Busico Vincenzo, Cipullo Roberta, Cutillo Francesco, Friederichs Nic, Ronca Sara, Wang Bing
Dipartimento di Chimica, Università di Napoli "Federico II", Via Cintia, 80126 Naples, Italy.
J Am Chem Soc. 2003 Oct 15;125(41):12402-3. doi: 10.1021/ja0372412.
The presence of "free" trimethylaluminum (TMA) in methylalumoxane (MAO) solutions can be highly detrimental to the performance of metallocene and "post-metallocene" olefin polymerization catalysts. The most used strategy to remove "free" TMA is to evaporate MAO solutions to dryness, until a free-flowing white powder ("solid MAO") is left. This procedure is tedious and potentially hazardous, because in some cases the distillate is a concentrated hydrocarbon solution of TMA. Moreover, "solid MAO" is poorly soluble in common polymerization media, and once in solution it can regenerate TMA to some extent. This communication reports on a facile alternative, which consists in the controlled addition of a sterically hindered phenol, such as 2,6-di-tert-butylphenol, effectively trapping "free" TMA. We show here that 2,6-di-tert-butylphenol/MAO solutions activate equally well the dichloro-precursors of well-known zirconocene and bis(phenoxyimine)Ti catalysts, and that their use in propene polymerization results in a substantially higher productivity, polymer stereoregularity, and/or average molecular mass compared with activation by MAO alone.
甲基铝氧烷（MAO）溶液中“游离”三甲基铝（TMA）的存在可能对茂金属和“后茂金属”烯烃聚合催化剂的性能极为不利。去除“游离”TMA最常用的策略是将MAO溶液蒸发至干，直到留下自由流动的白色粉末（“固体MAO”）。该过程繁琐且有潜在危险，因为在某些情况下馏出物是TMA的浓缩烃溶液。此外，“固体MAO”在常见聚合介质中的溶解度很差，并且一旦溶解，它会在一定程度上再生TMA。本通讯报道了一种简便的替代方法，该方法包括可控地添加空间位阻酚，如2,6-二叔丁基苯酚，有效地捕获“游离”TMA。我们在此表明，2,6-二叔丁基苯酚/MAO溶液能同样良好地活化著名的二氯锆茂和双（苯氧基亚胺）钛催化剂的前体，并且与单独用MAO活化相比，它们用于丙烯聚合时可显著提高生产率、聚合物立构规整度和/或平均分子量。
