Persistence Length of PEGMA Bottle Brushes Determined by Pyrene Excimer Fluorescence.

Seven pyrene-labeled poly(oligo(ethylene glycol) methyl ether methacrylate)s (PyEG 5 -PEG n MAs) were prepared with n = 0, 3, 4, 5, 7, 9, and 19 ethylene glycol units by copolymerizing a small amount of penta(ethylene glycol) 1-pyrenemethyl ether methacrylate with an EG n MA monomer. The conformation of the PyEG 5 -PEG n MA polymers evolved from a random coil for PyEG 5 -PEG 0 MA or poly(methyl methacrylate) to a polymeric bottle brush (PBB) architecture with increasing side chain length. The fluorescence decays of the PyEG 5 -PEG n MA samples were fitted according to the fluorescence blob model (FBM) whose parameters were used, in combination with the Kratky-Porod equation, to calculate the persistence length of these polymers. The persistence lengths obtained from the PEF experiments were found to increase with the square of the number ( N S ) of non-hydrogen atoms in the side chain as expected theoretically. The persistence lengths found with the PyEG 5 -PEG n MA samples in DMF also matched those found earlier for another series of PEG n MA samples labeled with 1-pyrenebutanol. The good agreement found between the persistence lengths obtained with the PEG n MA samples labeled with two different pyrene derivatives illustrates the robustness of the method and its applicability for measuring the unknown persistence length of polydisperse polymer samples.