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 un derstand the relationship between molecular structure and dynamic mechanica l properties. Different branch lengths, from methyl to longer, and their co ntents in these ethylene homopolymers, dramatically affects the crystallini ty of these poIyethylene samples, as shown by differential scanning calorim etry (DSC) and crystallization analysis fractionation (CRYSTAF). T-m and CR YSTAF profiles are related not only to the branch content but also to the d istribution on the chain. The dynamic mechanical thermal analysis showed th ree different groups of materials, where the stiffness Varies according to the short-chain branching (SCB) content. Polyethylenes with high SCB showed a strong p-transition (tan delta > 1) despite the lack of any detectable c rystallinity. (C) 2001 EIsevier Science Ltd. All rights reserved.