# Highly Flowable Nano TiO2/Porous Organic Polymer (POP) Supports for Efficient Metallocene Catalysts
## 3 Results and Discussion
### Particle Size and Particle Size Distribution  
Due to the replication effect during the olefin polymerization, the particle size and particle size distribution of a potential catalyst support also need to be evaluated. Generally, for a suitable olefin polymerization catalyst support in commercial applications, the particle size of D(0.5) of the support ranges from 20 to 60 \(\upmu\)m and the particle size distribution is less than 2. The particle size and particle size distribution results of the prepared TiO\({}_{2}\)/POP composites are presented in Table 3 and Figure 6. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & **Temperature Zone** & **Weight Loss, \%** & **TiO\({}_{2}\) Content (Calculated), \%** \\ \hline \multirow{2}{*}{POP-1} & 20 \({}^{\circ}\)C-300 \({}^{\circ}\)C & 1.94 & \multirow{2}{*}{13.8} \\ \cline{2-3}  & 20 \({}^{\circ}\)C-800 \({}^{\circ}\)C & 85.98 & \\ \hline \multirow{2}{*}{POP-2} & 20 \({}^{\circ}\)C-300 \({}^{\circ}\)C & 2.51 & \multirow{2}{*}{24.0} \\ \cline{2-3}  & 20 \({}^{\circ}\)C-800 \({}^{\circ}\)C & 75.83 & \\ \hline \multirow{2}{*}{POP-3} & 20 \({}^{\circ}\)C-300 \({}^{\circ}\)C & 1.72 & \multirow{2}{*}{27.9} \\ \cline{2-3}  & 20 \({}^{\circ}\)C-800 \({}^{\circ}\)C & 71.99 & \\ \hline \multirow{2}{*}{POP-4} & 20 \({}^{\circ}\)C-300 \({}^{\circ}\)C & 1.89 & \multirow{2}{*}{44.0} \\ \cline{2-3}  & 20 \({}^{\circ}\)C-800 \({}^{\circ}\)C & 55.88 & \\ \hline \multirow{2}{*}{POP-5} & 20 \({}^{\circ}\)C-300 \({}^{\circ}\)C & 1.69 & \multirow{2}{*}{29.8} \\ \cline{2-3}  & 20 \({}^{\circ}\)C-800 \({}^{\circ}\)C & 70.08 & \\ \hline \multirow{2}{*}{POP-6} & 20 \({}^{\circ}\)C-300 \({}^{\circ}\)C & 1.86 & \multirow{2}{*}{32.4} \\ \cline{2-3}  & 20 \({}^{\circ}\)C-800 \({}^{\circ}\)C & 67.44 & \\ \hline \multirow{2}{*}{POP-7} & 20 \({}^{\circ}\)C-300 \({}^{\circ}\)C & 1.46 & \multirow{2}{*}{38.4} \\ \cline{2-3}  & 20 \({}^{\circ}\)C-800 \({}^{\circ}\)C & 61.48 & \\ \hline \multirow{2}{*}{POP-8} & 20 \({}^{\circ}\)C-300 \({}^{\circ}\)C & 1.41 & \multirow{2}{*}{0} \\ \cline{2-3}  & 20 \({}^{\circ}\)C-800 \({}^{\circ}\)C & 99.79 & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The thermogravimetric analysis results of the prepared TiO\({}_{2}\)/POP particles. From Table 3, we can see that relatively narrow particle size distribution with a span of less than 2 was obtained from the TiO\({}_{2}\)/POP composites. The average particle size D(0.5) of POP-8 was 47.3 \(\upmu\)m, and when nano TiO\({}_{2}\) beads were added, an obvious decreasing trend of particle size of the prepared TiO\({}_{2}\)/POP particles could be observed when increasing the TiO\({}_{2}\) amount in the support synthesis. The average particle size D(0.5) reduced from 31 \(\upmu\)m of POP-1 to 17.6 \(\upmu\)m of POP-4. The trend could be well explained by the hydrophilic nature of the nano TiO\({}_{2}\) beads absorbing the hydrophilic functional HEMA molecules, and its template role as a seed during the radical polymerization. As seen from the schematic preparation of TiO\({}_{2}\)/POP particles (Figure 1), the nano TiO\({}_{2}\) beads (about 100 nm) could absorb HEMA, AIBN initiator, and even DVB molecules around their surfaces, and radical polymerization was initiated around the nano beads. When HEMA and DVB molecules diffuse around the nano beads, and the polymer would grow around the nano template as the copolymerization and cross-linking reaction happened. When the added nano template beads increased, more DVB/HEMA molecules polymerize around the nano beads, so narrower particle size distribution and less fine particles (1-10 \(\upmu\)m) were noticed. When a DVB/HEMA molar ratio of 3:1 was adopted in the synthesis of POP-6 and POP-7, narrower particle size distributions with a span of less than 1.0 were achieved, and the average particle sizes were 24.7 and 24.1 \(\upmu\)m, respectively. From Figure 6, POP-7 obtained a normal distribution of its particle sizes with the same average particle size D(0.5) and mode values.