Ethylene/1-Heptene Copolymers as Interesting Alternatives to 1-Octene-Based LLDPE: Molecular Structure and Physical Properties

Classical linear low density polyethylenes (LLDPEs) are copolymers of ethylene and 1-octene or 1-hexene, respectively. In the past, other 1-olefins have been tested as comonomers but the resulting LLDPEs were never commercialized as large scale products. The present study focuses on the use of 1-heptene as an interesting comonomer for the synthesis of LLDPE. For a comparison of the molecular structure and the physical properties of 1-heptene- and 1-octene-based LLDPEs, five Ziegler-Natta LLDPEs of varying comonomer contents based on 1-heptene and 1-octene, respectively, were acquired and analysed using advanced methods. The comonomer contents of the resins were between 0.35 and 6.4 mol %. Crystallization-based techniques revealed similar bimodal distributions that are due to the formation of copolymer and polyethylene homopolymer fractions. The compositional distribution of the copolymers was studied by high-temperature (HT) HPLC and HT-2D-LC. The analytical results indicate similar chemical heterogeneities and molar mass distributions of the two sets of LLDPE up to a comonomer content of 3 mol %. Similar to the molecular structure, the physical properties of the materials are quite similar. At comonomer contents of >= 3 mol % differences between the two sets of samples are seen that are attributed to differences in the abilities of 1-heptene and 1-octene in disrupting the crystal arrangements of the polymer chains in solid state. (C) 2015 Wiley Periodicals, Inc.