Hideo Nomura

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. The 13 C 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 the 13 C 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.