Linear and Extensional Rheology of Model Branched Polystyrenes: From Loosely Grafted Combs to Bottlebrushes

Abstract

Monodisperse comb polystyrenes (comb-PS) with loosely to densely grafted architectures up to loosely grafted bottlebrush structures were synthesized via anionic polymerization. This comb-PS series, named PS290-Nbr-44, had the same entangled backbone, Mw,bb = 290 kg/mol, corresponding to a number of entanglements along the backbone Zbb ≅ 20, and similar branch length, Mw,br ≅ 44 kg/mol or Zbr ≅ 3, but varied in the number of branches per molecule, Nbr, from 3 to 190 branches. Consequently, the average number of entanglements between two consecutive branch points along the backbone (branch point spacing), Zs, ranged from well entangled, Zs ≅ 5, to values that were far less than one entanglement, Zs ≅ 0.1. Linear viscoelastic data including the zero-shear rate viscosity, η0, diluted modulus, GN,s0, and a new diluted modulus extracted from the van Gurp–Palmen plot, |G*| at δ = 60°, were analyzed as a function of the Mw of the combs. Scaling of η0 versus Mw revealed three different regions for increasing Nbr o...