Micellization and Clouding Behavior of EO–PO Block Copolymer in Aqueous Salt Solutions

Aqueous solution properties of polyethylene oxide–block-polypropylene oxide–block-polyethylene oxide TBP [(PEO)₁₀₃(PPO)₃₉(PEO)₁₀₃] were studied in the presence of sodium salts with different anions (NaI, NaBr, NaCl, NaF, Na₂SO₄, Na₃PO₄) to investigate unimer-to-micelle transition [critical micelle concentration (CMC), critical micellization temperature (CMT)], micelle size and the phase separation (cloud point). This TBP, due to its very hydrophilic (80% PEO) nature does not form micelles at ambient temperatures. Micellization can be induced much below its CMT in water on addition of sodium salts having different anions. Analytical methods viz. fluorescence, FTIR and dynamic light scattering (DLS) were used to monitor the salt-induced micellization. The hydration of respective anion and resultant contribution to its salting-out effect was found to be the governing factor in promoting micellization. The presence of salt decreases the CMC, CMT and phase separation temperature. The salts affect the aggregation process in agreement with an order mentioned in Hofmeister series.     

Poly(ethylene glycol)-block-poly(butyl acrylate). I. Synthesis

Prepolymers of poly(ethylene oxide) (Pre-PEO) were synthesized by reacting azoisobutyronitrile (AIBN) with poly(ethylene glycol) (PEG), and their structures were characterized by IR and UV. The molecular weight of pre-PEO was related to the feed ratio and reaction time. These prepolymers can be used to prepare block copolymers—poly(ethylene oxide)-block-poly(butyl acrylate) (PEO-b-PBA) by radical polymerization in the presence of butyl acrylate (BA). Solution polymerization was a suitable technique for this step. The yield and the molecular weight of the product were related to the ratio of the prepolymer to BA, the reaction time, and temperature. GPC showed that the molecular weight increased with a higher ratio of BA to pre-PEO. The intrinsic viscosity of the copolymers was only slightly dependent on reaction time, but decreased at higher reaction temperatures, as did the amount of PBA homopolymer. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1667–1674, 1997     

Synthesis of poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene triblock copolymers by two-step atom transfer radical polymerization

The synthesis of ABC triblock copolymer poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene (PEO-b-PMMA-b-PS) via atom transfer radical polymerization (ATRP) is reported. First, a PEO-Br macroinitiator was synthesized by esterification of PEO with 2-bromoisobutyryl bromide, which was subsequently used in the preparation of halo-terminated poly(ethylene oxide)-block-poly(methyl methacrylate) (PEO-b-PMMA) diblock copolymers under ATRP conditions. Then PEO-b-PMMA-b-PS triblock copolymer was synthesized by ATRP of styrene using PEO-b-PMMA as a macroinitiator. The structures and molecular characteristics of the PEO-b-PMMA-b-PS triblock copolymers were studied by FT-IR, GPC and ¹H NMR.     

Aggregation properties of amphiphilic poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymer studied by cyclic voltammetry

The cyclic voltammetric behaviors at a platinum electrode of an amphiphilic block copolymer [poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (F127)] in aqueous solutions were investigated. The mechanism of the electrochemical reaction of F127 at a platinum electrode was deduced. The diffusion coefficients of different-shaped aggregates formed by F127 were determined on this basis. The first and second critical micelle concentrations, corresponding to the formation of spherical micelles and the transition of the spherical to rod-like micelles, were 3.72×10⁻⁴ mol·L⁻¹ and 1.49×10⁻³ mol·L⁻¹, respectively, which could be confirmed by the fluorescent anisotropy of pyrene in the F127 aggregates and the morphology of F127 micelles observed by freeze-fracture transmission electron microscopy.     

