Preparation and characterization of thermal- and light-triggered self-healing azobenzene polymer

Both temperature- and light-triggered self-healing azobenzene polymer was successfully synthesized via radical copolymerization of 4-(furan-maleimide ethyl) methyl methacrylate (MMA-FMI), 4′-(oxyhexyl methacrylate)-4-(oxyfuran-2-carbomethoxy) azobenzene (MMA-FAzo) and 6-(4′-methoxy-4-oxyazobenzene)-hexyl methacrylate at 50°C. The structure of the polymer was characterized by proton nuclear magnetic resonance (¹H-NMR) spectroscopy, Fourier transform infrared spectroscopy, and gel permeation chromatography. Interestingly, furan and maleimide thermally reversible groups were introduced into the polymer. After the furan rings on the MMA-FMI were removed at high temperatures, the exposed maleimide groups were further added with the furan rings on the MMA-FAzo to form a crosslinked network. The crosslinked polymer film was still soluble in the anisole after heating, which could further illustrate the thermal reversibility of the polymer film and realized the recyclability and reworkability of the side-chain azobenzene polymer. ¹H-NMR could prove that the crosslinked polymer was completely decrosslinked and the polymer was thermoreversible. Ultraviolet–visible (UV–Vis) absorption spectra showed rapid photoisomerization of the polymer, and surface-relief grating formed on the crosslinked PAzo film was also investigated using illumination from a linearly polarized Kr⁺ laser beam. The surface modulation depth and grating spacing were about 149 nm, and 1.7 μm, respectively. What is more, the polarized light microscopy showed that the crosslinked polymer film could be self-repaired under the combined action of UV light and heating.