Loading and release capabilities of charged dendronized polymers revealed by EPR spectroscopy

Abstract

The incorporation of stearic acids into peripherally charged dendronized polymers (denpols) and their release, initiated by external triggers, is characterized in solution. Using continuous wave electron paramagnetic resonance (CW EPR) spectroscopy on spin-labeled stearic acid derivatives it is found that – depending on the generation (1–4) of the dendron side groups – up to 2.2 of these spin probes can be hosted per macro-monomer unit of a denpol. The orientation of the stearic acid guests inside the denpols is further determined by double electron–electron resonance (DEER) experiments. To this end, the dipolar coupling between ¹⁵N-labeled dianionic spin probes (Fremy's salt), self-assembled on the surface of the cylindrical denpols, and the incorporated spin-labeled fatty acids is measured. The arrangement of these fatty acid guest molecules is comparable to the arrangement of fatty acids incorporated in layers of ionic surfactants, the carboxyl group pointing towards the periphery and the hydrophobic tail into the hydrophobic interior. The loading capacity of the denpols scales exponentially with their generation. Finally, the fatty acid guests can be released from the denpols by increasing pH or charge screening.