Paper of the week: Binding and supramolecular organization of homo- and heterotelechelic oligomers in solutions

Supramolecular chemistry, defined as the chemistry of noncovalent bonds (such as hydrogen bonding, π–π stacking, hydrophobic interactions, etc.), is a promising tool to create functional materials. Indeed, noncovalent bonds introduce reversibility and stimuli-responsiveness to materials. Therefore, compared to high-molecular-weight covalent polymers, processing and recycling of supramolecular polymers could be easier. Furthermore, incorporating noncovalent bonds into materials can impart original properties, such as self-healing. The simplest situation occurs when oligomers are equipped with complementary or self-complementary functional end-groups. They can in principle associate to form linear chain supramolecular polymers. The strength of the association constant controls the length of the polymer. Furthermore, supramolecular organizations at mesoscopic scales often appear and they lead to a richer and interesting behavior in comparison with classical covalent polymers. Complex mesoscopic organizations were observed both in the bulk and in solution.

Graphical abstract: Binding and supramolecular organization of homo- and heterotelechelic oligomers in solutions

In this study, Leibler and co-workers reported on the subtle influence of solvent on the organization of supramolecular polymers. They synthesized homotelechelic and heterotelechelic oligomers of poly(propylene oxide) (PPO) equipped with complementary hydrogen bonding functional ends, thymine (Thy) and diaminotriazine (DAT). In a solvent that dissociates Thy–DAT hydrogen bonds, such as DMSO, the viscosity was low for all functional telechelic oligomers. In non-dissociative solvents, the addition of functional oligomers increased the viscosity. For both the homotelechelic blends and the heterotelechelics, the viscosity in toluene was about two times higher than that in chloroform. Additionally, the Thy–DAT association constant was 22 times higher. Carbon relaxation times measured by NMR and viscosity variation for solutions of different concentrations suggest a distinct supramolecular organization in chloroform and toluene: linear and cyclic supramolecular chains in chloroform and small π-stacked objects with a PPO shell and a Thy, DAT core in toluene. One might expect that when the materials are obtained by solvent evaporation, the organization in the bulk is solvent dependent as this is often the case for ABC block copolymers.

Binding and supramolecular organization of homo- and heterotelechelic oligomers in solutions by Jessalyn Cortese, Corinne Soulié-Ziakovic and Ludwik Leibler Polym. Chem. 2014, 5, 116-125.

Julien Nicolas is a web-writer and advisory board member for Polymer Chemistry. He currently works at Univ. Paris-Sud (FR) as a CNRS researcher.

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