Hydrophilic Catalysts with High Activity and Stability in the Aqueous Polymerization of Ethylene to High‐Molecular‐Weight‐Polyethylene

Abstract Water‐soluble synthetic transition metal catalysts have been studied extensively for many reactions, but for olefin polymerization such catalysts have been lacking. We report herein a straightforward synthesis of phosphinephenolato NiII catalysts endowed permanently with a hydrophilic sulfonate moiety bound to the chelating ligand. These catalysts’ hydrophilic active sites promote aqueous ethylene polymerization with high activity (TOF up to 6.3×104 molEthylene molNi −1 h−1) to high molecular weight polyethylene (HDPE), with half‐lives on the order of hours also at elevated temperatures. The obtained polyethylene dispersions feature narrow particle size distributions without any aggregates.


2-(2-(2',6'-(MeO)2-3'-SO3Na-C6H2)C6H4)(Ph)P-4-F-6-t Bu-C6H2OH (1c): 1c was prepared by
modification of a reported procedure. [7] 10 mL conc. H2SO4 were placed in a 50 mL round bottom flask and cooled to 0 o C. The powder of 1b (3 mmol, 1.46 g) was added into conc. H2SO4 over the course of 30 mins in several portions at 0 o C. The solution slowly turned yellow in color. The mixture was stirred for 3 hours, and the solution was added dropwise to a 100 mL conical flask with 50 g crushed ice. 6.0 M NaOH in water was then added dropwise to the cooled solution until it became neutral (pH ~7.0 as monitored by pH indicator paper). The aqueous solution was extracted with 50 mL CHCl3 three times. The organic phases were combined and dried over MgSO4 for 6 hours. The drying agent was filtered off, and the filtrate was concentrated under reduced pressure to give a light-yellow solid. This crude material was dissolved in 10 mL methanol, filtered and concentrated (this cycle was repeated) to give the desired product as a light yellow solid (1.68g, 2.85 mmol, 95%).
Two diastereomers are observed, with a ratio of isomer A to B of 1.3 to 1. Resonances originating from isomer B are indicated by a dash ('). 1 Figure S4. 1 H NMR spectrum of 1c in CD3OD at 300 K. Figure S5. 13 C{ 1 H} NMR spectrum of 1c in CD3OD at 300 K. S13 Figure S6. 13 C{ 1 H} NMR spectrum of 1c in CD3OD at 300 K (details of aromatic regime). was observed, and the reaction mixture turned to yellow. The reaction mixture was stirred for 4 hours at room temperature, and volatiles were removed in vacuo. The residue was dispersed with benzene again, and nickel black formed during the reaction was removed via centrifugation. The yellow solution was frozen by cooling in liquid nitrogen und the solvent removed by freeze drying to give the desired product as a yellow powder (73 mg, 95 μmol, 95%). S14 Two diastereomers are observed, with a ratio of isomer A to B of 1.3 to 1. Resonances originating from isomer B are indicated by a dash ('). 1
2-(2-(2',6'-(MeO)2C6H3)C6H4)(Ph)P-4-F-6-C6F5-C6H2OH (2b): 2b was prepared by modification of a reported procedure. [8] At 0 o C, n-BuLi (6.9 mL, 1.6 M in hexane, 11 mmol, 1.1 equiv) was added dropwise to a solution of 2a (5.2 g, 10 mmol, 1.0 equiv.) in THF (30 mL). The reaction mixture was warmed to room temperature and stirred for 2 hours to give a brown suspension. The mixture was cooled to -78 o C, and C6F6 (9.3 g, 50 mmol, 5.0 equiv.) was added dropwise to the above solution at -78 o C. The mixture was warmed to room temperature slowly and stirred overnight to afford a red solution. The mixture was concentrated, the residue was dissolved in 20 mL degassed ethyl acetate, and 2 ml of conc. HCl were added. The mixture was stirred at room temperature overnight, and added slowly to a solution of 5 g NaHCO3 in 60 mL water and stirred for 30 minutes. The organic phase was separated, and the aqueous phase was extracted with ethyl acetate (2 × 20 mL). The combined organic phase were concentrated in vacuo, and the residue was subjected to column chromatography on silica using petrol ether/ethyl acetate = 20/1 as eluent to give pure 2b (3.8 g, 6.3 mmol, 63%).
Two diastereomers are observed, with a ratio of isomer A to B of 1.3 to 1. Resonances originating from isomer B are indicated by a dash ('). injected into the reactor, and the mixture was stirred at 1000 rpm. The reactor was pressurized with ethylene and brought to the desired temperature. During the polymerization experiment, constant pressure was applied, and the ethylene uptake was monitored. After the desired reaction time, the pressure was released stepwise. Below 15 bar residual pressure, the reactor was vented manually into a beaker to collect migrating dispersion due to foaming. The entire dispersion was weighed, filtered over cotton wool and the solids content was determined by precipitation of a 50 g aliquot of dispersion in 300 mL of methanol. After stirring for 30 minutes, the precipitated bulk polymer was filtered and washed thoroughly with water and methanol and dried in a vacuum oven (60 °C, 30 mbar) overnight.    (Table 1, entry 12).    Table   1, entry 1).      The thickness of the obtained polyethylene particle is independent of the duration of the polymerization experiment but influenced by the polymerization temperature (Table S1). At 30 ºC, the polymerization yields particles with a thickness of 8.1 ± 0.4 nm, at 50 ºC polymerization temperature slightly thicker particles (10.4 ± 0.5 nm) are obtained. This trend and these dimensions are in line with a single lamella nanoparticles of polyethylene. [9] The average volume of a particle Vpart was calculated according to Supplementary Equation S1. The average mass of one particle mpart was determined assuming a polyethylene density of ρPE = 0.94 g cm -1 (Supplementary Equation S2). The mass of a polymer chain mchain was calculated from the mass-average molecular weight Mw determined by GPC (Supplementary Equation S3).

NMR analysis
Together with the mass of a particle this provides the chains per particle ratio Nchain/Npart S39 (Supplementary Equation S4). The particle number per Ni Npart/Ni was calculated based on the yield of polyethylene mPE and the amount of Ni catalyst nNi used in the aqueous polymerization (Supplementary Equation S5). The particle number density cpart was calculated based on the particle number Npart and the volume of obtained dispersion. The quality of the data allows for an order of magnitude estimation of the chains per particle and the particle numbers (Table S2).     250 nm