Abstract
We have measured polymer and solvent self-diffusion at 50°C in equiarmed star-branched polyisoprenes of low molecular weights in solution with C6F5Cl and CCl4, using pulsed-gradient spin-echo methods supplemented by NMR T2 relaxation. In solutions and melts of stars with M(arm) ≃ 104 and f ≤ 18, entanglements are less pronounced than in linear polymers of equal molecular weight. Polymer diffusion depends differently on M(arm) and f, the f dependence becoming weak at high f at all solvent concentrations. In dilute solution, diffusion behavior shows that these stars are relatively highly expanded; at high polymer concentrations, segmental diffusion mechanisms begin to contribute. Free volume theories explain solvent but not polymer diffusion. © 1982, American Chemical Society. All rights reserved.