C-13 NMR SPECTRAL ASSIGNMENTS OF REGIOIRREGULAR POLYPROPYLENE DETERMINED FROM 2-DIMENSIONAL INADEQUATE SPECTRA AND CHEMICAL-SHIFT CALCULATIONS

The C-13 NMR spectrum of regioirregular polypropylene containing up to 40 mol % of inverted propylene units was assigned using the 2D INADEQUATE technique, the INEPT technique, and C-13 chemical shift calculations based on the C-13 NMR gamma-effect and the application of the rotational isomeric state model and also on the additive rules for C-13 chemical shifts of methyl-substituted alkanes. The presence of four kinds of sequences containing head-to-head and/or tail-to-tail units in the sample was confirmed. The C-13-C-13 connectivities of the 2D INADEQUATE spectrum were extremely useful in the assignment of overlapping peaks as well as the identification of several such sequences. The peaks were assigned to each carbon in these sequences by taking tacticity into account. There is exclusively a meso head-to-head unit in the sequence where a single inverted unit is contained in several head-to-tail units.