A supramolecular multi-block copolymer with a high propensity for alternation

Alternating, multi-block supramolecular copolymers were created using quadruple hydrogen bonding as the noncovalent binding force. One block consisted of two guanosine butyl urea (UG) units attached at the ends of a triethylene glycol linker or a PEG chain (MW = 2 kD). The other block contained a 2,7-diamido-1,8-naphthyridine (DAN) unit at each end of a short alkane diester linker or a 100 kD poly(butyl methacrylate) macromolecule. The UG unit presents an ADDA hydrogen bonding array that is complementary to the DAAD array of DAN, and these form a very strong complex (K_assoc ∼ 5 × 10⁷ M^-1), whereas UG and DAN weakly self-associate. These recognition properties allowed a multi-block supramolecular polymer to form which exhibits a high propensity for alternation. The self-assembled polymeric structure was shown to be reversibly formed and it was characterized by a combination of dynamic light scattering (DLS), ¹H NMR, size exclusion chromatography (SEC), and viscometry.