Influence of molar mass distribution and long-chain branching on strain hardening of low density polyethylene

Low-density polyethylenes (LDPE) were synthesized in a laboratory-scale autoclave under high pressure. These samples were found to possess a high molar mass tail, resulting in a distinctly bimodal molar mass distribution and a lower concentration of long-chain branching than typical of commercial LDPEs. Rheological experiments in elongation showed that these samples exhibit a very pronounced strain hardening, which could be favorable for distinct processing operations. Although the samples have a rather high molar mass (M_w = 2̇ × 10⁶ g/mol), their zero shear-rate viscosities η₀ and their shear thinning behavior are still in a range, where thermoplastic processing is possible. A qualitative understanding of the experimental results is tried by the model of the Cayley tree.