Controlled photoisomerization in acrylic copolymer nanoparticles based on spironaphthoxazine for reduced thermal reversion

• Published in: European polymer journal 2019-10, Vol.119, p.487-498
• Main Authors: Sanjabi, Samira, Alinejad, Zeinab, Mouraki, Alireza, Mahdavian, Ali Reza
• Format: Article
• Language: English
• Subjects: Absorption spectra; Acrylic copolymer; Copolymerization; Copolymers; Decoloring; Isomerization; Latex; Low temperature; Nanoparticle; Nanoparticles; NMR spectroscopy; Opto-thermal; Photochromic; Photochromism; Polymethyl methacrylate; Reversion; Room temperature; Smart materials; Spironaphthoxazine; Spironaphthoxazines; Spirooxazine; Temperature; Temperature dependence; Terpolymers; Ultraviolet radiation
• ISSN: 0014-3057; 1873-1945
• DOI: 10.1016/j.eurpolymj.2019.07.019

[Display omitted] •Stimuli-responsive acrylic copolymers as a new class of smart materials.•Employment of a spironaphthoxazine derivative with improved photofatigue resistance.•Controlled temperature-dependent photochromic behavior of the nanoparticles.•Kinetic study on photoisomerization in the copolymer nanoparticles. Stimuli-responsive materials based on spirooxazines are new class of smart materials that have received great deal of attentions in the recent decades. Spirooxazine derivatives, as photochromic compounds, represent many advantages like high photofatigue resistance. But, they usually suffer from very short life time of the colored form and quick reversion to its colorless isomer which limits their application at ambient conditions. Here, spironaphthoxazine (SNO) and spironaphthoxazine acrylate (SNO-Ac, as the monomer) were synthesized and characterized by FTIR and 1H NMR spectroscopy. Then, temperature-dependent photochromic behavior of SNO solution in different solvents was studied by UV–Vis spectroscopy at room and low temperatures. The absorption band relating to the obtained meronaphthoxazine (MNO) in 500–600 nm was not clearly observed after UV irradiation (365 nm) at room temperature, while an intensive absorption was appeared at −30 and −20 °C. SNO-Ac was then copolymerized with methyl methacrylate through solution and miniemulsion polymerizations. The obtained nanoparticles (ranging from 64 to 94 nm in size) represented reduced thermal reversion in comparison with the solution-based copolymers, but still not enough for room-temperature observations. Thereafter, an evident coloration was gained at normal conditions by introducing butyl acrylate to the above-mentioned copolymeric latex. The obtained flexible copolymer chains were found to facilitate SNO to MNO isomerization and the kinetic of photoisomerization in such systems were studied comprehensively. This resulted in photothermal stability enhancement of MNO at ambient conditions by their embedding in the prepared acrylic terpolymer nanoparticle to decrease its decoloration rate as a novel approach in such systems.