Ultimate Molecular Mechanical Properties of Polyolefin Chains

There has been a growing interest in the ultimate mechanical properties of single polymer chains, as they are related to the fracture toughness of solid polymers, networks, and gels, and to the processability of their melts and solutions. The breakup of a polymer chain under tension is also a quintessential, albeit rather crude, example of a mechanochemical reaction. We simulate this phenomenon in polyethylene, polypropylene, and polystyrene single chains by Langevin dynamics with a reactive force field capable of describing bond dissociation in a chemically realistic way. The force–elongation curves show a clear transition between entropic and enthalpic elasticity, followed by chain scission at elongations that generally exceed the nominal contour length of the chains. We highlight an intriguing dependence of the chains’ mechanical properties on the chain tacticity. Somewhat unexpectedly, chain scission may often lead to the formation of three or more fragments depending also on the chains’ stereochemistry and the relaxation time of the Langevin thermostat employed in the simulations.