Study of the compositional heterogeneity of ethylene-1-hexene copolymers via thermal fractionation with the use of differential scanning calorimetry

The compositional heterogeneity of ethylene-1-hexene copolymers synthesized with various types of supported catalysts, namely, the titanium-magnesium catalyst TiCl4/MgCl2 and the zirconocene catalyst SiO2(MAO)/Me2Si(Ind)2ZrCl2, is studied via the method of successive self-nucleation-annealing (SSA) with the use of differential scanning calorimetry. On the basis of the data on the temperatures of individual peaks on SSA curves, the thickness of lamellas composed of macromolecules with a certain degree of short-chain branching is estimated. The copolymer synthesized with the zirconocene catalyst has a narrower range of fusion and does not contain large lamellas composed of molecules with a low degree of short-chain branching. With the use of the broadness index, it is shown that the copolymer synthesized with the zirconocene catalyst has a more uniform distribution of the comonomer than does the copolymer synthesized with the titanium-magnesium catalyst. For the copolymers synthesized with the titanium-magnesium catalyst, the compositional heterogeneity increases with an increase in the content of 1-hexene.