In situ gas phase polypropylene (PP) information over heterogeneous ball-milled TiCl4-MgCl2 Ziegler-Natta (Z-N) catalysts (containing no electron donors or selectivity control agents) has been observed for the first time in real time using environmental transmission electron microscopy (ETEM). The MgCl2 support and associated Z-N catalysts were characterized with electron diffraction and high-resolution electron microscopy. The support was found to be composed of highly defective β-MgCl2 nanocrystallites, 3 mn in size. Ball milling these supports in TiCl4 to create the pro-catalyst increased the degree of disorder and resulted in a higher fraction of amorphous material. The surfaces of the catalysts consist of amorphous material, various terminations of β-MgCl2, and other contaminant phases. The ETEM observations revealed initial nanoscale PP growth in the form of globules and continuous non-uniform polymer layers. The growth rate was measured to be 0.2 nm s-1 at 1 Torr of C3H6 pressure. The continuous growth implies that the active Ti sites are located on both the crystalline and non-crystalline regions of the MgCl2 surface. These active Ti sites appear to be located at the polymer/MgCl2 buried interface and there does not appear to be any significant diffusion limitation for polymer layers up to 150 nm in thickness. Our data and calculations show that only 1 in 105 collisions with the active site results in monomer insertion into the polymer chain.
|Original language||English (US)|
|Journal||Journal of Electron Microscopy|
|State||Published - Jul 11 2002|
- Ziegler-Natta catalysts
ASJC Scopus subject areas