Self Dilution of Model Polystyrene Pom-Poms and Combs by Unentangled Side Arms

We present linear-viscoelastic characterization and elongational viscosity start-up data of 4 model polystyrene pom-poms and 2 model polystyrene combs. All 6 model systems have a self-entangled backbone, but unentangled side arms. Pom-poms consist of a linear backbone with one branching point with q arms at each end of the backbone. Analysis by the Enhanced Relaxation of Stretch (ERS) model shows that the elongational rheology of all model polymers is equivalent to that of polymer melts consisting of long linear chains diluted by short, unentangled linear polymer chains of the same chemistry. Strain hardening increases with increasing intrinsic dilution of the backbone by the arms. The comparison of the elongational viscosity data of pom-poms versus that of the combs with several branching points along the backbone chain suggests that the location of the unentangled side arms does not result in significant differences. At higher elongation rates, brittle filament fracture is observed, which is well described by the fracture criterion for linear melts and polymer solutions, thus confirming the self-dilution of the backbone chains of pom-poms and combs by unentangled side arms.