Studies On Synthesis,characterization And Olefin Polymerization Behaviors Of Transition Metal Complexes Containing Bulky Group

Preparation of polyolefin with well-defined microstructures anddesired properties has been a long-standing researchsubject in the field of polymer science,the key of which relies on theinnovation of catalysts.Since olefin-based polymers are used in a myriad of fields in our daily life,the design and synthesis of highly efficient catalysts capable of producing polyolefins with excellent thermal,mechanical,and rheological properties are experiencing ever growing demand.In this dissertation,a series of novel transition metal catalysts with bulky steric hindrance such as half-titanocene complexes bearing bulky dibenzhydryl-substituted aryloxide ligands,imino-pyridine cobalt complexes and half-titanocene containing pyrene groups were synthesized,and their catalytic behaviors were further investigated in ethylene,conjugated diene,and ethylene/1-hexene?co?polymerizations.1.Three half-titanocene complexes 2a-2c bearing dibenzhydryl-substituted aryloxideligandsCpTiCl₂?O-2,6-Ph₂CH-C₆H₂-4-Me?,2a;CpTiCl₂?O-2,6-Ph₂CH-C₆H₂-4-OMe?,2b;Cp*TiCl₂?O-2,6-Ph₂CH-C₆H₂-4-Me?,2c were synthesized.All the complexes werecharacterized by NMR spectroscopy and elemental analysis.The molecular structures of complex 2a and 2b were further determined by single crystal X-ray diffraction,both of them adopt a three-legged distorted tetrahedral geometry in which the aryl substituents were orthogonally to the aryloxide group.Introducing the bulky dibenzhydryl on the aryloxide ligand could provide large steric force to open the Ti-O-C angle of the titanium complex for the more electron donation to the metal centre,which was benefit to stabilize the active specie for the high activity towards the ethylene polymerization.Activated by methylaluminoxane?MAO?,these complexes showed high activities(up to 2100 kg mol^-1?Ti?h^-1)for ethylene polymerization.The resultant polyethylenes had high molecular weight and narrow molecular weight distributions.Furthermore,for the ethylene/1-hexene copolymerization,these complexes exhibited moderate activites and moderate to high 1-hexene incorporation ability.The sequence distributions of poly?ethylene-co-1-hexene?were greatly influenced by the substituent on the cyclopentadineylgroup of titanium complexes.2.Half-titanocene complexes bearing dibenzhydryl-substituted aryloxide ligands?2a-2d?were prepared.Among them,2d adopted a three-legged distorted tetrahedral geometry evidenced by X-ray crystallography.The poly-1,3-butadiene with high molecular weight and narrow molecular weight distribution was obtained by using these complexes as the catalysts activated with methylaluminoxane?MAO?.The catalytic activities of the complexes depended on their structures.The Ti-O-C bond in the complexes with large angle afforded them with higher activity,while Cp*-based complexes exhibited lower activities than the Cp-based analogues.The activity of complex increased with increasing the polymerization temperature while the selectivity remained no change,indicating the high thermal stability.Furthermore,the polymerization of 1,3-butadiene catalyzed by 2a/MAO at 0°C has been found in a living fashion.3.A series of imino-based cobalt complexes Co1-Co5 bearing bulky group on the ortho-position of aniline were synthesized.Determined by single crystal X-ray crystallographic analysis,Co3 and Co4 existed as distorted tetrahedron geometry in which the dibenzhydryl substituent shields the metal center on the axial space.Activated by EASC,all the complexes exhibited high activity in 1,3-butadiene polymerization,affording polymers with high cis-1,4 regularities?97.8%?and narrow molecular weight distributions.When activated by MAO,the selectivity of the catalytic system can be switched from 1,4 to 1,2 by the addition of triphenylphosphine?PPh₃?,leading to generate syndiotactic 1,2 polybutadienes.Furthermore,Co4/DMAO catalytic system promoted a quasi-Living polymerization of 1,3-butadiene at 0°C by suppressing the chain transfer reaction,and the cis-1,4-1,2 stereodiblock polybutadiene was prepared with this catalytic system by one-pot polymerization via adding PPh₃ during the polymerization.The micro-phase separation of the stereodiblock polymer morphology was investigated by TEM.4.Half-titanocene complexes 2a and 2b containing pyrene tag were synthesized.Single crystal X-ray crystallographic analysis revealed that complex 2a displayed a three-legged distorted tetrahedral geometry.The 2a-2b/MAO systems exhibited high activities for ethylene polymerization(up to 7830 kg·mol^-1?Ti?h^-1),and the resultant polyethylenes had high molecular weights and narrow polydispersities.Particularly,the 2b/MAO system exhibited extremely high activityfor ethylene/1-hexene copolymerization(10260 kg·mol^-1?Ti?h^-1),which is even higher than that for ethylene homopolymerization.The obtained copolymers possessed relatively high molecular weights(M_w³0×10⁴ g·mol^-1)and narrow molecular weight distributions?M_w/M_n².3?.Furthermore,a facile method to further improve the catalyst performance via a?-?interaction was achieved,that is,addition of pyrene into the system could markedly increase the catalytic activity and suppress?-H elimination,generating ultrahigh molecular weight polyethylenes.