Supramolecular ABC Triblock Copolymers via One-Pot, Orthogonal Self-Assembly

A heterotelechelic poly(norbornene imide) containing two terminal and orthogonal hydrogen-bonding receptors, N,N'-bis[6-(alkanoylamino)pyridin-2-yl] isophthalamide (often referred to as the Hamilton receptor or Wedge) and 2,7-diamido-1,8-naphthyridine (DAN), at the opposite ends of the polymer was synthesized via ring-opening metathesis polymerization (ROMP) through the employment of a Hamilton receptor-functionalized ruthenium initiator and a DAN-based chain-terminator. In parallel, two monotelechelic polymers containing either cyanuric acid (CA)- or ureidoguanosine (UG)-end groups that are complementary to the hydrogen-bonding receptors along the poly(norbornene imide) were synthesized either also via ROMP by terminating the polymerization of norbornene octyl ester with a CA-based chain-terminator or by the reaction of poly(ethylene oxide) with UG. Complete incorporations of the hydrogen-bonding receptors at the chain-ends of all polymers were confirmed by H-1 NMR spectroscopy. The telechelic polymers can be self-assembled into ABC triblock copolymers following either a stepwise or a one-pot, orthogonal self-assembly protocol. The self-assembly process was monitored by H-1 NMR spectroscopy, revealing full orthogonality of the two recognition pairs, Hamilton receptor-CA and DAN-UG. The resulting supramolecular ABC triblock copolymers were further characterized by a series of methods including 2-D NOESY, isothermal titration calorimetry, and viscometry, proving that the two orthogonal hydrogen-bonding interactions are strong enough to hold the three polymer chains together. We suggest that a self-assembly methodology solely based on the fully orthogonal hydrogen-bonding recognition motifs will allow for an easy and rapid synthesis of architecturally controlled supramolecular polymeric assemblies with a high degree of complexity.