CRYSTALLIZATION OF VERY-LOW-DENSITY COPOLYMERS OF ETHYLENE WITH ALPHA-OLEFINS

Differential scanning calorimetry (DSC) was used to analyze the crystal distribution in homogeneous ethylene-octene copolymers polymerized by the constrained geometry catalyst technology (CGCT). To minimize ambiguities from thermal history effects, copolymers were isothermally annealed at temperatures within the melting range. The cumulative crystallinity was related to the crystal distribution by the Gibbs-Thomson equation. The results provided a clear distinction between Type I copolymers (density less than 0.89 g/cc) and Type II copolymers (densities between 0.89 and 0.91 g/cc). The former had a single-crystal population that was identified with the bundled crystals seen in transmission electron micrographs. In comparison, the latter had two crystal populations that correlated with lamellar crystals and bundled crystals. (C) John Wiley & Sons, Inc.