Highly Tunable Catalyst Supports for Single-Site Ethylene

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Highly tuneable catalyst supports for single-site ethylene polymerization Jean-Charles Buffet, Nidwaree Wanna, Thomas A Q Arnold, Emma K. Gibson, Peter P. Wells, Qiang Wang, Jonggol Tantirungrotechai, and Dermot O'Hare Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/cm503433q • Publication Date (Web): 06 Feb 2015 Downloaded from http://pubs.acs.org on February 18, 2015

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35x35mm (300 x 300 DPI)

ACS Paragon Plus Environment


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Highly tuneable catalyst supports for single-site ethylene polymerization Jean-Charles Buffet,a Nidwaree Wanna,a,b Thomas A. Q. Arnold,a Emma K. Gibson,c,d Peter P. Wells,c,d Qiang Wang,a,e Jonggol Tantirungrotechai,b and Dermot O'Hare*a a

Chemistry Research Laboratory, Mansfield Rd, Oxford, OX1 3TA, UK, E-mail: [email protected]. Center for Catalysis, Department of Chemistry and Center for Innovation in Chemistry, Faculty of Science, Mahidol University, 272 Rama VI Rd., Thung Phayathai, Ratchathewi, Bangkok 10400, Thailand. c UK Catalysis Hub, Research Complex at Harwell, Rutherford Appleton Laboratory, Harwell Oxon, Didcot, OX11 0FA, UK d Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK. e College of Environmental Science and Engineering, Beijing Forestry University, 35 Qinghua East Road, Haidian District, Beijing 100083, China. b

ABSTRACT: A new class of tuneable crystalline solid supports for metal complexes have been synthesised and used for ethylene polymerization. We have developed a family of high surface area, highly dispersible layered double hydroxides (AMO-LDHs) which, on treatment with alkyl aluminum activators, are able to support metallocene and non-metallocene complexes to make active catalyst systems for the slurry polymerization of ethylene. We show that the chemical composition of the AMO-LDH support can dramatically affect catalyst activity, polymer morphology, and polymer microstructure. A Zr K-edge EXAFS study of these active catalysts has enabled us to observe a metallocene-derived single-center catalytic species in close proximity to the support. 10-11

INTRODUCTION Polyethylene is the most widely used polyolefin with a global production in 2011 of over 75 million tons per year. Innovation in both the synthesis and the properties of polyethylene is still at the forefront in both industry 1 and academia. Polyethylene production using supported metallocene catalysts is an important and growing com1 ponent in polyethylene production. It is now more than thirty years since the first discovery of highly active homogeneous molecular metal catalysts for olefin polymerization. Since then intensive research and innovation has led to greater control over polymerization productivities and polymer structure than cannot generally be obtained with the original type of heterogeneous Ziegler– 2 Natta catalysts. Homogeneous catalysts, such as metallocenes are now successfully used on a commercial scale in solution phase (e.g. Nova Surpass, Exxon EXACT, Dow Elite). We understand it well because the complexes are well defined and the mechanism is well understood through stochi3 ometric reaction for mechanistic studies. However, heterogeneous catalysts systems based on metallocenes require immobilization on a suitable support material in order to prevent reactor fouling in gas-phase and slurry-phase processes. Many different supports (eg. SiO2, Al2O3, MgO, SiO(F)2, MgCl2, MgF2, CaF2, AlCl3, and clays) and immobiliza4-9 tion procedures have been investigated. Most frequently, immobilization of the catalyst leads to much lower activity than was obtained under homogeneous polymerization condition, however occasionally catalyst immobilization results in the stabilization of the active catalytic species and a reverse of this trend. Most commercial metallocene support systems strive to reproduce “single-site” catalyst performance

on systems based on porous spherical silica/aluminas. Recently, surface organometallic chemistry became a tool for synthesizing and studying well-defined species on the surface, helping us to understand the surface species involved in 12 the polymerization. Layered double hydroxides (LDHs) are a family of compounds containing brucite-like layers with general ' y+ n– chemical composition [M1–xM x(OH)2] [A y/n].zH2O, 2+ where M is typically a divalent cation such as Mg and 3+ M' is typically a trivalent cation such as Al , A = anions, although many other metal combinations are possible. LDHs have captured much attention in recent years due to their impact across a range of applications such as 13 14 15,16 catalysis, optics, medical science, and in inorganic17-20 organic nanocomposites. To date, there have been almost no reports on the use of LDHs as a support for organometallic catalyst systems. Zhang and co-workers reported the use of an organo-modified LDH using a supported nickel di-imine catalyst for the synthesis of 21,22 Recently, we have reported ethylene nanocomposites. the synthesis of a new family of dispersible, hydrophobic LDHs using the aqueous miscible organic solvent treat23 ment (AMOST) method. These AMO-LDHs disperse in non-polar hydrocarbons, retain the crystalline structure of LDHs but remarkably exhibit surface areas in excess 2 of 400 m /g and pore volumes in excess of 2.15 cc/g which is nearly two orders of magnitude higher than 23 conventional layered double hydroxides. Here, we introduce AMO-LDHs as a new class of well-defined, cost effective, scaleable solid support for heterogeneous olefin polymerization and the characteri-


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zation of single-site catalyst centers on these active supports.

