Self-assembled nanostructures: preparation, characterization, thermal, optical and morphological characteristics of amphiphilic diblock copolymers based on poly(2-hydroxyethyl methacrylate-block-N-phenylmaleimide) (original) (raw)
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Journal of Polymer Science Part A: Polymer Chemistry, 2008
A series of optically active amphiphilic block copolymers were synthesized by using potassium alkoxide of poly(ethylene glycol) monomethyl ether (MeOPEGO À K þ ) to initiate the anionic polymerization of N-{o-(4-phenyl-4,5-dihydro-1,3-oxazol-2-yl)phenyl}maleimide [(R)-PhOPMI]. The PEG-macroinitiators generated in situ in the reaction between MeOPEGOH and potassium naphthylide in tetrahydrofuran. The synthetic procedure may provide the PEG-b-PPhOPMI copolymers with well-defined structure, as evidenced by gel permeation chromatography, 1 H NMR, FTIR, and elemental analysis. In particular, the preparation of block copolymers having a laevorotation or dextrorotation activity was accomplished by changing the feed composition. The micellization was examined for the amphiphilic block copolymers in aqueous milieu by fluorescence spectroscopy, dynamic light scattering, and circular dichroism. The results indicate that the copolymers could form regular spherical micelles with core-shell structure when the hydrophilic component was long enough; in contrast, the copolymers containing shorter PEG segments formed aggregates in large dimension due to the considerable interaction between hydrophobic PPhOPMI components. Also, it was found that the aggregated structure of the polymeric micelles is strongly dependent on the medium nature and the polymer concentration.
Journal of the American Chemical Society, 2000
An efficient approach to the syntheses of amphiphilic rod-coil diblock and coil-rod-coil triblock copolymers was developed. Each diblock copolymer consists of a perfectly monodispersed oligo(phenylene vinylene) covalently bonded to a poly(ethylene glycol) block with a very low polydispersity (<1.05). The structure and basic physical properties of these copolymers were characterized by various spectroscopic techniques such as NMR, MALDI-TOF, GPC, DSC, UV/vis, and the fluorescence study. These diblock copolymers were shown to possess remarkable self-assembling abilities, and long cylindrical micelles (>1 µm) were formed. TEM, SANS, and AFM studies showed that the core of the micelles has a diameter of ∼8-10 nm and was composed of an OPV block. TEM and SANS studies revealed that these OPV-PEG micelles have a cylindrical OPV core surrounded by a PEG corona. Cryo-TEM and SANS studies indicate that fibers were formed even in very dilute THF/H 2 O solutions. Since the conjugated OPV blocks exhibit liquid crystallinity and electric and optical properties, these micelles are interesting for studying the electroactive effect in a nanometer scale.
Polymers
Self-assembly of amphiphilic block copolymers display a multiplicity of nanoscale periodic patterns proposed as a dominant tool for the ‘bottom-up’ fabrication of nanomaterials with different levels of ordering. The present review article focuses on the recent updates to the self-association of amphiphilic block copolymers in aqueous media into varied core-shell morphologies. We briefly describe the block copolymers, their types, microdomain formation in bulk and micellization in selective solvents. We also discuss the characteristic features of block copolymers nanoaggregates viz., polymer micelles (PMs) and polymersomes. Amphiphilic block copolymers (with a variety of hydrophobic blocks and hydrophilic blocks; often polyethylene oxide) self-assemble in water to micelles/niosomes similar to conventional nonionic surfactants with high drug loading capacity. Double hydrophilic block copolymers (DHBCs) made of neutral block-neutral block or neutral block-charged block can transform on...
Collection of Czechoslovak Chemical Communications, 2002
The micellization behavior of a hydrophobically modified polystyrene-block-poly(methacrylic acid) diblock copolymer, PS-N-PMA-A, tagged with naphthalene between blocks and with anthracene at the end of the PMA block, was studied in 1,4-dioxane-methanol mixtures by light scattering and fluorescence techniques. The behavior of a single-tagged sample, PS-N-PMA, and low-molar-mass analogues was studied for comparison. Methanol-rich mixtures with 1,4-dioxane are strong selective precipitants for PS. Multimolecular micelles with compact PS cores and PMA shells may be prepared indirectly by dialysis from 1,4-dioxane-rich mixtures, or by a slow titration of copolymer solutions in 1,4-dioxane-rich solvents with methanol under vigorous stirring. In tagged micelles, the naphthalene tag is trapped in nonpolar and fairly viscous core/shell interfacial region. In hydrophobically modified PS-N-PMA-A micelles, the hydrophobic anthracene at the ends of PMA blocks tends to avoid the bulk polar solvent and buries in the shell. The distribution of anthracene tags in the shell is a result of the enthalpy-to-entropy interplay. The measurements of direct nonradiative excitation energy transfer were performed to estimate the distribution of anthracene-tagged PMA ends in the shell. The experimental fluorometric data show that anthracene tags penetrate into the inner shell in methanol-rich solvents. Monte Carlo simulations were performed on model systems to get reference data for analysis of time-resolved fluorescence decay curves. A comparison of experimental and simulated decays indicates that hydrophobic traps return significantly deep into the shell (although not as deep as in + The study is a part of the long-term Research Plan of the School of Science No. MSM 113100001. aqueous media). The combined light scattering, fluorometric and computer simulation study shows that the conformational behavior of shell-forming PMA blocks in non-aqueous media is less affected by the presence of nonpolar traps than that in aqueous media.
