Damping Behavior of Entangled Comb Polymers: Experiment

The stress relaxation dynamics of entangled polyisoprene comb polymers were investigated, specifically under nonlinear step deformations, in order to identify the damping mechanism characteristic of comb topology. The damping behavior of two different comb polymers with branches of two and four entanglement lengths clearly exhibited less strain softening (type B) above the universal Doi−Edwards damping function at all strains. However, the corresponding damping functions gradually approached the universal Doi−Edwards damping function with increasing observation time. The observed type B behavior was clearly different from that of H-shaped/multibranch and dendritic star polymers exhibiting a novel damping transition from type B toward the universal Doi−Edwards damping function (i.e., the branch-point withdrawal motion). These results support the proposal that the damping mechanism for combs is due to the gradual stretching and retracting motions caused by branches at the multiple branch points along the comb backbone.