Effect of Side Chain Length in Polystyrene POM–POMs on Melt Rheology and Solid Mechanical Fatigue
Marie‐Christin Röpert, Max G. Schußmann, Masood K. Esfahani, Manfred Wilhelm, Valerian Hirschberg
Abstract
The POM–POM architecture is the simplest yet defined branched architecture, showing both strain hardening in elongation and strain softening in shear. The molecular structure consists of q side chains at each end of a backbone segment. To study the rheological and mechanical properties, we synthesized low-disperse POM–POM-shaped polystyrenes (PS) with well-defined molecular properties via anionic polymerization and grafting-onto method. All samples had a backbone with a weight-average molecular weight of Mw,b ≅ 100 kg mol–1 and approximately similar numbers of side chains per star q = 11–14. We varied the side chain length systematically from unentangled up to highly entangled side chains (Mw,a = 9–300 kg mol–1, 0.5–18 entanglements). The POM–POMs having Mw,a ≈ 3Me ≈ Mc have a maximum decrease in zero-shear viscosity η0 of over 3 decades compared to linear PS with the same molecular weight, together with the highest strain hardening factor of SHF = 43. Moreover, POM–POMs having Mw,a > 5Me displayed enhanced mechanical fatigue resistance beyond those of linear, ultrahigh-molecular-weight PS, by up to a factor of 10.