Synthesis Of Conjugated Diene Homopolymers And Block Copolymers With Highly Cis-1,4 Unit Content And Narrow Distributed By Coordination Polymerization

With the rapid development of the world industry,the demand for yield and performance of butadiene rubber（PB）and isoprene rubber（PI）are also increasing.Studies have shown that increasing the cis-1,4 unit content can not only increase PB’s or PI’s tensile strength and elongation ratio mutually,but also improve the fatigue and crack resistance significantly.Moreover,increasing the cis-1,4 unit content is an effective method for reducing the glass transition temperature（T_g）of conjugated diene rubber,which result in a better low temperature resistance.Similarly,high cis-1,4 structure was able to attributed to improve the low temperature resistance of styrene-butadiene-styrene（SBS）and styrene-isoprene-styrene（SIS）block copolymers,and their tensile strength and flexibility effectively.In addition to the structural content of cis-1,4 unit content,the molecular weight distribution（M_w/M_n）of rubber is also an important indicator affecting the performance of conjugated diene rubber.Narrow molecular weight distribution（M_w/M_n<3.0）is conducive to the construction of a uniform vulcanization cross-linking network of elastomer materials,thereby improving the mechanical strength,and has the advantages of low heat generation and low hysteresis loss.Therefore,it is of great significance to synthesize conjugated diene homopolymers or conjugated diene/styrene block copolymers with a high cis-1,4 unit content and narrow molecular weight distribution.This thesis focuses on the preparation of conjugated diene homopolymers and their block copolymers with styrene with high cis-1,4 unit content,controllable molecular weight and narrow molecular weight distribution.In the second and third chapter of this thesis,polybutadiene and polyisoprene with high cis-1,4 unit content and narrow molecular weight distribution（M_w/M_n<1.5）were prepared by coordination polymerization through structural improvement of main catalyst and screening of alkylation reagent.In the chapter 4,the butadiene/isoprene-styrene block copolymer with high cis-1,4 unit content was obtained by adding triphenylphosphine（PPh₃）to regulate the electron cloud density of the active central metal atom in the ternary rare earth or nickel catalyst system,after the polymerization of butadiene or isoprene.In chapter 5 and 6,a series of styrene-butadiene/isoprene triblock copolymers with high cis-1,4 unit content,controllable styrene content,controllable molecular weight and distribution of polymers were synthesized by a novel synthetic strategy via changing the catalyst active centres,which was based on a transfer technique from anionic to coordination polymerization.Relevant research contents and results are summarized as follows:（1）Nd（CF₃SO₃）₃ and trioctyl phosphate（TOP）were mixed directly and the reaction was carried out at 120°C to obtain a novel metal complex Nd（CF₃SO₃）₃*3TOP.The Nd（CF₃SO₃）₃*3TOP was combined with Al（i-Bu）₃ to prepare a binary rare earth catalyst,which was used to initiate the polymerization of butadiene,a polybutadiene with a high cis-1,4 unit content（cis-1,4>98.5%）and a narrow molecular weight distribution（M_w/M_n=1.32）was obtained.The catalyst performance of Nd（CF₃SO₃）₃*3TOP was compared with the complex Nd（CF₃SO₃）₃*3TBP synthesized via the same synthesis process,and the reason for a narrower molecular weight distribution of polybutadiene obtained by Nd（CF₃SO₃）₃*3TOP was discussed.DSC was used to measure the low temperature resistance of PBs obtained by Nd（CF₃SO₃）₃*3TOP/Al（i-Bu）₃ binary system（Nd-PB）and n-butyllithium catalyst system（Li-PB）,the result showed that the T_g of Nd-PB was significantly lower than that of Li-PB.The influence of cis-1,4 unit content on the T_g of the polymer was discussed.In addition,the Nd（CF₃SO₃）₃*3TOP/Al（i-Bu）₃ catalyst system was applied to the polymerization of isoprene,and it also has high catalytic activity for isoprene monomer and obtained a polymer with a high cis-1,4 unit content,but the product has a broad molecular weight distribution.