Block Copolymers And Nanogels Based On PAA And PNIPAM:Synthesis And Aggregation

In this thesis, we synthesized a series of copolymers and-microgels based on polyelectrolytes, and studied their properties in solution dispersion. Specifically, we synthesised poly(acrylic acid)-b-poly(N-isopropylacrylamide) diblock copolymer and studied their association behaviors, especially in the presence of Ca2+cations; prepared poly(acrylic-acid-co-N-isopropylacrylamide) core-shell microgels and investigated their temperature and pH sensitivities; and synthesized (PtBA-b-PS-b-PMA)n and (PtBA-b-PS-b-PEA)n multi-block copolymers by using a combination of atom transfer radical polymerization and Click reaction. Main results are as follows:(1) Poly(t-butyl acrylate)-b-poly(N-isopropylacrylamide)(PtBA-b-PNIPAM) was first synthesized by sequential reversible addition fragmentation chain transfer (RAFT) polymerization of tert-butyl acrylate and N-isopropylacrylamide. Its hydrolysis led to amphiphilic poly(acrylic acid)-b-poly(N-isopropylacrylamide)(PAA-b-PNIPAM) that can form micelles in aqueous solutions when the solution temperature is higher than～37℃. In the presence of Ca2+, the complexation between one Ca2+and two COO-groups on different PAA blocks can induce the chain association. Using a combination of static and dynamic laser light scattering, we studied the effect of Ca2+and temperature as well as the sequence of adding Ca2+ions and heating the solution on such association. We found that1) the association is controllable and reversible;2) a distinct hysteresis is observed between the heating and cooling processes;3) the time evolution of the average aggregation number (Nagg) and the average hydrodynamic radius (<Rh>) of the aggregates can be expressed by a single exponential equation;4) the aggregates have a fractal dimension of1.5-1.9, suggesting a diffusion-limited cluster-cluster aggregation;5) adding Ca2+before heating results in the aggregates with a more open and looser structure; and6) adding Cu2+before heating leads to less chain association and smaller aggregates, which has some implication in the stabilization of proteins.(2) A series of poly(potassium acrylate) macromolecular chain transfer agents with different lengths were synthesized by RAFT polymerization and characterized by1H NMR and Gel Permeation Chromatography. These poly (potassium acrylate) macromolecular chain transfer agents were used to prepare multi-responsive core-shell microgels by using dispersion polymerization of N-Isopropylacrylamide in water with poly(potassium acrylate) macro-RAFT agents as electrosteric stabilizer. We found that the average size of the microgels decreases with the amount of the poly(potassium acrylate) macro-RAFT agents, indicating that the average surface area occupied per polyelectrolyte group is a key parameter in stabilizing the microgels. The size change and the zeta potentials of the nanogels in aqueous solutions were studied by dynamic light scattering (DLS) and zetasizer analyzer, respectively.(3) a-trimethylsilyl-alkyne-ωo-bromine-terminated triblock copolymers of PtBA-b-PS-b-PMA and PtBA-b-PS-b-PEA were made by sequential Atom Transfer Radical Polymerization (ATRP). TMS-protecting groups were removed by tetra-butyl ammonium fluoride. Azidation of the terminal bromine was followed in DMF with sodium azide so that a-alkyne-ω-azido-terminated PtBA-b-PS-b-PMA or PtBA-b-PS-b-PEA precursors were obtained for preparing (PtBA-b-PS-b-PMA)n and (PtBA-b-PS-b-PEA)n multi-block copolymers via the Cu-catalyzed Click coupling.