Coordination-induced Micellization Behaviors Of NH₂-based Hydrophilic Block Copolymer

Dynamic combinatorial chemistry is a type of combinatorial chemistry underthermodynamic control. Difference between dynamic combinatorial chemistry andtraditional combinatorial chemistry is that the reaction in dynamic combinatorialchemistry that links the building blocks together is reversible. There is a continuousexchange of building blocks between the different members of dynamic combinatoriallibrary (DCL). The composition of the library is governed by thermodynamics ratherthan kinetics. Nowadays, polymer self-assembly of dynamic combinatorial chemistryis an emerging field of polymer chemistry. Our previous studies demonstrate thatusing RAFT polymerization can readily synthesize a variety of thermo-responsive andmedium-tunable polymers that may coordinate with metal ions. In this thesis, wesynthesized a water-soluble N-(2-hydroxypropyl)-2-methylacrylamide (HPMA), a2-aminoethyl methacrylamide (AEMA) monomer, and a RAFT chain transfer agent(4-cyanovaleric acid)trithioacetate (CESA). RAFT polymerization of HPMA affordeda water-soluble macromolecular chain transfer agent (PHPMA macro-CTA). Awell-defined block copolymer was achieved by chain extension of PHPMA usingAEMA monomer. The chemical structure of the as-synthesized block copolymer wascharacterized by1H NMR and GPC. Thereafter, the dynamic imine formation in thewater-soluble polymers (PHPMA-b-PAEMA) with an aldehyde compound and thecorresponding complexes NiII(HMBA)2were intensively studied. The reaction-triggered phase transition and aggregation behavior of the polymer chains wereinvestigated. The results demonstrate that both HMBA and NiII(HMBA)2rapidly reactwith the primary amine groups of PAEMA blocks, leading to the collapse of PAEMAchains, and thus led to the formation of hydrophobic domains. Addition of smallamount of NiII(HMBA)2remarkably shortens the critical time to start phase transition,effectively prevent formation of large aggregates, and gives rise to rapid micellization.Moreover, the effect of coordination-directed collapse was amplified on adding excessamount of NiII(HMBA)2. The critical time to start phase transition on coordinationwith PHPMA-b-PAEMA is longer than that with PHPMA-b-PAHMA as previouslyreported by our group. After adding a good solvent DMF, the micelles are dissociated.Although the system exists inter-chain cross-linking between polymer chains, but nocross-linking between these aggregates. The results demonstrate that coordination- induced micellization of hydrophilic NH2-based block copolymer can be finely tunedby the chemical structure of polymer units.