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

Differential scanning calorimetry (DSC) was used to analyze the crysta l distribution in homogeneous ethylene-octene copolymers polymerized b y the constrained geometry catalyst technology (CGCT). To minimize amb iguities from thermal history effects, copolymers were isothermally an nealed at temperatures within the melting range. The cumulative crysta llinity was related to the crystal distribution by the Gibbs-Thomson e quation. The results provided a clear distinction between Type I copol ymers (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 populatio n that was identified with the bundled crystals seen in transmission e lectron micrographs. In comparison, the latter had two crystal populat ions that correlated with lamellar crystals and bundled crystals. (C) John Wiley & Sons, Inc.