Triblock and star-block copolymers of N-(2-hydroxypropyl)methacrylamide or N-vinyl-2-pyrrolidone and D,L-lactide: synthesis and self-assembling properties in water

Novel A-B-A triblock and star-block amphiphilic copolymers, i.e. poly(N-(2-hydroxypropyl)methacrylamide)-block-poly(D,L-lactide)-block-poly(N-(2-hydroxypropyl)metha-crylamide), poly(N-vinyl-2-pyrrolidone)-block-poly(D,L-lactide)-block-poly(N-vinyl-2-pyrrolidone), star-poly(D,L-lactide)-block-poly(N-(2-hydroxypropyl)methacrylamide) and star-poly(D,L-lactide)-block-poly(N-vinylpyrrolidone), were synthesized and characterized. These polymers were prepared by free radical polymerization of N-(2-hydroxypropyl)methacrylamide and N-vinyl-2-pyrrolidone in the presence of either poly(D,L-lactide) dithiol or star-poly(D,L-lactide) tetrakis-thiol, both biodegradable macromolecular chain-transferring agents. All copolymers self-assembled in aqueous solution to form supramolecular aggregates of 20–180 nm in size. The critical aggregation concentration of the copolymers ranged from 5 to 24 mg/L, depending on their hydrophobicity. The partition equilibrium constant of pyrene in the hydrophobic core of micelles was between 0.71×10⁵ and 1.63×10⁵. The triblock copolymer micelles were loaded with two model poorly water-soluble drugs, namely, indomethacin (1.5–16.4% w/w) and paclitaxel (0.4–1.5% w/w), by a dialysis procedure. These triblock and star-block copolymers could prove useful as nanocarriers for the solubilization and delivery of hydrophobic drugs.     

Catalytic activity of a thermosensitive hydrophilic diblock copolymer-supported 4-N,N-dialkylaminopyridine in hydrolysis of p-nitrophenyl acetate in aqueous buffers

This article reports on the synthesis of a thermosensitive hydrophilic diblock copolymer with the thermosensitive block containing a catalytic 4-N,N-dialkylaminopyridine and the study of the effect of thermo-induced micellization on its catalytic activity in the hydrolysis of p-nitrophenyl acetate (NPA). The block copolymer, poly(ethylene oxide)-b-poly(methoxydi(ethylene glycol) methacrylate-co-2-(N-methyl-N-(4-pyridyl)amino)ethyl methacrylate), was synthesized by ATRP. The critical micellization temperatures (CMTs) of this block copolymer in the pH 7.06 and 7.56 buffers were 40 and 37 °C, respectively. The polymer was used as the catalyst for the hydrolysis of NPA. We found that below CMT, the logarithm of initial hydrolysis rate changed linearly with inverse temperature. With the increase of temperature above CMT, the plot of logarithm of reaction rate versus 1/T leveled off, i.e., the hydrolysis rate did not increase as much as anticipated from the Arrhenius equation. This is likely because the reaction rate at temperatures above CMT was controlled by mass transport of NPA from bulk water phase to the core of micelles where the catalytic sites were located.     

Reversible pH-Responsive Hydrogels of Softwood Kraft Lignin and Poly[(2-dimethylamino)ethyl Methacrylate]-based Polymers

Softwood kraft lignin (SKL) pH-responsive hydrogels were prepared through controlled aggregation using poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) and poly(2-(dimethylamino)ethyl methacrylate)-block-poly(ethylene oxide)-block-poly(2-(dimethylamino) ethyl methacrylate) triblock copolymer (PDMAEMA-co-PEO-co-PDMAEMA). At low SKL concentrations, the SKL/polymer (PDMAEMA and PDMAEMA-co-PEO-co-PDMAEMA) aqueous solutions exhibited pH-dependent aggregation arising from the formation of strong intermolecular hydrogen bonds. Decreasing the SKL/polymer weight ratio resulted in the pH-reversible soluble-insoluble (S-I) transition to become a soluble-insoluble-soluble (S-I-S) transition, which upon increasing the SKL concentration resulted in hydrogel formation. Under neutral conditions relatively strong hydrogels were formed, which upon either increasing or decreasing solution pH resulted in the hydrogels collapsing to liquid solutions, but were readily reformed upon neutralization. The effects of polymer structure, concentration, and intermolecular interactions on solution behavior and gelation are thoroughly discussed.     

