Photoreversible Smart Polymers Based on 2π + 2π Cycloaddition Reactions: Nanofilms to Self-Healing Films

A simple nanostructured, photoresponsive film made from a coumarin-modified tetrafunctional monomer, which is both photodegradable and photoreproducible, was prepared using a simple spin-coating process and UV irradiation. The film produced from this system self-healed scratches using only UV light, with no need for catalyst, heat, or other stimuli. The photoreversible mechanism was investigated, and a range of techniques were used to characterize the resultant photoproducts after the polymerization and depolymerization processes. Infrared spectroscopy was used to determine the optimal energy for a complete reversible polymerization reaction, and the mechanism was further confirmed by UV-vis spectroscopy which was able to monitor key structural changes. GPC analysis was used to track the molecular weight changes after the depolymerization reaction, which showed that the polymer was able to be converted back to monomers and oligomers, demonstrating the highly reversible polymerization and suggesting a potential for recyclability. Microhardness measurements of neat and irradiated samples were also used to determine the changes in mechanical properties before and after cleavage of the polymer network, and following the recovery of its structure, the latter showed a recovery of up to 91% of its mechanical properties.