Differential scanning calorimetry, small-angle X-ray scattering, and wide-angle X-ray scattering on homogeneous and heterogeneous ethylene-alpha-copolymers

The objective of this work was to use both X-ray and differential scanning calorimetry techniques in a comparative study of the lamellar and crystalli ne structures of heterogeneous and homogeneous ethylene-a-copolymers. The s amples differed in the comonomer type (1-butene, 1-hexene, 1-octene, and he xadecene), comonomer content, and catalyst used in the polymerizations. Ste p crystallizations were performed with differential scanning calorimetry, a nd the crystallinity and lamellar thicknesses of the different crystal popu lations were determined. Wide-angle X-ray scattering was used to determine crystallinities, average sizes of the crystallites, and dimensions of the o rthorhombic unit cell. The average thickness, separation of the lamellae, a nd volume fractions of the crystalline phase were determined by small-angle X-ray scattering (SAXS). The results revealed that at densities below 900 kg/m(3), polymers were organized as poorly organized crystal bundles. The l amellar distances were smaller and the lamellar thickness distributions wer e narrower for the homogeneous ethylene copolymers than for the heterogeneo us ones. Step-crystallization experiments by SAXS demonstrated that the lon g period increased after annealing. (C) 2001 John Wiley & Sons, Inc. J Poly m Sci Part B: Polym Phys 39: 1860-1875, 2001.