Topological control of mechanical response in polymer networks

The mechanical properties of polymer networks are governed by their polymer chemistry and network topology. A fundamental challenge, however, is to decouple the influence of topology from specific chemical interactions. To isolate the effect of topology, we employ a generalized bead-spring model with a graph-based approach to generate unentangled networks, by systematically varying crosslink functionality (degree) distributions from regular networks, with a high mean degree and low variance, to heterogeneous ones with a broad distribution of functionalities and defects. Our molecular dynamics (MD) simulations reveal that while local segmental diffusion is independent of topology, the macroscopic mechanical response is highly sensitive to these topological features. We show that the regular networks are stiff and brittle, while networks with heterogeneous degree distributions, such as those formed during the earlier stages of curing, are significantly more ductile. Our results demonstrate that mechanical behavior can be tuned independently of local dynamics through topological design. This work establishes network topology as a distinct design axis, potentially orthogonal to traditional chemical modifications, for creating functional materials with targeted mechanical responses.