Influence of Chemical Side Groups on Extensional Rheology and Elastic Fracture of Polymer Melts

In the classic tube model, there are three independent parameters which describe the dynamics of entangled polymer liquids, i.e., the number of entanglements per chain (Z), the number of Kuhn segments per entangled strand (N_e), and the relaxation time of an entangled strand (τ_e). The effect of chemistry is on the value of N_e. A few experiments have already revealed that polymer melts with the same Z, N_e and τ_e but different chemistry show different rheological behavior in nonlinear extensional flow. However, the exact influence of chemistry on extensional rheology is still largely unexplored, and different even contrary explanations exist.



In this work, we systematically investigate the influence of chemical side groups on extensional rheology and elastic fracture (which terminates the extensional flow). The samples include amorphous polymers with both stiff and flexible side groups, e.g., polystyrene and poly(n-butyl acrylate), as well as their counterparts with an extra methyl group on the C-C backbone, e.g., Poly(α-methylstyrene) and poly(n-butyl methacrylate). We first study their linear viscoelasticity at high frequencies and their conformations at equilibrium using temperature-dependent wide-angle X-ray scattering (WAXS). Subsequently, extensional rheology and fracture measurements are carried out, and the data is analyzed together with WAXS to reveal the connection between chemical side groups and rheological properties.