The profiles of X-ray diffraction patterns have been examined for several powder samples of di-TiCla, obtained by mechanical activation of 3,-TIC13 and presenting different catalytic activities in the Ziegler-Natta stereospecific polymerization of propylene to isotactic polypropylene. Particular attention has been paid to the 6-TiCI3 samples showing the best catalytic properties.
On the basis of a previous investigation by Allegra, a mathematical treatment has been developed and a disorder function has been elaborated taking into account, in calculating the profiles of the X-ray diffraction intensities, not only the disorder effects but also the sizes of the 6-TiCI3 crystallites. The selected experimental pattern (3-TiCI 3, highly activated) has been well reproduced in this way and fitted by overlapping the calculated spectra of two disordered forms, labelled ~t and ~2. which differ in the relative amounts of cubic and hexagonal sequences of the CI-Ti-CI layers constituting the violet forms of TiCI3. The best fit was achieved by introducing into the calculations crystallite sizes of about 70 A.
The results of the structural investigation are also discussed in terms of activity of the 6-TiCI 3 based catalyst for the stereospecific polymerization of propylene.