Application Of Unsymmetrical Strategy In Olefin Coordination Polymerization

To achieve the purpose of modifying the polymer,people usually take the way of altering the structure of the late transition metal catalyst.Based on predecessors of research results,we introduced large sterically hindered substituents into the N-aryl group of the ligand to reduce the conversion speed between the cis and trans isomers of the catalyst.When the mutual conversion speed is low enough,we can approximate that a single catalyst with asymmetric structure is obtained.This kind of late transition metal catalysts with asymmetric structure has excellent catalytic performance.Therefore,we conducted in-depth research on this type of catalyst through the following work.In the second chapter,we further proved that in the polymerization of ethylene with?-diimide nickel and palladium,the"rotation restriction"effect of the dibenzosuberyl substituent can also inhibit chain transfer and increase the molecular weight of the polymer.A series of acenaphthene-based?-diimine ligands bearing merely one diarylmethyl or dibenzosuberyl moiety on the ortho-positions of N-aryl rings and the corresponding Ni(II)and Pd(II)complexes were synthesized and characterized.These Ni(II)complexes exhibited very high activities(up to 6.32×10~6g/mol.h)in ethylene polymerization even at 80?,generating high molecular weight polyethylenes with varying branching densities.The resultant polyethylene products showed excellent mechanical properties and elastic recovery(SR up to 76%).Correspondingly,the palladium complexes displayed moderate activities,generating highly branched polyethylene with moderate molecular weight(ca.10~4 g/mol)in ethylene polymerization.Moreover,these Pd(II)complexes also displayed moderate copolymerization activity and generated moderate molecular weight polar functional copolymers(11.9-28.5 Kg/mol)with low to moderate incorporation ratio(0.50-1.29mol%).Compared with diarylmethyl-substituted species,the?-diimine Ni(II)and Pd(II)complexes containing rotationally restricted dibenzosuberyl substituents possess a superior ability to retard the chain transfer in the ethylene(co)polymerization process,resulting in higher molecular weight polyethylenes and copolymers.In the third chapter,a series of bulky unsymmetrical bis(imino)pyridyl Fe(II)complexes with different electronic effect substituents at the para-position of the N-aryl group have been synthesized and characterized.These highly robust thermostable Fe(II)complexes display very high activity(up to 2.5×10~7 g/mol.h.)in ethylene polymerization at high pressure,and can generate highly linear polyethylene(T_m=131.6-135.7 ~oC)with high molecular weight(M_w up to 185.7×10~4 g/mol)and broad molecular weight distributions(PDI:2.34-13.68).The electronic effect and influence of polymerization conditions on activity and molecular weight of polyethylene are investigated in detail.The electronic perturbations show great influence on the activity and polyethylene molecular weight in ethylene polymerization.Compared with the classical isopropyl substituted Fe(II)complexes,the bulky Fe(II)complexes show higher activity and thermal stability in ethylene polymerization at high temperature.In the fouth chapter,we also synthetized fluorinated polyethylene via late-t ransition-metal catalyzed ethylene copolymerization with semifluorinated acrylate s.Fluorinated polymers with different topologies can be generated via insertion polymerization with various late-transition-metal catalysts.Linear main chain fl uorinated polyethylene with a high incorporation of up to 25 mol%can be ach ieved via the PO-palladium-catalyzed ethylene and fluorinated acrylates copolym erization.While,hyperbranched chain end fluorinated polyethylene with a high molecular weight of up to 270 KDa can be realized via?-diimine-palladium-cat alyzed ethylene and fluorinated acrylates copolymerization.The above works prove that this kind of asymmetric structure catalysts dis palys excellently in polymerization,and has outstanding performance in polyme r yields and microstructure control.