# Porous Organic Polymers-Supported Metallocene Catalysts for Ethylene/1-Hexene Copolymerization
## 2 Results and Discussion
### Differential Scanning Calorimetry (DSC) and Temperature Rising Elution Fractionation (TREF) Results  
The TREF technique was adopted to characterize the chemical composition distributions (CCDs) of the produced ethylene/1-hexene copolymers prepared from POPs- and silica-supported metallocene catalysts. Figure 5a shows the TREF analysis of PE copolymers from POPs- and silica-supported metallocene catalysts. Although similar TREF curves in these PE samples are observed, the specific results of soluble fraction and fractionation temperature peaks are different. The soluble fractions at room temperature of ethylene/1-hexene copolymers prepared from POPs-supported metallocene catalysts--which mainly contain very-low-molecular-weight PE molecules (\(\mathrm{Mw<1000\;g/mol}\)) [43]--were higher than from silica-supported metallocene catalyst. An interesting phenomenon is also observed from Table 3--the ethylene/1-hexene copolymers (PE-1/PE-2/PE-3) prepared from POPs-supported metallocene catalysts have relatively less fraction in the main elution peak around 94 \({}^{\circ}\)C (due to less relative content of branching, especially short chain branching--SCB) and have a greater fraction in the secondary elution peak around 52-64 \({}^{\circ}\)C (due to a greater relative content of SCB) than PE-4 from silica-supported metallocene catalyst. From this evidence, we can reasonably conclude that the active sites in the nanoporous POP supports would facilitate redistributions of SCB in the main peak and the secondary peak by tuning the diffusion of ethylene and 1-hexene, etc. A wider distribution of pore size of POP-1 and POP-3 obviously had a better effect on the redistributions of SCB with PE-1 and PE-3.PE-1 had a soluble fraction of 1.8%, 96.3% around the main peak at 94 \({}^{\circ}\)C and 0.7% around the secondary peak at 52 \({}^{\circ}\)C, and PE-3 had a soluble fraction of 0.6%, 96.8% around the main peak at 94\({}^{\circ}\)C and 1.0% around the secondary peak at 52 \({}^{\circ}\)C.  
Figure 4: IR analysis results. (**a**) IR spectrum of PE-1; (**b**) IR spectrum at 2019 cm\({}^{-1}\); (**c**) IR spectrum of methyl groups at 1378 cm\({}^{-1}\) and methylene groups at 1369 cm\({}^{-1}\); (**d**) IR spectrum of RCH=CH\({}_{2}\) groups at 908 cm\({}^{-1}\) and R\({}_{1}\)R\({}_{2}\)C=CH\({}_{2}\) groups at 888 cm\({}^{-1}\). Differential scanning calorimetry (DSC) results (Figure 5b) reveal that the ethylene/1-hexene copolymers from both POPs- and silica-supported metallocene catalysts had similar thermal behavior with Tm (peak) in the range of 120-122 \({}^{\circ}\)C and Tc (peak) in the range of 103-109 \({}^{\circ}\)C, which was mainly caused by the same active site species in the polymerization process. As for crystalline polymer, the crystallinity \(\mathrm{Xc}\) of polymer can be estimated by the following equation:  
\[\mathrm{Xc}=\Delta\mathrm{Hm}/\Delta\mathrm{H}^{0}\mathrm{m}, \tag{1}\]  
where \(\Delta\mathrm{Hm}\) is the melting endothermic enthalpy of the polymer, and \(\Delta\mathrm{H}^{0}\mathrm{m}\) is the melting endothermic enthalpy of the polymer with 100% crystallinity. According to this Equation (1), the values of \(\Delta\mathrm{Hm}\) of ethylene/1-hexene copolymers could be estimated for their crystallinity. From Table 2, we can see the \(\Delta\mathrm{Hm}\) of PE-4 had the lowest value of 120.6 J/g. Therefore, the lowest crystallinity of PE-4 among these samples could be estimated, which is consistent with nearly the highest branching degree from the IR results. Although a discrepancy between the values of \(\Delta\mathrm{Hm}\) from PE-1/PE-2/PE-3 and their branching degree was observed, the discrepancy combined with a relatively wide range of Tc (peak) value of these PE samples might be partly explained by the different distribution and content of SCB in the their chains, which was caused by tuning the diffusion of ethylene and 1-hexene in different pore sizes.