Analysis of elongational flow of star polymers

Abstract

Star polymers with three arms are the simplest example of branched polymers. Elongational rheology data of three well-characterized monodisperse polystyrene melts, a symmetric star, an asymmetric star, and a linear polymer with the same span molecular weight of 180 kg/mol reported by Huang et al. (Macromolecules 49:6694−6699, 2016) are analyzed by the enhanced relaxation of stretch (ERS) model (Wagner and Narimissa, J Rheol 65:1413–1421, 2021). All three melts show the same elongational stress growth coefficient and the same steady-state elongational viscosity in fast extensional flows when the stretch-related Weissenberg number $${Wi}_R=\dot{\varepsilon}{\tau}_R>1$$ Wi R = ε ˙ τ R > 1 . Excellent agreement between experimental data of elongational stress growth coefficient and model predictions is obtained, based exclusively on the linear-viscoelastic characterization of the polymer systems. Stress relaxation following steady elongational flow depends on the presence of the branch point and the length of the arm, and a new process regarding relaxation of the orientation of the stars is identified.

Threading Polystyrene Stars: Impact of Star to POM‐POM and Barbwire Topology on Melt Rheological and Foaming Properties

“…Researchers have investigated their rheological behavior in the melt, as dilute solutions or as blends with linear polymer chains. [1][2][3][4][5][6][7][8][9][10][11][12] In the so-called POM-POM topology, two similar stars are covalently connected with a linear polymer chain, representing the simplest topology with exactly two branching points. The POM-POM topology gained a lot of interest, as it represents the most straightforward topology, which combines shear thinning and strain hardening in DOI: 10.1002/macp.202200288 elongational flow.…”

Molecular Dynamics Simulation of Entangled Melts at High Rates: Identifying Entanglement Lockup Mechanism Leading to True Strain Hardening

“…These regimes II–IV have been studied in some detail [ 26,27 ] and termed [ 24 ] decohesion, necking and melt rupture respectively to indicate the corresponding physics. It is particularly obvious that an entangled melt acts like a vulcanized (crosslinked) rubber in regime IV during startup uniaxial melt stretching at a sufficiently high Hencky rate $$\dot \varepsilon $$, [ 26–32 ] typically ten times the reciprocal Rouse relaxation time τ R , i.e., for Wi R = $$\dot \varepsilon $$ τ R > 10. In regime IV, true strain hardening, i.e., stronger than neo‐Hookean response is observed, characterized by a monotonic increase of the engineering stress with the Hencky strain.…”

Preparation and Characterization of H-Shaped Polylactide

“…For each H-polymer melt, a “kink” in the data is observed at low values of | G *|, which is not found for the linear melt. Note, this feature is also absent in star polymer melts. , Each of the unique phenomena in Figure A–C is due to the hierarchical relaxation mechanism that occurs in architectures with more than one branch point. This results in a backbone that is “pinned” between branches that cannot diffuse until the multiple constraints created by the arms have been lifted (i.e., the arms have fully relaxed).…”