Tunable Adhesion from Stoichiometry-Controlled and Sequence-Defined Supramolecular Polymers Emerges Hierarchically from Cyanostar-Stabilized Anion–Anion Linkages

Sequence-controlled
supramolecular polymers offer new design paradigms
for generating stimuli-responsive macromolecules with enhanced functionalities.
The dynamic character of supramolecular links present challenges to
sequence definition in extended supramolecular macromolecules, and
design principles remain nascent. Here, we demonstrate the first example
of using stoichiometry-control to specify the monomer sequence in
a linear supramolecular polymer by synthesizing both a homopolymer
and an alternating copolymer from the same glycol-substituted cyanostar
macrocycle and phenylene-linked diphosphate monomers. A 2:1 stoichiometry
between macrocycle and diphosphate produces a supramolecular homopolymer
of general formula (A)n comprised of repeating
units of cyanostar-stabilized phosphate–phosphate dimers. Using
a 1:1 stoichiometry, an alternating (AB)n structure
is produced with half the phosphate dimers now stabilized by the additional
counter cations that emerge hierarchically after forming the stronger
cyanostar-stabilized phosphate dimers. These new polymer materials
and binding motifs are sufficient to bear normal and shear stress
to promote significant and tunable adhesive properties. The homopolymer
(A)n, consisting of cyanostar-stabilized anti-electrostatic linkages, shows adhesion strength comparable
to commercial superglue formulations based on polycyanoacrylate but
is thermally reversible. Unexpectedly, and despite including traditional
ionic linkages, the alternating copolymer (AB)n shows weaker adhesion strength more similar to commercial white
glue based on poly­(vinyl acetate). Thus, the adhesion properties can
be tuned over a wide range by simply controlling the stoichiometric
ratio of monomers. This study offers new insight into supramolecular
polymers composed of custom-designed anion and receptor monomers and
demonstrates the utility of emerging functional materials based on
anion–anion linkages.