Positioning a fluorescent probe at the core of a glassy star polymer for detection of local dynamics

Abstract

Accessing local dynamics within a single macromolecule is the key to understand the physical origin of the viscoelasticity and especially the glass transition. In order to extract specific information on the dynamics of the branch point of a star polymer around its glass transition temperature, four-arm star poly (n-butyl methacrylate) with a fluorescent core was synthesized using perylene diimide as initiator and polymerization conducted via atom transfer radical polymerization. The process is found to be effective in positioning the fluorophore at the branch point with the fluorophore intact, which allows the successful application of single molecule fluorescence defocus imaging in examining the local site-sensitive dynamics. The power spectra of rotation trajectories, the population of rotating fluorophores as well as the distribution of angular displacement were used to revel the difference in local dynamics between branch point and the arm’s end. It is discovered that the local dynamics at the core of the star polymer is much less activated than that at the arm’s end. The results demonstrate the strong effect dues to the topological constrain at the branch point and the more free space at the arm’s end.