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 X105 to 1.9 X104. 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.

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SYNOPSISAn ethylene/ 1-octene linear low-density polyethylene (LLDPE B ) has been fractionated with respect to the short-chain branching content of the molecules, using the preparative temperature-rising elution fractionation ( PTREF) technique. The LLDPE B studied, which is characterized by a high degree of heterogeneity on the level of the molecular weight and the comonomer content, was fractionated into six fractions having a more homogeneous intermolecular comonomer distribution. As a result of the differences in the chain microstructure of the fractions, a strong change in the thermal characteristics such as onset temperature of crystallization from the melt and melting temperature has been found. The morphology of the fractions, i.e., spherulitic texture and semicrystalline lamellar ordering, also strongly depends on the chain microstructure. In an attempt to elucidate the mutual influence of molecules having a different chain microstructure, as occurring within the unfractionated copolymer, blends of preparative TREF fractions were prepared and investigated with respect to their thermal behavior and morphology. 0 1993 John Wiley & Sons, Inc.