Kinetically Controlling the Length of Self-Assembled Polymer Nanofibers Formed by Intermolecular Hydrogen Bonds.

Abstract

Strong directional hydrogen bonds represent a suitable supramolecular force to drive the one-dimensional (1D) aqueous self-assembly of polymeric amphiphiles resulting in cylindrical polymer brushes. However, our understanding of the kinetics in these assembly processes is still limited. We here demonstrate that the obtained morphologies for our recently reported benzene tris-urea and tris-peptide conjugates are strongly pathway-dependent. A controlled transfer from solutions in organic solvents to aqueous environments enabled a rate-dependent formation of kinetically trapped but stable nanostructures ranging from small cylindrical or spherical objects (<50 nm) to remarkably large fibers (>2 μm). A detailed analysis of the underlying assembly mechanism revealed a cooperative nature despite the steric demands of the polymers. Nucleation is induced by hydrophobic interactions crossing a critical water content, followed by an elongation process due to the strong hydrogen bonds. These findings open an interesting new pathway to control the length of 1D polymer nanostructures.