Titre : Methylaluminoxane Activation of Single-Site Polymerization Catalysts: Friend or Foe?
La conférence (en anglais) sera prononcée par le professeur Scott Collins, qui est actuellement un chercheur invité au département de chimie de l'University of Victoria. Ce dernier sera de passage à Montréal à titre d'examinateur externe d'une soutenance de thèse en chimie.
Résumé : Ever since its discovery in the 1970s by Sinn and Kaminsky, methylaluminoxane (MAO) has been the activator of choice for transition metal complexes that give rise to single-site polymerization catalysts which affect the coordination-insertion polymerization of simple alkenes to furnish polyolefins.In the case of bent metallocene or constrained geometry, cyclopentadienylamido complexes of group 4, this technology forms the basis for a variety of commercial processes that account for more than 10% of global production of polyolefins each year. Despite the success of this new technology, MAO is typically used in large excess over the transition metal complex and represents a significant fraction of the total cost of the catalyst. Moreover, despite intensive study, the structures and functions of this complex mixture of organoaluminum compounds remains a mystery to this day.
In this presentation we will review the current understanding of MAO and its mode(s) of action, and illustrate some of the unusual or unexpected aspects of its behavior with reference to a number of projects we have been involved with over the years, both in Canada and elsewhere.These studies hint that MAO is not always the activator of choice when one moves away from metallocene complexes of group 4 and in fact its use may be quite misleading in certain cases as to transition metal catalyst structure and function. In the final part of our presentation, we will discuss recent electrospray ionization mass spectrometric studiesas well as conventional techniques such as NMR spectroscopythat make clear how MAO activates metallocene complexes, and why this chemical “chameleon” behaves in the unique fashion it does.