FT k2χ (R) / Å-3

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Data Fit

Data Fit Zr-C(path) Zr-C-C(multiplescattering path) Zr-O Zr-Al

0

1

2

3

4

5

6

R(Å) Figure 1. Zr K-edge EXAFS study of MgAl-SO4/MAO/(EBI)ZrCl2. a) Magnitude component of the k2 weighted Fourier transform for the EXAFS data and fit for each pathway and b) suggested local structure (black: carbon, red: oxygen, purple: zirconium, magenta: hydrogen, green: sulfate anion, blue: magnesium and yellow: aluminum).

RESULTS AND DISCUSSION Synthesis and characterizations of the catalysts AMO-LDHs have a unique chemical composition given z+ y+ a+ n– by [M 1–xM' x(OH)2] (A )a/n•bH2O•c(AMO-solvent) wherein M and M’ are metal cations, z = 1 or 2; y = 3 or 4, 0 < x < 1, b = 0 - 10, c = 0 - 10, A is an anion, n = 1 to 3 and a = z(1–x)+xy–2 which instantly distinguishes them from conventional LDHs, we have abbreviated these LDHs to 24,25,26 MM’-A (e.g. MgAl-CO3 or MgAl-SO4). Most importantly and uniquely AMO-LDHs are hydrophobic and can be dispersed in non-polar aromatic hydrocarbons which enables facile surface modification using organometallic reagents. Low temperature thermal o treatment (150 C for 6 h) of the AMO-LDHs followed by reaction with half equivalent of methylaluminoxane (MAO) in toluene leads to the immediate evolution of methane and the synthesis of an AMO-LDH/MAO. Treatment of a dispersion of a hundred equivalents of AMO-LDH/MAO in toluene with either two equivalents of a zirconocene dichloride complex (e.g. racethylenebis(1-indenyl) zirconium dichloride; (EBI)ZrCl2) or bis(imino)pyridine iron complex, 2,4,6-MeMes C6H3N=CMe)2C5H3N, ( PDI)FeCl2 leads to rapid decolorization of the solution and the formation of a colored solid defined as AMO-LDH/MAO/complex. X-ray powder diffraction of the AMO-LDH/MAO/complex show that these materials are crystalline and retain the basic LDH layered structure (Figures SI2-7). The IR spectra of all the AMO-LDH/MAO/complex materials exhibit three characteristic absorptions of meth–1 ylaluminoxane (MAO) at 3090, 3020, and 2950 cm and the characteristic bands for the intercalated anions (Figures SI15). Both AMO-LDH/MAO/(EBI)ZrCl2 and AMOLDH/MAO/(EBI)ZrMe2 exhibit the expected Zr-Me –1 bands at around 800 cm , Figure SI16, which is similar 32 to the report by Rytter and co-workers. This suggests that the methylation of the Zr-Cl bond occurred when

reacting with the aluminoxane surface. Solid state MAS 27 27 Al NMR spectroscopy shows only one Al resonance for MgAl-CO3/MAO/(SBI)ZrCl2 {(SBI)ZrCl2 = dimethylsilylbis(1-indenyl) zirconium dichloride} due to both the LDH and the MAO, Figure SI17. The solid state MAS 13 1 C{ H} NMR spectroscopy is able to highlight the changes which occur due to the MAO surface treatment and then complex immobilization steps. Initially, MgAl-CO3 13 exhibits a single C resonance at 160 ppm due to the 2– intercalated CO3 ion, MgAl-CO3/MAO exhibits reso2– nances at 160 and –10 ppm (due to CO3 and -CH3, respectively), and MgAl-CO3/MAO/(SBI)ZrCl2 has reso2– nances at 160, 30 and –10 ppm) (CO3 , SiCH3, and CH3, respectively), Figure SI18. In order to gain further insights into the nature of the metal complexes bound to these supports we have carried out Zr K-edge EXAFS studies on (EBI)ZrCl2 supported on a series of AMO-LDH/MAO supports (Table 1). EXAFS studies on metallocene-based olefin polymeriza27-31 tion solid catalysts are extremely rare. O'Hare and coworkers published the first example for (EBI)ZrCl2 on a 27 MAO-modified mesorporous silica (MCM-41). Basset and co-workers reported a study of zirconocene alkyl 28 complex supported on silica and alumina. Dos santos and co-workers described various metallocenes on 29,31 methylaluminoxane derived silica supports. The fitting of Zr K-edge EXAFS data for MgAlSO4/MAO/(EBI)ZrCl2 is shown in Figure 1a and the refined parameters for the series of materials are summarized in Table 1. A representation of the surface structure based on the refinements of the EXAFS data is shown in Figure 1b. The 2 magnitude component of the k weighted Fourier transform 2 for the EXAFS data, k χ, and fit for MgAl-SO4 AMOLDH/MAO/(EBI)ZrCl2, (EBI)ZrMe2 and (EBI)ZrCl2-TIBA, and MgAl-borate AMO-LDH/MAO/(EBI)ZrCl2 are represented in Figures SI20-21. The Zr K-edge EXAFS data demonstrated that the zirconium is in tetrahedral environment with the (EBI) ligand, a



