Full Assignment of the ¹³C NMR Spectra of Regioregular Polypropylenes:  Methyl and Methylene Region

Abstract

13 C NMR spectroscopy is the main source of information on the stereochemistry of Ziegler−Natta and related transition metal catalyzed propene polymerizations. In simple cases, like those of polypropylenes formed under pure enantiomorphic-site or chain-end control, the origin of the stereoselectivity can be easily recognized from the steric pentad distribution obtained from routine 13 C NMR spectra. On the other hand, the variety of innovative polymers that can now be prepared with “high-yield” heterogeneous and metallocene-based homogeneous catalysts under hybrid, multiple, or oscillating stereocontrol represent very complex systems, which are beyond the possibilities of configurational analysis by routine 13 C NMR. In such cases, high-field 13 C NMR can be highly advantageous. Indeed, in this paper we show that from the methyl and methylene regions of 150 MHz 13 C NMR spectra of polypropylenes of various tacticities, the stereosequence distribution can be determined at a much finer level of detail, so as to obtain an adequate experimental basis for the investigation of the many complicated mechanisms of stereocontrol presently encountered in Ziegler−Natta catalysis.