Viscoelastic properties of comb-shaped ring polystyrenes

In this study, we examined the viscoelastic properties of a series of comb-shaped ring (RC) polystyrene samples with different branch chain lengths, i.e., the molecular weights of the ring backbone M bb (≃ 4 M e where M e is the entanglement molecular weight) and branch chains M br (≃ M e , 2 M e , and 4 M e ). Even for the RC sample with the shortest branch chains, a plateau region was observed for the dynamic modulus G * ( ω ) in the middle angular frequency ω region, suggesting that intermolecular branch chain entanglement occurred. In the ω region between the plateau and terminal regions, G * ( ω ) was observed with a weaker ω dependence than the terminal relaxation. This behavior was more pronounced for RC samples with shorter branch chains and for the corresponding linear comb (LC) samples than for the RC ones. The molecular weight dependence of the zero-shear viscosity η 0 and the steady-state recoverable compliance J e o of the RC and LC samples was evaluated, and the effects of different backbone molecular structures (i.e., ring or linear) on the terminal relaxation behavior was discussed. Moreover, the G * ( ω ) data were analyzed with two models: the comb-Rouse model, in which the structures of the RC/LC molecules are taken into account by graph theory, and the Milner-McLeish model for entangled star-shaped polymers. The former model qualitatively described the terminal relaxation behavior of G * ( ω ) at low ω but failed to reproduce the plateau in the middle ω range. Conversely, the latter model described the entanglement plateau in the middle ω range, but the difference in the terminal relaxation regime for the RC/LC samples seen in the data and the comb-Rouse model disappeared. Viscoelastic properties of comb-shaped ring (RC) polystyrenes with different branch chain lengths were investigated. Even for the RC sample with short branches, a plateau of the dynamic modulus G * ( ω ) was observed, suggesting the intermolecular branch chain entanglement occurred. In the region between the plateau and terminal regions, G * ( ω ) was observed with a weaker angular frequency dependence than the terminal relaxation. The G * ( ω ) data were analyzed with two models: the comb-Rouse model, in which the structures of RC molecules are taken into account by graph theory, and the Milner-McLeish model for entangled star-shaped polymers.