Effect of Side Chain Length in Polystyrene POM-POMs on Melt Rheology and Solid Mechanical Fatigue

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 M-w,M-b congruent to 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 (W-w,W-a = 9-300 kg mol(-1), 0.5-18 entanglements). The POM-POMs having M-w,M-a approximate to 3M(e) approximate to M-c have a maximum decrease in zero-shear viscosity eta(0) 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 M-w,M-a > 5M(e) displayed enhanced mechanical fatigue resistance beyond those of linear, ultrahigh-molecular-weight PS, by up to a factor of 10.

Automated summary

This study investigates the rheological and mechanical properties of POM-POM-shaped polystyrenes (PS) with different side chain lengths. It shows that POM-POMs with specific side chain lengths exhibit a significant decrease in viscosity and strain hardening, along with enhanced mechanical fatigue resistance.