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methyl and in close contact with an oxygen atom from the surface.

a) b) Figure 2. Ethylene polymerization activities, molecular weights (Mw) and polydispersities (Mw/Mn) of various AMO-LDH/MAO/(EBI)ZrCl2. a): activity (kgPE/molZr complex/h) in black (left); molecular weights, Mw, (g/mol) in blue (right) and polydispersities, Mw/Mn, in parentheses. b): a) CaAl-NO3 (purple line); b) MgAl-NO3 (blue line); c) MgAl-CO3 (red line); d) MgGa-CO3 (green line). Polymerization conditions: 10 mg of catalyst, 1 bar, 0.25 h, [MAO]0/[M]0 = 2000, Hexane (25 mL). Table 1. EXAFS fitting parameters for MgAlSO4/MAO/(EBI)ZrCl2, MgAl-SO4/MAO/(EBI)ZrCl2-TIBA, and MgAl-SO4/MAO/(EBI)ZrMe2 Abs – Sc N R 2σ2 Eo Rfactor (set) (Å) (Å2) (eV) MgAl-SO4/MAO/(EBI)ZrCl2 Zr – C (Cpring) 10 2.51(2) 0.006(1) 20 3.21(4) 0.004(set) – Zr – C-C 0.049 2(2) Zr-O 1 2.26(4) 0.004(set) Zr-Al 1 3.34(5) 0.004(set) MgAl-Borate/MAO/(EBI)ZrCl2 Zr – C (Cpring) 10 2.50(2) 0.006(1) 20 3.26(3) 0.004(set) Zr – C-C –3(2) 0.048 Zr-O 1 2.20(4) 0.004(set) Zr-Al 1 3.30(5) 0.004(set) MgAl-SO4/MAO/(EBI)ZrCl2-TIBA Zr – C (Cpring) 10 2.48(1) 0.005(1) 20 3.22(4) 0.004(set) – Zr – C-C 0.040 8(2) Zr-O 1 2.20(set) 0.004(set) Zr-Al 1 3.32(3) 0.004(set) MgAl-SO4/MAO/(EBI)ZrMe2 Zr – C (Cpring) 10 2.53(2) 0.011(1) 20 3.23(3) 0.004(set) Zr – C-C 0(2) 0.035 Zr-O 1 2.5(1) 0.004(set) Zr-Al 1 3.36(5) 0.004(set) Fitting parameters: S02 = 0.8 as deduced by ZrO2 standard; Fit range 3 < k< 11.5, 1.1 < R < 4; # of independent points = 15, Zr-C-C denotes a multiple scattering path.

Ethylene-bis(1-indenyl) zirconium dichloride, (EBI)ZrCl2, and the bis(imino)pyridine iron complex, (2,4,6-MeMes C6H3N=CMe)2C5H3N, ( PDI)FeCl2 supported on these AMO-LDH/MAO have been tested for their performance in the slurry-phase polymerization of ethylene in hexanes in the presence of an aluminum activator. Typical reaction conditions are 10 mg of solid catalyst, 1 or 2 bar ethylene and [MAO]0/[M]0 = 2000 or [TIBA]0/[M]0 = 2000. The polymerization reactions proceed very smoothly producing free flowing spherical polyethylene in high yields. There was no evidence in any experiments of reactor fouling or leaching of the catalyst from the support. One of the most remarkable features we discovered was that the chemical composition of the AMO-LDH (MM’-A) had a significant effect on the activity of the catalyst systems and the nature of the polyethylene formed. For example, when (EBI)ZrCl2 is supported on a range of AMOLDH/MAOs we observe a variation in catalyst activity between 898-5516 kgPE/molZr complex/h under identical catalyst loading and polymerization conditions. A graphical summary of this variation is shown in Figure 2 and the data are collated in Table 2. Table 2. Ethylene polymerization activities, molecular weights (Mw) and polydispersities (Mw/Mn) of various AMOLDH/MAO/(EBI)ZrCl2.a

