Fluorescent star-shaped polystyrenes: "Core-first" synthesis from perylene-based ATRP initiators and dynamic mechanical solid-state properties

This paper describes the synthesis of two novel tetra 2-bromoisobutyric acid-substituted perylene fluorophores and their use as initiators for the atom transfer radical polymerization of styrene. Different star-shaped polystyrenes covering a wide range of molecular weights were prepared by variations in the initial molar ratio between styrene and the perylene chromophores. Bulk properties of the star polymers were investigated by X-ray scattering, differential scanning calorimetry, and dynamic mechanical measurements. These studies revealed that the polystyrene arms effectively suppress the aggregation of the perylene chromophores and indicated that, especially at low degrees of polymerization, the rigid-core moiety significantly affects the segmental dynamics of the arms. Spin-casting of the polystyrene stars afforded optically transparent films, which displayed high fluorescent quantum yields. Due to the covalent linkage between the polystyrene chains and the perylene chromophore, the dye-contents of such films can be much higher than those achievable by dissolution of the corresponding low-molar-mass perylene dye in a polystyrene matrix. In addition, the polystyrene arms are likely to reduce the mobility of the chromophore within a polystyrene matrix. These features make these fluorescent star-shaped polymers of interest to improve the migration fastness of colored polystyrene samples.