Advances in the 13C NMR characterization of ethene/propene copolymers, 1 - C2-symmetric ansa-metallocene catalysts

The microstructure of a number of ethene/propene copolymers prepared with three representative C-2-symmetric ansa-metallocene catalysts was investigated by means of high-field (150 MHz) C-13 NMR. Thanks to the exceedingly high resolution of the spectra, an unprecedented experimental basis for the constitutional sequence analysis was achieved, which enabled us to test complex statistical models of chain propagation in a significant manner. In particular, the need for a 2(nd)-order Markov model, previously suggested by some authors on the basis of triad data, was confirmed by our study at pentad/heptad level. Some correlations between metallocene structure and copolymerization statistics were also modified.