Application Of Lewis Acid Modification And Self-assembly In Olefin Polymerization

As an important class of polymeric material,the annual production of polyolefins exceeds 180 million tonnes,accounting for over half of the global plastics market.In this field,transition-metal catalysts based on various ligands have been playing critical roles for the evolvement of new technologies and new materials.The majority of the research works involve the discovery of a catalyst lead,followed by extensive ligand electronic/steric modifications.Recently,some strategies beyond simple electronic/steric modulations for catalyst designing have emerged,which bear promising features of being applicable to different catalyst systems.In the field of metal-complex-catalyzed olefin polymerization,Lewis acid in situ modulation plays an important role.Recently,supramolecular systems that are held together by noncovalent bonds have found wide applications in many domains of chemistry.Specifically,multi-nuclear metal complexes can be assembled together through diverse noncovalent interactions such as metal-ligand coordination,hydrogen bonding,van der Waals interactions,aromatic stacking,etc.This really provides a simple and versatile strategy that enables rapid construction and modulation of dinuclear multinuclear systems for catalysis.In this dissertation,we designed two new sets of catalysts that can be easily regulated by stimulus.Through the introduction of Specific functional groups,we were able to regulate the active metal center in the polymerization.1.Two kinds of pyridazine-imine ligands and the corresponding nickel complexes Nil and Ni2 were prepared,characterized and investigated in ethylene(co)polymerization.In the homo-polymerization of ethylene,the B(?)Lewis acidic additives results in increased catalytic activities(up to 19.2 × 105 g·mol-1.Ni-1.h-1 using Nil).Moreover,the B(?)Lewis acidic additives can modulate microstructures of polyethylene products,resulting in increased branching densities and long chain branches.In the copolymerization of ethylene with methyl 10-undecenoate,both catalytic activity and polar monomer incorporation ratio(up to 2.0%)were increased by using B(?)Lewis acidic additives.It was indicated that the Lewis acid-base interaction between B(?)Lewis acids and the pyridazine moiety reduced the electron density from the Ni center and in situ modulated the pyridazine-imine Ni catalyzed ethylene(co)polymerization.2.In another chapter,the strategy of supramolecular chemistry is employed to construct multi-nuclear olefin polymerization catalysts.Specifically,urea functional groups were installed into some ?-diimine palladium catalysts to take advantage of the hydrogen-bonding induced self-assembly.By comparison with methylated counterparts(devoid of supramolecular interactions),it was demonstrated that the assembled structures as well as catalytic properties can be affected by concentration,ligand sterics,temperature and solvents,which translated into modulations in polymerization properties.Furthermore,the introduction of azobenzene unit into the catalyst framework enables photo-responsive behaviors of the assembled complexes.In the study of ethylene monopolymerization,important parameters can be facilely modulated,including activity,polymer branching density,molecular weight and molecular weight distribution.And in copolymerization with methyl acrylate,comonomer incorporation can also be greatly regulated.