Effects of Connectivity Defects on the Structure and Dynamics of Star Polymer Networks

We use coarse-grained simulations to investigate how connectivity defects impact the structure and dynamics of reversible polymer networks, formed by four-armed star polymers, which can be considered as a model for tetra-PEG (tPEG) hydrogels. We consider both homoleptic and heteroleptic systems, with noncovalent bonds formed by monovalent functionalized end groups of the star polymers. The defect density is systematically altered by either incorporating stars with inert end groups in the homoleptic systems, or by deviating from the ideal 1:1 stoichiometry in the heteroleptic mixtures. Connectivity defects – quantified via the fraction of connected end groups, single links, and loops – and network dynamics are found to be strongly coupled: With increasing defect density, the long-time self-diffusion coefficient of individual stars increases substantially, while the network’s zero-shear viscosity systematically decreases, reflecting the reduced topological constraints in defective networks. These findings provide new insights into the origin and role of defects for the structure and dynamics of polymer networks.