ZIEGLER-NATTA CATALYSIS - A THEORETICAL-STUDY OF THE ISOTACTIC POLYMERIZATION OF PROPYLENE

The stereotacticity of ansa-zirconium metallocene Ziegler-Natta propylene polymerization catalysts is studied using a combination of ab initio electronic structure techniques and empirical force field molecular mechanics techniques. The experimental observation of isotacticity for the rac-(1,2-ethylenebis(eta-5-indenyl)zirconium and rac-(1,2-ethylenebis(eta-5-tetrahydroindenyl)zirconium based catalysts is computationally reproduced, and an explanation for the reduced rate of reaction and the atacticity for the meso-(1,2-ethylenebis(eta-5-indenyl))zirconium catalysts is provided. In addition, modified rac-(1,2-ethylenebis(eta-5-tetrahydroindenyl))zirconium catalysts with predicted increased isotacticity and decreased isotacticity (despite the presence of a chiral metal center), respectively, are proposed. Further, a new catalyst is proposed which should yield syndiotactic polypropylene.