Molecular structure, melting behavior, and crystallinity of 1‐octene‐based very low density polyethylenes (VLDPEs) as studied by fractionation and heat capacity measurements with DSC

Heat capacity measurements with DSC on 1‐octene‐based very low density polyethylenes (VLDPEs), with densities from 888 to 907 kg/m3, show crystallization between 120 and −60°C and melting between −60 and 130°C. Under the assumption that hardly any octene groups are present in the crystal lattice, the experimental heat capacity values were compared with reference values for purely amorphous and purely crystalline linear polyethylene on the basis of a two‐phase model. The enthalpy‐based weight crystallinity data as a function of temperature show that the crystallinities at −60°C are about 40% higher than those at room temperature, which vary from 25 to 40% and are in good agreement with volume‐based weight crystallinities. The crystallization and melting curves show several peaks. Fractionations by the crystallization/dissolution method and the direct extraction method show that this is due to intermolecular heterogeneity of comonomer incorporation and that VLDPE is a reactor blend of molecules ranging from the uncrystallizable and poorly crystallizable type to the HDPE type.