MOLECULAR, THERMAL, AND MORPHOLOGICAL CHARACTERIZATION OF NARROWLY BRANCHED FRACTIONS OF 1-OCTENE LINEAR LOW-DENSITY POLYETHYLENE .3. LAMELLAR AND SPHERULITIC MORPHOLOGY

The semicrystalline lamellar morphology, the crystalline phase, and the spherulitic structure of 1-octene linear low-density polyethylene (LLDPE) fractions with a narrow short chain branching distribution were studied. The average short chain branching content of the fractions studied increases from 2.9 to 28.2 branches per 1000 carbon atoms while the weight-average molecular weight concomitantly decreases from 2.7 X 10(5) to 1.9 X 10(4). Characteristic morphological parameters include the number-average lamellar thickness, the thickness of the crystalline core and of the transition layers, the periodicity of the lamellar stacks, the unit cell dimensions of the crystalline phase, and the average radius of the spherulites. The core thickness of the crystalline lamellae decreases and the transition layer thickness increases with increasing branching content. Fair agreement was found between the values of the lamellar thickness obtained in this study and those obtained in a previous TEM study. The expansion of the unit cell of the crystals with increasing branching content is related to a decrease of the thickness of the lamellae. The average spherulitic radius of the fractions decreases with increasing short chain branching content. The spherulitic morphology is deteriorated at high values of either the branching content or the molecular weight.