Synthesis and Characterization of Solid Polymethylaluminoxane: A Bifunctional Activator and Support for Slurry-Phase Ethylene Polymerization

Abstract

An insoluble form of methylaluminoxane, also known as solid polymethylaluminoxane (sMAO), has been synthesized by the controlled hydrolysis of trimethylaluminum (TMA) with benzoic acid, followed by thermolysis. Characterization of sMAO by multinuclear NMR spectroscopy in solution and the solid state reveals an aluminoxane structure that features "free" and bound TMA and incorporation of a benzoate residue. Total X-ray scattering (or pair distribution function, PDF) measurements on sMAO allow comparisons to be made with simulated data for DFT modeled structures of MAO. Several TMA-bound (AlOMe) n cage and nanotubular structures with n>10 are consistent with the experimental data. The measured Brunauer-Emmett-Teller (BET) surface area of sMAO ranges between 312 -606 m 2 g -1 and shows an N 2 adsorption/desorption isotherm consistent with a non-porous material. sMAO can be utilized to support metallocene pre-catalysts in slurry-phase ethylene polymerization reactions. Metallocene pre-catalyst rac-ethylenebis(1-indenyl)dichlorozirconium, rac-(EBI)ZrCl 2 was immobilized on sMAO samples, to afford solids which showed very high polymerization activities in hexane, comparable to those of the respective homogeneous catalysts formed by treatment of the pre-catalysts with MAO. rac-(EBI)ZrCl 2 immobilized on an sMAO containing an Al:O ratio of 1.2 gave the highest ethylene polymerization activity.

Slurry-Phase Ethylene Polymerization Using Pentafluorophenyl- and Pentafluorophenoxy-Modified Solid Polymethylaluminoxanes

“…Solid polymethylaluminoxane (sMAO) may be synthesized by the controlled hydrolysis of TMA with benzoic acid, 48 followed by two thermolysis steps (Scheme 3). We have reported that the ratio of these reactants is critical to the function of sMAO as an activating support, 43 with an [Al]:[O] ratio of 1.2 giving highest ethylene polymerization activity. Our starting point for the current study focussed on introducing C 6 F 5 OH as a modifier compound at different stages in this procedure.…”

“…The 27 Al Hahnecho 59 SSNMR spectra of sMMAO (0.10/B(C 6 F 5 ) 3 ) and (0.10/C 6 F 5 OH) at 15 kHz both show a broad envelope between 630 --715 ppm, which is very (b) (a) similar to that of the unmodified sMAO (Figures S12 and S17 in the Supporting Information). 43 Diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy was employed to further characterize the structural properties of the active supports (Figures S18-S20 in the Supporting Information). The DRIFT spectrum of sMAO shows several bands between 2700-3100 cm −1 and ca.…”

Interaction of Neutral Donors with Methylaluminoxane

“…Through baseline subtraction (or deconvolution) it is possible to determine both Me 3 Al and activator content by integration of these two signals with respect to the total integral due to MAO. The assumption used in our work is that the repeat unit of MAO is (Me 1.5 AlO 0.75 ).…”

Synthesis of zirconocene complexes and their use in slurry-phase polymerisation of ethylene

“…This insoluble 'solid MAO' can act simultaneously as both co-catalyst and support in slurry phase ethylene polymerisation. 28,29 Results and discussion Synthesis of ( 3-R Ind # ) 2 ZrX 2 (R ¼ Me, Et or Ph; X¼ Cl, Br or CH 2 Ph)…”