Styrene Polymerization Catalyzed By Heterocyclic Mono-cyclopentadienyl RareEarth Catalysts

Olefin polymerization catalyzed by metallocene catalysts has a long history.Since the beginning of the new century,mono-cyclopentadienyl（Cp’）rare earth metal（RE）catalyzed olefin polymerization received extensive attention.In this paper,indeno[1,2-b]indole derivatives(C₁₅H₉N（C₆H₆）R（R=H,1H:R=Ph,1-Ph）)and indeno[2,1-b]indole derivatives(C₁₅H₁₀N（C₆H₆）,2)were synthesized.The inden oindole derivatives and THF-coordinated rare earth chloride RECl₃（THF）_n（RE=Y,n=3.5;RE=Nd,n=4;RE=Gd,n=3.8）reacted with n-butyllithium in toluene or tetrahydrofura n to form indenoindolinyl-RE dichloride[(C₁₅H₉N（C₆H₆）R]RECl₂)（R=H,Ph;RE=Y,1H-Y,1Ph-Y;RE=Nd,1H-Nd;RE=Gd,1H-Gd）.The Indenoindole RE dichloride[(C₁₅H₉N（C₆H₆）R]RECl₂)（R=H,Ph;1H-Y,1Ph-Y,1H-Nd,1H-Gd）reacted with 2 equiv o-di methylaminobenzyllithium（o-C₆H₄NMe₂CH₂Li）in toluene or tetrahydrofuran solution to prepare seven heterocyclic mon-cyclopentadienyl rare earth metal complexes.[C₁₅H₉N（C₆H₆）R]RE（CH₂C₆H₄NMe₂-o）₂（RE=Y（1a）,RE=Nd（1b）,RE=Gd（1c）,R=Ph,RE=Y（1d））,and N-phenylindeno[2,1-b]indole dialkyl-RE complexes[(C₁₅H₁₀N（C₆H₆）]RE（CH₂C₆H₄NMe₂-o）₂（RE=Y（2a）;RE=Nd（2b）;RE=Gd（2c））.Two indenoindole complexes were used to catalyze the homo-polymerization of styrene,and a tri-components catalytic system with[Ph₃C][B（C₆F₅）₄]as cocatalyst and TIBA as scavenger was created.The homo-polymerization of styrene in toluene solution was conducted.The use of 5 equivalents of TIBA relative to RE complexes was established.Increasing the feed ratio of styrene monomer/complex（monomer concentration effect）can facilitate the catalytic activity of the complex,but reduce the percentage of monomer conversion.Higher reaction temperature affects the activity positively,while in the temperature range of 70℃to 80℃,the activity of the catalytic system reaches the maxima for styrene homopolymerization(up to 1.73×10⁶ g·mol^-1·h^-1).Kinetic study of the polymerization process revealed that the conversion rate of styrene monomer with time following the first-order kinetic law.The micro-structures of the polystyrene（PS）polymer were measured with NMR and FT-IR methodologies,and it was found that the PSs so obtained are mainly syndiotactic configuration,and the syndiotacticity average to ca.89.6%or higher in some cases.The cationic coordination polymerization process of styrene homopolymerization catalyzed by this catalytic systemand the effect of ligand structure on the homopolymerization of styrene were further discussed.It was considered that the catalytic activity and stereoselectivity were affected by both steric hindrance and electronic effect of substituents.In the two selected catalyst ligand structures,the electronic effect was dominant.