# Porous Organic Polymers-Supported Metallocene Catalysts for Ethylene/1-Hexene Copolymerization
## 2 Results and Discussion
### Molecular Structure Analysis from IR Results  
The microstructure of PE could be characterized by IR spectroscopy. The branching degree and relative double bond content of polyethylene can be calculated by IR analysis results [39; 40; 41]. Figure 4 shows the spectra of PE-1, PE-2, and PE-3 at room temperature. The 1378 cm\({}^{-1}\) peak is the characteristic peak of the methyl group due to its deformation vibration, and the absorbance in the methyl peak could be used to determine the branching degree. The 1369 cm\({}^{-1}\) peak and 1352 cm\({}^{-1}\) peak are caused by conformational CH\({}_{2}\) wagging, which might overlap the methyl absorbance at 1378 cm\({}^{-1}\), but they do not cause significant interference in this test method because their intensities are not significantly affected by the comonomer content, but rather by the plaque thickness. The band at 2019 cm\({}^{-1}\) was used as internal thickness correction approach to calibrate the methyl content. The branching degree of PE can be calculated by determining the value of absorbance (A) at 1378 cm\({}^{-1}\)/area (2019 cm\({}^{-1}\)) in a standard curve, which was plotted in A (1378 cm\({}^{-1}\))/Area (2019 cm\({}^{-1}\)) vs. Number of branches (N) per 1000 carbons as determined by \({}^{13}\)C NMR results.  
The peaks at 908 cm\({}^{-1}\) and 888 cm\({}^{-1}\) are the characteristic peaks of the unsaturated groups of PE. The peak at 908 cm\({}^{-1}\) is caused by the wagging vibration of CH\({}_{2}\) in RCH=CH\({}_{2}\) groups, and the peak at888 cm\({}^{-1}\) is caused by the same vibration mode of CH\({}_{2}\) in R\({}_{1}\)R\({}_{2}\)C=CH\({}_{2}\) groups. According to the similar internal standard to correct the variation, the relative content of RCH=CH\({}_{2}\) groups and R\({}_{1}\)R\({}_{2}\)C=CH\({}_{2}\) groups could be obtained by Area (908 cm\({}^{-1}\))/Area (2019 cm\({}^{-1}\)) and Area (888 cm\({}^{-1}\))/Area (2019 cm\({}^{-1}\)), respectively.  
The results of branching degree as well as relative content of RCH=CH\({}_{2}\) groups and R\({}_{1}\)R\({}_{2}\)C=CH\({}_{2}\) groups are listed in Table 2 in accordance with the method above. From Table 2, we can see that the branching degree of these ethylene/1-hexene copolymers varied from 10.1 to 11.6, and the branching degree of PE-4 (11.4) was nearly the highest among them, despite their different polymerization activity. This variation can be partly explained by the controlling diffusion of ethylene and \(\alpha\)-olefin, etc. to the active sites by the nanoporous POP supports with narrower pore size than silica; in turn, the different concentrations of ethylene and \(\alpha\)-olefin determine different chain growth rates and chain transfer rates of the active sites. However, the results of PE branching degree seemed to have no obvious bearing on the relative content of unsaturated groups due to their different formation mechanism [42], as seen from Table 2. The formation of RCH=CH\({}_{2}\) groups and the R\({}_{1}\)R\({}_{2}\)C=CH\({}_{2}\) groups are caused by \(\beta\)-hydrogen elimination to Zr+ and/or to ethylene or the comonomer, while the branching degree of PE is mainly generated by the insertion of 1-hexene. PE-1 had the lowest branching degree of 10.1, while the relative content of RCH=CH\({}_{2}\) groups and R\({}_{1}\)R\({}_{2}\)C=CH\({}_{2}\) groups were 0.05 and 0.11-0.12, respectively. Moreover, the addition of 1-hexene caused a dramatic increase of R\({}_{1}\)R\({}_{2}\)C=CH\({}_{2}\) groups of ethylene/1-hexene copolymer compared to ethylene homopolymer (0.01-0.04).