Synthesis and characterization of poly(methylphenylsilylene)–poly(ethylene oxide) and poly(methylphenylsilylene)–polyisoprene multiblock copolymers

Multiblock copolymers were synthesized through condensation reactions of end‐groups of α,ω‐dichloro‐poly(methylphenylsilylene) with hydroxyl end‐groups of poly(ethylene glycol) or the chain‐ends of ‘living’ polyisoprenyl disodium. Optimum conditions have been sought through kinetic studies and by investigation of model reactions. The overall molecular weight distribution of poly(methylphenylsilylene)‐block‐poly(ethylene oxide) is characterized in terms of Flory's theory of condensation reactions, while the limiting step in the reaction is tentatively attributed to the formation of aggregates. © 2001 Society of Chemical Industry     

A facile synthesis of hydrophilic glycopolymers with the ether linkages throughout the main chains

A series of well-defined block glycopolymer with the ether linkages throughout the main chains were synthesized by an easy and efficient way. First, the block copolymer intermediates poly(ethylene oxide)-b-poly(allyl glycidyl ether) (PEO-b-PAGE) with narrow molecular weight distribution were prepared by living anionic ring-opening polymerization. Then, 2,3,4,6-tetra-O-acetyl-β-thioglucopyranose (AcGSH) molecules were attached to the PAGE blocks by free-radical addition reaction of –SH groups of saccharide molecules with the double bonds. Finally, removal of the acetyl protective groups afforded the corresponding glycopolymers poly(ethylene oxide)-b-poly(allyl glycidyl ether-glucose) (PEO-b-P(AGE-glucose)). The composition and structure of the glycopolymers were characterized by ¹HNMR, ¹³CNMR and FT-IR.     

The influence of hydrophobic substitution on self-association of poly(ethylene oxide)-b-poly(n-alkyl glycidyl carbamate)s-b-poly(ethylene oxide) triblock copolymers in aqueous media

A series of amphiphilic poly(ethylene oxide)-b-poly(n-alkyl glycidyl carbamate)s-b-poly(ethylene oxide) triblock copolymers were synthesized by reaction between poly(ethylene oxide)-b-polyglycidol-b-poly(ethylene oxide) precursor copolymer and four n-alkyl isocyanates: ethyl, propyl, butyl and pentyl. After dissolution in water at room temperature the copolymers spontaneously form micelles. The critical micellization concentrations were determined by UV-VIS spectroscopy. The dimensions of the micelles, the aggregation numbers, and in some cases the micellar shape were determined by dynamic and static light scattering in a relatively broad temperature range. Special attention has been paid to the influence of the number of the carbon atoms in the alkyl chains, and respectively, the relative hydrophobicity of the middle block upon the self-association process. Clouding transition was observed for all of the copolymers, the clouding point being dependent upon the length of the alkyl chain.     

Thermodynamics of micellization of poly-styrene-block-poly(ethylene/propylene) copolymers in decane

Light scattering was used to establish the dependence of the critical micelle temperature, CMT, on concentration for solutions of three polystyrene-block-poly(ethylene/propylene) copolymers in decane. Electron microscopy studies of particles isolated from the solutions showed that the micelles had narrow size distributions and micellization could be treated thermodynamically as a closed association. The light scattering results were used to calculate the standard Gibbs energies of micellization, ΔG^φ, and the standard enthalpy, ΔH^φ, and entropy contributions, —TΔS^φ. The values of ΔH^φ were large and negative, and markedly dependent on the molecular weight of the polystyrene block. The values of ΔG^φ for the three samples were on the other hand very similar to each other. The standard entropy contributions were unfavourable to micelle formation.     

Hydrolysis of poly(ester-ether-ester) block copolymers in the presence of endothelial cells: in vitro modulation of endothelin release

In previous papers, we studied the hydrolytic degradation of six poly(ester-ether-ester) block copolymers, i.e. three poly(ε-caprolactone)-block-poly(oxyethylene)-block-poly(ε-caprolactone) copolymers and three poly(l-lactide)-block-poly(oxyethylene)-block-poly(l-lactide) copolymers. Their degradation products, 6-hydroxyhexanoic acid and l-lactic acid, have now been found to modulate endothelin release by human umbilical vein endothelial cells, with no significant alteration of the vasoconstrictor-vasodilator balance previously determined. The influence of the same degradation products on the cell proliferation has also been determined and discussed. Received: 13 January 1997/Revised: 2 May 1997/Accepted: 3 May 1997     

