Salt metathesis reactions between pyridyl-methylene-cyclopentadienyl lithium salt and LnCl_3 followed by the addition of two equivalents of LiCH_2SiMe_3 afforded a series of constrained-geometry-configuration rare-ear...Salt metathesis reactions between pyridyl-methylene-cyclopentadienyl lithium salt and LnCl_3 followed by the addition of two equivalents of LiCH_2SiMe_3 afforded a series of constrained-geometry-configuration rare-earth metal bis(alkyl) complexes(Cp′CH_2-Py)Ln(CH_2SiMe_3)_2(THF)_n(Py = C_5H_4N, Cp′ = C_5H_4(Cp), Ln = Sc, n = 0(1); Cp′ = C_9H_6(Ind), Ln = Sc, n = 0(2); Cp′ = 3-Me_3Si-C_9H_5(3-Me_3Si-Ind), Ln = Sc, n = 0(3a), Ln = Lu(3b), Y(3c), n = 1; Cp′ = 2,7-(~tBu)_2C_(13)H_8(2,7-(~tBu)_2-Flu), Ln = Sc(4 a), n = 0, Ln = Lu(4b),Y(4c), n = 1) in moderate to good yields, which were characterized by NMR spectroscopy and single-crystal X-ray diffraction(for complex 3a). In the presence of [Ph_3C][B(C_6F_5)_4] and Al^iBu_3, these complexes displayed different performances towards styrene polymerization. Rare-earth metal bis(alkyl) precursors bearing Cp, Ind, and 3-Me_3Si-Ind segments exhibited very low catalytic activity to afford syndiotactic polystyrene. All electron-donating t Bu substituted complexes 4 a, 4 b, and 4 c showed very high activity and perfect syndiotactivity(rrrr > 99%), producing high molecular weight polystyrene(up to 54.1 × 10~4) with relatively narrow molecular distribution(PDI = 1.28-2.49).展开更多
The cure kinetics for two-component silicone rubber formed by addition reaction was studied by the rheological method. The influence of reaction temperature （7） on the cure kinetics was explored in detail. It was ob...The cure kinetics for two-component silicone rubber formed by addition reaction was studied by the rheological method. The influence of reaction temperature （7） on the cure kinetics was explored in detail. It was observed that the data of gel time （tgel, i.e. the time when the reaction reaches the gel point） or a specific reaction time （tnc） （defined as the reaction time before which time the influence of confinement of network on the diffusion of reaction components can be neglected） versus T obey certain functional relationship, which was well explained by the cure kinetics model of thermoset network. The cure kinetics for the two-component silicone rubber can be well fitted by the Kamal-Sourour（autocatalyst） reaction model rather than Kissinger model. When the reaction time was before or equal to tnc, the reaction order obtained by the Kamal-Sourour reaction model was 2, which was consistent with the reaction order inferred from the two components chemical reaction when the diffusion of reaction components was not influenced by the formed cross-linked polymer network. When the reaction time was larger than tnc, such as to the end of reaction （re）, the influence of confinement of network on the diffusion of reaction components cannot be neglected, and the reaction order obtained by the Kamal-Sourour reaction model was larger than 2. It was concluded that the confinement effect of network had a greater influence on the cure kinetics of the silicone rubber. The reaction rate constants （kτ） under different temperatures were also determined by Kamal-Sourour reaction model. The activation energy （E） for the two-component silicone rubber was also calculated from the results of lntgcl, lnlnc, and lnkτ versus 1/T, respectively. The three values of E were close, which indicated that above analyses were self-consistent.展开更多
The catalytic performa nee of rare-earth metal dialkyl complexes in combi nation with DMAO(dry methylalumi no xane)is explored.In the presence of 60 equivalents of DMAO,the half-sandwich complex(C_(13)H_(8)CH_(2)Ph)Sc...The catalytic performa nee of rare-earth metal dialkyl complexes in combi nation with DMAO(dry methylalumi no xane)is explored.In the presence of 60 equivalents of DMAO,the half-sandwich complex(C_(13)H_(8)CH_(2)Ph)Sc(CH_(2)SiMe_(3))_(2)(THF)(1)is inert for styrene polymerization,but(C_(5)Me_(4)Ph)Sc(CH_(2)C_(6)H_(4)NMe_(2)-o)_(2)(2)con verts 18% styre ne into syn diotactic polystyrene.Under the same conditi ons,the con strained-geometry configuration sandium complex(C13H8CH2Py)Sc(CH_(2)SiMe_(3))_(2)(3a)displays extremely high catalytic activity(>6420 kg·mol_(sc)^(-1)h^(-1))and perfect syndiospecific(rrrr>99%)for styrene polymerization,while its lutetium(3b)and yttrium(3c)analogues are nearly inactive.Although the binary catalytic system 3a/DMAO exhibits very low activity for 4-methoxystyrene polymerization,it is an efficient catalyst for the syndioselective polymerization of other styrene derivatives such as 2-methoxystyrene,4-methylthiostyrene,4-fluorostyrene,4-dimethylhydrosilylstyrene,alkyne-susbstituted styrenes and 4-methylstyrene.In addition,the binary system 3a/DMAO can copolymerize ethylene and styrene to give alternating copolymers with a single glass tran sition at 80℃ and 0.4 MPa ethylene pressures.By in creasing styrene feed amount from 20 mmol to 60 mmol,the styre ne con tent slight in creases from 48.2 mol% to 53.8 mol%,but the polymerizatio n activity is obviously promoted from 240 kg·mol_(Sc)^(-1)·h^(-1) to 532 kg·mol_(sc)^(-1)·h^(-1).展开更多