The least squares best fit for the Zr K-edge EXAFS data clearly shows an intact “(EBI)Zr” moiety in close contact with the AMO-LDH/MAO surface. Furthermore, the EXAFS refinement improve dramatically on inclusion of Zr-O contacts of 2.20(4)-2.26(4) Å for the (EBI)ZrCl2 based catalyst systems and 2.5(1)Å for (EBI)ZrMe2; both distances are longer than 28 those shown by Basset and co-workers (2.01(3) Å). All Zr-Al contacts are between 3.30(5) < R < 3.36(5) Å. Unfortunately, EXAFS is not able to distinguish if this is due to an ion-pair interaction or a covalent Zr-O-Al linkage. Figure 2b is our current best interpretation of the EXAFS data. Overall, the quality of the refinements are excellent and we ascribe this to the ordered nature of the solid support system.


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LDH support

Activitiesb

Mwc,d

CaAl-NO3

1983

195404

MgAl-NO3

936

221647

MgAl-Cl

2545

244467

MgAl-SO4

5613

270964

MgAl-CO3

3405

286980

MgAl-borate

898

240361

Mw/Mnd 3.08 3.29 3.08 3.14 3.47 3.47 3.39

MgGa-CO3 3256 275826 polymerization conditions: 10 mg of catalyst, 1 bar, 0.25 h, [MAO]0/[M]0 = 2000, Hexane (25 mL). bkgPE.molcomplex/h. cg/mol. d determined by gel permeation chromatography. a

In terms of the divalent cations in the layer structure of the 2+ 2+ catalyst, Ca exhibited double the activity of Mg which we believe is due to the higher basicity to the support. In contrast, no difference in activity was observed between the tri3+ 3+ valent cations; Al and Ga (Table SI2). Catalytic performance was also dependent on the nature of the intercalated 2– 2– – – anion (A) in the following order: SO4 > CO3 > Cl > NO3 ~ borate. So far, no reliable correlation has been found between the anion size or the d-spacing of the layered double hydroxide support. Considering these results, divalent anions seem to yield a more active catalyst system than the monovaMes lent. When the iron complex ( PDI)FeCl2 was used, the activities are higher than with the zirconium catalysts by a factor of seven (on MgAl-CO3 AMO-LDH/MAO: 13396 and 2233 kgPE/molM complex/h, respectively). We have also investigated the nature of the polyethylene produced by these systems. (EBI)ZrCl2 supported AMOLDH/MAO displayed a polydispersity index (Mw/Mn) in the range of 3.08 - 3.47 which is consistent with single-site catalytic behavior. Among the AMO-LDH/MAO catalysts, MgAlCO3, MgGa-CO3 and MgAl-SO4 expressed both high catalytic performance and produced high molecular weight polymer (Mw = 270964 – 286980 kg/mol), whereas polyethylene obtained from CaAl-NO3 AMO-LDH/MAO catalyst showed the lowest molecular weight (Mw = 195404 kg/mol). Hence, demonstrating the tuneable effect of the polymer properties (up to 35% variation in molecular weights) and activities (up to 125% variation) due to the various AMO-LDH supports. Furthermore, polyethylene obtained from most of the catao lysts started to degrade (oxidize) at approximately 450 C unlike that from those based on MgAl-borate and MgAl-Cl o AMO-LDH which decomposed at 150 and 350 C respectively, Figure 3.

Figure 3. Thermal behavior of polyethylene (in air) using AMOLDH/MAO/(EBI)ZrCl2 catalyst with varied LDH components: a) CaAl-NO3 (dark blue line), b) MgAl-NO3 (red line), c) MgAl-Cl (green line), d) MgAl-SO4 (purple line), e) MgAl-CO3 (turquoise blue line), f) MgGa-CO3 (orange line), and g) MgAl-borate (grey blue line), under the condition of under the condition of: 10 mg of catalyst, 1 bar, 0.25 h, 60 °C, [MAO]0/[M]0 = 2000, Hexane (25 mL).

