Roles of Salicylate Donors in Enhancement of Productivity and Isotacticity of Ziegler-Natta Catalyzed Propylene Polymerization

Roles of internal salicylate donors (SID) in enhancing activity and stereoselectivity of Ziegler-Natta catalyzed propylene (PP) polymerization were examined using DFT calculations. Five salicylate donors were studied. The chelate mode is the preferred adsorption mode. The linear relationship (R = 0.96) between calculated adsorption energies (E) of five SIDs and the experimental PP activities was observed. Thus, the SID with the strongest adsorption energy will provide the highest activity in agreement with our previous studies. Compared with diisobutyl phthalate (DIBP), which is the industrial electron donor, SID has stronger E. The insertion step, which involves the π-complex formation (∆E and the insertion activation or intrinsic activation energy (E) for PP polymerization was also examined. The relation between ln(activity) and apparent activation energy (E(app)), which is ∆E + E for the primary(1,2)- insertion with R = 0.99, was observed. The salicylate donor also has a lower E(app) than that of DIBP. This explains the better catalytic performance of SID. Our results also demonstrated that the size and the type of hydrocarbon substituents play a key role in controlling stereoselectivity and activity. In addition, we found a good relationship between E and both intrinsic (E) and apparent (E(app)) activation energies of five salicylate donors with R of 0.90 and 0.97, respectively.