Polyion Complexation For Polymerization-induced Self-Assembly

The most of currently-reported aqueous polymerization-induced self-assembly(PISA) was based on hydrophobic interactions, and suitable monomers were limited. Actually, besides hydrophobic interactions, electrostatic interactions, hydrogen bonding and metalligand complexation can also serve as driving forces for the self-assembly of block copolymers. However, PISA based on other interactions is sparse. For instance, dehydrated complexes can be achieved by electrostatic interactions between a pair of oppositelycharged polymer in water, which may provide new opportunities for aqueous PISA of ionic monomers. In this thesis, we explored the use of polyion complexation(PIC) for polymerization-induced self-assembly(PIC-PISA) in water, using aqueous RAFT under visible light irradiation at room temperature as previously developed by our group. As such, suitable monomers for PISA were expanded, PISA-context was enriched and a new strategy for one-step synthesis of PIC-assembled materials was exploited.Poly(sodium 2-acrylamido-2-methylpropanesulfonate)(PAMPS91; 1H NMR: DP = 91; GPC: PDI = 1.19) was used as an external PIC-template to drive phase transition and thus aqueous PISA. This anionic polymer was synthesized by aqueous RAFT under visible light irradiation at 25 oC. The trithiocarbonate chain-ends were converted into thiols by aminolysis in the presence of ethylenediamine, and addition with 2-hydroxyethylacrylate(HEA) to deactivate the as-generated thiol chain-ends. UV-vis spectroscopy, 1H NMR and GPC results demonstrated that intactness and low MW dispersity of PAMPS91.Furthermore, the features of PIC-PISA were studied by aqueous dispersion RAFT of NH3+-based 2-aminoethylacrylamide hydrochloride(AEAM) using poly2-hydroxypropylmethacrylamide(PHPMA) nonionic macromolecular chain transfer agent(macro-CTA) in the presence of PAMPS template in water under visible light irradiation at 25°C. Excess of AEAM monomer to PAMPS91 units([AEAM]0/[AMPS]0 = 2.18) was used to examine the impact of electrostatic interactions, as evolved from cationic starving to oversaturated ratio, under light-off suspending reaction at predetermined time points. The results demonstrated the soothed chain-growth rate after the isoelectric point(IEP), owing to the PIC association of growing chains with the template, which immobilized the growing-chain radicals. The dehydration and light scattering intensity reached maximal values at the specific IEP, as judged by aqueous electrophoresis measurements. The chain-growth led to the reaction solution changed from free-flowing liquid to viscous liquid and free-standing physical gel, back to viscous liquid and ultimately free-flowing liquid, in which zeta potential parameter, i.e. surface charge, evolved from negative to neutral and positive values. Accordingly, the superstructures evolved from PIC-micelles to networks and then back to micelles, due to gradual inter/intra-particle variation of electrostatic interactions. The disruption of supracolloidal networks under dilution and mechanistic stirring confirmed that the electrostatic interactions acted as the predominant driving force for PISA. All these confirmed that this PIC-PISA is entirely different from those as driven by the hydrophobic interactions. As a control experiment, spherical micelles(Dh=41 nm), rather than aforementioned supracolloidal networks were observed in stoichiometric mixture of PAMPS91 and PHPMA175-bPAEAM93. These results confirmed that the as-generated supracolloidal networks in PICPISA attributed to the interparticle PIC around IEP.Therefore, the as-achieved unique PIC-PISA has largely expanded the scope of PISA monomers and also PISA family members. This PIC-PISA is directed and tunable by PIC association caused by chain growth, showing superstructures underwent morphological evolution from micelles to networks and then back to micelles, which is different from those in the PISA driven by hydrophobic interactions. Therefore, the PIC-PISA strategy underlines amazing prospects in large-scale one-pot production of the PIC-assembled materials at high solids in aqueous solution.