The Effect of Intrachain Cross-Linking on the Thermomechanical Behavior of Bulk Polymers Assembled Solely from Single Chain Polymer Nanoparticles

Chemical cross-linking of polymer chains is a powerful means for tailoring the thermomechanical properties of bulk plastics. Nonetheless, upon cross-linking, processability is reduced as the plastic becomes thermoset. Here, molecular dynamics simulations are used to study the effects of intramolecular chemical cross-linking on chain topology and thermomechanical properties of a bulk, thermoplastic polymer. Polyethylene (PE)-like plastics are assembled purely from chains which have undergone a set level of intrachain cross-linking (to form single chain polymer nanoparticles, SCPNs). We have analyzed the chain topology at an equilibrated state in terms of chain unfolding and entanglement by radius of gyration and primitive path, respectively. The extents of both chain unfolding and chain entanglement were found to decrease with increasing intrachain cross-linking ratio. By applying simulated cooling, uniaxial tension, and uniaxial compression, we characterized the thermomechanical properties at the glassy state. The simulated mechanical testing shows that the bulk polymer becomes stiffer, stronger, and more brittle as the intrachain cross-linking ratio is increased. We observe that the failure of the SCPN-based bulk polymers is a consequence of separation between SCPNs. This study successfully elucidates the effect of intramolecular cross-linking on the thermomechanical properties at bulk, as a clear correlation is shown between the amount of covalent intrachain collapse and interchain interactions.