Microscopic Relaxations of Polystyrene Solutions Cross-Linked by Dynamic Imine Bonds

Vitrimers are polymer networks cross-linked by dynamic covalent bonds that undergo associative exchange, where new linkages form before existing ones break. This exchange mechanism enables the network to rearrange its topology but still maintain overall connectivity. In this presentation, we investigate the impact of associative cross-link exchange on the microscopic relaxations of semi-dilute polystyrene (PS) solutions. PS with pendant aldehyde groups was synthesized using a combination of controlled radical polymerization and photochemistry. Semi-dilute PS solutions were cross-linked by reacting the pendant aldehydes with hexane-1,6-diamine to form imine bonds, which exchange via transimination. Using ¹H nuclear magnetic resonance spectroscopy, the cross-linking kinetics were tracked as a function of solvent dielectric constant (ε) and amine-to-aldehyde ratio (r). Decreasing ε led to an increase in aldehyde conversion, while increasing r increased the aldehyde conversion and accelerated the reaction kinetics. Dynamic light scattering was used to evaluate how the formation of imine cross-links altered the diffusion and microscopic relaxations of the PS chains.