Synthesis And Catalytic Behavior Of Salicylaldimide Tridentate Binuclear And Polynuclear Titanium Complexes

China is the largest consumer of polyolefin products,and the demand for high-quality polyolefin is increasing year by year.The performance of polyolefin is determined by catalysts,so it is of great importance to develop new high-performance olefin polymerization catalysts.In recently years,tridentate salicylaldimide-based dinuclear and polynuclear complexes have demonstrated excellent activity and control over the polymer structure.In order to combine their advantages,a series of salicylaldimide tridentate titanium complexes3a-3d and polynuclear titanium complexes 13a-13c were designed and synthesized,and their catalytic properties were studied.The main contents of this work are as follows:（1）A series of novel alkyl bridged salicylaldimine dinuclear titanium complexes 3a-3d were synthesized and characterized by ¹H NMR,¹³C NMR,FI-IR and elemental analysis.These salicylaldimine dinuclear titanium complexes can catalyze the homopolymerization of ethylene with high activity with the activation of MMAO.At a low Al/Ti ratio of 500:1,the activity of complex 3c can reach 0.77×10⁶ g/（mol Ti.h.atm）.With the growth of the length of the bridging alkyl chain,the activity of the dinuclear complex gradually increased.The activity of the octylene bridged dinuclear complex 3d was the highest,reaching 1.10×10⁶g/（mol Ti.h.atm）.The molecular weight of the polymer obtained by the binuclear titanium complex was significantly higher than that obtained by the corresponding mononuclear titanium complex.The molecular weight of the polymer obtained by the propylene bridged complex 3a was about 8 times that obtained by the mononuclear complex 7.With the increase of the length of the bridging alkyl chain,the molecular weight of the polymer decreased,and the molecular weight distribution also decreased gradually.（2）The copolymerization of ethylene with 1-hexene,dicyclopentadiene and 9-decene-1-alcohol catalyzed by the dinuclear titanium complex 3a-3d were investigated.These catalysts can effectively catalyze the copolymerization of ethylene and 1-hexene with the activation of MMAO,and the activity of 3c increased with the increase of the amount of comonomer,showing a significant comonomer effect.With the increase of the length of the bridging alkyl chain,the catalytic activity of the dinuclear complexes increased,and the insertion rate of the comonomer also increased.These dinuclear catalysts can also catalyze the copolymerization of ethylene and 9-decene-1-alcohol with an activity of more than 10⁵ g/（mol Ti.h.atm）.As the amount of polar monomer increased during copolymerization,the melting point of the copolymer gradually decreased,but the catalytic activity changed little,indicating that these dinuclear titanium complexes had good compatibility with polar monomers.The dinuclear complexes can also catalyze ethylene copolymerization with dicyclopentadiene with activity above 10⁵ g/（mol Ti.h.atm）,demonstrating good selectivity to comonomers with high steric resistance.（3）A series of salicylaldimine polynuclear titanium complexes 13a-13c anchored on polystyrene main chain were synthesized.The ligands and complexes were characterized by¹H NMR,FI-IR and elemental analysis,the content of titanium in various polynuclear complexes was determined by ultraviolet analysis.The catalytic properties of polynuclear complexes under different conditions were studied by using MMAO as the cocatalyst.It was found that the polynuclear complexes 13a-13c could catalyze ethylene polymerization with high activity above 10⁵ g/（mol Ti.h.atm）.At an aluminum to titanium ratio of 1000,the complex 13a which has a higher Ti content was more active than 13b,13c,and the mononuclear complex 16.Meanwhile,the molecular weight and molecular weight distribution of the polymer obtained by the polynuclear complexes were higher than that of complex 16.The polynuclear complex 13a-13c can also effectively catalyze the copolymerization of ethylene and 1-hexene,showing obvious copolymer effect.