Studies of intermolecular heterogeneity distribution in ethylene/1-hexene copolymers using DSC method

The investigation of the intermolecular composition distribution of an ethylene/1-hexene copolymers using DSC method has been carried out. The known methods: step crystallization (SC) and successive self-nucleation/annealing (SSA) have been adapted for this purpose, and particularly, the optimal condition of the process have been chosen to enable the best fractional crystallization of the copolymer. The method has been applied for fractionation of two ethylene/1-hexene copolymers synthesized with supported vanadium and zirconocene catalysts and having similar concentrations of 1hexene. Although metallocene catalysts are known from their more homogeneous structure of active sites in comparison to multi-site Ziegler-Natta catalysts, the copolymers obtained over both catalytic systems gave DSC curves resolved into several peaks but with different melting points. Using the Thomson-Gibbs equation, comparable average lamellar thickness of the separated peaks has been calculated. The amounts of copolymer fraction with defined lamellar thickness have been determined. It was obtained that the copolymer produced from the metallocene system contains a thinner and more homogeneous lamella thickness than that obtained with Ziegler-Natta vanadium catalyst supported on the same carrier.