Stimuli Responsive Size Control of Hyperbranched Polymers

The synthesis of stimuli-responsive hyperbranched polymers is reported. Through polymeranalogous amidation of polyethylenimine (PEI) with 5-hexynoic acid and 10-undecynoic acid two polymers were obtained, with different spacer lengths between the hyperbranched PEI- and the triple bond. In a further step, these triple bonds were clicked with mono-(6-azido-6-desoxy)- beta-cyclodextrin (CD-N3). The resulting polymers PEI-(CH2)(3)-CD and PEI-(CH2)(8)-CD show stimuli-responsive contractions and expansions, which was observed by use of dynamic light scattering (DLS). These size effects depend on the formation of inter-and intramolecular aggregates due to the different spacer length between the triazol and the CD. Furthermore, the size of the polymer with the longer spacer (PEI-(CH2)(8)-CD) could be influenced with adamantyl carboxylate through host-guest-complexation resulting in a reassemble of the aggregates. Moreover, the pH dependent size control was studied by adding sodium hydroxide. The deprotonation of the ammonium groups from the PEI scaffold leads to a further decrease in the hydrodynamic diameters of PEI-(CH2)(3)-CD and PEI-(CH2)(8)-CD. Thus, the different polymer systems exhibit a wide range (4-170 nm) of mean size. Furthermore, successful complexation experiments of the obtained polymer with phenolphthalein were carried out.