Synthesis Of Chiral Imidazoline Co(Ⅱ) Catalysts And Their Application In Isoprene Polymerization

The polyolefins are widely used and relevant to human life.Since catalyst of olefin polymerization discovered by Ziegler and Natta,transition metal-catalyzed olefin polymerization has achieved great success in both industry and academia.Among these late-transition-metal cobalt complexes,which are simple to synthesize and stable,have important applications in the polymerization of isoprene.In this thesis,a series of chiral imidazoline cobalt complexes(Co1-Co8)and achiral imidazoline cobalt complex Co9 were synthesized and their catalytic performance in isoprene polymerisation reactions was investigated in detail using these cobalt complexes as catalysts.The details of this thesis are as follows.Ⅰ.Current status of natural rubber and prospects for the synthesis of isoprene rubber.1.It outlines the origin of natural rubber and its applications in production and life.Then,we summarise the advantages of natural polyisoprene rubber,and also describe the problems and challenges it now faces.In order to solve those challenges,the best solution is to develop synthetic polyisoprene rubber.2.The microstructures of synthetic isoprene rubber and the applications of different microstructures of isoprene rubber are summarized.The catalysts used for the polymerization of isoprene are also reviewed and at the same time,the advantages and disadvantages of each type of catalyst are explained.Ⅱ.Synthesis of chiral imidazoline cobalt complexes Co1-Co8 and achiral imidazoline cobalt complexes Co9,their application in the polymerisation of isoprene.1.We synthesized chiral[N,N,N]pincer cobalt complexes Col and Co2,and explored their application in isoprene polymerization.Col successfully catalyzed the polymerization of isoprene under the activation of methylaluminoxane(MAO),and obtained an addition product rich in trans-1,4 structure with a monomer conversion rate of 99%,but the molecular weight was only 563 g-mol-1.2.We systematically adjusted the electronic and steric effects of ligands and synthesized chiral imidazoline pyridine cobalt complexes Co3-Co8 and achiral imidazoline cobalt complexes Co9,which were characterized by IR,Elemental analysis,X-ray single crystal diffraction and other methods.Using the synthesized Co3-Co9 cobalt complexes as catalysts,their application in isoprene polymerization was explored.Using Co5 as the catalyst and MAO as the co-catalyst,a polymer product with a trans-1,4 structure as the main product was obtained in a low yield(26%),and the trans-1,4 content reached 97%.Using diethylaluminum chloride(AlEt2Cl)as a cocatalyst,a cis-1,4 structure-based polymerization product was obtained,and the monomer conversion rate was as high as 95%.The ratio of cis-1,4 structure content to 3,4-structure content was about 7/3.3.Based on the above experimental results,the effects of reaction conditions such as the type of cocatalyst,the amount of monomer feeding,the molar ratio of cocatalyst to catalyst,reaction time and temperature on the catalyst activity,polymer stereoselectivity and molecular weight were investigated in detail.The experimental results show that the optimized cocatalyst is AlEt2Cl.After activation with AlEt2Cl,the highest activity of the cobalt complex is 1.02×106 g·mol-1·h-1.Also,the molecular weight(Mn)of the polyisoprene is up to 1.53×105 g·mol-1,and the molecular weight distribution of the polymer is narrow(PDI=1.5～3.4).The molar ratio of cocatalyst to cobalt complex(Al/Co)affects the molecular weight and molecular weight distribution of the polymer product.When the amount of cocatalyst is reduced,the molecular weight of the polymer increases and the molecular weight distribution narrows,while its microstructure is not affected.When Al/Co=5,the conversion of isoprene monomer can reach 90%.When the steric hindrance of the catalyst is increased,the activity of the catalyst decreases,but the thermal stability of the catalyst does not improve.Co5 was used as the catalyst,and the conversion rate of monomer decreased from 99%to 10%when the reaction temperature was 90℃,The achiral catalyst Co9 with the same structure as Co7 was synthesized,and its activity was higher in the polymerization of isoprene,which proved that the introduction of chiral groups had little effect on the polymerization process.