Preparation and Characterization of a pH-Responsive Nanogel Based on a Photo-Cross-Linked Micelle Formed From Block Copolymers with Controlled Structure
Department of Materials Science and Chemistry, Graduate School of Engineering, University of Hyogo, 2167 Shosha, Himeji, Hyogo 671-2280, Japan. Langmuir
(Impact Factor: 4.46).
03/2009; 25(9):5258-65. DOI: 10.1021/la803878s
Poly(ethylene glycol)-b-poly(2-(diethylamino)ethyl methacrylate-co-2-cinnamoyloxyethyl acrylate) (PEG-b-P(DEAEMA/CEA)) was prepared by reversible addition-fragmentation chain transfer (RAFT)-controlled radical polymerization. As solution pH is increased from an acidic pH, the hydrodynamic radius (R(h)) increases abruptly near pH 7, indicative of the micelle formation at pH > 7. The micelle formation at pH > 7 was supported by (1)H NMR and light scattering data. Upon irradiation of light, polymer chains in the core of the polymer micelle are cross-linked as a result of the photodimerization of the cinnamoyl groups, yielding a nanogel. The nanogel was characterized by gel-permeation chromatography (GPC), light scattering, small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and fluorescence techniques. The nanogel displayed an ability to solubilize N-phenyl-1-naphthylamine (PNA) and 1-pyrenemethanol (hydrophobic guest molecules) into the hydrophobic core at pH > 7. It was confirmed with PNA that the solubilization of a guest molecule occurred at polymer concentrations (C(p)) lower than the critical micelle concentration (cmc) for PEG-b-P(DEAEMA/CEA) because the nanogel retains its micellar structure at C(p) < cmc. 1-Pyrenemethanol is strongly captured by the nanogel at pH 10, whereas it is easily released from the nanogel when pH is reduced to 3. This indicates that the hydrophobicity of the core of the nanogel can be modulated by a change in the degree of protonation of the DEAEMA units in the core, and thus the capture of a guest molecule and its release can be controlled by a change in solution pH.
Available from: San H. Thang
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ABSTRACT: This paper provides a second update to the review of reversible deactivation radical polymerization achieved with thiocarbonylthio compounds (ZC(=S)SR) by a mechanism of reversible additionfragmentation chain transfer (RAFT) that was published in June 2005 (Aust. J. Chem. 2005, 58, 379410). The first update was published in November 2006 (Aust. J. Chem. 2006, 59, 669692). This review cites over 500 papers that appeared during the period mid-2006 to mid-2009 covering various aspects of RAFT polymerization ranging from reagent synthesis and properties, kinetics and mechanism of polymerization, novel polymer syntheses and a diverse range of applications. Significant developments have occurred, particularly in the areas of novel RAFT agents, techniques for end-group removal and transformation, the production of micro/nanoparticles and modified surfaces, and biopolymer conjugates both for therapeutic and diagnostic applications.
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ABSTRACT: In this review we provide an analysis of recent literature reports on the synthesis and applications of stimuli-responsive polymeric and hybrid nanostructured particles in a range of sizes from nanometers to a few micrometers: nano- and microgels, core–shell structures, polymerosomes, block-copolymer micelles, and more complex architectures. The review consists of two major parts: synthesis and applications of nanoparticles in colloidal dispersions, thin films, delivery devices and sensors. We also broadly discuss potential directions for further developments of this research area.
Available from: Marco Diociaiuti
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ABSTRACT: Thermosensitive and pegylated polyion complex (PIC) micelles were formed by coassembly of oppositely and permanently charged poly(sodium 2-acrylamido-2-methylpropanesulfonate)-block-poly(N-isopropylacrylamide), PAMPS-b-PNIPAAM, and poly[(3-acrylamidopropyl)-trimethylammonium chloride]-block-poly(ethylene oxide), PAMPTMA-b-PEO, block copolymers under stoichiometric charge neutralization conditions and polyelectrolyte chain length matching. PAMPTMA-b-PEO block copolymers with different block lengths were prepared for the first time by atom transfer radical polymerization (ATRP) using a PEO macroinitiator. PIC micelles were characterized by 1H NMR, static light scattering (SLS), dynamic light scattering (DLS), and transmission electron microscopy (TEM). At room temperature, spherical almost monodisperse PIC micelles, consisting of a mixed PAMPTMA/PAMPS coacervate core and a mixed PEO/PNIPAAM shell, were formed, with size of about 80−110 nm. The PIC micelles completely dissociated to unimers by increasing NaCl concentration above 0.4−0.6 M. PNIPAAM segments in the shell gave rise to a temperature induced transition at 34−37 °C forming a hydrophobic shell around the coacervate core in a core−shell-corona type PIC micelle, with a PEO corona which stabilized the nanoparticles in aqueous solution. A fully interconnected and continuous collapsed PNIPAAM shell was formed, with PEO chains forming channels across the PNIPAAM membrane. The association properties of the PIC micelles were influenced by the length of the block segments. Longer polyelectrolyte chains gave rise to bigger micelles, more stable with respect to the ionic strength. PNIPAAM chain length allowed to modulate the temperature of the thermal transition. Long PEO chains (114 repeating units) were necessary to effectively stabilize PIC micelles both below and above LCST of PNIPAAM. Micelle parameters (core radius, Rc, shell radius, Rs, thickness and volume, ΔRPNIPAAM and VPNIPAAM, of the collapsed PNIPAAM shell and surface density, Φ, of shell and corona chains before and after the thermal transition) were determined and discussed in terms of block copolymer structure. Precipitation was observed by addition of salt at temperature above LCST because of the release of PEO-b-PAMPTMA chains. A model was proposed explaining the formation and the response to temperature and ionic strength of the PIC micelles. This is the first example of pegylated and thermosensitive PIC micelles having a coacervate core formed by two strong polyelectrolyte blocks with no pH dependence.
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