C-13 NMR CHEMICAL-SHIFT ASSIGNMENTS OF COMONOMER SEQUENCES IN A 1-BUTENE PROPYLENE COPOLYMER

C-13 NMR chemical shift assignments of comonomer sequences in a 1-butene-propylene copolymer were obtained from the C-13 two-dimensional INADEQUATE NMR experiment and from the calculated chemical shifts due to the gamma-effect. By tracing carbon-carbon connectivities in the 2D-INADEQUATE spectrum, the validity of previous assignments of triad and tetrad sequences was confirmed. Referring to the confirmed assignments, the chemical shift differences among comonomer sequences longer than pentad were predicted by the chemical shift calculation (the gamma-effect method) based on the gamma-effect of the C-13 chemical shift and Mark's rotational isomeric state model modified by considering the side-chain conformation in a 1-butene unit. Assignments provided in this study agree well with Cheng's assignments by a reaction probability model. Further, the conformational probability of the side chain in a 1-butene unit was evaluated through the chemical shift calculation.