Table SI4 shows that MgAl-CO3 AMO-LDH/(EBI)ZrCl2 has an activity 25% higher than an equivalent conventionally prepared LDH (2252 and 1753 kgPE/molZr complex/h). The reMes sults are more dramatic when ( PDI)FeCl2 was used. The Mes MgAl-CO3 AMO-LDH/( PDI)FeCl2 activity is 10 times higher than that of a commercial hydrotalcite (13396 and 1311 kgPE/molZr complex/h respectively). This is also true when MgAl-Cl AMO-LDH was used in comparison to conventional-LDH (6816 and 682 kgPE/molZr complex/h, respectively). This could be explained by the fact that the pore volumes of the AMO-LDH were found to be much bigger than the conven3 tional synthesised ones (0.031 to 0.63 cm /g and 0.00035 to 3 24a 0.11 cm /g respectively, an increase up to 147239%). The activities increased and with increasing temperature up to 70 °C (2142 kgPE/molZr complex/h) while the molecular weights decreased with increasing temperature (from 223350 –1 at 50 °C to 66042 g/mol at 90 °C), Figure 4. The relatively low molecular weights at higher temperature is may be due to an increase in the rate of chain termination and/or chain transfer to the monomer or a decrease rate of ethylene 33 polymerization. Hence, the difference between the rate of ethylene polymerization and termination is the highest at 70 °C.

Figure 4. Ethylene polymerization activities, molecular weight (Mw) and polydispersities (Mw/Mn) with variable temperature. Activity (kgPE/molcomplex/h) in black (left); molecular weights, Mw, (g/mol) in blue (right) and polydispersities, Mw/Mn, in parentheses. Polymerization conditions: MgAl-CO3/MAO/(EBI)ZrCl2, 10 mg of catalyst, 2 bar, 1 hour, [TIBA]0/[M]0 = 1000, Hexane (50 mL).



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The time of the polymerization was varied and the activities and polyethylene characteristic were studied, Figure 5 and Table SI8. At 80 °C, The activity decreased with increasing time from 15 minutes to 2 h (1590 and 402 kgPE/molZr complex/h respectively) possibly due to an increase in termination reaction or in diffusion rate (small volume of polymerization). The molecular weights slightly decreased following the time of polymerization, highlighting low termination due to transfer to the monomer (Mw of 143826 and 114028 g/mol, respectively). The polydispersities are constant between 3.25 < Mw/Mn < 3.99.

Figure 5. Variation in ethylene polymerization activities and molecular weights vs. temperature of polymerization using AMO-Mg3AlCO3/MAO/(EBI)ZrCl2: Mw (blue square) and activities (red circle). Polymerization conditions: 10 mg of pre-catalyst, 2 bar, 80 °C, [TIBA]0/[M]0 = 1000, hexane (50 mL).

We also studied the effect of the metallocene loading on the surface. We investigated the AMO-Mg3AlCO3/MAO/(EBI)ZrCl2 as the pre-catalyst system with the AMO-Mg3Al-CO3/MAO:complex ratio between 100:1 – 100:4 at 60 °C. The results are collated in Figure 6.

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site decreases. Commercially there is always a play off between productivity per gram catalyst and catalyst price. The fact that the activities are similar with a small complex loading is a good compromise. As a co-catalyst, triisobutylaluminum (TIBA) improved the morphology of the polymer but not the catalytic performance with respect to MAO (Figure SI31). Using TIBA as a co-catalyst afforded a lower molecular weight polymer than 34 MAO, similarly found by Peng et al.. The distribution beo came bimodal at 80 C when MAO was used (Figure SI25). The activity increases with increasing amount of scavenger in the system, from a ratio of [MAO]0/[Zr]0 of 1000 to 4000 (1871 and 3256 kgPE/molcomplex/h respectively) (Table SI9). Furthermore, the activity increases with increasing amount of catalyst in the system, from 10 to 40 mg of catalyst (1983 and 2170 kgPE molcomplex /h respectively) (Table SI10). Addition of a co-monomer improved the activity of the catalyst (Table SI12). As the 1-hexene content increased, copolymer became more translucent. However, the monomer content did not significantly affect thermal properties of the polymer (Figure SI26). In comparison to spherical commercial grade silica supported catalysts under the same conditions, to date these AMO-LDH/MAO supports have demonstrated 25% lower activities. However, the molecular weights were higher, Figures SI29-SI30. The system is far from optimized and we are hopeful that by careful tuning of the metal cations and the intercalated anions more active support systems can be prepared. More importantly, the AMO-LDH/MAO support system induces much better control over the polymer properties (molecular weights and polydispersities) (Figures SI28-SI30 and Table SI7) compared to grade silica supports. Commercially these supports make a significant impact as it would relatively straightforward to prepare them on a commercial scale and at current catalogue prices they are more than five 35 times cheaper than silica.

CONCLUSIONS

Figure 6. Variation in ethylene polymerization activity, polyethylene molecular weights (Mw) and polydispersities, (Mw/Mn) in parentheses as a function of metallocene loading using AMO-Mg3AlCO3/MAO/(EBI)ZrCl2: Mw (blue square) and activities (black square). Polymerization conditions: 10 mg of pre-catalyst, 2 bar, 1 hour, [TIBA]0/[M]0 = 1000, hexane (50 mL).