Shape Memory and Physical Properties of Composites of Polyethylene Oxide/Poly(Propylene Glycol)-Block-Poly(Ethylene Glycol)-Block-Poly(Propylene Glycol)/2,4-Toluene Diisocyanate,Polypyrrole, and Modified MWCNT

Structural variation and its influence on morphology, mechanical, thermal, and electrical conductivity properties of polyethylene oxide/poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol)/2,4-toluene diisocyanate/polypyrrole (PEO/P(P-E-P)G/TDI/PPy) blends and nanocomposites with varying PPy content were reported. The chemical and fundamental linkages were confirmed by FTIR. SEM micrographs demonstrated homogeneous PEO/P(P-E-P)G/TDI/PPy blend formation and globular morphology for nanocomposites. The mechanical and DSC parameters were found to increase systematically with increasing PPy content in blend films. While for nanocomposites, better results were observed for 0.1% PPy content. Maximum electrical conductivity and good shape recovery of 94% was obtained for the nanocomposite with 1% PPy content.     

Investigation on Self-assembled Blend Membranes of Polyethylene-block-poly(ethylene glycol)-block-polcaprolactone and Poly(styrene-block-methyl methacrylate) with Polymer/gold Nanocomposite Particles

A block copolymer of polyethylene-block-poly(ethylene glycol) and polycaprolactone was prepared via co-ordination–insertion polymerization. Blend membranes of poly(styrene-block-methyl methacrylate) and polyethylene-block-poly(ethylene glycol)-block-polcaprolactone were used as matrix. Gold/polystyrene nanoparticles were used as nanofiller in polyethylene-block-poly(ethylene glycol)-block-polcaprolactone/poly(styrene-block-methyl methacrylate)/gold/polystyrene nanoparticles membranes. The double gyroid pattern was depicted by blend chains in polyethylene-block-poly(ethylene glycol)-block-polcaprolactone/poly(styrene-block-methyl methacrylate)/gold/polystyrene nanoparticles. An improvement of 22% in tensile strength and 54% in tensile modulus was observed with 1 wt% nanoparticle addition. Polyethylene-block-poly(ethylene glycol)-block-polcaprolactone/poly(styrene-block-methyl methacrylate)/gold/polystyrene nanoparticles 1 showed water flux of 45.2 mL cm^?2 min^?1 and salt rejection ratio of 17.5%. Efficiency of gold nanoparticles–polystyrene nanoparticles reinforced membranes in removal of heavy metal ions was 100%.     

Doubly thermo-responsive brush-linear diblock copolymers and formation of core-shell-corona micelles

Doubly thermo-responsive brush-linear diblock copolymer of poly[poly(ethylene glycol) methyl ether vinylphenyl]-block-poly(N-isopropylacrylamide) (PmPEGV-b-PNIPAM) is prepared by RAFT polymerization. The obtained brush-linear diblock copolymer exhibits two lower critical solution temperatures (LCSTs) corresponding to the linear poly(N-isopropylacrylamide) (PNIPAM) block and the brush poly[poly(ethylene glycol) methyl ether vinylphenyl] (PmPEGV) block in water. This brush-linear diblock copolymer undergoes a two-step temperature sensitive micellization. At temperature above the first LCST, the brush-linear diblock copolymer self-assembles into core-corona micelles with the dehydrated PNIPAM block forming the core and the solvated brush PmPEGV block forming the corona. When temperature increases above the second LCST, the polystyrene backbone in the brush PmPEGV block collapses onto the dehydrated PNIPAM core to form core-shell-corona micelles, in which the dehydrated PNIPAM block forms the core, the collapsed polystyrene backbone in the brush PmPEGV block forms the shell and the solvated poly(ethylene glycol) side-chains forms the corona. The effect of the length of the PNIPAM block and the length of the poly(ethylene glycol) side-chains on the thermo-responsive micellization and the size of core-shell-corona micelles is investigated.     

