Ingénierie de nouveaux polymères supramoléculaires à base d’urées pour la caractérisation d’interactions faibles en solution : la balance supramoléculaire

New self-assembling bis-urea molecules bearing an ester moiety have been synthesized and their properties studied. These ester bis-ureas display two new assemblies: a helical filament and a double helical filament. A cooperative transition is observed between the two structures at a temperature T**. The structure of these assemblies was studied using a combination of FTIR, SANS, CD and molecular modeling. This new design allows an easy access to chiral bis-ureas that were used in the context of three different projects. (1) In the context of chirality amplification, the majority rules effect in ester bis-ureas was studied in order to determine a structure-property relationship. (2) Some ester bis-ureas presented all the necessary properties for their use as a supramolecular balance designed to measure weak interactions in solution. We used this system to measure halogen···halogen interactions in low polarity solvents as those were, to our knowledge, never observed in solution. (3) With specific ester bis-ureas, a third type of assembly was observed at lower temperature that is characterized by the formation of hydrogen bonds between urea and ester moieties. Surprisingly, the reorganization of these hydrogen bonds during heating is responsible for an increase in viscosity. This property allows these compounds to be potential thermothickening additives.De nouvelles molécules de bis-urée contenant une fonction ester et ayant la capacité de s’auto-assembler en solution ont été synthétisées. Ces bis-urées ester forment deux types d’assemblages : un filament hélicoïdal et un double filament hélicoïdal. Une transition coopérative entre les deux structures est observée à une température T**. La structure de ces assemblages a été étudiée à l’aide d’une combinaison de FTIR, SANS, CD et modélisation moléculaire. Ce nouveau design permet un accès simplifié à des structures chirales qui ont été utilisées dans le contexte de trois projets différents. (1) Dans le contexte de l’amplification de chiralité, l’effet « majority rules » que présente les bis-urées ester a été étudié de façon à déterminer une relation structure-propriété. (2) Certaines bis-urées ester présentent toutes les propriétés nécessaires à leur utilisation en tant que balance supramoléculaire pour la mesure d’interactions faibles en solution. Nous avons utilisé ce système pour mesurer des interactions halogène···halogène dans des solvants de faible polarité. A notre connaissance, ces dernières n’avaient jamais été observées en solution. (3) Dans le cas de quelques bis-urées ester, un troisième type d’assemblage est observé à plus basse température qui est caractérisé par la formation de liaisons hydrogène entre les groupements urée et ester. De manière surprenante, la réorganisation de ces liaisons hydrogène pendant le chauffage est responsable d’une augmentation de la viscosité. Cette propriété fait de ces composés de potentiels additifs thermoépaississants

A Competing Hydrogen Bonding Pattern to Yield Thermo-Thickening Supramolecular Polymer

International audienceIntroduction of competing interactions in the design of a supramolecular polymer (SP) creates pathway complexity. Ester–bis‐ureas contain both a strong bis‐urea sticker that is responsible for the build‐up of long rod‐like objects by hydrogen bonding and ester groups that can interfere with this main pattern in a subtle way. Spectroscopic (FTIR and CD), calorimetric (DSC), and scattering (SANS) techniques show that such ester–bis‐ureas self‐assemble into three competing rod‐like SPs. The previously unreported low‐temperature SP is stabilized by hydrogen bonds between the interfering ester groups and the urea moieties. It also features a weak macroscopic alignment of the rods. The other structures form isotropic dispersions of rods stabilized by the more classical urea‐urea hydrogen bonding pattern. The transition from the low‐temperature structure to the next occurs reversibly by heating and is accompanied by an increase in viscosity, a rare feature for solutions in hydrocarbons

Structural Control of Bisurea-Based Supramolecular Polymers: Influence of an Ester Moiety

A few examples of monomers are known that self-assemble into various high molar mass structures in solution. Controlling the morphology of the resulting supramolecular polymers is a highly desirable goal for many applications. Herein, we compare the self-assembling properties of newly prepared ester bisurea monomers with those of previously investigated alkyl bisurea monomers. The ester functionality decreases the hydrogen bonding strength of the bisurea monomers but does not prevent the formation of long assemblies in nonpolar solvents: gels are formed at millimolar concentration. Surprisingly, ester bisureas self-assemble at room temperature into rod-like urea-bonded supramolecular polymers that are different from the ones formed by alkyl bisureas. The rods formed by ester bisurea supramolecular polymers are compact (instead of tubular in the case of alkyl bisureas) and display two monomers in the cross-section (instead of three in the case of alkyl bisureas). The stability of the structures formed by ester bisureas can be easily tuned by changing the nature of the substituent in the α-position of the urea functions and/or the nature of the alkyl side chains