(411d) Mechanical Properties of Highly Cross-Linked Network Polymers

Realistic Cross-linked networks are generated using a novel reactive molecular dynamics (RMD) technique. This methodology was developed as the coarse-grained representation of explicit-atom simulations of the reaction pathways in dicyclopentadiene (DCPD), which polymerizes according to a ring opening metathesis mechanism facilitated by Grubbs catalyst. Each DCPD monomer possesses two distinct reactive sites, which is responsible for the different reaction rates for linear polymerization and cross-linking. In the coarse-grained scheme each monomer/repeat unit is represented as weakly interacting near-spherical entities. Covalent bonds between such units form depending on steric criteria and in the presence of catalyst molecules, so that the location of all network bonds delineates the propagation path of the catalysts. We evaluated the mechanical properties of the polymer structures so generated as a function of the degree of reaction. For comparison sake we created other cross-linked networks in more artificial ways, such as random and regular bond insertions. We compare the thermo-mechanical properties such as bulk modulus, Young's modulus, the ultimate tensile strength and the glass transition temperature of these systems. In general, the elastic properties of these systems depend to a lesser extent on network generation algorithm than the tensile strength and glass transition temperature.