Comparison Of Polymers Bearing Iodine And Bromine On Their Side Groups In Halogen-Bonded Layer-by-Layer Assembly

Layer-by-layer (LbL) assembly is an important branch of supramolecular chemistry. LbL assembly technique has many advantages. For example, various substances could be assembled into membrane by LbL assembly. The LbL assembly process was not affected by the size and type of the substrate. The drive forces of LbL assembly was developed from electrostatic interaction to hydrogen bonding, charge transfer interaction, molecular specificity interaction, coordination bonding, host - guest interaction,Ï€-Ï€stacking and halogen bonding, which has greatly enriched the type of assembled materials. Halogen bonding is non-covalent interaction between a halogen atom and a Lewis base, and it is similar to hydrogen bonding at the mode of interaction. Theoretical and experimental data prove that three halogens work as XB donors, and the tendency to form strong interactions is I > Br > Cl. The more electron withdrawing the halogen atom is, the stronger is the XB to which it gives rise. The current understanding and systematic research of the halogen bonding is still in its infancy, but there are many important applications in crystal engineering, supramolecular liquid crystals, biological sciences and solid-state synthesis.LbL assembly based on halogen bonding was reported firstly by Wang, F. et al. of our research group. In this dissertation, we designed two polymers bearing iodine and bromine on their side groups poly(2-(4-iodo-2,3,5,6-tetrafluorophenoxy)-ethyl methacrylate) (PIPEMA) and poly(2-(4-bromo-2,3,5,6-tetrafluorophenoxy)-ethyl methacrylate) (PBrPEMA). They are assembled with polymers bearing halogen bonding acceptor on their side groups by LbL. We compare the difference of iodine and bromine in LbL assembly, and we find PIPEMA bearing iodine its side groups could form multilayer film with polymers bearing halogen bonding acceptor by LbL assembly, but PBrPEMA bearing bromine on its side groups couldn't form multilayer membrane with polymers bearing halogen bonding acceptor by LbL assembly. We choose side groups of polymers as a model molecule, and NMR titration was used to measure association constant of halogen bonding donors and acceptors. The association constant of iodopentafluorobenzene and N,N-dimethylbutylamine is 2.07 L/mol, while we did not observe chemical shift changes aroused from halogen bonding in the system of bromopentafluorobenzene and N,N-dimethylbutylamine. We guess this is why PBrPEMA could not form multilayer films with polymers bearing halogen bonding acceptor by LbL assembly. PIPEMA could form multilayer membrane with halogen-bonding polymers by LbL assembly. However, PIPEMA is a fluoric polymer, and its raw material is expensive. Herein, we designed a fluorine-free polymer poly(2-(4-iodo-benzoyloxy)- ethylmethacrylate) (PIBEMA). PIBEMA can form multilayer film with polyvinylpyrrolidone(PVPON) bearing halogen bonding acceptor by LbL assembly.