TiCh-based catalysts

Thus, in the often used TiCh-based catalysts diluted TiCl4 is first reduced by reacting with, for instance, AlEt.s to a solid brown, black, or sometimes purple reaction product which is subsequently activated with the same or sometimes another alkylaluminum compound. Cooper and Rose (10) showed that the composition of the reaction product formed in the reducing step may... 

A number of models for catalytic active sites have been proposed to explain the isospecific polymerisation of propylene in the presence of TiC -based catalysts [68]. It was Natta who proposed [366], for the first time, that the steric control in isospecific propylene polymerisation is caused by the structure of the active species located on the borders of crystal layers of violet titanium trichloride. Arlman and Cossee [277] suggested that the isospecific active sites are located on lateral crystal surfaces, which in violet titanium trichloride such as oc-TiCh correspond to (110) planes. Titanium atoms present on the above-defined fracture surface have a vacant octahedral site bonded to five chlorine atoms (Figure 3.26) [1,68]. 

Catalyst Systems Based on Various TiCh-Containing Precipitates... 

Another rule that manifests itself is that polypropylene, produced with TiCh-containing precipitate reduced at 170° C., normally has a lower hexane soluble polymer content than polypropylene prepared with corresponding catalysts based on TiCL reduced at 80° C. 

Crystallinity of the polypropylene formed is strongly influenced by the type of transition metal compound and to a less extent by type of alkylaluminum compound of the catalyst. Catalysts based on Y-TiCh, /J-TiCh, and VCb and activated for instance with AlEt2Cl produce in typical cases, polymers of 4, 21, and 72% hexane soluble polymer content, respectively. This is a strong indication that the type of transition metal compound not only... 

---