"振荡"的金属催化剂:什么阻止了振荡?
Vincenzo Busico1, Valeria Van Axel Castelli, Paola Aprea
1Dipartimento di Chimica, Università di Napoli Federico II, Via Cintia, 80126 Naples, Italy. busico@chemistry.unina.it
Journal of the American Chemical Society
|May 2, 2003
概括
金属催化剂具有不同的固体阻碍控制聚烯微结构. 高度受阻的催化剂产生异性-立体积聚合物,而较少受阻的催化剂产生立体正规聚烯,在特定条件下有可能产生异性分数.
科学领域:
- 聚合物化学 聚合物化学
- 有机金属化学 有机金属化学
- 材料科学 材料科学 材料科学
背景情况:
- 金属催化剂对于立体选择性烯聚合是至关重要的.
- 了解催化剂的行为,特别是"振荡"的金属,是控制聚合物微观结构的关键.
- 以前的模型很难解释某些金属催化剂产生的聚烯中的立体控制.
研究的目的:
- 分析由两种"振荡"的金属催化剂产生的聚烯的微观结构,具有不同的硬质阻碍.
- 阐明这些聚合过程中立体控制的机械起源.
- 调查催化剂构成的作用及其与 counterions 的相互作用.
主要方法:
- 150 MHz (13)C 聚烯样品的NMR微结构分析.
- 催化剂的比较: [(2-(3,5-di-tert-butyl-4-methoxyphenyl) 烯基) ((2) ZrP] ((+) 和 [(2-phenylindenyl) ((2) ZrP] ((+).
- 对离子对进行计算机建模,以测试对立体刚性的假设.
主要成果:
- 这种高度阻碍的催化剂产生了同态立体积聚烯,表明在等离体形状的rac类构造之间发生了振荡.
- 较少阻碍的催化剂由于更快的联结体旋转,产生了主要的立体正规聚烯.
- 来自较少受阻的催化剂的特定分数表明,受反星邻近的影响,像rac类物种的构造被锁定.
结论:
- "振荡"机制需要改进,以考虑观察到的聚合物配置.
- 绝缘阻碍和连接体动力学显著影响聚烯的立体规律性.
- 对比的接近可以诱导金属催化剂的立体刚性,影响聚合物微观结构.
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