(670i) Relating Mechanics to Chain-Level Architecture in Glassy Crosslinked Polymers

We explore the influence of chain-level network architecture (i.e., topology) on the mechanics of glassy polymer networks using a combination of coarse-grained molecular simulations and graph-theoretic concepts. The topological properties of networks are controlled using a modified version of the Watts-Strogatz graph-generation model, allowing the corresponding physical properties to be studied with simulations. First, polymer networks architectures assembled via a dynamic curing approach are compared to the modified Watts-Strogatz model, revealing surprisingly good agreement. The final cured structures of dynamically-assembled networks are nearly intermediate between lattice and random graphs, as a result of the restrictions imposed by finite contour length. Then, we systematically vary the degree of architectural disorder, and analyze the linear and nonlinear uniaxial stress response, nature of bond scission, and non-affine displacements of fully-cured glassy networks. We show that the architecture strongly affects the flow stress, onset of bond breaking, and ultimate stress, but leaves the modulus and yield point unchanged. Our results indicate that architectural disorder imposes internal restrictions that alter the chain-level response through changes to crosslink motions in the flow regime, and through the intensity of coordinated chain failure near the ultimate stress. The mechanical properties considered herein are sensitive to even incremental changes in topology. Thus, the overall network architecture – beyond simple point defects, like loops and dangling ends – is predicted to be a meaningful physical parameter affecting the mechanics of glassy polymer networks.