Figure 1: Switching the thermal healability of dynamic polymer networks by light.
(a) Schematic representation of a photoswitchable crosslinker XON in its reactive state and polymer P carrying complementary reactive groups forming the dynamic covalent polymer network X@PON, which can be de-crosslinked on heating. On illumination with ultraviolet-light the crosslinker X as well as the polymer network X@P are reversibly transformed into their inactive state (XOFF and X@POFF, respectively), where both crosslinking as well as de-crosslinking are inhibited. (b) Chemical structures of the tetrafuryl-substituted diarylethene crosslinker, which in its activated form XON reacts with maleimide-functionalized poly(lauryl methacrylates) via the Diels–Alder reaction (for simplicity only two of four crosslinking units are shown). On heating the network is de-crosslinked due to the retro Diels–Alder reaction. Illumination with ultraviolet-light induces 6π-electrocyclization to the ring-closed isomers of the deactivated crosslinker XOFF and the polymer X@POFF, respectively. This process can be reversed and the crosslinker as well as the network can be activated by illumination with visible light.