（2）Liquid Nd(P₂₀₄)₃ was used as the main catalyst,and Al（i-Bu）₂H and CHCl₃ were used as the alkylating agent and chlorine source,respectively.The order of addition followed was Nd+Ip+Al+Cl.The optimized ternary catalyst system was prepared with a ratio of[Nd]:[Ip]:[Al]:[Cl]=1:20:20:3.After aging at 50℃for 30 min,a tentary Nd-Based catalsyt system Nd(P₂₀₄)₃/Al（i-Bu）₂H/CHCl₃was obtained.This catalyst system was successfully used to initiate the polymerization of isoprene,affording a high cis-1,4 unit content（cis-1,4>97%）,a narrow molecular weight distribution（M_w/M_n<1.2）,and precisely controlled molecular weight of the liquid polyisoprene（LIR）.It was found that the molecular weight of the obtained polyisoprene can be precisely controlled by the Nd(P₂₀₄)₃/Al（i-Bu）₂H/CHCl₃ catalyst system.The number average molecular weight（M_n）was about one-seventh of the theoretical calculation conforming to the formula for coordination chain transfer polymerization（CCTP）,while other alkylating agents such as Al（i-Bu）₃ and Al Et₃ did not have this characteristic when catalyzed the polymerization of isoprene with Nd(P₂₀₄)₃ and CHCl₃.The Nd(P₂₀₄)₃/Al（i-Bu）₂H/CHCl₃catalyst system was also used to initiate the polymerization of butadiene,and the polybutadiene with a high cis-1,4 unit content was also obtained,but the molecular weight of the obtained polymer does not match the formula for CCTP.（3）After the polymerization of butadiene or isoprene initiated by rare earth catalyst system Nd(P₂₀₄)₃/Al（i-Bu）₃/CHCl₃,triphenylphosphine（PPh₃）was added to regulate the electrons cloud density of the active center.The catalytic activity of the catalyst system on styrene can be significantly improved,and the block copolymers PB-b-PS or PI-b-PS with a high cis-1,4 unit content was obtained.However,the conversion rate of styrene in the second polymerization step was only about 56%.The catalytic activity for styrene can be significantly improved by using catalyst system Ni（naph）₂/n-Bu Li/BF₃*Et₂O with PPh₃,insteading of the rare earth catalyst system.The conversion rate of styrene in the second step was over than 90%.（4）A novel synthesis strategy on styrene-butadiene di-block copolymer（PS-b-PB）with high cis-1,4 unit content was developed,based on a transfer technique from anionic to coordination polymerization.Firstly,the styrene monomer was initiated by n-butyllithium（n-Bu Li）utilizing anionic polymerization at 50℃,which resulted in a macromolecular alkylating initiator（PSLi）.Secondly,PSLi was aged with nickel naphthenate（Ni）and boron trifluoride etherate（B）for obtaining a complex catalyst system（Ni/PSLi/B）.Then,Ni/PSLi/B was applied to initiate the butadiene（Bd）polymerization.Following this new strategy,a series of PS-b-PBs（Ni-PS-b-PBs）with a high cis-1,4 content（cis-1,4=97.2%）,narrow molecular weight distribution（M_w/M_n～1.3）and controlled styrene content and molecular weight were successfully synthesized.The experiment result show that the low temperature mechanical properties of Ni-PS-b-PB via"anion to coordination"conversion mechanism was much better than using only anionic polymerization to obtain PS-b-PB（Li-PS-b-PB）.In addition,the polymerization mechanism of PS-b-PB synthesized by Ni/PSLi/B polymerization system was discussed.（5）After the polymerization of butadiene initiated by the Ni/PSLi/B catalyst system,the triphenylphosphine（PPh₃）was added to regulate the electrons cloud density of the active center.Then the polymerization of styrene was initiated.Finally,a styrene-butadiene-styrene block copolymer（Ni-SBS）with a high cis-1,4 unit content,controllable styrene content and molecular weight,a narrow molecular weight distribution was obtained.Compared with the SBS via anion polymerization（Li-SBS）which has been industrially produced,Ni-SBS has better low temperature mechanical properties and high temperature resistance.The synthesis process study of Ni-SBS shown that the optimum amounts of n-butyllithium and triphenylphosphine are[Li]/[Ni]=5 and[PPh₃]/[Ni]=1,respectively.The Ni/PSLi/B/PPh₃system was applied to the block copolymerization of styrene and isoprene in this experiment,and the styrene-butadiene-styrene triblock copolymer（SIS）with high cis-1,4 unit content（cis-1,4>98%）and a narrow molecular weight distribution（M_w/M_n<2）are also obtained.