Journal of Polymer Science Part A: Polymer Chemistry, 2011
In this study, a novel type of amphiphilic block copolymers poly(lactic acid)-block-poly(ascorbyl acrylate) (PLAblock-PAAA) with biodegradable poly(lactic acid) as hydrophobic block and poly(ascorbyl acrylate) (PAAA) as hydrophilic block was successfully developed by a combination of ringopening polymerization and atom transfer radical polymerization, followed by hydrogenation under normal pressure. The chemical structures of the desired copolymers were characterized by 1 H NMR and gel permeation chromatography. The thermal physical properties and crystallinity were investigated by thermogravimetric analysis, differential scanning calorimetry, and wide angle X-ray diffraction, respectively. Their self-assembly behavior was monitored by fluorescence-probe technique and turbidity change using UV-vis spectrometer, and the morphology and size of the nanocarriers via self-assembly were detected by cryo-transmission electron microscopy and dynamic light scattering. These polymeric micelles with PAAA shell extending into the aqueous solution have potential abilities to act as promising nanovehicles for targeting drug delivery. V
Journal of Macromolecular Science, Part A, 2014
The synthesis and characterization of eight novel PEG-based amphiphilic block copolymers is reported. The polymers have been synthesized by reacting poly(ethylene glycols) (PEGs) of different molecular weights viz. 600, 1000, 1500 and 2000 and dimethyl 5hydroxyisophthalate in the presence of concentrated H 2 SO 4 as catalyst and further alkylating the resulting polymers by attaching heptyl and tetradecyl chains to phenolic hydroxyl group. The resulting functionalized amphiphilic polymers have been characterized by 1 H and 13 C-NMR spectroscopy. These polymers, when dissolved in water, aggregate to form micelles, giving size ranging from 26.50 to 85.10 nm as determined by Dynamic Light Scattering (DLS) instrument. The molecular weights have been also calculated from the DLS and are in the range 8.8 £ 10 3 to 8.5£10 4 KDa (Kilo Daltons). Critical Micelle Concentrations (CMC) of the synthesized polymers was determined using electrical conductivity meter with values in the range 115 to 148 mgL ¡1 (milligrams per litre).
Polymer, 2004
Series of amphiphilic diblock copolymers with poly(N-isopropylacrylamide) as a hydrophilic block and a hydrophobic block consisting of either polystyrene or poly(tert-butyl methacrylate) were synthesised using RAFT polymerisations. Differential scanning calorimetry showed the chemically different blocks being phase separated in dry polymers. Light scattering and microcalorimetry studies were performed on aqueous solutions to investigate the phase behavior of the diblock copolymers. By carefully transferring the polymers from an organic solvent to water, either micellar particles or large aggregates were obtained depending on the relative lengths of the blocks. Large aggregates collapsed upon heating, whereas collapse occurred slowly within a broad temperature range in the case of micelle like structures. However, microcalorimetrically the collapse of the PNIPAM chains was observed to take place in all samples, suggesting that the shells of the micellar particles are crowded in a way which hinders the compression of the poly(N-isopropylacrylamide) chains.
Macromolecules
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 un...
Macromolecules, 1999
Amphiphilic diblock copolymers were synthesized based on poly(2-ethyl-2-oxazoline) (PEtOz) as a hydrophilic block and aliphatic polyesters such as poly(L-lactide) (PLA) or poly(-caprolactone) (PCL) as a hydrophobic block. Their micellar characteristics in an aqueous phase were investigated by using dynamic light scattering and fluorescence techniques. The block copolymers formed micelles in the aqueous phase with critical micelle concentrations (cmcs) in the range of 1.0-8.1 mg/L. The cmc values become lower upon increasing the length of the hydrophobic block. The mean diameters of the micelles were in the range of 108-192 nm, with a narrow distribution. In general, the micelle size increased as the hydrophobic PLA or PCL block became larger. The partition equilibrium constants, K v, of pyrene in the micellar solutions of the block copolymers were from 1.79 × 10 5 to 5.88 × 10 5. For each block copolymer system of PEtOz-PLA or PEtOz-PCL, the Kv value increased as the length of the hydrophobic block increased. The steady-state fluorescence anisotropy values (r) of 1,6-diphenyl-1,3,5-hexatriene (DPH) were 0.265-0.284 in PEtOz-PLA solution and 0.189-0.196 in PEtOz-PCL solution. The anisotropy values of PEtOz-PLAs were higher than those of PEtOz-PCLs. The anisotropy values were independent of the length of the hydrophobic block when the chemical structures of the hydrophobic blocks were identical. The micelles underwent hydrogen bonding at pH <3.5 with poly(acrylic acid), which produced polymer complex precipitates that could be reversibly dispersed as micelles at pH >3.8.
Macromolecules, 2003
Amphiphilic AB, A 1 A 2 B, and A2B block copolymers, where A ) polyisobutylene, B ) poly-(methyl vinyl ether), and the superscripts denote molecular weight asymmetry, with constant molecular weight and composition have been synthesized by living cationic polymerization. The influence of architecture on aqueous micellar properties of these block copolymers were investigated in the temperature range 20-30°C by fluorescence spectroscopy and static and dynamic light scattering (SLS and DLS). The critical micelle concentration (cmc) measured at 23°C increased in the order A 2B < A 1 A 2 B < AB. The partition equilibrium constants, Kv of pyrene, characteristic of hydrophobicity, increased in the opposite order of cmc. The hydrodynamic radii (Rh) and aggregation numbers (Nagg) of micelles remained approximately constant in the whole temperature range for A 1 A 2 B and A2B and below 25°C for AB. At ∼25°C, however, there was a sudden increase in both Rh and Nagg for AB. Below 25°C both Rh and Nagg increased in the order AB < A 1 A 2 B < A2B. The particle size distribution for all block copolymers remained narrow in the whole temperature range. The results are discussed in terms of possible morphologies.