Branch-point motion in architecturally complex polymers: estimation of hopping parameters from computer simulations and experiments

Relaxation of branched polymers under tube-based models involves a parameter p² characterizing the hop size of relaxed side arms. Depending on assumptions made in rheological models (e.g., about the relevant tube diameter for branchpoint hops), p² had been set to values varying from 1 to 1/60 in the literature. From large-scale molecular dynamics simulations of melts of entangled branched polymers of different architectures, and from experimental rheological data on a set of well characterized comb polymers with many (~30) side arms, we estimate the values of p2 under different assumptions in the hierarchical relaxation scheme. Both the simulations and the experiments show that including the backbone friction and considering hopping in the dilated tube provides the most consistent set of hopping parameters in different architectures.