| Abstract: | 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 1‐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 1‐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. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3000–3018, 2005 |
