Abstract
13C NMR chemical shifts of the model compounds for ethylene–propylene (E-P) copolymer with a low ethylene content were calculated using the gamma-effect of 13C chemical shift and Mark’s rotational isomeric state matrices of E-P copolymer. The carbons of interest in the model compounds are included in the same monomer unit surrounded by different comonomer sequences due to the substitution of monomer unit between ethylene and propylene. Observed 13C chemical shift differences for the carbons of interest were reasonably explained by the calculation. The magnitude of the gamma-effect was found to be sensitive to the change of the comonomer sequences. These estimated chemical shift differences are comparable to the stereosequence dependence of 13C chemical shifts. The calculated 13C NMR chemical shifts of stereoregular E-P copolymer with a low ethylene content allow the assignments of complicated tactic and comonomer sequence dependent resonances in the methyl resonance region. This calculation method also predicted the 13C NMR chemical shift differences for the methylene carbons included in ethylene unit situated in two different comonomer sequences, namely, (I) the ethylene unit surrounded by the isotactic polypropylene chain, and (II) the ethylene unit which is the structural element of the isotactic poly(1-methyltetramethylene) as a model of regularly alternating ethylene–propylene copolymer.
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Hayashi, T., Inoue, Y., Chûjô, R. et al. 13C NMR Chemical Shifts Calculation for Model Compounds of Ethylene–Propylene Copolymer with a Low Ethylene Content. Polym J 20, 107–118 (1988). https://doi.org/10.1295/polymj.20.107
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DOI: https://doi.org/10.1295/polymj.20.107
