Subcomponent Self-assembly Of Polymer Chains Through Coordination With Metal Ions

A variety of proteins are coordinated with metal ions in living systems, which play important role in implementing life functions. Metal ions can construct the high order structures of proteins through inter-or intrachain coordination, which give rise to the folding and aggregation of polypeptide, not only leading to the living function but also the diseases. Thus the studies on coordination-induced self-assembly of polymer chains are of academic importance and can also provide a new way to the construction of the dative metal-polymer hybrid functional materials. Dynamic combinatorial chemistry (DCC) offers a new approach to construct metal-polymer hybrid functional materials. DCC is the combination of reaction and self-assembly. One of the achievements is Nitschke’s subcomponent self-assembly, which allows construction of the sophisticated architectures from simple building blocks. However, the reports only focused on small molecules. For natural protein, metal ions coordination occurs by interchain or intrachain of polypeptide, and subsequently builds high-order structure and realizes life functions. Thus what deserves more investigations is how metal ions to regulate and control behavior of subcomponent self-assembly based on synthetic polymer. Metal ions with different coordination geometries will be great importance on subcomponent self-assembly process of the chain-like polymers.Three metal ions are used in this thesis as model and the subcomponent self-assembly of synthetic polymer regulated by metal ions coordination are investigated. We design a copolymer with two blocks, one is permanent hydrophilic, the other contains the primary amine groups. The latter can produce imidization reaction, promote the formation of hydrophobic block and eventually affect the coordination of metal ions and self-assembly. A series of studies will be conducted to reveal the effect of coordination on regulation and the control of subcomponent self-assembly of synthetic polymer. Firstly, an NH2-based poly(N-2-hydroxypropyl methacrylamide)-block-poly(6-amino-hexylmethacrylamide hydrochloride)(PHPMA-b-PAHMA) was synthesized via aqueous RAFT polymerization under visible light irradiation at25oC. And then the NH2-functional hydrophilic block copolymer, Ni(II), Cu(II), Zn(II) ions and a salicyladehyde derivative were selected as subcomponents.2-Hydroxy-4-methoxybenzaldehyde (HMBA) was used as a subcomponent, which can conjugate to polymer chains via imine formation thus converting into the bidentate ligands for the metal ions. Imine formation and assembly were studied using1H NMR, DLS, GPC and UV-vis spectroscopy. The dynamic imine formation, phase transition, aggregation and Mt(II)-dependent inter/intrachain coordination were studied using1H NMR, UV-vis spectroscopy, DLS and GPC.The results demonstrate that the reaction of primary amine groups with HMBA drive the self-assembly with typical characteristics of self-replication. The results also present that the different coordination stability constants and geometries of these metal ions led to remarkable difference in subcomponent self-assembly. The order of autocatalytic effect of metal ions is as follow: Cu(II)> Zn(II)>Ni(II). Ni(II) ions have the ability to induce the inter-chain coordination, rapid phase transition to macro-phase separation but with the lowest efficiency of autocatalysis. However, Cu(II) ions could induce intra-chain collapse, produce well-defined hybrid nanoparticles and have remarkable autocatalysis performance, but with delayed phase transition. The behaviour of Zn(II) ions was in between Ni(II) and Cu(II) ions. Metal ion concentration effectively regulates phase transition critical time of subcomponent self-assembly based on polymer. A small amount of Ni(II) ions tend to coordination between polymer chains with the shortest critical time of phase transition; Cu(II) associates with the slowest phase transition critical time because the metal ions tend to be intra-chain coordination; The critical time of phase ransition induced by Zn(II) ions are in between. There are significant differences in selectivity of the intra/inter chain coordination. Ni(II) is easy to induce inter-chain coordination; Cu (II) tend to be intra-chain coordination; The behaviour of Zn(II) ions was in between. This striking difference demonstrated that the dynamic/geometrical coordination diversity of the abundant first row transition metal ions effectively controlled the subcomponent self-assembly of the polymer, and thus the hierarchical nanostructures of the dative metal-polymer hybrid functional materials. Therefore, results in this thesis expand and enrich the subcomponent self-assembly of the polymer. This is a new method to construct and regulate metal-polymer hybrid functional materials with hierachical nanostructures.