# Ionic Liquid-Modified Porous Organic Polymers as Efficient Metallocene Catalyst Supports
## 3 Results and Discussion
### IL-POPs Supported Zr/MAO Catalysts  
As illustrated in Figure 5, IL-POPs were pretreated with MAO and reacted with (BuCp)\({}_{2}\)ZrCl\({}_{2}\) subsequently to obtain IL-POPs supported metallocene catalysts, and the prepared IL-POPs were treated under vacuum at 80 \({}^{\circ}\)C to remove impurities before use.  
It can be seen from the IR spectrum (Figure 6) that the hydroxyl bands (from HEAM groups and adsorbed water) of supported catalysts disappeared after MAO pretreating, and the broad and strong bands of Zr/MAO@IL-POPs system at 683 cm\({}^{-1}\) assigned to Al-O stretching vibration, confirming that MAO cages were successfully immobilized on  
Figure 4: SEM images of the IL-POPs (**a**,**b**) POP-3; (**c**,**d**) POP-8.  
Figure 5: The schematic preparation of Zr/MAO@IL-POPs.  
IL-POPs [32]. Moreover, the C-H stretching vibration of imidazolium cation at 3100 cm\({}^{-1}\) disappeared, so we infer that part of MAO cages were anchored on the imidazolium cations.  
X-ray photoelectron spectroscopy analysis displays a good advantage in studying the chemical composition and state information on samples' surface [33]. In this work, comparing the chemical state of nitrogen shown in the N 1s XPS spectra of POP-3 and Zr/MAO@POP-3 [Figure 5a], an obvious shift of the peak to lower binding energy (BE) was observed, implying that nitrogen becomes electron-rich after being treated by MAO. Besides, when analyzing Zr XPS spectra in Figure 5b, due to the spin-orbit coupling of the 3d electrons, the Zr 3d spectrum can be separated to two peaks at BE of 182.6 ev (3d\({}^{5/2}\)) and 185.0 ev (3d\({}^{3/2}\)), respectively. The reported BE of (n-BuCp)\({}_{2}\)ZrCl\({}_{2}\) in free form is 181.6 ev with Zr 3d\({}^{5/2}\), the shift to higher BE could be ascribed to the methylation of zirconium by MAO [34; 35; 36]. It can be deduced that an ion pair with [(n-BuCp)\({}_{2}\)ZrCH\({}_{3}\)]\({}^{+}\) as cation and [(MAO@IL-POPs)-Cl]\({}^{-}\) as the anion has formed after the immobilization of Zr/MAO in IL-POPs, and the formed ion pair has a great influence on the activity of ethylene polymerization initiated by Zr/MAO@IL-POPs [37; 38].  
The contents of zirconium and aluminum loaded in IL-POPs were determined by ICP analysis after calcination and acidolysis. It can be seen from Table 2 that different quantities of zirconium and aluminum were loaded on different supports, for the reason that supports obtained different pore structure, and it is also affected by the functional groups on IL-POPs. As high as 43.8 umol of zirconium (Al/Zr ratio at 94.7) was immobilized  
Figure 6: (**a**,**b**) FT-IR spectra of IL-POP supports and Zr/MAO@IL-POPs; (**c**) N 1s XPS spectra of POP-3 and Zr/MAO@POP-3; (**d**) Zr 3d XPS spectra of BCZ-1@POP-3.  
on 1 g of POP-3 (SSA = 496.0 m\({}^{2}\)/g), and the ethylene polymerization activity of POP-3 supported catalyst was 3606 kg PE/mol\(\cdot\)Zr-bar-h. POP-5 with low IL adding amount and SSA value, 5% and 47.8 m\({}^{2}\)/g, respectively, immobilized less zirconium and MAO, and exhibited low polymerization activity as a result. POP-9 and POP-10 also exhibit a high porosity, and the supported catalysts perform greatly in polymerization, with activity of 3700 kg PE/mol\(\cdot\)Zr-bar-h and 3219 kg PE/mol\(\cdot\)Zr-bar-h, respectively. This is higher than the Zr/MAO@Silica-2408 system (2595 kg PE/mol\(\cdot\)Zr-bar-h from the reference [16]).