FULL ASSIGNMENT OF THE C-13 NMR-SPECTRA OF REGIOREGULAR POLYPROPYLENES - METHYL AND METHYLENE REGION

C-13 NMR spectroscopy is the main source of information on the stereoc hemistry of Ziegler-Natta and related transition metal catalyzed prope ne polymerizations. In simple cases, like those of polypropylenes form ed 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 C-13 NMR spectra. On the other hand , the variety of innovative polymers that can now be prepared with ''h igh-yield'' heterogeneous and metallocene-based homogeneous catalysts under hybrid, multiple, or oscillating stereocontrol represent very co mplex systems, which are beyond the possibilities of configurational a nalysis by routine C-13 NMR. In such cases, high-field C-13 NMR can be highly advantageous. Indeed, in this paper we show that from the meth yl and methylene regions of 150 MHz C-13 NMR spectra of polypropylenes of various tacticities, the stereosequence distribution can be determ ined at a much finer level of detail, so as to obtain an adequate expe rimental basis for the investigation of the many complicated mechanism s of stereocontrol presently encountered in Ziegler-Natta catalysis.