Synthesis Of Styrene-butadiene Block Copolymer With High Both Cis-1,4 Content And Isotacticity By α-diimine Nickel Catalyst

With the rapid development of the polyolefin industry,the types of polyolefins are increasing and special high performance polyolefin materials are emerging.However,the non-polarity of the polyolefin chain structure has a serious impact on its properties such as printability,rheology,compatibility and blendability,and the studies have show that block copolymerisation of different olefin monomers can effectively improve the above problems.At present,it is difficult to achieve block copolymerisation of different types of monomers（butadiene,styrene,norbornene,etc.）in a single catalytic system,which greatly limits the development of polyolefins.Compared with traditional Ziegler-Natta catalysts and metallocene catalysts,α-diimine post-transition metal catalysts have attracted much attention from academia and industry due to their unique catalytic performance and excellent monomer adaptability.Based on this,α-diimine nickel catalysts were obtained by synthesizing a series ofα-diimine ligands with different structures and coordinating them with nickel naphthenate in this thesis.By aging with triisobutyl aluminium（Al（i-Bu）₃）,boron trifluoride diethyl etherate（BF₃·Et₂O）and triphenyl phosphins（PPh₃）to form quaternary catalytic system,the block copolymerization of styrene（St）and butadiene（Bd）was achieved by this quaternary catalytic system to obtain a styrene-butadiene block copolymer（PS-b-PB）with high isotactic and high cis-1,4 content.Details of the study are as follows:（1）Fourα-diimine ligands,L1,L2,L3 and L4,were synthesized and coordinated with nickel naphthenate to obtain Ni-Ⅰ,Ni-Ⅱ,Ni-Ⅲand Ni-Ⅳα-diimine nickel catalysts based on the steric hindrance effect of N-aryl 2,6-position substituent with imine bridge substituent,and electron donating/absorbing effect on the microstructure of the polymers.The preparedα-diimine nickel catalysts were characterized by infrared spectroscopy（FT-IR）,nuclear magnetic resonance spectroscopy（NMR）,X-ray photoelectron spectroscopy（XPS）and scanning electron microscopy（SEM）,etc.（2）Catalytic activity of the catalytic system on different monomers of butadiene,1-hexene,isoprene,styrene and norbornene,as well as the relationship between the catalyst and the spatial stereoselectivity of the polymer was investigated,usingα-diimine nickel as the main catalyst,Al（i-Bu）₃ and BF₃·Et₂O as the co-catalysts and PPh₃ as the electron donor.The results show that the catalytic system exhibits excellent catalytic activity for both styrene and butadiene monomers,and the catalysts with larger steric hindrance have higher spatial stereoselectivity for the polymers.（3）Theα-diimine Ni/Al（i-Bu）₃/BF₃·Et₂O/PPh₃ catalytic system was used for the block copolymerisation of styrene and butadiene.The structure of PS-b-PB was characterized by NMR,FT-IR,gel permeation chromatography（GPC）and transmission electron microscopy（TEM）.The effects of BF₃·Et₂O content and feeding ratio of the two monomers on the copolymerisation process of styrene and butadiene were investigated.The effect of catalyst spatial structure on the microstructure of PS-b-PB and the polymerization mechanism of this catalytic system were investigated.The thermal and corrosion resistance of PS-b-PB were evaluated by differential scanning calorimetry（DSC）and electrochemical tests.The results show that the PS-b-PB prepared using Ni-IV catalysts with a large steric hindrance has a controlled styrene chain segment content,high isotactic（mmmm>65%）,narrow molecular weight distribution（M_w/M_n<1.6）and high cis-1,4 structure（>95%）.The high cis-1,4 content and high degree of regularity of PS-b-PB show excellent high and low temperature resistance and corrosion resistance.α-Diimine Ni combines with Al（i-Bu）₃ and BF₃·Et₂O to form a stable Ni-F-Al structure,which can be modulated by the electron donor PPh₃ to achieve block copolymerisation of styrene and butadiene.