The weight ratio of AMO-Mg3Al-CO3/MAO:complex of 100:2 and 100:3 demonstrated the highest polymerization activities (up to 3083 kgPE/molZr complex/h) and molecular weights (Mw around 300000 g/mol). These data show that above a certain catalyst loading the effectiveness of an individual catalytic

In conclusion, we have described the synthesis and characterization of a new family of solid supports for use in heterogeneous ethylene polymerization catalysis. Zr EXAFS studies resulted in high quality data that demonstrate that these supports produce a single-center metallocene on the surface of a highly ordered AMO-LDH/MAO. The catalysts supported on an AMO-LDH/MAO demonstrate higher polymerization activities than the same catalysts supported on both conventional and commercial LDHs. The Mw of the polyethylene and the catalyst productivities vary with the type of AMO-LDH with MgAl-SO4 currently demonstrating the highest performance indicators. Single-site ethylene polymerisation catalysts supported on AMO-LDHs may offer a new opportunities to affect the properties of polyethylene.

Experimental section Synthesis of solid support pre-catalyst. A mixture of M2+ and M3+ salts with M2+:M3+ molar ratio of 3 was dissolved in deionized water, in which the concentration of M2+ was 0.75 mol/L. An aqueous solution of anion source was prepared with An–/M3+ molar ratio of 2, of which the pH was set at 10 by NaOH aqueous solution. The M2+/M3+ solution was added dropwise into an anion solution at room temperature under a nitrogen flow whilst maintaining the constant pH. After addition, the resulting slurry was vigorously stirred at room


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temperature overnight. The precipitate was then filtered, washed with acetone, and dried under vacuum to afford [Mz+1– y+ a+ n– xM’ x(OH)2] (A )a/n•bH2O•c(acetone). The AMO-LDHs was thermally treated at 150 oC for 6 h at 1 x 10–2 mbar and then stored under a nitrogen atmosphere. Thermally-treated AMO-LDH was weighed and slurried in toluene. Methylaluminoxane (MAO) with MAO:LDH mole ratio of 1:2 was prepared in toluene solution and added to the thermally-treated LDH slurry. The resulting slurry was heated at 80 oC for 2 h with occasional swirling. The product was then filtered, washed with toluene, and dried under dynamic vacuum to afford the AMO-LDH/MAO support. The AMO-LDH/MAO support was weighed and slurried in toluene. The solution of the chosen complex in toluene was added to the AMO-LDH/MAO slurry. The resulting slurry was heated at 80 oC for 2 h with occasional swirling. The product was then filtered and dried under dynamic vacuum to afford AMO-LDH/MAO/complex. Polymerization procedure. The AMO-LDH/MAO/complex, aluminum scavenger and hexane were weighed with the desired ratio and added to a high pressure ampoule. Ethylene gas was continuously fed into the ampoule at 2 bar during polymerization at the targeted temperature. After the desired time, the reaction was stopped by adding iPrOH/toluene solution. The polymer was quickly filtered and washed with toluene as well as pentane. The polymer was dried in a vacuum oven at 55 oC over-night and weighted.

ASSOCIATED CONTENT Electronic Supplementary Information (ESI) available: [X-ray powder crystallography, scanning electron microscopy, thermogravimetric analysis, infra-red spectroscopy, solidstate NMR spectroscopy, EXAFS details and polymerization graphs and tables]. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author *[email protected]

Notes The authors declare no competing financial interest

ACKNOWLEDGMENTS J.-C.B., N.W., T.A.Q.A. and Q.W. would like to thank SCG Chemicals Ltd, Thailand for funding and the EPSRC Catalysis Hub for beamline access. Q.W. thanks the Fundamental Research Funds for the Central Universities (TD-JC-2013-3), the Program for New Century Excellent Talents in University (NCET-12-0787). We thank Dr. T. Khamnaen and Dr. P. Thipphaya (SCG Chemicals Ltd, Thailand) for the gel permeation chromatography results. We thank Dr. Nicholas H. Rees (University of Oxford) for solid state NMR spectroscopy.

REFERENCES (1) (a) Kageyama, K.; Tamazawa, J.-I.; Aida, T. Science 1999, 285, 2113-2115. (b) Tailor-made Polymers via Immobilization of Alpha-Olefin Polymerization Catalysts, ed. Severn, J. R.; Chadwick, J. C. Wiley-VCH Verlag GmbH, Weinheim, 2008. (2) (a) Kaminsky, W.; Arndt, M. Adv. Polym. Sci. 1997, 127, 143– 187. (b) Kaminsky, W. J. Polym. Sci., Part A: Polym. Chem. 2004, 42, 3911–3921. (c) Brintzinger, H. H.; Fischer, D.; Mülhaupt, R.; Rieger, B.; Waymouth, R. M. Angew. Chem., Int. Ed. 1995, 34, 1143–1170. (d) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev. 2003, 103, 283–315. (e) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F.

