Elongational Flow Response of Linear Associative Polymer Melts: Interplay of Entanglements and Associative Groups

The flow response of entangled associative polymers, such as ionomers whose inherent structure and dynamics are governed by the clustering of multiple groups, remains a multifaceted fundamental challenge with immense technological impact. Using molecular dynamics simulations, we probe the effects of elongational flow on compressible, entangled, linear associative polymer melts. A bead-spring chain, randomly decorated with associating beads, was used, enabling the assembly of multiple groups into distinct clusters while tuning their interaction strengths. Under flow, the macroscopic properties, including extensional viscosity and density, increase with a distinct transition to a higher-density state, except at low interaction and low flow rates. At the molecular level, the chains extend under flow as expected and are highly oriented; however, the extent of stretching is a complex function of the strength of associative interactions and strain. The effects of entanglements dissipate at relatively low strain, as the chains stretch and the associative assemblies are largely fragmented. At high interaction strengths, new flow-induced conformations emerge in which the chains fold on themselves, forming kinks stabilized by the associating groups, yet the clusters remain fragmented, affecting the properties of the melts.