Highly Efficient Synthesis Of Polar Polyolefins With Ultra High Molecular Weight By Novel[N,P]ti-based Non-metallocene Complexes And Their DFT Studies

Polyolefins have excellent comprehensive performance and are widely used in film,pipe,plastic packaging,auto parts and other fields.However,the non-polar nature of traditional polyolefin hinders the further improvement of its comprehensive performance and limits their application range,so it cannot further improve the commercial application value.Functional polyolefin has good surface properties,such as printing and dyeing property,rheological property,printing property and good compatibility with other polymers,which make functional polyolefin having broad application prospects and high commercial value.Direct copolymerization of ethylene with polar monomers is the most effective method to synthesize polar functional polyolefin.However,the polymerization catalysts used in this method also face great challenges.For example,such as the active center of the complexes is easily poisoned by polar groups and deactivated;Polar polyolefin with high molecular weight and high activity can not be obtained from the later transition metal complexes due to hydrogen elimination reaction.Therefore,the development and design of novel high-performance catalysts and the basic theoretical research are the key parts to promote the development of polyolefin industry.In this thesis,five novel[N,P]Ti non-metallocene complexes were designed and synthesized(among which complex 2b has been prepared in the laboratory).In the presence of polar monomers,the complexes exhibited high catalytic activity,and the obtained polar olefin copolymers had ultra high molecular weight.By comparing[N,P]Ti with[N,P,N,Si]Ti complexes,it is fully explained that[N,P]Ti complexes has high activity,and the resulting polymer has ultra high molecular weight.Through the above work,the following research results have been obtained:1.Five novel[N,P]Ti non-metallocene complexes were synthesized.The successful synthesis of several complexes was demonstrated by mass spectrometry,1H NMR and 13C NMR analysis.The content of Ti element in five novel[N,P]Ti non-metallocene complexes was determined by XPS.The thermal stability of the five complexes was investigated by thermogravimetric analysis(TGA),and the results showed that these non-metallocene complexes had good thermal stability.2.Five newly synthesized[N,P]Ti non-metallocene complexes were selected to carry out olefin polymerization experiments.The optimal polymerization conditions of these five novel complexes were investigated,and the structural relations of molecular structure and catalytic activity of the complexes were investigated.The results showed that the optimal polymerization conditions of the five complexes were 60? and Al/Ti=550 in the homopolymerization of ethylene under atmospheric pressure.The activity of complex 2e can be as high as 3.68×105 gPolymer(mol·Ti)-1 h-1.The activity of the complexes can be improved by introducing or increasing the number of electron-withdrawing functional groups into the ligand structure of the complexes.In the copolymerization of ethylene/1-octene,the results of the copolymerization under the optimum experimental conditions(60 ?,Al/Ti=550)show that the five complexes all have good olefin copolymerization ability.With the increase of octene content,the amount of octene inserted into the polymer increased.In the experiment of ethylene/octene/9-decene-1-alcohol terpolymer at atmospheric pressure,in the presence of polar monomers,the five complexes all maintained high activity,and the terpolymer with ultra high molecular weight was obtained.3.The novel[N,P]Ti complexes were designed and synthesized in the process of structural optimization of[N,P,N,Si]Ti complexes.[N,P]Ti complexes showed higher catalytic activity than[N,P,N,Si]Ti complexes,and the resulting polymer had higher molecular weight.Based on the electron effect and steric hindrance effect of the complexes,the mechanism of the higher catalytic polymerization activity of[N,P]Ti complex has been theoretically calculated by using density functional theory.(a)The energy profiles of ethylene homopolymerization,ethylene/1-octen e copolymerization and ethylene/1-octene/9-decene-1-alcohol terpolymer catalyzed by[N,P]Ti complexes can be obtained by density functional theory.The results show that the activation energy of the novel[N,P]Ti complexes for olefin polymerization is lower than that of the[N,P,N,Si]Ti complexes,which proves that the[N,P]Ti complexes have a higher polymerization activity.(b)The introduction of the electron-withdrawing functional group(F)into the novel[N,P]Ti complexes results in a significant increase in the ?-hydrogen elimination energy,indicating that the electron-withdrawing functional group makes the elimination reaction difficult to occur,improves the activity of the complexes and increases the molecular weight of the polymer.(c)According to steric hindrance analysis,the burial volume of[N,P]Ti complexes is smaller than that of[N,P,N,Si]Ti complexes,which indicates that the novel[N,P]Ti complexes has more selectivity and more active sites with olefin coordination.It is further demonstrated that the[N,P]Ti complexes has high polymerization activity.The reason why the novel[N,P]Ti complexes has higher catalytic activity than[N,P,N,Si]Ti complexes is explained by density functional theory.The theoretical results are in good agreement with the experimental results.4.The theoretical study of olefin polymerization has been carried out on the other two newly designed[N,P]Ti non-metallocene complexes(substituted aniline+dicyclohexyl/diisopropyl phosphorus chloride as ligands)by density functional theory.Theoretical calculation results show that the molecular orbital energy level difference(? Egap=EHOMO-ELUMP)of[N,P]Ti complexes is less than that of[N,P,N,Si]Ti complexes,indicating that the activity of[N,P]Ti complexes is higher than that of[N,P,N,Si]Ti complexes.It can be seen from the energy profiles of olefin polymerization that the activation energy required for the[N,P]Ti complexes is less than that of the[N,P,N,Si]Ti complexes.The catalytic activity of[N,P]Ti complexes is higher than that of[N,P,N,Si]Ti complexes.Theoretical calculation results show that the newly designed[N,P]Ti complexes has excellent performance in catalyzing olefin polymerization.5.The theoretical calculation of ethylene/hexene copolymerization was carried out using[N,P]Ti complexes(substituted aniline+diphenylphosphorus chloride as ligand).The results showed that in the experiment of ethylene/hexene copolymerization catalyzed by[N,P]Ti complexes,the activation energy required gradually decreased 2a>2b>2c>2e>2d(12.06 vs 11.90 vs 9.55 vs 9.22 vs 8.52 kcal/mol).Theoretical calculation results show that the introduction of electron-withdrawing functional groups into the ligand reduced the activation energy required for the polymerization,which in turn can increase the activity of the complexes.