Angew. Chem., Int. Ed. 1999, 38, 429–447. (f) Resconi, L.; Cavallo, L.; Fait, A.; Piemontesi, F. Chem. Rev. 2000, 100, 1253–1346. (3) Noda, S.; Nakamura, A.; Kochi, T.; Chung, L. W.; Morokuma, K.; Nozaki, K. J. Am. Chem. Soc. 2009, 131, 14088-14100. (4) (a) Klapper, M.; Daejune, J.; Nietzel, S.; Krumpfer, J. W.; Müllen, K. Chem. Mater. 2014, 26, 802-819. (b) Satyanarayana, G.; Sivaram, S. Macromolecules 1993, 26, 4712–4714. (c) Zakharov, V. A.; Paukshtis, E. A.; Mikenas, T. B.; Volodin, A. M.; Vitus, E. N.; Potapov, A. G. Macromol. Symp. 1995, 89, 55–61. (d) Mikenas, T. B.; Zakharov, V. A.; Echevskaya, L. G.; Matsko, M. A. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 2128–2133. (e) Huang, R.; Duchateau, R.; Koning, C. E.; Chadwick, J. C. Macromolecules 2008, 41, 579–590. (f) Huang, R.; Malizia, F.; Pennini, G.; Koning, C. E; Chadwick, J. C. Macromol. Rapid Commun. 2008, 29, 1732– 1738. (f) Matsui, S.; Mitani, M.; Saito, J.; Tohi, Y.; Makio, H.; Matsukawa, N.; Takagi, Y.; Tsuru, K.; Nitabaru, M.; Nakano, T.; Tanaka, H.; Kashiwa, N.; Fujita, T. J. Am. Chem. Soc. 2001, 123, 6847–6856. (g) Severn, J. R.; Chadwick, J. C.; Van Axel Castelli, V. Macromolecules 2004, 37, 6258–6259. (h) Kim, S. H.; Somorjai, G. A. Proc. Nat. Acad. Sci. 2006, 103, 15289-15294. (i) Garoff, T.; Mannonen, L.; Väänänen, M.; Eriksson, V.; Kallio, K.; Waldvogel, P. J. Appl. Polym. Sci. 2010, 115, 826-836. (5) (a) Arriola, D. J.; Carnahan, E. M.; Hustad, P. D.; Kuhlman, R. L.; Wenzel, T. T. Science 2006, 312, 714-719. (b) Bonini, F.; Fraaije, V.; Fink, G. J. Polym. Sci., Part A: Polym. Chem. 1995, 33, 2393–2402. (c) Kaminsky, W.; Strübel, C. J. Mol. Catal. A: Chem. 1998, 128, 191–200. (d) Kaul, F. A. R.; Puchta, G. T.; Schneider, H.; Bielert, F.; Mihalios, D.; Herrmann, W. A. Organometallics 2002, 21, 74–82. (e) Zheng, Z.; Liu, J.; Li, Y. J. Catal. 2005, 234, 101–110. (f) Han, W.; Müller, C.; Vogt, D.; Niemantsverdriet, J. W.; Thüne, P. C. Macromol. Rapid Commun. 2006, 27, 279–283. (6) (a) Hlatky, G. G. Chem. Rev. 2000, 100, 1347-1376. (b) Small, B. L.; Brookhart, M.; Bennett, A. M. A. J. Am. Chem. Soc. 1998, 120, 4049–4050. (c) Britovsek, G. J. P.; Gibson, V. C.; Kimberley, B. S.; Maddox, P. J.; McTavish, S. J.; Solan, G. A.; White, A. J. P.; Williams, D. J. Chem. Commun. 1998, 849–850. (7) Alt, H. G.; Köppl, A. Chem. Rev. 2000, 100, 1205-1222. (8) Busico, V.; Cipullo, R.; Pellechia, R.; Ronca, S.; Roviello, G.; Talarico, G. Proc. Nat. Acad. Sci. 2006, 103, 15321-15326. (9) Coates, G. W. Chem. Rev. 2000, 100, 1223-1252. (10) (a) Severn, J. R.; Chadwick, J. C.; Duchateau, R.; Friederichs, N. Chem. Rev. 2005, 105, 4073-4147. (b) Severn, J. R.; Chadwick, J. C. Dalton Trans. 2013, 42, 8979-8987. (11) Copéret, C.; Chabanas, M.; Petroff Saint-Arroman, R.; Basset, J.