A Competing Hydrogen Bonding Pattern to Yield a Thermo‐Thickening Supramolecular Polymer

Abstract

Introduction of competing interactions in the design of asupramolecular polymer (SP) creates pathway complexity. Ester-bis-ureas contain both as trong 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 as ubtle 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.T he previously unreported low-temperature SP is stabilized by hydrogen bonds between the interfering ester groups and the urea moieties.I ta lso features aw eak macroscopic alignment of the rods.T he 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,arare feature for solutions in hydrocarbons.SPs are chain-like assemblies of self-complementary monomers with unique properties and applications. [1][2][3][4] Ther eversible but directional non-covalent interactions responsible for their self-assembly provides tunability and responsiveness [5] to various stimuli. This has contributed to the development of innovative catalysts, [6,7] fluorescent systems, [8,9] self-healing materials, [10,11] and gels, [12,13] among other potential applications.O ne fascinating consequence of the dynamic character of supramolecular assemblies is the capability of molecular building blocks to assemble into distinct thermodynamically or kinetically stable nanostructures. [14] An umber of studies describe the possibility of selecting one of these nanostructures by carefully controlling the conditions of aggregation, namely,t ime, [15][16][17][18] concentration, [19] temperature, [20] solvent, [21][22][23][24][25] and diffusion, [26] or by tuning the nature of the monomer. [27][28][29] This pathway complexity in the aggregation ability of the monomers is usually revealed by spectroscopic techniques that identify the structural differences in the assemblies at the nano or mesoscale (for example,kinetics of aggregation, helicity,s tacking mode,c onformation). [30,31] However,achange in the properties of the supramolecular assemblies at the macroscale has been reported for very few cases. [20,32] In fact, the properties of SPs can be considerably diversified when they form in competition with other assemblies.I ndeed, pathway complexity can be responsible for unusual behaviors such as aself-assembly that is triggered by dilution, [19] or by both increasing or decreasing the temperature. [33] In particular,w hen two competing SPs can assemble from the same monomer, [25] the transition between the two structures can result in noticeable macroscopic property changes. [20] Thei ntroduction of competing interactions in the design of as upramolecular assembly is al ogical approach to create pathway complexity.I np ractice,t his can be done through solvents [21,34,35...

From Photoinduced Supramolecular Polymerization to Responsive Organogels

“…trans - SG1 shows a strong vibrational band centered at 3333 cm –1 , attributed to hydrogen-bonded N–H in urea moieties. 53 , 69 cis - SG1 shows a broader band centered at 3396 cm –1 , at higher wavenumbers in comparison to the band of trans - SG1 but lower than the free N–H stretching vibration (ca. 3445 cm –1 ).…”

Chain-End Effects on Supramolecular Poly(ethylene glycol) Polymers

“…In recent years, the highly directional physical interactions based on H-bonds have been applied in a fundamentally different way to form supramolecular polymers, as a means to mimic the biological self-assembly and organization [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ]. Indeed, in these materials, modification of low molar mass polymers with functional groups that associate via H-bonding interactions give rise to a rich variety of self-organizing structures on the mesoscale with a multiplicity of macroscopic properties [ 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ]. In particular, the nature of the H-bond interactions will largely influence the structure and dynamics of the supramolecular self-assembled structures.…”

Energetics of Competing Chiral Supramolecular Polymers

“…It was recently realized that the properties of these supramolecular polymers can be considerably diversified when their formation occurs in competition with other assemblies. Indeed, pathway complexity can lead to supramolecular polymorphism, when two supramolecular polymers form under kinetic [16–21] or thermodynamic [22–35] control. In the latter case, the transition between the two competing structures can be responsible for unusual behaviors such as self‐assembly triggered by increasing the temperature, [28] or by dilution [23] .…”

“…In the latter case, the transition between the two competing structures can be responsible for unusual behaviors such as self‐assembly triggered by increasing the temperature, [28] or by dilution [23] . The modification of the supramolecular structure is particularly useful when it leads to a controllable and sudden change of macroscopic (such as rheological [22,30] or emissive [31,32] ) properties. In addition, the sharpness of the transition can actually be exploited to quantify weak intermolecular interactions [36,37] or solvation effects [38] …”