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

• Published in: Macromolecules Vol. 43; no. 1; pp. 467 - 472
• Main Authors: Fruth, Andrea, Klapper, Markus, Müllen, Klaus
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 12.01.2010
• Subjects: Aminoacid polymers; Applied sciences; Exact sciences and technology; Physicochemistry of polymers; Synthetic biopolymers; Circular dichroism spectrum; Graft copolymer; Solution polycondensation; Carbazole derivative copolymer; Aminoacid copolymer; Lysine polymer; Experimental study; Macromer; Suzuki coupling; Polyelectrolyte; Solid state; Preparation; pH; Molecular aggregation; Lysine copolymer; Aqueous solution; Conformation; Amphiphilic polymer
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma901020v

Amphiphilic polyelectrolyte brush polymers with a 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 a 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 13C 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 can 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 can be considered due to the stiffness of the backbone and the switchable PLL side chains either as a rod-g-coil or a rod-g-rod polymer.