Stimuli‐responsive micelles of amphiphilic AMPS‐b‐AAL copolymers in layer‐by‐layer films

Abstract

Aqueous reversible addition‐fragmentation chain transfer polymerization was used to synthesize poly(N‐[3‐(dimethylamino)propyl]acrylamide) (PDMAPA) cationic homopolymers and micelle‐forming, pH‐responsive, amphiphilic diblock copolymers of poly(sodium 2‐acrylamido‐2‐methyl‐1‐propanesulfonate‐block‐N‐acryloyl‐L‐alanine) (P(AMPS‐b‐AAL)). At low pH, the AAL blocks are protonated rendering them hydrophobic, whereas the AMPS blocks remain anionically charged because of the pendant sulfonate groups. Self‐assembly results in core–shell micelles consisting of hydrophobic cores of AAL and negatively charged shells of AMPS. Using solutions of these micelles with anionic coronas and of the cationic homopolymer PDMAPA, layer‐by‐layer (LbL) films were assembled at low pH, maintaining the micelle structures. Several block copolymers with varying AMPS and AAL block lengths were synthesized and used in the formation of LbL films. The thickness and morphology of the films were examined using ellipsometry and atomic force microscopy. The stimuli‐responsive behavior can be triggered by submersion of the film in water at neutral pH to disrupt the micelles. This behavior was monitored by observing the decrease in film thickness and alteration of the film morphology. The micelles were also loaded with a model hydrophobic compound, pyrene, and incorporated into LbL films. The release of pyrene from the films was monitored by fluorescence spectroscopy at varying pH values (1, 3, 5, and 7). As the pH of the solution increases, the rate of release increases. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Dispersion RAFT polymerization of 4‐vinylpyridine in toluene mediated with the macro‐RAFT agent of polystyrene dithiobenzoate: Effect of the macro‐RAFT agent chain length and growth of the block copolymer nano‐objects

“…5(D)] are prepared at the four cases of polymerization‐induced self‐assembly, respectively. Clearly, this conclusion is very similar with those reported in the self‐assembly of block copolymer in the block‐selective solvent 39, 43, 62, 63. That is, reducing the hydrophilic block typically either poly(acrylic acid) or poly(ethylene oxide) while fixing the hydrophobic polystyrene block leads to the morphological transition from micelles to rods to vesicles to LCMs.…”

“…Second, the size of the block copolymer particles generally increases with the insoluble P4VP block extension during the dispersion RAFT polymerization, whereas the particle morphology transition occurs only when a macro‐RAFT agent with a very short chain length (PS 9 ‐CTA) is employed. In the block copolymer self‐assembly in the block‐selective solvent, it is generally found that increasing the hydrophobic block leads to morphological transition from spheres to rod‐like or vesicular structure,39, 43, 62, 63 which is somewhat different from the present polymerization‐induced self‐assembly.…”

Amino‐Acid‐Based Block Copolymers by RAFT Polymerization

“…Subsequently, the anionic poly(sodium 2‐acrylamido‐2‐methyl‐1‐propanesulfonate) micelle shells were ionically cross‐linked with a RAFT‐synthesized cationic homopolymer of either poly( N ‐[3‐(dimethylamino)propyl]acrylamide) or poly( N,N ‐dimethylaminoethyl methacrylate) (Scheme b) 125. McCormick and co‐workers126 also used the pH‐responsive micelles of poly(sodium 2‐acrylamido‐2‐methyl‐1‐propanesulfonate)‐ b ‐poly(A‐( L )Ala‐OH) in layer‐by‐layer films. Self‐assembly resulted in the formation of core shell micelles consisting of hydrophobic cores of poly(A‐( L )Ala‐OH) and negatively charged shells of poly(sodium 2‐acrylamido‐2‐methyl‐ 1‐propanesulfonate).…”

Living Radical Polymerization by the RAFT Process – A Third Update

“…15. [203,587] 357 [357] 358 [582] 356 [239] 353 [222] 352 [222] 354 [236] 355 [427] 359 [170] 360 [533] 368 [292] 366 [486] 367 [423] 369 [58] 370 [383] 371 [245,246] 372 [464] AMPS Ϫ ϩ ϩ Ϫ ϩ ϩ Ϫ 363 [245,246] 361 [328] 362 [328] 364 [289] 365 [383] Ϫ Fig. 8.…”