Molecular Design And Synthesis Of Advanced Vinyl Polyolefin Materials And Novel Metallocene Catalysts

Polyolefin materials with stable physical and chemical properties,especially polyethylene PE and polypropylene PP,are widely used daily and first in the global production of synthetic polymers.Furthermore,polyolefins have lower production costs and toxicity than other commodity plastics,which also meet the requirements of sustainable development and green polymer chemistry.At present,China’s polyolefin production is large.However,there are still problems that need to be solved,mainly in two aspects:First,although China is the world’s largest producer and consumer of polyolefin,compared with developed countries in the West,China’s polyolefin industry is gradually emerging structural shortcomings:low-end products are in surplus,and future competitiveness is worrying;high-end products rely heavily on imports and cannot be localized.Second,high-end polyolefin is limited by the catalyst and polymerization technology monopolized by foreign countries,with high technical barriers and great difficulty in the introduction.Therefore,the original technology of high-end polyolefin in China urgently needs a breakthrough,and it is urgent to accelerate the development of high-performance catalysts and high-end products.Currently,the Ziegler-Natta catalyst,non-metallocene catalyst and metallocene catalyst are the three main catalysts for coordination polymerization.Among them,Ziegler-Natta catalysts have polydispersed active centers and poor copolymerization performance with advancedα-olefins,which are suitable for preparing simple structured polyolefins.The non-metallocene catalysts have been disclosed abroad with complex catalyst structures and unclear application prospects,and the prepared products have a narrow market application range.Metallocene catalysts have a single active center and very high catalytic activity.The catalyst structure and performance can be easily adjusted to precisely control the structure of polyolefins and effectively catalyze the homopolymerization or copolymerization of olefins to prepare high-performance and high-value-added polyolefins.In this thesis,five novel constrained geometry catalysts and three[Cp-P]-type metallocene complexes were designed and synthesized.Based on our many years of research and the proposed new theory of active site modulation for olefin coordination polymerization catalysts,this thesis proposes to use aniline,phenyl phosphine,cyclopentadiene and its derivatives containing-F strong electron-absorbing substituents as the main raw materials for the synthesis of new metallocene catalysts.The Lewis basicity of-F substituent is stronger,and the Lewis acidity of transition metal Ti is lowered to weaken theβ-H elimination in olefin polymerization and obtain higher molecular weight ethylene/advancedα-olefin copolymer;the Lewis acidity of transition metal Ti is weakened,and the catalyst is more stable at high temperature.The research focuses on the intrinsic relationship between catalyst structure and its catalytic performance,and the structure and performance of co-polyolefins,and further explore the influence of catalyst structure on catalytic performance with the help of the DFT technique to reveal the regulation of active catalytic sites by aniline containing-F substituent at the adjacent and para positions.The realization of this topic will provide scientific and technological support for the molecular design and synthesis of new metallocene catalysts,high-performance polyolefins and industrial applications.The main research results obtained in this thesis are as follows.1.Five constrained geometry catalysts and three new[Cp-P]-type metallocene complexes were designed and synthesized,and the intermediates,ligands and complexes were characterized and analyzed by ¹H NMR,¹³C NMR,GCMS,XPS and other testing methods,respectively,which proved the successful synthesis of the complexes.The effects of different electron-effect substituents on the buried volume and weak interaction forces of the catalyst active centers were investigated by DFT calculations,Samb Vca 2.1 and Multiwfn study methods.The calculation results show that the introduction of strong electron-absorbing group F into the main ligand of the complex gradually decreases the percent buried volume of the active center and increases the interaction space between the catalyst active center and the olefin monomer with fluorine-containing groups.The introduction of fluorine-containing groups gradually enhances the hydrogen bonding and van der Waals interaction between the complex and the olefin,favouring the coordination and insertion of the copolymer monomer and increasing the copolymer monomer incorporation.The new[Cp-P]-type metallocene catalyst designed and synthesized from the consideration of both the electronic effect of the catalyst active center and the spatial site resistance effect is less than47.4%of the buried volume of active center,which is more favourable to catalyze the