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

Polymer topology highly impacts rheological melt and foaming properties. Grafting sidechains onto a linear polymer typically results in shear thinning and strain hardening in elongation flow. To study the influence of an increasing number of covalently connected polystyrene (PS) stars s with a linear PS chain (M$_{w,PS}$ = 90 kg mol$^{−1}$), low-disperse branched polymers with s ranging from one to four are synthesized. Each star contains approximately 12 sidechains with a length of M$_{w,a}$≈ 25 kg mol$^{−1}$. Oscillatory shear measurements indicated that the zero-shear viscosity η$_0$ scales with η$_0$ ≈ $M$$_{w,}^3$$_t^9$ at T$_{ref}$ = 180 °C. Moreover, uniaxial elongation rheology allows determining the strain hardening factor SHF, which varies between SHF = 2–135, with increasing s. Foaming experiments revealed that combining viscosity reduction with the improvement of stretchability promotes higher volume expansion ratios (VER = 3.21–10.41) and the formation of larger cells (D = 4.8–14.8 µm).