Synthesis of Mononuclear Transition Metal Complexes and their Applications as Catalysts for Ethylene Polymerization

The synthesis of titanium, zirconium and vanadium complexes with bis(benzimidazole)s, bis(benzothiazole)s and bis(benzoxazole)s is a main objective of this study. Their catalytic performance towards ethylene polymerization reactions was also studied. The ligand systems mentioned above were synthesized via condensation reactions using polyphosphoric acid which acts as solvent, oxidizing and dehydration agent. The condensation reactions proceeded readily to produce high yield products. Bis(benzimidazole)s can also be prepared by refluxing the reactant in 4 N hydrochloric acid for ten hours or longer. The organic compounds mentioned above, when reacted with the tetrahydrofuran adducts of titanium and zirconium tetrachloride, are capable to produce 1:1 complexes via ligand displacement in very good yields. The vanadium complexes were prepared using the vanadium trichloride salt in diethylether. Secondly, titanium, zirconium and vanadium complexes derived from 2-(benzimidazolyl)pyridine, 2-(benzothiazolyl)pyridine and 2-(benzoxazolyl)pyridine were prepared and used as olefin polymerization catalysts upon activation with MAO. The potential ligand precursors were obtained in high yields and very good purity. The titanium, zirconium and vanadium complexes were synthesized as described earlier. The synthesis of titanium, zirconium and vanadium complexes with N-allyl substituted benzimidazoles was one of the study goals. These complexes were tested for ethylene polymerization reactions. Their ability of self immobilization was also investigated. The ligands were synthesized by the reaction of allylbromide with benzimidazole in the presence of potassium carbonate and DMF as a solvent. The titanium, zirconium and vanadium complexes were synthesized as described earlier. The titanium, zirconium and vanadium complexes after activation with methylaluminoxane (MAO) were used for the homogeneous polymerization of ethylene. They showed good to moderate catalytic activities towards ethylene polymerization reactions. The vanadium complexes showed the highest activities, followed by titanium complexes, while zirconium complexes showed the lowest activities. The catalytic activities seem to depend on several factors but the substitution patterns and types played significant roles in addition to the ligand structures and the natures of the metal ions. It was observed that both electron withdrawing and electron releasing groups meta to the imino nitrogen atom reduced the activities compared to the unsubstituted complexes. However, complexes with electron releasing groups showed higher activities compared to those with electron withdrawing groups. The nature of the hetero atoms (N, O and S) also influenced the catalytic activities of the complexes. The introduction of one allyl substituent in 2-(benzimidazolyl)pyridine complexes increased the activities of the complexes compared to unsubstituted ones. However, the activity of the vanadium complex was increased by a factor of 20. The introduction of two allyl substituents in 1,2-bis(benzimidazole) complexes lowered the activities compared to the unsubstituted complexes and to those with only one allyl group. The polyethylenes produced by the above mentioned complexes as catalysts were in most cases of higher molecular weights (> 1000000g/mol) associated with broad and/or bimodal molecular weight distributions. The bimodality was thought to arise from the presence of more than one isomer (diastereomer) for each complex in addition to the different active centres resulting from different kinds of interactions with the cocatalyst MAO.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Bayreuth

Year

2008

Author dc:creator

• Hamdi, Elagab

Contributors dc:contributor

• Alt, Helmut

Repository record source_url

https://epub.uni-bayreuth.de/id/eprint/538/

OAI identifier oai:identifier

oai:epub.uni-bayreuth.de:538