Time Marching Algorithm for Predicting the Linear Rheology of Monodisperse Comb Polymer Melts

We extend van Ruymbeke et al.'s time marching algorithm (TMA) ( Macromolecules 2006, 39, 6248) in order to predict the linear viscoelastic properties of comb polymer melts. While former tube models have shown limitations for predicting the relaxation of comb polymer with short side branches, we observe here a good agreement between predictions and the experimental data for both combs with long and short side branches. In order to determine the origin of this improvement, we study the influence of the different elements present in the TMA model. In particular, we show the importance of taking into account the monomeric friction coming from the backbone itself in the total drag of the molecule, considering the modification of early time fluctuations and introducing the tube dilation process as a continuous function evolving through time. Then, based on a wide range of experimental data on different comb structures, we explore the limits of the relaxation behavior that comb polymers can show. If the friction from the relaxed side branches is significant, the backbone segments seem to fluctuate with respect to the closest branching point, just like a Cayley-tree molecule. On the other hand if the extra friction is negligible in comparison to the potential barrier of retraction along the backbone, the segments fluctuate with respect to the middle of the molecule, just like a linear chain.