Unraveling Decisive Structural Parameters for the Self-Assembly of Supramolecular Polymer Bottlebrushes Based on Benzene Trisureas

Abstract

By introducing strong directed hydrogen bonds to an amphiphilic polymer, we demonstrate that phase transitions from spherical to cylindrical morphologies in aqueous solutions can significantly be shifted to favor the assembly of supramolecular polymer bottlebrushes. In water, a forced self-assembly of polymers into cylindrical structures remains a challenge as the often required hydrophobic shielding induces forces, which tend to minimize the surface area. The herein presented novel benzene trisureas can overcome these limitations due to strong hydrogen bonds and alter the morphology to cylinders despite an unfavorable packing parameter, which dominated the previously reported trisamide analogues. The systematic variation of composition and architecture revealed that a transition to spherical morphologies still occurs, but the phase-transition boundaries appear to be shifted to tolerate larger hydrophilic polymer chains. The strength of the directing interactions appears to be decisive for the shift, though we additionally observed that any restrictions of lateral aggregation can diminish the effect of the directing hydrogen bonds. Overall, the straightforward synthesis and versatile design render the presented systems an interesting blueprint for the development of more advanced supramolecular polymer bottlebrushes and multifunctional nanostructures.

Facilitating functionalization of benzene-1,3,5-tricarboxamides by switching amide connectivity

“…33 A strategy to circumvent statistical reactions and to introduce one different side arms onto the core is to start from a C 2symmetrical core. [34][35][36][37][38][39][40][41] The group of Bouteiller synthesized Nsubstituted benzene-1-urea-3,5-biscarboxamide (BUBA) monomers with a significantly enhanced yield, starting from a commercially available dimethyl 5-aminoisophthalate core. 42 The BUBA molecules showed cooperative self-assembly into long helices in organic media, similar to BTAs.…”

Overcoming the Necessity of a Lateral Aggregation in the Formation of Supramolecular Polymer Bottlebrushes in Water

“…[ 12–27 ] Considering the latter, we have previously shown that the number of H‐bonds per central motif, and thus the interaction strength, is decisive to obtain SPBs. [ 28–30 ] However, next to the strength of the supramolecular interaction and the main axial assembly, a lateral assembly appears to be crucial for the formation of cylindrical structures, which is similarly observed for other of the above‐mentioned motifs.…”

“…Compounds 1a–c were further studied via sedimentation velocity experiments in the AUC to resolve apparent distributions of the sedimentation coefficients, s (Figure 1B). [ 28,29,33 ] For all three compounds, roughly monomodal distributions of s were observed with signal (weight) average sedimentation coefficients of s = 1.0 S ( 1a ), s = 2.4 S ( 1b ), and s = 3.3 S ( 1c ). The very small s ‐value for 1a is in accordance with the SAXS and cryoTEM results indicate the presence of unimers next to small aggregates.…”

Adjusting the length of supramolecular polymer bottlebrushes by top-down approaches

“…The general structure of the tested BTP and BTU is depicted in Figure 1 [ 19 – 20 ]. While the hydrogen bonding moieties are either urea-based or peptide-based (i.e., phenylalanine) units, the dodecyl chains act as hydrophobic shields to induce the amphiphilic assembly in water and prevent the surrounding water from interfering with the hydrogen bonds in the interior [ 29 ].…”

“…An alternative is the use of molecular motifs capable of forming directional supramolecular interaction forces, such as hydrogen bonds or π-interactions, to guide the one-dimensional (1D) assembly of established, commercial polymers in solution [17]. We recently reported the self-assembly of polyethylene oxide (PEO) polymers into cylindrical nanostructures, also called supramolecular polymer bottlebrushes (SPBs), based on the end group modification with hydrogen bond forming benzenetrisurea (BTU) and benzenetrispeptide (BTP) motifs [18][19][20]. The resulting amphiphilic character of the materials facilitated a control of the kinetic assembly, which provided access to stable nanostructures on a broad length range (<100 nm-2 µm).…”