Abstract
Polymerization-induced self-assembly (PISA) is used for the highly convenient and efficient preparation of ampholytic diblock copolymer nanoparticles directly in acidic aqueous solution. Cationic nanoparticles comprising a protonated polyamine stabilizer block and a hydrophobic polyacid core-forming block are formed at pH 2. Micelle inversion occurs at pH 10 to produce anionic nanoparticles with an ionized polyacid stabilizer block and a hydrophobic polyamine core-forming block. Macroscopic precipitation occurs at around pH 6–7, which lies close to the isoelectric point of this ampholytic diblock copolymer. Incorporation of fluorescein and rhodamine dye labels into the acid and amine blocks, respectively, leads to dual-color bifluorescent self-reporting pH-responsive nanoparticles.
Highlights
It is well-known that amphiphilic AB diblock copolymers selfassemble in aqueous solution to form spherical micelles, wormlike micelles, or vesicles.[1−4] Stimulus-responsive diblock copolymers have been well-studied: amphiphilic character can be triggered by a change in pH5−9 or temperature,[8−13] which leads to in situ self-assembly
Amphiphilic diblock copolymer nanoparticles can be prepared directly in water via reversible addition−fragmentation chain transfer (RAFT) aqueous dispersion polymerization[50,52,58−60] or RAFT aqueous emulsion polymerization.[52,61−63] RAFTmediated Polymerization-induced self-assembly (PISA) has been used to prepare thermosensitive diblock copolymer nano-objects.[64−66] For poly(glycerol monomethacrylate)−poly(2-hydroxypropyl methacrylate) (PGMA− PHPMA) block copolymer worms synthesized by RAFT aqueous dispersion polymerization, a worm-to-sphere transition can be induced by cooling from 20−25 °C to 5−10 °C.67,68
The same morphological transition has been observed for poly(lauryl methacrylate)−poly(benzyl methacrylate) (PLMA−PBzMA) worms prepared by RAFT dispersion polymerization in n-dodecane, but in this case heating to 90 °C was required to induce the change in morphology.[69]
Summary
It is well-known that amphiphilic AB diblock copolymers selfassemble in aqueous solution to form spherical micelles, wormlike micelles, or vesicles.[1−4] Stimulus-responsive diblock copolymers have been well-studied: amphiphilic character can be triggered by a change in pH5−9 or temperature,[8−13] which leads to in situ self-assembly. A typical protocol for the synthesis of PDEA88−P(MAA0.7-st-BzMA0.3)[100] diblock copolymer was as follows: PDEA88 macro-CTA (0.1200 g), MAA monomer (0.0505 g, 0.5866 mmol), BzMA (0.0443 g, 0.2514 mmol), ACVA (0.5 mg, 1.676 μmol; CTA/initiator molar ratio = 5.0), and water (1.2198 g, 15% w/w) were weighed into a 25 mL round-bottom flask, and the pH of the reaction solution was adjusted to pH 2.5. P(DEA-stat-RhBMA)[85] macro-CTA (0.0800 g), MAA (0.0697 g, 0.8094 mmol), BzMA (0.0611 g, 0.3469 mol), fluorescein O-methacrylate (0.9 mg, 2.3124 μmol), ACVA (0.3 mg, 1.156 μmol; CTA/initiator molar ratio = 5.0), and water (1.1962 g, 15% w/w) were weighed into a 25 mL round-bottom flask, and the pH of the reaction solution was adjusted to pH 2.5. Data were reduced using the Foxtrot software package developed by SOLEIL and further analyzed using Irena SAS macros[78] for Igor Pro
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