ABSTRACT
The discovery of Ziegler–Natta polymerization catalysts has been one of the most important achievements of modern chemistry. The emergence of metallocene catalysts has been one of the two major milestones in the progress of coordination polymerization of olefins after the Ziegler–Natta catalysts. The other milestone is the discovery of post-metallocenes, the name that encloses a plethora of transition metal complexes, capable of performing as single-site olefin polymerization catalysts. This chapter presents some results of nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopic studies of methylalumoxane (MAO) and ion pairs formed upon the activation of metallocenes and post-metallocenes with MAO. Commercially available solutions of MAO consist of a polymeric MAO fraction and residual trimethylaluminum (TMA). The chapter summarizes recent data on the structure of MAO, obtained by other techniques. Apparently, with decreasing temperature, oligomeric molecules of MAO tend to associate to form larger aggregates, invisible by Al NMR spectroscopy due to dramatic line broadening.
