Synthesis and Characterization of Amphiphilic Polyelectrolyte Brush Copolymers Based on Poly(2,7-carbazole)

Amphiphilic polyelectrolyte brush polymers with,I rigid, hydrophobic backbone formed by poly(2,7-carbazole) and flexible pH-sensitive side chains of poly(L-lysine) (PLL) are presented and their aggregation is studied. The hydrophilic polyelectrolyte side chains of PLL are attached to the 9-position of every second carbazole unit, alternatingly to hydrophobic alkyl side groups, Substituting the residual moieties. The PLL side chains can be switched between different conformations by varying the pH. At lower pH the free amino, groups in PLL become protonated and the side chains have,I rodlike conformation, while at higher pH values the PLL, chains form in their unprotonated form coil structures. This process is proven by circular dichroism and C-13 NMR experiments. Fluorescence emission spectra, dynamic light scattering, and atomic force microscopy (AFM) experiments demonstrate that the aggregation behavior of the synthesized polyelectrolyte brush polymers call be controlled by the pH as well. In the charged form the polymers are observed as single molecules due to the electrostatic repulsion; in its unprotonated form. however, large aggregates are formed. The water-soluble brush polymers call be considered due to the stiffness of the backbone and the switchable PLL side chains ether as a rod-g-coil or a rod-g-rod polymer.