Sequence-Controlled Polymerization-Induced Self-Assembly

Polymerization-induced self-assembly(PISA)combines controlled/"living" radical polymerization and self-assembly of block copolymers able to prepare nanomaterials in high solids.Nanospheres,worms,nanowires,nanotubes,vesicles and other nanomaterials have been successfully prepared by the aqueous dispersion polymerization based PISA.However,there are limitations in the PISA process,and only a few monomers are suitable for aqueous dispersion polymerization-induced self-assembly.Spontaneous polyion complexation(PIC)occurs when mixing two polyelectrolytes of opposite charge in aqueous solution,leading to self-assembly into polyelectrolyte or polyion complexes(PICs).PIC is driven by increased free energy due to release of counter ions,which increases the entropy and drives the polyion complex to form assemblies,while electrostatic enthalpy only perturbs the water molecule hydrogen bonds.PICs can be used for drug carriers,gene carriers,nanoreactors,and stimulus-responsive materials.However,PICs were conventionally prepared by vortexing at low concentrations,and the scalable preparation was impossible.Previously,our group developed polymerization-induced electrostatic self-assembly(PIESA),in which the phase separation was driven by PIC of growing chains to added polyelectrolyte of opposite charge during visible light initiated RAFT aqueous polymerization of a charged monomer.PIESA method is applicable to all water-soluble ionic monomers,thereby breaking the monomeric limitations of the RAFT aqueous dispersion polymerization.More importantly,unlike the as-reported electrostatic self-assembly in the dilution,PIESA can be fulfilled in concentrated aqueous solutions,and capable of predictable scalable preparation of low-dimensional PIC nanomaterials.It is well known that sequence control is the basic molecular structural feature of natural biomacromolecules(such as proteins,DNA and RNA),which determines their living functions.This thesis aims to develop the sequene-controlled polymerization-induced self-assembly on the base of fundamentally understanding of zwitterionic copolymerization behavior of a pair of ionic monomers of opposite charge.First,a poly(ethylene glycol)macromolecular chain transfer agent(PEG-TTC macro-CTA),containing a trithiocarbonate(TTC)chain-end,with a degree of polymerization of 45 was prepared.The results demonstrate high chain-extension efficiency of this macro-CTA for RAFT polymerization.The thorough visible light initiated RAFT block copolymerization of ionic monomers of opposite charge resulted in DP-dependent PEGylated A45BxCx PICs(A:PEG,B:PAMPS,C:PAEAM,x:DP).Consequently,PEG-based ABC-mode PIESA was established.1H NMR results demonstrate>99%conversion and the successful complexation PIC s undergoes a phase transition from spheres to micrometer-sized films and vesicles upon increase in x,and the vesicle membrane size and thickness also changed.The kinetic results demonstrate spontaneous alternating zwitterionic copolymerization of ionic monomers of opposite charge.As such,the alternating and gradient zwitterionic copolymer sequences can be achieved by adjusting the stoichiometric ratios.By means of the on-off switchable visible light initiated RAFT aqueous dispersion polymerization-induced electrostatic self-assembly namely AB(BC)-mode PIESA,we established sequence-controlled polymerization-induced self-assembly.Using A45B55C55 as a reference,under conditions that chemical composition and DP of polyelectrolyte complex remain unchanged,first AMPS anionic monomer conversion was controlled by irradiation time,and the cationic monomer was added in the dark and the monomers copolymerized completely.A45Bx(B55-xC55)with a block-gradient sequence was prepared at different first AMPS conversions.PICs evolved from multilayered giant vesicles into monolayered giant vesicles,followed by the decrease in membrane thickness.Similarly,sequence control of A45Bx(B100-xC100)PICs are also achieved,in which PICs evolved from irregular aggregates to monolayer nanofilms,the film thickness decreased with increased x.These results demonstrate that the sequence-controlled PISA enables the control of not only morphology but also size and thickness of low-dimensional PIC nanomaterialsIn short,the thorough block copolymerization leads to ABC-mode PIESA,by which the PEGylated PIC spheres,lamellae and vesicles were synthesized.The ionic monomers of opposite charge shows spontaneous alternating zwitterionic copolymerization.As such,the alternating and gradient zwitterionic copolymer sequence can be achieved by adjusting the stoichiometric ratio during zwitterionic copolymerization.Hence,we developed a sequence controlled PISA method using photo-switched AB(BC)-mode PIES A.This method provides a simple and efficient platform for controlled synthesis of block-gradient PIC nanoparticles Sequence controlled PISA can control not only morphology but also the size and thickness without changing overall chemical composition and DP.Moreover,the PIESA proceeded under eco-friendly visible light aqueous conditions.This strategy provides a new platform for the predictable scalable preparation of nonspherical PIC nanomaterials.