Monomer sequence characterization of propylene-1-olefin copolymers by carbon-13 NMR spectroscopy

Complete comonomer sequence assignments were made for a series of propylene-1-olefin copolymers, including 1-butene, 1-hexene, and 1-octene, to establish the effect of branch length on the sequence sensitivity of the backbone carbon chemical shifts. Particular attention was paid to the effect of branch length on the monomer sequence sensitivity of the αα carbon chemical shifts. As opposed to the ethylene-1-olefin copolymers where the reported αα carbon chemical shifts were exclusively tetrad sensitive regardless of the branch length, the αα carbons in each of the three propylene-1-olefin systems examined showed apparent tetrad, triad, and dyad monomer sequence sensitivities as the center dyad changed from PP to PX to XX where X represents the individual 1-olefin.