Different kinds of supports and catalysts for propylene polymerization were prepared by ball-milling with different mole ratio (0.1~0.8) of ethyl benzoate(EB)/$MgCl_2$ and different Ti content in the catalyst (1~8 wt%) to understand the nature of the $MgCl_2-EB-TiCl_4$ complex.
Carbonyl (C=O) bonds of EB in the supports and catalysts were investigated through infrared(IR) spectrophotometer. When small amount of EB (EB/Mg<0.4) was added to the $MgCl_2$, the carbonyl bonds were detected simultaneously at $\nu_1=1690$ and $\nu_2=1636cm^{-1}$. With the amount of EB in the support increasing, however, the carbonyl bond at $\nu_2$=1636cm^{-1}$ disappeared gradually while the one at $\nu_1=1690cm^{-1}$ remained. If small amount of $TiCl_4$ is impregnated to the support with carbonyl band at $\nu_1$ and $\nu_2$, only one carbonyl characteristic band of was detected at $\nu_1^\prime=1685cm^{-1}$, which is near to $\nu_1$. With large amount of $TiCl_4$, the bands for carbonyl group were detected simultaneously at $\nu_1^\prime=1685$, $\nu_3=1600$ and $\nu_4=1564cm^{-1}$. For the support with carbonyl band only at $\nu_1=1690cm^{-1}$, the activation could be made even with small amount of $TiCl_4$, and the carbonyl bands were also identified simultaneously at $\nu_1^\prime$, $\nu_3$ and $\nu_4$.
From these results, a model for the $MgCl_4-EB-TiCl_4$ complex was proposed as follow. The bands at $\nu_1=1690cm^{-1}$ and $\nu_2=1636cm^{-1}$ represent the characteristic peaks of linear $EB-MgCl_2$ and bridge and $EB<^{MgCl_2}_{MgCl_2}$ complex, respectively. With small amount of EB added on $MgCl_2$, both(linear and bridged) $EB/MgCl_2$ complexes could be formed. Further increase in the amount of EB will make all of the complexes to be linear type.
The active site for propylene polymerization seems to be the $TiCl_4$-$MgCl_2$ complex generated by activation with $TiCl_4$ of the bridged $EB<^{MgCl_2}_{MgCl_2}$ complex, part of which is converted to the linear $EB-MgCl_2$ complex. However, the linear $EB-MgCl_2$ complex will make inactive $EB-TiCl_4$ complex. The activity pattern could be well interpreted with the aforementioned argument, and there seems to be optimum composition of EB and $TiCl_4$ for the $MgCl_2$ support, respectively ; i.e., $EB/MgCl_2<0.4$, $Ti< 4$wt%.
Ti valence state was investigated with electron paramagnetic resonance(EPR) spectrum. With increasing Ti contents (1, 2, 4 and 8 wt%), the peak intensity at g=1.97 decreased slightly but the peak at g=1.94 increased. It is known for that the peaks at g=1.94 and 1.97 represent the $Ti^{+3}$ states for the Ti-Ti and Mg-Ti cluster, respectively. Addition of $TiCl_4$ seems to favor the formation of inactive Ti-Ti cluster rather than active Mg-Ti cluster.
