# Highly Flowable Nano TiO2/Porous Organic Polymer (POP) Supports for Efficient Metallocene Catalysts
## 3 Results and Discussion
### Pore Structure of the Prepared TiO\({}_{2}\)/POP Particles  
As seen from Table 1 and Figure 2, similar pore structure was obtained with the same comonomers formula and cross-linking degree of DVB. When 55% cross-linking degree DVB and a DVB/HEMA molar ratio of 3:1 were added, the pore structure of the prepared TiO\({}_{2}\)/POP particles (POP 1-4) varied a little with similar nitrogen isotherm and pore size distribution curves. The specific surface area and pore volume of the four samples were about 190-220 m\({}^{2}\)/g and 0.31-0.37 cm\({}^{3}\)/g, respectively. Compared to our previous work, the bulk density of the prepared P(DVB-co-HEMA) supports typically ranges from 0.15 to 0.30 g/mL. However, higher bulk density of the prepared TiO\({}_{2}\)/POP composites can be achieved by adding nano-TiO\({}_{2}\), with bulk density ranging from 0.26 to 0.35 g/mL, which approved that the nano-TiO\({}_{2}\) is an effective component to tune the bulk density of the prepared supports.  
The cross-linking degree of DVB and the functional comonomer HEMA are also significant pore-modulating factors of the prepared TiO\({}_{2}\)/POP particles. Typically, when higher cross-linking DVB was used, more highly porous TiO\({}_{2}\)/POP particles can be obtained  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Entry**} & \multicolumn{2}{c}{**TiO\({}_{2}\) Adding**} & \multirow{2}{*}{**DVB**} & \multirow{2}{*}{**DVB:HEMA (Molar Ratio)**} & \multirow{2}{*}{**Specific**} & \multirow{2}{*}{**Total Pore**} & \multirow{2}{*}{**Average Pore**} & \multirow{2}{*}{**Bulk Density**} \\  & **Amount/Total Monomer** & & & & **Surface Area** & & **Volume** & **Diameter** \\  & **wt\%** & & & **m\({}^{2}\)/g** & **cm\({}^{3}\)/g** & **nm** & \\ \hline POP-1 & 10\% & 55\% & 3:2 & 224 & 0.368 & 6.58 & 0.26 \\ POP-2 & 20\% & 55\% & 3:2 & 191 & 0.367 & 7.71 & 0.26 \\ POP-3 & 30\% & 55\% & 3:2 & 198 & 0.350 & 7.06 & 0.33 \\ POP-4 & 50\% & 55\% & 3:2 & 204 & 0.312 & 6.12 & 0.35 \\ POP-5 & 30\% & 80\% & 3:2 & 309 & 0.315 & 4.08 & 0.31 \\ POP-6 & 37.5\% & 55\% & 3:1 & 136 & 0.150 & 4.41 & 0.25 \\ POP-7 & 37.5\% & 80\% & 3:1 & 279 & 0.246 & 3.53 & 0.30 \\ POP-8 & 0 & 80\% & 3:2 & 424 & 0.410 & 3.86 & 0.26 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Pore structure from N\({}_{2}\) sorption and bulk density results of nano TiO\({}_{2}\)/POP particles.  
Figure 1: Preparation of TiO\({}_{2}\)/POP particles.  
due to higher cross-linking degree in the produced polymer network. The characteristic pore size peak of around 1.475 nm due to a higher cross-linking of DVB could be clearly observed in POP-5, POP-7, and POP-8 (see Figure 2b). The SSA of POP-5 was increased to 309 m\({}^{2}\)/g from 204 m\({}^{2}\)/g of POP-3, and POP -7 had a higher SSA of 279 m\({}^{2}\)/g compared to 136 m\({}^{2}\)/g of POP-6. The SSA of POP-6 decreased from about 200 m\({}^{2}\)/g to 136 m\({}^{2}\)/g when decreasing the HEMA content from 3:2 to 3:1 of DVB/HEMA molar ratio. An obvious peak around 2.21 nm of POP-6 and POP-7 could be noticed in the curves of NLDFT pore size distribution, and the decrease in HEMA content also resulted in the less porous N\({}_{2}\) isotherm in consequence of the reduced pore size distributions mainly from 2.3 to 5.0 nm. The reason why the HEMA content influences the pore size distribution was discussed in detail in our previous research [33]; it is mainly caused by the change in solubility parameter of the prepared polymer when increasing the HEMA content.