Effects of Poly(Propylene Oxide)–Poly(Ethylene Oxide)–Poly(Propylene Oxide) Triblock Copolymer on the Gelation of Poly(Ethylene Oxide)–Poly(Propylene Oxide)–Poly(Ethylene Oxide) Aqueous Solutions

Poly(ethylene oxide)-poly(propylene oxide)–poly(ethylene oxide) ((EO)_n–(PO)_m–(EO)_n) block copolymers, commercially available as Pluronics (BASF Corp.) and Poloxamers (ICI Corp.), have been widely applied in medicine, biochemistry, and other fields because of their ability to form reversible micelles and physical gels in aqueous solution. Generally, for PEO–PPO–PEO block copolymers with higher ethylene oxide concentration, the micellization and gelation in aqueous solution are easier. However, if we introduce the reverse block copolymer PPO–PEO–PPO into PEO–PPO–PEO aqueous solutions, the micellization and gelation of the system will be more complex. In this work, the reverse block copolymer PO₁₄–EO₂₄–PO₁₄ (17R4) was added to the Pluronics EO₂₀–PO₇₀–EO₂₀ (P123), EO₁₀₀–PO₆₅–EO₁₀₀ (F127), and EO₁₃₃–PO₅₀–EO₁₃₃ (F108) aqueous solutions with different molar ratios. The rheological properties of different mixtures were measured to study the additive effect on the gelation behavior. The sol–gel transition temperature of the P123, F127, and F108 solutions shifted to a higher temperature when 17R4 was added to the solutions. In addition, the existence of 17R4 greatly affected the stability of gels. These results help to better understand the gelation of Pluronic aqueous solutions.     

Development of novel formulations for photodynamic therapy on the basis of amphiphilic polymers and porphyrin photosensitizers. Pluronic influence on photocatalytic activity of porphyrins

Effect of ethylene and propylene oxide tri-block copolymers (Pluronics) on the photocatalytic activity of tree porphyrins differing by their hydrophobicity was studied. It was shown that Pluronics induce considerable increase in the photocatalytic activity of the tetraphenylporphyrin, hematoporphyrin disodium salt (Dimegine) and relatively hydrophilic N-methyl-bis-glucamine salt of chlorine e₆ (Photoditazine) in the reaction of photooxidation of tryptophan in water solution. This effect was maximal for Pluronics F127 and P85 with intermediate hydrophobicity, while more hydrophilic F68 and more hydrophobic L61 were less effective. Pluronic effect on the photocatalytic activity of tetraphenylporphyrin and dimegine is attributed to their disaggregation in water solution, while PD activity is elevated due to the local concentrating of the photocatalyst and the substrate within micellar volume. It was found by AFM that the structure of Pluronic F127 thin films prepared by water solution evaporation on mica surface significantly changed in the presence of porphyrin. This effect can be attributed to the interaction of Pluronics with porphyrins in water solution.     

牛血清白蛋白对Pluronic聚合物胶团形成的影响研究

用吡啶作为荧光探针研究了嵌段共聚物PluronicF108胶团形成以及牛血清白蛋白(BSA)对嵌段共聚物胶团形成的影响。研究表明,BSA阻碍嵌段共聚物的胶团形成,BSA与嵌段共聚物疏水链段的疏水相互作用是其阻碍嵌段共聚物胶团形成的主要原因。     

Contrast variation SANS experiments to the study of detergent-induced micellization of block copolymers

PEO—PPO—PEO triblock copolymer P85 [(EO)₂₆(PO)₃₉(EO)₂₆] dissolves as unimers and detergent sodium dodecyl sulfate (SDS) forms micelles in aqueous solution at 20°C. The mixing of detergent with triblock copolymer induces the micellization of triblock copolymers. Contrast variation small-angle neutron scattering measurements show that triblock copolymer forms mixed micelles with detergent and the mixing of two components in the mixed micelles is uniform.     

用1H NMR研究正丁醇对PEO-PPO-PEO嵌段共聚物胶团形成的影响

采用¹H NMR波谱技术研究了正丁醇对PEO-PPO-PEO嵌段共聚物温度依赖的胶团化过程影响. 实验结果表明,正丁醇的加入急剧地降低嵌段共聚物的临界胶团温度（CMT）. 化学位移变化表明正丁醇烷基端与嵌段共聚物PPO链段之间的疏水相互作用是导致嵌段共聚物CMT降低的主要原因. 选择性激发ROE实验进一步证实,在形成的嵌段共聚物-正丁醇混合胶团中,正丁醇的烷基链段进入胶团内核而正丁醇的羟基端则处于胶团外壳一侧.     

Small angle neutron scattering study of doxorubicin-surfactant complexes encapsulated in block copolymer micelles

Self-assembling behaviour of block copolymers and their ability to evade the immune system through polyethylene oxide stealth makes it an attractive candidate for drug encapsulation. Micelles formed by polyethylene oxide-polypropylene oxide- polyethylene oxide triblock copolymers (PEO-PPO-PEO), pluronic P123, have been employed for encapsulating the anti-cancer drug doxorubicin hydrochloride. The binding affinity of doxorubicin within the micelle carrier is enhanced through complex formation of drug and anionic surfactant, aerosol OT (AOT). Electrostatic binding of doxorubicin with negatively charged surfactants leads to the formation of hydrophobic drug-surfactant complexes. Surfactant-induced partitioning of the anti-cancer drug into nonpolar solvents such as chloroform is investigated. SANS measurements were performed on pluronic P123 micelles in the presence of drug-surfactant complex. No significant changes in the structure of the micelles are observed upon drug encapsulation. This demonstrates that surfactant- drug complexes can be encapsulated in block copolymer micelles without disrupting the structure of aggregates.      

