Degree of branch inclusion into the lamellar crystal for various ethylene/α-olefin copolymers

Various copolymers of ethylene with α-olefins, i.e. propylene, but-1-ene, hex-1-ene, oct-1-ene, dodec-1-ene and 4-methylpent-1-ene, were degraded oxidatively with fuming nitric acid (FNA). For all copolymers, the fraction of residue after FNA treatment was in close agreement with the degree of crystallinity before treatment. The X-ray diffraction pattern of the treated sample did not show any amorphous peak. These results indicate that selective removal of the amorphous region occurs by FNA treatment. The13C nuclear magnetic resonance (n.m.r.) spectrum and size exclusion chromatogram of the degraded sample suggested that the main component of the residue was dicar☐ylic acid, with a molecular weight dependent on the lamellar crystal thickness. Inclusion of short-chain branches into the crystalline core was also proved directly via the13C n.m.r. spectrum. The probability of branch inclusion determined from the n.m.r. spectrum is in the order>methyl>ethyl>n-butyl=n-hexyl=n-decyl>isobutyl, which seems to depend on the bulkiness of the branch. The difference in the probabilities of branch inclusion between n-butyl and isobutyl could be explained from the viewpoint of the mobility of the branch when the methylene sequences containing the branches crystallize from the molten state.