Molecular Mechanisms of Polymer Crosslinking via Thermal Activation

Abstract: Developing efficient and universal polymer crosslinking strategies is pivotal for advanced material design, especially for challenging matrixes like polyethylene, polypropylene, and polystyrene. Traditional crosslinkers such as divinylbenzene (DVB) often requires high-temperature radical initiators and are limited by poor compatibility with saturated hydrocarbon matrices. In contrast, bis-diazirine (BD) crosslinkers offer a promising alternative by harnessing thermally or photochemically generated carbene intermediates for highly selective C-H bond insertions. Here, we employ density functional theory (DFT)-based electronic structure calculations to elucidate the molecular mechanisms and energetics of BD-mediated crosslinking across PE, PP, and PS. We demonstrate that BD enables efficient covalent linkage through low free energy barriers , facilitating crosslinking at moderate temperatures without catalysts and with minimal sensitivity to polymer chain length. Moreover, BD exhibits selective reactivity towards the tertiary and secondary C-H bonds in PP and PS, respectively. Comparative analysis shows that BD dramatically outperforms DVB, especially in saturated polymers, enabling reaction times that are orders of magnitude faster. Our findings provide atomistic insights into BD crosslinker reactivity and establish a mechanistic foundation for next-generation, universal C-H activation-based crosslinking technologies.