Aqueous RAFT Synthesis of Micelle-Forming Amphiphilic Block Copolymers Containing N -Acryloylvaline. Dual Mode, Temperature/pH Responsiveness, and “Locking” of Micelle Structure through Interpolyelectrolyte Complexation
2007; American Chemical Society; Volume: 40; Issue: 18 Linguagem: Inglês
10.1021/ma070921v
ISSN1520-5835
AutoresBradley S. Lokitz, Adam W. York, Jonathan E. Stempka, Neil D. Treat, Yuting Li, William L. Jarrett, Charles L. McCormick,
Tópico(s)Hydrogels: synthesis, properties, applications
ResumoTemperature- and pH-responsive, micelle-forming, amphiphilic block copolymers were prepared from N,N-dimethylacrylamide (DMA), N-isopropylacrylamide (NIPAM), and N-acryloylvaline (AVAL) utilizing aqueous reversible addition−fragmentation chain transfer (RAFT) polymerization. A series of block copolymers were synthesized by employing DMA as a macro-chain transfer agent to mediate the statistical copolymerization of NIPAM with AVAL. Structural organization and solution behavior were investigated utilizing dynamic light scattering, two-dimensional NMR spectroscopy, and transmission electron microscopy. It has been demonstrated that the critical micellization temperature for the block polymers can be tuned to range from ≈10 to 36 °C by adjusting the solution pH. Micelles with apparent hydrodynamic diameters from 45 to 86 nm are formed between pH 2 and 5. Above pH 5, a sufficient number of the AVAL units are deprotonated which prevents micellization. The extent of pH and temperature changes on the apparent hydrodynamic diameters have been illustrated via 3-D plots. Significantly, micelles assembled within a specified range of pH and temperature can be "locked" by interpolyelectrolyte complexation of anionic AVAL segments with those of a cationic polymer, in this case a RAFT-generated poly([ar-vinylbenzyl]trimethylammonium chloride) (PVBTAC). When the temperature is lowered to room temperature, the polymeric micelles remain "locked" in their multimeric structures which remain dispersed in water. Addition of 0.3 M NaCl to the aqueous solution results in dissociation of the complexes into the respective water-soluble components.
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