Linear Supramolecular Polymers Driven by Anion–Anion Dimerization of Difunctional Phosphonate Monomers Inside Cyanostar Macrocycles

Abstract

Supramolecular polymers have enabled far-reaching fundamental science and the development of diverse macromolecular technologies owing to the reversible and noncovalent chemical connectivities that define their properties. Despite the unabated development of these materials using highly tailorable recognition elements, anion-based polymers remain rare as a result of the weak interactions they mediate. Here, we use design rules inspired by cation-driven polymers to demonstrate a new noncovalent link based on receptor-stabilized anion−anion interactions that enables the efficient linear polymerization of simple difunctional phosphonates. The linear main chain connectivity and molecular topology were confirmed by single crystal X-ray diffraction, which demonstrates the rare 2:2 stoichiometry between the anionic phosphonate end groups and a pair of π-stacked cyanostar macrocycles. The stability of these links enables rapid polymerization of difunctional phosphonates employing different aliphatic linkers (C 6 H 12 , C 8 H 16 , C 10 H 20 , C 12 H 24 ). Diphosphonates with greater chain flexibility (C 12 H 24 ) enable greater polymerization with an average degree of polymerization of nine emerging at 10 mM. Viscosity measurements show a transition from oligomers to polymers at the critical polymerization concentration of 5 mM. In a rare correlation, NMR spectroscopy shows a coincident molecular signature of the polymerization at 5 mM. These polymers are highly concentration dependent, reversibly polymerize with acid and base, and respond to competitive anions. They display the design simplicity of metallo-supramolecular polymers with transfer of the strong 2:2 recognition chemistry to macromolecules. The simplicity and understanding of this new class of supramolecular polymer is anticipated to open opportunities in tailoring anion-based functional materials.

Synthesis of a Bolaamphiphilic Alkenyl Phosphonic Acid by Ru-catalyzed Olefin Cross Metathesis Reaction

“…Flood et al reported the self-assembling behavior of dodecanediyl-bis phosphonic acid without the trans-P-C C moiety in organic solvents. They revealed that this compound formed a linear supramolecular polymer via intermolecular hydrogen bonding of the phosphonic acid moieties 28 . These results suggest that introduction of the trans-P C C moiety significantly increases the hydrophilicity, while the two trans-P C C moieties at both ends of BPC 12 may induce dense packing via hydrogen bond interactions.…”

Thermally Responsive Poly(ethylene oxide)‐Based Polyrotaxanes Bearing Hydrogen‐Bonding Pillar[5]arene Rings**

“…[1][2][3][4][5][6][7] Polyrotaxanes, in which many macrocycles are threaded onto a polymer chain and trapped by terminal bulky stoppers, have recently attracted considerable interest for their simple structures and properties different from conventional polymers. [8][9][10][11][12][13] Poly(ethylene oxide)s (PEOs) are a class of polymers, which exhibit crystalline and thermoplastic behavior, as well as high solubility in both water and organic solvents. PEOs have a broad scope of applications in materials science and biochemistry because of their excellent biological compatibility and commercial availability in a wide range of molecular weights.…”

“…This method of assembly allows for some forms of molecular motion, which endows these materials with unique mechanical and thermal properties [1–7] . Polyrotaxanes, in which many macrocycles are threaded onto a polymer chain and trapped by terminal bulky stoppers, have recently attracted considerable interest for their simple structures and properties different from conventional polymers [8–13] …”

“…13 C chemical shifts were expressed as values relative to tetramethylsilane (TMS) using the 29.50 ppm line of adamantane as an external reference. In the 2D 1 H- 13 C heterocorrelated NMR measurement, the 1 H signals were detected using Phase Modulated Lee-Goldburg (PMLG) homonuclear decoupling. 58 Gel permeation chromatography (GPC) analysis.…”

Controlled Diffusion of Photoswitchable Receptors by Binding Anti-electrostatic Hydrogen-Bonded Phosphate Oligomers

“…While AEHB interactions have been identified in solid-state crystal structures, detection of unchaperoned anion dimers or oligomers in solution is challenging due to limited spectroscopic signatures, weak anion–anion bonds, labile protons, and rapidly exchanging bound species. These difficulties can be attenuated by the use of an anion-binding host to template AEHB interactions, 17 leading to reports of HSO 4 – dimers 15 , 18 and H 2 PO 4 – dimers 19 and oligomers 20 , 16 in solution. Conductimetric and spectroscopic techniques have shown the formation of AEHB dimers of HCO 3 – and H 2 PO 4 – in water 21 or DMSO 22 and suggested the possibility of higher order oligomers.…”