Computer simulations of entropic cohesion in reversibly crosslinked polymers†

Reversibly crosslinked polymer networks – polymer networks that can undergo bond association and dissociation reactions – rearrange their structures while maintaining their overall integrity, thus resulting in unique properties such as self-healing, reprocessability, shape memory and adaptability. Here, we show that the introduction of crosslinks, whether reversible or permanent, directly impacts the equilibrium polymer density and hence the material's surface tension. For a limiting case where the bonds are the same size as the polymer chain bonds, simulations, Flory hypotheses and thermodynamic calculations show that the crosslinks induce an increased entropic cohesion in the liquid. These findings implicate density as a key variable in polymers with (dynamic) crosslinkers, one that can be used to facilely tune their properties.