基金financially supported by the National Natural Science Foundation of China (Nos. 51773193 and 21634007)department of science and technology of Jilin province (No.20180101171JC)the "973" project (No. 2015CB654702)
文摘Salt metathesis reactions between pyridyl-methylene-cyclopentadienyl lithium salt and LnCl_3 followed by the addition of two equivalents of LiCH_2SiMe_3 afforded a series of constrained-geometry-configuration rare-earth metal bis(alkyl) complexes(Cp′CH_2-Py)Ln(CH_2SiMe_3)_2(THF)_n(Py = C_5H_4N, Cp′ = C_5H_4(Cp), Ln = Sc, n = 0(1); Cp′ = C_9H_6(Ind), Ln = Sc, n = 0(2); Cp′ = 3-Me_3Si-C_9H_5(3-Me_3Si-Ind), Ln = Sc, n = 0(3a), Ln = Lu(3b), Y(3c), n = 1; Cp′ = 2,7-(~tBu)_2C_(13)H_8(2,7-(~tBu)_2-Flu), Ln = Sc(4 a), n = 0, Ln = Lu(4b),Y(4c), n = 1) in moderate to good yields, which were characterized by NMR spectroscopy and single-crystal X-ray diffraction(for complex 3a). In the presence of [Ph_3C][B(C_6F_5)_4] and Al^iBu_3, these complexes displayed different performances towards styrene polymerization. Rare-earth metal bis(alkyl) precursors bearing Cp, Ind, and 3-Me_3Si-Ind segments exhibited very low catalytic activity to afford syndiotactic polystyrene. All electron-donating t Bu substituted complexes 4 a, 4 b, and 4 c showed very high activity and perfect syndiotactivity(rrrr > 99%), producing high molecular weight polystyrene(up to 54.1 × 10~4) with relatively narrow molecular distribution(PDI = 1.28-2.49).
基金financially supported by the National Natural Science Foundation of China(No.21274152)the Science and Technology Development Project of Jilin Province,China(No.20150301002GX)
文摘The cure kinetics for two-component silicone rubber formed by addition reaction was studied by the rheological method. The influence of reaction temperature （7） on the cure kinetics was explored in detail. It was observed that the data of gel time （tgel, i.e. the time when the reaction reaches the gel point） or a specific reaction time （tnc） （defined as the reaction time before which time the influence of confinement of network on the diffusion of reaction components can be neglected） versus T obey certain functional relationship, which was well explained by the cure kinetics model of thermoset network. The cure kinetics for the two-component silicone rubber can be well fitted by the Kamal-Sourour（autocatalyst） reaction model rather than Kissinger model. When the reaction time was before or equal to tnc, the reaction order obtained by the Kamal-Sourour reaction model was 2, which was consistent with the reaction order inferred from the two components chemical reaction when the diffusion of reaction components was not influenced by the formed cross-linked polymer network. When the reaction time was larger than tnc, such as to the end of reaction （re）, the influence of confinement of network on the diffusion of reaction components cannot be neglected, and the reaction order obtained by the Kamal-Sourour reaction model was larger than 2. It was concluded that the confinement effect of network had a greater influence on the cure kinetics of the silicone rubber. The reaction rate constants （kτ） under different temperatures were also determined by Kamal-Sourour reaction model. The activation energy （E） for the two-component silicone rubber was also calculated from the results of lntgcl, lnlnc, and lnkτ versus 1/T, respectively. The three values of E were close, which indicated that above analyses were self-consistent.
基金This work was partially financially supported by the National Natural Science Foundation of China(Nos.51773193 and 52073275).
文摘The catalytic performa nee of rare-earth metal dialkyl complexes in combi nation with DMAO(dry methylalumi no xane)is explored.In the presence of 60 equivalents of DMAO,the half-sandwich complex(C_(13)H_(8)CH_(2)Ph)Sc(CH_(2)SiMe_(3))_(2)(THF)(1)is inert for styrene polymerization,but(C_(5)Me_(4)Ph)Sc(CH_(2)C_(6)H_(4)NMe_(2)-o)_(2)(2)con verts 18% styre ne into syn diotactic polystyrene.Under the same conditi ons,the con strained-geometry configuration sandium complex(C13H8CH2Py)Sc(CH_(2)SiMe_(3))_(2)(3a)displays extremely high catalytic activity(>6420 kg·mol_(sc)^(-1)h^(-1))and perfect syndiospecific(rrrr>99%)for styrene polymerization,while its lutetium(3b)and yttrium(3c)analogues are nearly inactive.Although the binary catalytic system 3a/DMAO exhibits very low activity for 4-methoxystyrene polymerization,it is an efficient catalyst for the syndioselective polymerization of other styrene derivatives such as 2-methoxystyrene,4-methylthiostyrene,4-fluorostyrene,4-dimethylhydrosilylstyrene,alkyne-susbstituted styrenes and 4-methylstyrene.In addition,the binary system 3a/DMAO can copolymerize ethylene and styrene to give alternating copolymers with a single glass tran sition at 80℃ and 0.4 MPa ethylene pressures.By in creasing styrene feed amount from 20 mmol to 60 mmol,the styre ne con tent slight in creases from 48.2 mol% to 53.8 mol%,but the polymerizatio n activity is obviously promoted from 240 kg·mol_(Sc)^(-1)·h^(-1) to 532 kg·mol_(sc)^(-1)·h^(-1).
