalysts or a chain transfer agents. Lowering the MAO/gibbsite weight ratio enables unique switching from single -site to multisite nature of this catalyst system. In sharp contrast, ethylene polymerization on both homogeneous MAO/CrBIP and state-of-the-art heterogeneous CrBIP@MAO@Si02 catalysts exclusively produce HDPE wax (1000 g/mol) with narrow MWD (1.5). Both the MAO/gibbsite weight ratio of the CrBIP@MA0@gibbsite catalyst system and the polymerization time govern the HDPE wax/HDPE weight ratio. In addition, gibbsite single crystal nanoplatelets are calcinated at different temperatures prior to MAO tethering to establish the correlations between calcination temperature, MWDs, and catalyst activity. Upon calcination at 600 C, highly active catalysts are obtained, but the gibbsite single crystal structure is destroyed, and the resulting catalyst fails to produce higher molar mass HDPE. Cosupporting CrBIP together with quinolylsilylcyclopentadienylchromium(III) (CrQCp), which produces ultrahigh molar mass HDPE (U1-IMINPE), on the same gibbsite support yielded CrQCp&CrBIP@MA0@gibbsite dual-site catalysts producing trimodal MWDs. Here the UHMWPE content is increased by increasing the CrQCp/CrBIP molar ratio. Moreover, the nanophase separation of UHMWPE during polymerization and melt-flow processing accounted for the formation of all-hydrocarbon nanocomposites self-reinforced by unentangled extended chain UHMWPE 1D nanostructures.