Self-Assembly of Polyethylene Glycol Ether Surfactants in Aqueous Solutions: The Effect of Linker between Alkyl and Ethoxylate

The aqueous self-assembly behavior of two homologous series of poly(ethylene oxide) (PEO)-containing nonionic surfactants based on a C₁₀-Guerbet hydrophobe is reported. The two families of surfactants, alkyl ethoxylates and alkyl alkoxylates, are commercially available from BASF under the trade name Lutensol® XP-series and XL-series, respectively. The latter incorporate propylene oxide (PO) units in the surfactant chain. Dye solubilization was used to determine the critical micellization concentration (CMC) of each surfactant at 22 and 50 °C. The PO-containing alkyl alkoxylates displayed lower CMC values, which were also more sensitive to temperature. The Gibbs free energy, enthalpy, and entropy of micellization were computed from the CMC data and used to identify the contribution of each surfactant moiety (alkyl chain, PO unit, and PEO block) in controlling the CMC. The micellization properties are compared with compositionally similar surfactants with linear alkyl chains, yielding information about the effects of the Guerbet alkyl chain on micellization. Isothermal titration calorimetry was also used to characterize the CMC and enthalpy of micellization which generally compare well with the dye solubilization results. Cloud point data reveal nonmonotonic relationships for the Lutensol® surfactants with respect to composition, unlike linear alkyl chain surfactants. Finally, dilute solution viscosity measurements performed on some Lutensol® surfactants show a change in the slope, suggesting a structural change that tends to be more pronounced for surfactants with longer PEO blocks. The data presented herein enhance the understanding of surfactant structure–property relationships required for industrial formulation.     

The Synergism Effect Between Sodium Dodecylbenzene Sulfonate and a Block Copolymer in Aqueous Solution

The synergistic behavior of sodium dodecylbenzene sulfonate (SDBS) with poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) block copolymer was studied using surface tension measurements. The surface tension of single and mixed solutions of SDBS and the block copolymer in this study was measured at different concentrations and at 25 °C. The critical micelle concentration (CMC) of these solutions was determined from the surface tension measurements. The SDBS gives higher CMC values than those of the block copolymer. The results show that the CMC value of SDBS decreases as the molar ratio of SDBS increases in the mixture solution with the block copolymer. The surface parameters of adsorption and micellization for single and mixed solutions were investigated. The results show that the surface and micellization properties of SDBS were improved as a result of mixing with the block copolymer. The mole fractions in the micelles and interaction parameters of the mixed solutions were calculated. The foam stability of single and mixed solutions at 25 °C was determined. The results show that the SDBS has more foam stability than the block copolymer and the foam stability increases as the molar ratio of SDBS increase in mixed solution of it with block copolymer.

Facile synthesis and optical properties of polymer-laced ZnO-Au hybrid nanoparticles

Bi-phase dispersible ZnO-Au hybrid nanoparticles were synthesized via one-pot non-aqueous nanoemulsion using the triblock copolymer poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) as the surfactant. The characterization shows that the polymer-laced ZnO-Au nanoparticles are monosized and of high crystallinity and demonstrate excellent dispersibility and optical performance in both organic and aqueous medium, revealing the effects of quantum confinement and medium. The findings show two well-behaved absorption bands locating at approximately 360 nm from ZnO and between 520 and 550 nm from the surface plasmon resonance of the nanosized Au and multiple visible fingerprint photoluminescent emissions. Consequently, the wide optical absorbance and fluorescent activity in different solvents could be promising for biosensing, photocatalysis, photodegradation, and optoelectronic devices.     

Phase behavior of aqueous systems containing block copolymers of poly(ethylene oxide) and poly(propylene oxide)

Phase behavior of aqueous systems containing block copolymers of poly(ethylene oxide (PEO) and poly(propylene oxide) (PPO) was evaluated by building up temperature-concentration phase diagrams. We have studied bifunctional triblock copolymers (HO-PEO-PPO-PEO-OH) and monofunctional diblock copolymers (R-PEO-PPO-OH and R-PPO-PEO-OH, where R length is linear C₄ and C_12–14). The cloud points of the polymer solutions depended on EO/PO ratio, polarity, R length and position of the hydrophilic and hydrophobic segments along the molecule. Such factors influence on the solutions behavior was also analyzed in terms of critical micelle concentration (CMC), which was obtained from surface tension vs. concentration plots. Salts (NaCl and KCl) added into the polymer solutions change the solvent polarity decreasing the cloud points. On the other hand, the cloud points of the polymer solutions increased as a hydrotrope (sodium p-toluenesulfonate) was added. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1767–1772, 1997