Photoinduced Solubility Modulation in the Copolymers of Fluoroalkyl, Spiropyranyl, and Isobornyl Methacrylates

This article reports photoinduced solubility modulation in copolymer thin films derived from spiropyranyl, perfluoroalkyl, and isobornyl methacrylates. A random copolymer of spiropyranyl methacrylate (SPMA) and 1H,1H,2H,2H-perfluorooctyl methacrylate (FOMA) was first prepared in the absence of isobornyl methacrylate (IBMA). The resulting as-prepared thin film could be dissolved in highly fluorinated or fluorous solvents but became insoluble following exposure to UV light (lambda = 365 nm) via the photoisomerization transformation of spiropyran units into merocyanine moieties. On the other hand, the incorporation of IBMA into the copolymer structure above a certain threshold resulted in copolymers exhibiting the opposite dissolution behavior. UV-vis spectroscopic measurements on the copolymer films and solutions indicated that dipolar attraction between the photoisomerized merocyanine moieties contributed to the decrease in solubility. The incorporation of IBMA into the copolymer chains diluted the merocyanine moieties and increased their glass-transition temperature, resulting in the disruption of the intermolecular attraction and an increase in the solubility of the UV-exposed polymer chains. These results suggested that stencils could be developed without additives to generate strong acid molecules or free radicals in polymer thin films. The proposed processing technique for fluoroalkylated copolymers was thus tested in the fabrication of orthogonal copolymer stencils and demonstrated to be a useful tool for the pixel patterning of chemically vulnerable organic light-emitting diodes.