CONCENTRATION-DEPENDENCE OF STATIC AND DYNAMIC PROPERTIES FOR POLYMERIC STARS IN A GOOD SOLVENT

Equilibrium and dynamical properties were obtained by light scattering methods for solutions of multiarm polyisoprene star polymers in a good solvent, cyclohexane, over a wide concentration range. Results for 8-arm and 18-arm stars were compared with the behavior of linear polymers in the dilute and semidilute regimes and were analyzed in terms of recent theories based on the Daoud-Cotton model. In dilute solutions the temporal fluctuations on distance scales smaller than the overall dimensions were found to be markedly slower for stars than for linear chains of the same size. Evidence for star-star repulsion and liquidlike ordering near the overlap concentration was also obtained. Such differences between linear polymers and stars vanish in the semidilute region, however, with the osmotic pressure derivative and mutual diffusion coefficient becoming power law functions of the polymer concentration alone. The scaling law prefactors depend on the arm number but less strongly than predicted by theory.