Exploring Rheological and Dynamic Characteristics of Polymers with Complex Topological Features through Coarse-grained Molecular Dynamics

The synthesis of branched architectures with specific topologies has proven to be an effective approach for enhancing processability and mechanical properties compared to traditional linear polymers. Although topological variations are known to significantly influence the dynamics and flow behavior of polymers across many applications, a comprehensive understanding of how local variations in branch composition and spatial arrangement affect these properties at multiple scales is still lacking. This study investigates the rheological and dynamic behaviors of polymers with complex topological features that periodically combine densely grafted blocks with non-grafted blocks. We first developed a Taguchi-based surrogate model combined with coarse-grained molecular dynamics (CGMD) simulations to study various topological attributes, such as graft density, sidechain length, graft heterogeneity, and backbone length. Our statistical analysis of the surrogate model shows that the zero-shear viscosity of the polymer melts can be increased by increasing the graft density and backbone length, or by reducing the length of the grafted blocks. Additionally, we conducted a Rouse mode analysis to examine the impact of branch architectures on backbone relaxation. The results reveal a complex interplay of sidechains: they reduce the topological constraints on the backbone due to their excluded volume but also retard the backbone motion. Consequently, the backbone displays two contrasting relaxation modes, especially when the lengths of the grafted and non-grafted blocks are similar. The findings from our CGMD simulations provide valuable insights for polymer topology optimization toward improved processability.