Effects of Chain Parameters on Kinetics of Photochromism in Acrylic-Spiropyran Copolymer Nanoparticles and Their Reversible Optical Data Storage.

Chemical bonding between photochromic compounds and polymer matrices will induce several consitions such as photostability, photoreversibility, elimination of dye aggregation, and undesirable negative photochromism. In such polymeric systems, the switching rate and photoisomerization are closely dependent on several parameters like chain flexibility, steric restrictions, polarity, and even proticity of the surrounding medium. Here, copolymerization of a synthesized spiropyran-based monomer with butyl acrylate (BA) and methyl methacrylate (MMA) comonomers was carried out with various compositions of MMA and BA through emulsion polymerization, and the corresponding photoisomerization kinetics were studied. Particle sizes and their distributions were analyzed by dynamic light scattering, and morphologies were investigated by scanning and transmission electron microscopic analyses. The results showed the particles are spherical with diameter 62-82 nm. Differential scanning calorimetric thermograms were employed to determine Tg of the prepared copolymers, which ranged from -23 to 93 °C. The kinetics of photoisomerization was then studied by UV-vis spectroscopy. Finally, a latex containing spiropyran/acrylic copolymer with Tg of about 0 °C and optimum rate of coloration and decoloration was considered in reversible optical data storage studies due to its fast photochromism and good film-formation properties.