Abstract
Hexad comonomer sequences in stereoregular ethylene-propylene (E-P) copolymer were analysed on the basis of 13C nuclear magnetic resonance (n.m.r.) spectra. The chemical shifts of methylene resonances, which depend on the hexad comonomer sequences, were given by the chemical shifts calculation using the gamma effect on 13C n.m.r. chemical shift and the Mark's rotational isomeric state model for E-P copolymer. From comparisons between the observed and calculated chemical shifts, the hexad methylene peaks were assigned. Further, the overlap between methine and methylene peaks was discriminated by an INEPT (insensitive nuclei enhancement by polarization transfer) experiment. From these analytical results, the tetrad sequence distribution in stereoregular E-P copolymer was accurately determined. The validity of our hexad assignments was confirmed by the good correspondence between the observed tetrad sequence distribution and that predicted by the two-site statistical model for the E-P copolymerization mechanism.
Published Version
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