Molecular Mechanisms of Dynamic Crosslinks in Polymers

Permanently crosslinked polymers are traditionally utilized in various commodity products due to their superior mechanical properties. However, the traditional vulcanization process used to form these permanent crosslinks is energy intensive and leads to materials that cannot be easily reprocessed. In contrast, our recent work reports a promising class of crosslinkers based on bis-diazirine molecules that crosslink a wide range of polymers efficiently and enable bond exchange in their networks. In this study, we employed atomistic simulations using Density Functional Theory (DFT) to investigate the energy profiles of traditional disulfide crosslinkers and bis-diazirine based crosslinkers within polyethylene (PE) and poly(L-lactic acid) (PLLA) systems. Our DFT calculations shows that the bis-diazirine based universal crosslinkers exhibit negative formation energies (ΔE) for both PE and PLLA systems, indicating highly favorable crosslink formation. We further perform reactive molecular dynamics (MD) simulations to estimate the timescale of bond exchange in a bis-diazirine crosslinked polymer network and its dependency on the thermodynamics of the system. Our work provides fundamental insights into the dynamic crosslink formations and their correlations with crosslinker chemistry.