?-ketoimine Type Vanadium(?) Catalyst Containing Cyclic Skeleton Synthesis,Structures And Their Ethylene(co) Polymerization Behavior

The global demand for polyolefins is increasing year by year,and there are more requirements for the functionality of polyolefins,such as good mechanical properties,optical properties,wettability,and printability.Polyolefins with high molecular weight and unimodal distribution have excellent mechanical properties,but the deactivation and decomposition of olefin polymerization catalysts during polymerization will result in low molecular weight products and uneven distribution.In order to efficiently prepare polyolefin materials with excellent performance,it is necessary to develop olefin catalysts with excellent properties and stability.Aiming at the problem that olefin polymerization catalysts are easy to decompose at high temperatures,a series of?-ketoimine type vanadium?III?catalysts with cyclic skeleton and large steric hindrance groups have been synthesized.The specific research content is as follows:1.A series of?-ketoimine type vanadium?III?catalysts containing a cyclic skeleton and a large steric substituent were synthesized,and their structures were clearly characterized by Fourier infrared spectroscopy,nuclear magnetic resonance,and single crystal X-ray diffraction.According to the analysis of single crystal X-ray diffraction results,the introduced cyclic skeleton restricts the rotation of the large steric group,and increases the steric hindrance around the O donor.These?-ketoimine vanadium catalysts with cyclic skeletons have a catalytic activity of 10⁷ g_PE·mol_V^-1·h^-1 for ethylene.Compared with the?-ketoimine vanadium catalyst with non-cyclic skeleton,it has excellent thermal stability,no significant decrease in activity in the range of 50?to 70?,and the molecular weight of polyethylene obtained during the reaction at 100?is still a unimodal distribution.In addition,the performance of the catalyst can be optimized by adjusting the N-aryl structure.When the N-aryl group of the ligand is a phenyl group,the catalyst has a higher activity,up to 3.0×10⁷ g_PE·mol_V^-1·h^-1;when the N-aryl group is 2,6-diisopropylbenzene At the same time,higher molecular weight polyethylene?283-344 kDa?can be obtained.Different cyclic framework structures give the catalyst different characteristics.When five-or six-membered rings are introduced,the catalyst has higher activity.2.The five?-ketoimine vanadium catalysts with good thermal stability were used to catalyze the copolymerization reaction of ethylene and cyclic non-conjugated diene.The cyclic non-conjugated diene used was a bicyclic Pentadiene?DCPD?,5-ethylene-2-norbornene?ENB?and 5-vinyl-2-norbornene?VNB?.These catalysts show high activity in ethylene/DCPD copolymerization and ethylene/ENB copolymerization(ethylene/DCPD:1.51-2.8×10⁷ g_polymer·mol_V^-1·h^-1;2.02-6.83×10⁷ g_polymer·mol_V^-1·h^-1);Obtain high molecular weight?ethylene/DCPD:M_w=63.7-145 kDa;ethylene/ENB:M_w=136-256 kDa?and high comonomer content(DCPD:9.31-22.1 mol%;ENB:11.5-37.2?mol%?cycloolefin copolymer having a uniform molecular weight.In the ethylene/VNB copolymerization reaction,these vanadium catalysts showed significantly lower activity than the first two systems(0.84-4.92×10⁶ g_polymer·mol_V^-1·h^-1),and the molecular weight of the resulting copolymer?34.6-86.4 kDa?And comonomer content?2.77-8.32 mol%?are also much lower.The reason for this result is that the steric hindrance around the vinyl side groups of the VNB monomer is small,so it is highly reactive and prone to undesired compounding.Bit mode.All the obtained cyclic olefin copolymers showed a unimodal distribution?ethylene/DCPD:PDI=1.4-2.0;ethylene/ENB:PDI=1.6-1.8;ethylene/VNB:PDI=1.4-1.8?,indicating that even at high temperatures Next,the?-ketoimine type vanadium?III?catalysts prepared in this paper exhibits a single-site catalytic behavior during the copolymerization process.In addition,the main chain transfer pathway in the copolymerization process is to transfer to aluminum compounds.By changing the structure and reaction conditions of the catalyst,the conversion ratio of the feed monomer and the molecular weight and comonomer content of the copolymer can be effectively adjusted.All three comonomers are combined through the double bonds of norbornene,and the double bonds outside the norbornene ring remain unreacted.The polymer has good solubility in toluene,and the"unreacted double bond"Reactive Intermediate".