Halogen Bonding Polymers: Synthesis, Binding Studies, and Solution-Phase Assembly

This work explores interpolymer halogen bonding to direct solution-phase self-assembly. Halogen bonding is an attractive, non-covalent interaction between a halogen bond donor which bears an electron deficient halogen atom and a Lewis basic halogen bond acceptor. The donor halogen receives electron density from the Lewis base acceptor. Halogen bonding has received significant attention in materials chemistry but examples of polymeric donors are infrequent. Solution-phase polymer nanostructures are of interest for catalysis, drug delivery, and stimuli responsive materials. They have previously been formed through other non-covalent interactions but not by halogen bonding. This work contributes to the fields of halogen bonding and polymer chemistry through the synthesis of polymeric donors, the characterization of their interpolymer complexation with a polymeric acceptor, and the establishment of conditions yielding well defined solution-phase assemblies of complementary polymeric halogen bond donors and acceptors. Herein, the first examples of RAFT polymerization of halogen bond donors are described for methacrylate and styrene derivatives. X-ray photoelectron spectroscopy and 19F NMR titrations are employed to characterize interpolymer halogen bonding with polymeric acceptor PDMAEMA. Acceptor chain length dependent trends in binding affinity and occupancy of donor sites are established for polymer solutions. Assembly of the donors with block copolymers of the acceptor (PEO-b-PDMAEMA) was performed by multiple solvent switching protocols. Going from DMSO to water resulted in kinetically controlled morphologies, whereas a slow solvent changing procedure from acetone to acetonitrile to water allowed access to a rich variety of structures, including two infrequently reported inverted morphologies (hexagonal and bicontinuous). To further demonstrate the utility of halogen bonding, multicompartmental assemblies were formed with cores composed of both halogen bonding and non-halogen bonding segments. Halogen bonding and hydrophobic domains were assembled in stages using a multi-step assembly process with a donor homopolymer and a triblock terpolymer bearing an acceptor block, a hydrophobic non-halogen bonding block, and a corona block.