-M. Angew. Chem. Int. Ed. 2003, 42, 156-181. (12) Modern Surface Organometallic Chemistry, ed. Basset, J.M.; Psaro, R.; Roberto, D.; Ugo, R. Wiley-VCH Verlag GmbH, Weinheim, 2009. (13) (a) Zhao, Y.; Li, B.; Wang, Q.; Gao, W.; Wang, C. J.; Zheng, L.; Wei, M.; Evans, D. G.; Duan, X.; O'Hare, D.; Chem. Sci. 2014, 5, 951–958. (b) Zou, X.; Goswami, A.; Asefa, T. J. Am. Chem. Soc. 2013, 135, 17242-17245. (14) Liu, Z.; Ma, R.; Osada, M.; Iyi, N.; Ebina, Y.; Takada, K.; Sasaki, T. J. Am. Chem. Soc. 2006, 128, 4872-4880. (15) Gao, X.; Lei, L.; O'Hare, D.; Xie, J.; Gao, P.; Chang, T. J. Solid State Chem. 2013, 203, 174-180. (16) Choy, J.-H.; Kwak, S.-Y.; Jeong, Y.-J.; Park, J.-S. Angew. Chem. Int. Ed. 2000, 39, 4042-4045. (17) (a) Wang, Q.; Undrell, J.; Gao, Y.; Cai, G.; Buffet, J.-C.; Wilkie, C. A.; O'Hare, D. Macromolecules 2013, 46, 6145-6150. (b) Gao, Y.; Wu, J.; Wang, Q.; Wilkie, C. A.; O’Hare, D. J. Mater. Chem. A. 2014, 2, 10996-11016. (18) Wang, Q.; Zhang, X.; Zhu, J.; Guo Z.; O'Hare, D. Chem. Commun. 2012, 48, 7450–7452. (19) Abedi, S.; Abdouss, M. Appl. Cat. A. 2014, 475, 386-409. (20) Gao, Y.; Zhang, Z.; Wu, J.; Yi, X.; Zheng, A.; Umar, A.; O'Hare, D.; Wang, Q. RSC Adv. 2013, 3, 26017-26024.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(21) He, F.-A.; Zhang, L.-M. Compos. Sci. Technol. 2007, 67, 3226-3232. (22) He, F.-A.; Zhang, L.-M. J. Colloid Interface Sci. 2007, 315, 439-444. (23) Wang, Q.; O'Hare, D. Chem. Commun. 2013, 49, 6301-6303. (24) (a) Chen, C.; Yang, M.; Wang, Q.; Buffet, J.-C.; O'Hare, D. J. Mater. Chem. A. 2014, 2, 15102-15110. (b) Yang, M.; McDermott, O.; Buffet, J.-C.; O’Hare, D.; RSC Adv. 2014, 4, 51676-51682. (25) Funnell, N. P.; Wang, Q.; Connor, L.; Tucker, M. G.; O'Hare, D.; Goodwin, A. L. Nanoscale 2014, 6 , 8032-8036. (26) Wang, Q.; O'Hare, D. Chem. Rev. 2012, 112, 4124-4155. (27) Tudor, J.; O’Brien, S.; Maschmeyer. T.; O'Hare, D. Chem. Commun. 1997, 1905-1906. (28) Jezequel, M.; Dufaud, V.; Ruiz-Garcia, M. J.; CarrilloHermosilla, F.; Neugebauer, U.; Niccolai, G. P.; Lefebvre, F.; Bayard, F.; Corker, J.; Fiddy, S.; Evans, J.; Broyer, J.-P.; Malinge, J.; Basset, J.-M. J. Am. Chem. Soc. 2001, 123, 3520-3540. (29) Silveira, F.; Alves, M. C. M.; Stedile, F. C.; Pergher, S. B. C. and dos Santos, J. H. Z. Macromol. React. Eng. 2009, 3, 139-147. (30) Mäkelä-Vaarne, N. I.; Nicholson, D. G.; Ramstad, A. L. J. Mol. Cat. A 2003. 200, 323-332. (31) Silveira, F.; Alves, M. C. M.; Stedile, F. C.; Pergher, S. B. C.; dos Santos, J. H. Z. J. Mol. Cat. A 2010, 315, 213-220. (32) Eilertsen, J. L.; Stovneng, J. A.; Ystenes M.; Rytter, E. Inorg. Chem. 2005, 44, 4843-4851. (33) Brintzinger, H. H.; Fischer, D.; Mülhaupt, R.; Rieger, B.; Waymouth, R. M. Angew. Chem. Int. Ed. 1995, 34, 1143-1170. (34) Peng, K.; Xiao, S. J. Mol. Cat. 1994, 90, 201-211. (35) Sigma Aldrich price for a 1 kg of hydrotalcite is 73.50$ and 1 kg of spherical silica is 424.00$.


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8

Highly Tunable Catalyst Supports for Single-Site Ethylene

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