Hydrogen-Bond Engineering in Supramolecular Polymers: Polarity Influence on the Self-Assembly of Benzene-1,3,5-tricarboxamides

Benzene-1,3,5-tricarboxamides (BTAs) comprising alkyl side chains form supramolecular polymers in dilute solution and in the solid state as a result of the 3-fold helical arrangement of the intermolecular hydrogen bonds. We investigated systematically the role of polarity on the self-assembling behavior of BTAs in dilute solution and, when incorporated in polymeric materials, on their ability to phase segregate. In dilute solutions, the polarity was gradually increased by mixing in methyl tert-butyl ether (in which BTAs are molecularly dissolved) into methylcyclohexane (in which BTAs form stable helical aggregates). We observed a significant decrease in the stability of BTA aggregates after the addition of small amounts of ether. This strong dependence on the polarity of the environment was also found in the solid state. By end-capping telechelics of varying polarity with the BTA motif, a wide range of backbone polarities was covered. Commercially available polymers as well as polymers that were synthesized via ring-opening metathesis polymerization were evaluated. BTA motifs connected to apolar telechelics formed stable phase segregated nanorods. Increasing the polarity resulted in a decrease of the stability, and this eventually resulted in the loss of nanorod formation. This systematic study on the influence of polarity on self-assembly gives us a detailed understanding of the potential to use BTAs as functional nanorods in various applications.