Star polymer diffusion in concentrated solutions: Dependence on functionality via the coupling model

The coupling model is formulated in terms of the dynamic constraint entropy, S_c(t), and subsequently compared with measured tracer diffusion coefficients D for linear, 3‐arm star, and 12arm star polystyrenes in solutions of poly (vinyl methyl ether) (PVME) /o‐fluorotoluene. Inequalities between the dynamic constraint entropies, S_cf and S_cf′(t), respectively, for f‐arm and f′‐arm stars, enable us to explain the experimental observation that at constant arm molecular weight, the ratio D_star/D_linear decreases substantially with increasing concentration above the entanglement concentration for the PVME. This work indicates that not only the reptation model, but also the coupling model, can account for the experimental observation that in entangled solutions the mechanism for diffusion depends on diffusant architecture.