Spatially Inhomogeneous Crystallinity In Heterogeneous Ethylene-Alpha-Olefin Copolymers

The crystallinity development in heterogeneous ethylene-1-butene copolymers is compared with that in ethylene copolymers, with more bulky 1-heptene as a comonomer. The thermal transitions of the 1-heptene based copolymers persistently occur at higher temperatures than of the corresponding I-butene copolymers. The earlier crystallization onset is reflected in thicker primary crystals, which in turn are associated with the presence of longer ethylene sequences because of the inaccessibility of 1-heptene to sterically shielded catalytic sites. In addition, the 1-heptene based copolymers are characterized by a higher degree of primary crystallinity, whereas the 1-butene copolymers exhibit more prominent secondary crystallization. The I-butene based copolymers thus have a less heterogeneous chemical composition distribution. At high comonomer contents, the highly heterogeneous nature of the 1-heptene copolymers is emphasized by a more pronounced presence of low crystalline spherulite inclusions accomplished by the liquid-liquid phase separation of dissimilar polymeric chains before crystallization. (c) 2005 Wiley Periodicals, Inc.