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.