Stimuli Responsive Size Control of Hyperbranched Polymers

Abstract

AbstractThe synthesis of stimuli–responsive hyperbranched polymers is reported. Through polymer‐analogous 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)‐β‐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. magnified image