Synthesis Of Nanostructured Polyion Complexes Via One-component Polymerization-induced Electrostatic Self-assembly

Nanostructured polyion complexes(PICs)have a wide range of potential applications in proteins or nucleic acids delivery,nanoreactors or magnetic resonance imaging vehicles on account of their unique semipermeability,size/shape tunability and stimuli-responsive properties.Traditionally,PICs are prepared by mixing polyion-neutral block copolymer and oppositely charged polyelectrolyte,or a pair of polyion-neutral block copolymers of opposite charge,to co-assemble into AB+C mode two-component PICs.In contrast,one-component low-dimensional PICs were scarcely reported.Only spheres or precipitates of ampholytic ABC triblock copolymers available due to the tremendous synthesis and assembly challenge.Polymerization-induced self-assembly(PISA)is versatile for synthesis of block copolymer nanoparticles at high solids content.In particular,reversible addition-fragmentation chain transfer(RAFT)mediated aqueous dispersion polymerization has succeeded in preparation of nanowires,lamellae,vesicles,and nanotubes.It is also effective for preparation of ABC triblock copolymer nanoparticles.However,there are only a few monomers suitable for aqueous PISA.To overcome the limitation,we used polyion complexation(PIC)as PISA's driving force.It was validated by the preparaion of spheres,colloidal chains,networks via visible light-mediated aqueous RAFT polymerization of ionic monomer with the addition of a polyion of opposite charge,namely,polymerization-induced electrostatic self-assembly(PIESA).Basically,the ionic monomers are applicable to PIESA.In this thesis,we develop a PIESA approach for efficient preparation of one-component low-dimensional PICs.Visible light activated room temperature aqueous RAFT polymerization(Photo-RAFT)has been used to prepared poly(2-hydroxypropylmethacrylamide),PHPMA macro-CTA with mean degree of polymerization(DP)of 56 and polydispersity index(PDI)of 1.12.Iterative polymerization of 2-acrylamido-2-methylpropanesulfonic acid(AMPS)monomer yield a well-defined multiblock copolymer,suggesting the controlled and efficient character of this iterative technique in the preparation of multiblock co-polyelectrolyte.The one-component polymerization-induced electrostatic self-assembly was validated by the preparation of PHPMA56-PAMPSn-PHis AMn PICs(His AM: histamine acrylamide hydrochloride,n: DP of charged block).1H NMR signals of the charged block disappearred in D2 O due to the polyion complexation.However,these signals appearred in 4.5 M Na Cl,indicating the disassembly of as-obtained PICs.PICs underwent a DP-dependent sphere-film-vesicle phase transition,different from sphere-to-worm-to-vesicle transition in the traditional PISA.Furthermore,we studied effects of charge repulsion and solution polarity on PIESA.The results demonstrated that slight excess of His AM units is sufficient to transform flower-like vesicular aggregates into dispersed surface-charged vesicles.Extremely long and uniform diameter nanowires of PICs at n = 40 were prepared in a mixture over wide methanol/water ratio range.Tubular vesicles and “poly-vesicles” were prepared as targeting to n = 85 upon increase in methanolto-water weight ratio.Consequently,a series of unprecedented low-dimensional PICs,such as nanowires,ultrathin films,large ultrathin vesicles,tubular vesicles,and poly-vesicles have been achieved.This PIESA method offers a general platform for scalable and reproducible preparation of one-component low-dimensional PICs under eco-friendly conditions.