No abstract

The supramolecular crosslinking of polymer chains in water by specific, directional and dynamic non-covalent interactions has led to the development of novel supramolecular polymeric hydrogels. These aqueous polymeric networks constitute an interesting class of soft materials exhibiting attractive properties such as stimuli-responsiveness and self-healing arising from their dynamic behaviour and that are crucial for a wide variety of emerging applications. We present here a critical review summarising the formation of dynamic polymeric networks through specific non-covalent interactions, with a particular emphasis on those systems based on host-guest complex formation, as well as the characterisation of their physical characteristics. Aqueous supramolecular chemistry has unlocked a versatile toolbox for the design and fine-tuning of the material properties of these hydrogels (264 references).

Herein we report the photocontrol of cucurbit[8]uril (CB[8])-mediated supramolecular polymerization of azobenzene-containing monomers. The CB[8] polymers were characterized both in solution and in the solid state. These host-guest complexes can be reversibly switched between highly thermostable photostationary states. Moreover, a remarkable stabilization of Z-azobenzene was achieved by CB[8] complexation, allowing for structural characterization in the solid state.

We report the formation of cylindrical micelles, sheet-like micelles, tubular micelles, as well as polymer vesicles by a new series of amphiphilic linear-dendritic block-copolymers (BCs). The BCs, noted as PEGm-AZOn, are composed of poly(ethylene glycol) (PEG) chains of different molecular weights as hydrophilic blocks and the first four generations of azobenzene-containing dendrons based on 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) as hydrophobic blocks (m represents the degree of polymerization of PEG, and n is the number of azobenzene units at the periphery of dendron). The polymeric aggregates were formed by adding water to solutions of the BCs in dioxane. The micellar dispersions in water were finally obtained by removing dioxane via dialysis against water. The morphology of the micellar self-assemblies was studied by transmission electron microscopy (TEM), cryo-electron microscopy (cryo-TEM), and atomic force microscopy (AFM). A generation-dependent aggregation behavior was found for the series of BCs PEG45-AZOn. Core-shell structured nanofibers with an inner diameter of 8 nm were observed for the copolymer PEG45-AZO2 (hydrophilic/hydrophobic weight ratio equal to 67/33). Lyotropic liquid crystalline behavior was detected for the aqueous solution of the nanofibers. The coexistence of sheet-like aggregates and tubular micelles was detected for the copolymer PEG45-AZO8 in which the number of cyanoazobenzene units is increased to 8 (hydrophilic/hydrophobic weight ratio equal to 33/67). The tubular micelles could be intermediates in the sheet-like aggregate-to-vesicle transition. Polymer vesicles (polymersomes) with a diameter in the range 300-800 nm were observed for the copolymer PEG45-AZO16 (hydrophilic/hydrophobic weight ratio equal to 20/80). The membrane of the sheet-like aggregates, tubular micelles, and polymersomes was shown to have a bilayer structure, as revealed by cryo-TEM. UV illumination of the aqueous polymersome dispersion induced the formation of wrinkles in the vesicle membrane, thus showing that this type of polymeric aggregate is photoresponsive.