Effect of molecular structure on dynamic mechanical properties of polyethylene obtained with nickel–diimine catalysts

Polyethylene made with a nickel–diimine catalyst was studied in order to understand the relationship between molecular structure and dynamic mechanical properties. Different branch lengths, from methyl to longer, and their contents in these ethylene homopolymers, dramatically affects the crystallinity of these polyethylene samples, as shown by differential scanning calorimetry (DSC) and crystallization analysis fractionation (CRYSTAF). Tm and CRYSTAF profiles are related not only to the branch content but also to the distribution on the chain. The dynamic mechanical thermal analysis showed three different groups of materials, where the stiffness varies according to the short-chain branching (SCB) content. Polyethylenes with high SCB showed a strong β-transition (tan δ>1) despite the lack of any detectable crystallinity.