Poly(ionic liquid)-based nanogels and their reversible photo-mediated association and dissociation

Controlling the association and dissociation of polymers and nanoparticles has attracted tremendous interest in the past few decades. In this study, we reported a novel poly(ionic liquid) (PIL)-based nanogel that could undergo reversible photo-mediated association and dissociation through the trans–cis isomerizatioin of azobenzene (Azo) or host–guest interactions between the Azo group and β-cyclodextrin (β-CD) dimer. PIL nanogels were fabricated via the one-step cross-linking copolymerization of ionic liquid (IL) monomers and cross-linkers in a selective solvent, and characterized using dynamic light scattering (DLS), UV-vis spectroscopy, solid state carbon nuclear magnetic resonance (13C NMR), elementary analyses, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analyses (TGA), and scanning electron microscopy (SEM). The results demonstrated that the sizes of PIL nanogels containing Azo units could be facilely tuned through the feed ratio of IL monomers to cross-linkers, and their polarity could also be mediated through anion exchange. Moreover, due to the presence of Azo units, PIL nanogels in water could associate and dissociate reversibly under the alternative irradiation of UV and visible light. Additionally, by using PIL nanogels as the building blocks, supramolecular aggregates could be achieved via the host–guest interaction of Azo and β-CD dimers. The assembly process was testified by UV-vis spectroscopy, DLS, 2D nuclear Overhauser effect spectroscopy (NOESY), and SEM measurements. Therefore, our findings provided a feasible strategy for the photo-induced association and dissociation of polymer nanoparticles.