Molecular design and synthesis of crosslinked polyimides using radical isomerization of vinylcyclopropane with thiols

Reactive polyimides bearing a vinylcyclopropane (VCP) moiety in the main chain were successfully synthesized from the corresponding diamine with the VCP moiety. Their radical crosslinking using a dithiol proceeded with the radical ring-opening reaction (RROR) of the VCP moiety to afford the corresponding crosslinked polyimides with the CC bonds in crosslinking moieties. Thermal properties of those crosslinked polyimides were evaluated by thermal gravimetry and differential scanning calorimetry. As a result, the increase of the crosslinking degree in the crosslinked polymer exhibited great residual weight at 600°C. In contrast, the tendency of the glass transition temperature was inverse because the increase in the amount of dithiol unit as a crosslinker would enhance the mitigation of the polymer packing structure and activates the mobility of polymer chains.