co-polymerization of ethylene and large volume cyclic olefin monomers.2.Five constrained geometrical catalysts were selected to carry out ethylene/α-olefin co-polymerization experiments,and the polymerization results of these five complexes under different reaction conditions were investigated.The conformational relationships between the complexes’molecular structures and catalytic activities were examined.The results showed the optimum polymerization conditions for copolymerizing ethylene with 1-octene:polymerization temperature of 150℃,1-octene concentration of 0.96 mol/L,n（Al）/n（Ti）molar ratio of 300,and polymerization solvent of dodecane.The catalytic activity of complex 1e under the above conditions was up to 3.31×10⁵g/mol·_Ti·h,and the molecular weight was up to 3.57×10⁵g/mol,with an ultra-high monomer insertion rate of 16.43 mol%.The synthesized high-end vinyl copolymer POE has excellent properties.The copolymer structure and properties were characterized and analyzed in detail using ¹H NMR,¹³C NMR,DSC,DSC-SSA,FT-IR,XRD,POM,universal tensile force machine,DMA and other testing methods.The insertion of the copolymer monomer 1-octene disrupts the regularity of the polymer chains,thus decreasing the crystallinity.When the content of 1-octene reaches 14.00 mol%and above,the melting point disappears,and the diffraction peaks in the continuous self-core annealing（SSA）curves almost disappear.When the polymerization temperature exceeds 150℃,1-octene can be uniformly inserted into the copolymer molecular chain to produce a low crystallinity copolymer.Regarding mechanical properties,POE has excellent thermoplastic elastomer properties,with elongation at break up to 1200%and an elastic recovery rate of 74.7%.The experimental results were also verified by using the density functional theory.The strong electron-withdrawing group-F into the metallocene catalyst main ligand greatly enhanced the catalytic activity at high temperatures.The fluorine atom on the ligand reduced the Lewis acidity in metallic Ti,which weakened theβ-H elimination reaction and inhibited the occurrence of chain transfer,providing a guideline for the realization of high-temperature co-polymerization for the preparation of high-end polyolefins.3.Three[Cp-P]-type metallocene complexes were selected for the binary co-polymerization of ethylene/norbornene and the ternary co-polymerization of ethylene/1-octene/norbornene.The polymerization results of these three complexes under different reaction conditions were investigated to examine the conformational relationships between the complexes’molecular structures and catalytic activities.The results showed the optimum polymerization conditions for the dimer copolymerization of ethylene and norbornene:polymerization temperature of50℃,15 m L of norbornene,n（Al）/n（Ti）molar ratio of 300,polymerization solvent of toluene,and reaction time of 3 min.The catalytic activity of complex 2c under the above conditions was up to 4.68×10⁶g/mol·_Ti·h,and the molecular weight was up to 2.25×10⁵g/mol.An ultra-high monomer insertion rate of 40.56 mol%was obtained.The optimum polymerization conditions for ethylene/1-octene and norbornene:polymerization temperature of 50℃,10m L of 1-octene,2 m L of norbornene,n（Al）/n（Ti）molar ratio of 300,polymerization solvent of toluene,the reaction time of 20 min.The catalytic activity of complex 2c under the above conditions was up to 7.01×10⁵g/mol·_Ti·h,the molecular weight was up to 4.01×10⁵g/mol,and the insertion rate of 1-octene was obtained as 4.40 mol%and that of norbornene as 2.75mol%.The synthesized cyclic olefin copolymer COC and ethylene/1-octene/norbornene terpolymer POEN have excellent properties.The structures and properties of the copolymers were characterized and analyzed in detail using ¹H NMR,¹³C NMR,FT-IR,XRD,UV-vis spectrophotometer,universal tensiometer,DMA and other testing methods.The results showed that the[Cp-P]-type metallocene complexes with low buried volume easily catalyze the copolymerization of large site-resistant cyclic olefins,and the binary copolymer COC contains two consecutive norbornene NN units in an equatorial double full isostructure（meso）.A small amount of NNN terpolymer group appears.The COC with 40.56 mol%of norbornene has high transparency and 94%light transmittance.Introducing the third monomer,1-octene,into COC greatly improves the mechanical properties with elongation at 450%.It will provide ideas for the subsequent development of higher-value polyolefins.The experimental results were also verified by density functional theory.The catalytic activity and polymer molecular weight were greatly enhanced by introducing a stronger electron-withdrawing group-F in the main catalyst ligand.The fluorine atom on the ligand reduced the Lewis acidity in the metal Ti,which weakened theβ-H elimination reaction,inhibited the occurrence of chain transfer,and improved the monomer insertion,which laid a foundation for the industrialization of high-end polyolefins technology basis for industrialization of high-end polyolefins.