Study On The Catalytic Performance Of Polyolefin With Pyridine/Ppyrrolone Diamine Schiff Base Metal Complex

Polyolefin is widely used in automobile manufacturing,medical devices,food packaging,pipe construction and other industries because of its excellent physical and chemical properties.At present,China’s polyolefin industry mainly produces low-end homopolymer products,while high-end polyolefin products mostly rely on imports.Therefore,the development of high-performance polyolefin products has become the focus of research in this field.The research and development of polyolefin products mainly depends on the innovation of catalysts.Schiff base metal complexes are favored by people because of their simple synthesis method,high catalytic activity under mild reaction conditions and the modifiability of the catalyst.Based on this,a novel polyolefin transition metal catalyst with novel structure and high catalytic performance was obtained by synthesizing new pyridine/pyrrolidone diamine Schiff base ligands.Firstly,pyridine/pyrrolidone diamine Schiff base ligands were synthesized by Schiff base condensation of two different precursors 2-acetylpyridine and 2-acetylpyrrole with six different amino positions and kinds of diamines.Secondly,the nickel complex of pyridine/pyrrolidone diamine Schiff base was synthesized by the coordination reaction of the ligand with the late transition metal Ni（II）.Finally,the synthesized complexes were used to catalyze the polymerization of methyl methacrylate（MMA）,and the effects of ligand structure and polymerization conditions on the activity of the catalyst,the molecular weight and molecular weight distribution of polymethyl methacrylate（PMMA）were studied.The specific research contents of this thesis include:（1）Synthesis of ligands:a series of novel diamine Schiff base ligands were obtained by Schiff base condensation reaction of 2-acetylpyridine and 2-acetylpyrrole precursors with 6kinds of diamines with different structures in liquid phase.It was characterized by melting point,element,infrared,ultraviolet,hydrogen spectrum and X-ray single crystal diffraction.the experimental results show that the reaction is easier and the yield is higher when the amino group on the diamine is directly connected to the benzene ring,and the hindrance effect on the reaction is more obvious when the steric hindrance of diamine is larger.The reaction activity of diamine with 2-acetylpyridine is significantly higher than that of 2-acetylpyrrole,and the reaction activity of precursor with carbazide is generally higher.（2）Synthesis of complexes:the corresponding nickel complexes were prepared by liquid phase reaction of Ni Cl₂·6H₂O with diamine Schiff base ligands with different structures.The melting point,element,infrared,ultraviolet and thermogravimetric characterization of the complex showed that the diamine Schiff base ligand coordinated with Ni Cl₂,and Ni²⁺coordinated with N atoms on the ligand to form three different complexes:mononuclear（Ni Cl₂L）,mononuclear（Ni L）and binuclear（Ni₂Cl₄L）,showing symmetrical and asymmetric structures.（3）Activity test of catalyst:the synthesized complexes were used in the experiment of MMA polymerization.Firstly,the effects of polymerization time,temperature,the ratio of monomer to catalyst n（M）/n（Ni）,the ratio of main catalyst to initiator n（Ni）/n（AIBN）on the catalytic performance of MMA polymerization were studied.When the polymerization time was 6 h,the temperature was 90℃,and n（M）/n（Ni）=3000,n（Ni）/n（AIBN）=2,the best activity is 4.3281×10⁴g（PMMA）mol^-1·h^-1.Secondly,the effects of steric hindrance and electronic properties of the complexes on the catalytic activity of MMA polymerization were studied.When the two amino groups on the ligand are located in the para-position of the benzene ring,the catalytic activity is higher relative to the meta-position;when the amino group on the ligand is directly connected to the benzene ring,it is higher than that connected to the benzene ring through methylene;when the diamine of the synthetic ligand is straight chain amine carbazide,the catalytic activity is generally higher;the catalytic activity of pyridone diamine Schiff base catalyst is significantly higher than that of pyrrolidone diamine Schiff base catalyst.PMMA with molecular weight up to 7.7124×10⁵ g·mol^-1and narrow molecular weight distribution PDI=1.64 was obtained from MMA polymerization experiment.