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Clément Lansalot-Matras 《Journal of organometallic chemistry》2008,693(3):393-398
A library of N-tripodal ligands, based on a central nitrogen atom connected to three different functionalized arms, was investigated via a parallel approach for the polymerization of methyl-methacrylate (MMA) in presence of late transition metal salts. Copper salts CuCl2 and Cu(OAc)2 in combination with N-(2-furanylmethyl)-N-(1-3,5-dimethyl-1H-pyrazolylmethyl)-N- (phenylmethyl)amine were detected as efficient catalysts for the syndiotactic polymerization of MMA ([rr] up to 78%). Kinetic studies and X-ray structures of the best catalysts were reported. 相似文献
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使用桥连配体锂盐与MCl4络合, 合成了4个不同结构的双核茂金属化合物[μ,μ-(CH2)3]{[C(H)·(η5-C5H4)(η5-C13H8)](MCl2)}2[M=Zr or Ti](4, 5)和[μ,μ-(CH2)3]{[C(H)(η5-C5H4)(η5-C9H6)]·(MCl2)}2[M=Zr or Ti](6, 7), 配体和化合物都经过核磁氢谱(1H NMR)、 碳谱(13C NMR)、 红外光谱(IR)及元素分析等表征, 确认了化学结构. 以甲基铝氧烷(MAO)为助催化剂, 化合物4~7为催化剂催化丙烯聚合, 考察了聚合温度、 乙烯压力、 铝钛或铝锆比对催化剂活性及聚合物分子量的影响. 结果表明, 多亚甲基桥连双核茂金属是高活性乙烯和丙烯聚合催化剂, 乙烯聚合活性最高达到7.5× 106 g PE/(mol Zr·h)(化合物6), 丙烯聚合活性达 10 × 105 g sPP/(mol Zr·h)(化合物4). 所得间规聚丙烯(sPP)的间规度指数(SI, r) 达到90%. 在同样条件下, 双核化合物的催化活性、 聚合物分子量Mw(> 100000)以及分子量分布(MWD>2.5)均比相应的单核化合物高(Mw<70000, MWD≤2), 表明该体系中存在较强的核效应. 相似文献
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Poly(vinyl alcohol-b-styrene) (poly(VA-b-St)) diblock copolymers with different syndiotacticity of poly(vinyl alcohol) (PVA) block were synthesized via consecutive telomerization, atom transfer radical polymerization, and saponification. These amphiphilic block copolymeric micelles were prepared by dialysis against water. Dynamic light scattering and transmission electron micrograph measurements confirmed the formation of a micelles, and the size of a micelle was less than 100 nm and increased with the molecular weight of polystyrene (PS) block. From the fluorescence emission spectrum measurements using pyrene as a fluorescence probe, the copolymers formed micelles with critical micelle concentration (CMC) in the range of 0.125–4.47 mg/l. The CMC values increase with decrease of the molecular weight of the PS block and increase of the syndiotacticity of PVA block. Kinetic stability study of micelles showed increased stability for block copolymers containing PVA block with higher syndiotacticity. 相似文献
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The properties of the aged gels of high molecular weight syndiotacticity-rich poly(vinyl alcohol)s (HMW S-PVAs) with different
syndiotactic diad (s-diad) contents were investigated. HMW S-PVA gels with s-diad content of 61.5% and 58.2% showed the rapid increases of the syneresis and the turbidity from the early stage of aging
time, which is ascribable to the phase separation, while that with s-diad content of 55.7% did not. From the morphological study, it was confirmed that the phase separation in HMW S-PVA gel
with s-diad content of 61.5% occurred without the liquid-liquid phase separation in sol state, whereas both the liquid-liquid phase
separation in sol state and the subsequent phase separation in gel state occurred in the case of HMW S-PVA gel with s-diad content of 58.2%. On the other hand, HMW S-PVA gel with s-diad content of 55.7% showed neither the liquid-liquid phase separation in sol state nor the phase separation in gel state
in the long period of time. It was also confirmed from wide angle X-ray diffractogram that the crystallization was accompanied
by the phase separation in gel state in the aging process of PVA gel. However, the crystallization was hindered by the fast
network formation at the initial stage of time. Later the syndiotacticity promoted the crystallization. The tensile modulus
of HMW S-PVA gel with higher syndiotacticity increased more significantly with time.
Received: 2 December 1999/Accepted: 12 July 2000 相似文献
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聚合温度对聚氯乙烯树脂结构和性能的影响 总被引:4,自引:0,他引:4
采用凝胶渗透色谱法、13H NMR和DSC法测定了悬浮聚合PVC树脂的平均分子量、间规度、结晶度和玻璃化温度.结果表明:聚合温度下降,PVC的平均分子量上升,分子量的对数值与聚合温度的倒数成正比;PVC的间规度和结晶度均增大,在形成结晶的间规链段的最短长度(ξmin)为6时,由间规度计算的结晶度理论值与测定值接近;分子量和结晶度增加的共同作用,使PVC的玻璃化转变温度上升. 相似文献
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