Hydrogen bonding interactions in aqueous media are often very weak because of the competition from water molecules, but they can still have a decisive effect on self-assemblies when used in combination with other interactions. In the case of amphiphiles with a hydrophobic part made from flexible alkyl chains, the introduction of hydrogen bonds within the hydrophobic domains through urea groups has been shown to dramatically increase the viscosity of aqueous solutions, and to enable self-sorting between amphiphiles of distinct structures. Another popular approach to synthesise viscous solutions or gels consists in decorating water soluble high molar mass polymers with hydrophobic groups.
In this article, Bouteiller and co-workers investigated the properties of systems combining both design elements, i.e. macromolecules with hydrophobic groups able to form very long anisotropic hydrophobic domains. A strong influence of both the number of associative groups per chain and the polydispersity has been demonstrated. In water, where the interactions between stickers are strong, the monomer self-assembles into filaments, but all other compounds with more than one sticker per chain are insoluble. In methanol, where the interactions between stickers are weaker, neither the monomer nor the monodispersed dimer is assembled, whereas polydispersed chains with an average number of stickers per chain of 2 or 3 self-assemble into filaments, leading to macroscopic gelation.
Hydrogen bonded supramolecular polymers in protic solvents: role of multitopicity by Marion Tharcis, Thomas Breiner, Joël Belleney, François Boué and Laurent Bouteiller, Polym. Chem., 2012, 3, 3093-3099.
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