Structure of hydrophobically and hydrogen-bonded complexes between amphiphilic copolymer and polyacid in water

We observed by SANS and NMR the structure of intermolecular complexes formed through hydrogen bonding and hydrophobic interactions between a polyacid and a neutral copolymer surfactant (PEO-PPO-PEO). The polyacid is perdeuterated and the contrast variation method enables us to measure separately the structure factor of each component in the complex and the cross structure factor as a function of the pH and the temperature. The evolution of NMR spectra and relaxation times with pH and temperature give a complementary insight into the inner structure of the aggregates. The interaction between the aggregates and the aggregation number of polyacid chains are governed by electrostatic effects; they depend on the polyacid charge and are insensitive to temperature. The number of copolymer chains which results from the cooperative action of hydrogen bonding and hydrophobic interactions is sensitive to both pH and temperature. The complexation preserves the micellar core-corona structure of the copolymer and shrinks the polyacid chains which adopt a compact structure. The non-dissociated polyacid sequences are bound to the PPO part of the copolymer forming the hydrophobic core of the complex, whereas the ionized polyacid sequences form with the PEO a stabilizing hydrated corona.Received: 27 April 2004, Published online: 3 August 2004PACS: 61.12.-q Neutron diffraction and scattering - 82.56.-b Nuclear magnetic resonance - 61.25.Hq Macromolecular and polymer solutions; polymer melts; swelling - 82.70.-y Disperse systems; complex fluids     

Imidazole derivatives as absorption probes for pluronics core-shell aggregates micropolarity investigation

Using the absorption probes 1-H-imidazol-1-yloxy-4,5-dihydro-4,4,5,5-tetramethyl-2-ethyl-3-oxide, 1-H-imidazol-1-yloxy-4,5-dihydro-4,4,5,5-tetramethyl-2-nitrophenyl-3-oxide, and 1-H-imidazol-1-yloxy-4,5-dihydro-4,4,5,5-tetramethyl-2-undecyl-3-oxide, the micropolarity of micellar aggregates formed in aqueous solutions of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock copolymers, Pluronics L62, L64, and F127, as well as in reverse micellar systems of F127/butanol/water, has been investigated These absorption probes have different hydrophilic/hydrophobic features and solvatochromic properties. Their specific absorption parameters, sensitive to changes in micropolarity, were calibrated using the reference curves carried out in homogeneous tetraethyleneglycol/water mixtures. The probes were able to detect changes in the micelle micropolarity induced by hydration. Thus, with the help of calibration solutions, the effective local hydration of the polymeric chain sensed by the molecular probe solubilized in the guest aggregate was quantified and hypothetical relative locations of the probes in micelles have been proposed. The probes evidence differences in the micropolarity function of the structure (nature) and concentration of the Pluronic block copolymers.     

Sphere-to-rod transition of triblock copolymer micelles at room temperature

A room temperature sphere-to-rod transition of the polyethylene oxide-polypropylene oxide-polyethylene oxide-based triblock copolymer, (PEO)₂₀(PPO)₇₀ (PEO)₂₀ micelles have been observed in aqueous medium under the influence of ethanol and sodium chloride. Addition of 5–10% ethanol induces a high temperature sphere-to-rod transition of the micelles, which is brought to room temperature upon addition of NaCl. The inference about the change in the shape of the micelles has been drawn from small-angle neutron scattering (SANS) and viscosity studies.     

A simple swelling and anchoring method for preparing dense and stable poly(ethylene oxide) layers on polystyrene surfaces

In order to obtain dense and stable poly(ethylene oxide) (PEO) layers for reducing protein adsorption, polystyrene (PS) plates were first soaked in chloroform/methanol mixed organic solvent to swell the polymer. The swelled PS plates were then immersed into Pluronic F127 (amphiphilic block copolymer) aqueous solution, Pluronic F127 molecules were adsorbed favorably on the swelled PS surfaces. After evaporation of organic solvent, the adsorbed Pluronic F127 molecules were trapped and anchored permanently on the PS substrates. The dense and stable PEO layers anchored on the PS surfaces can effectively inhibit protein adsorption.     

共聚物Pluronic P103对牛血清白蛋白荧光光谱的猝灭

应用静态荧光光谱研究了嵌段共聚物PluronicP103对牛血清白蛋白(BSA)荧光光谱的猝灭。研究表明,PluronicP103对BSA的荧光有猝灭作用,动态猝灭是引起BSA荧光猝灭的主要原因。发现嵌段共聚物PluronicP103在水溶液中的蔟集状态影响其与BSA的相互作用,以胶团形式存在的PluronicP103对BSA的猝灭作用更强。     

Stimuli-responsive poly(ethylene oxide)-b-poly(2-vinylpyridine)-b-poly(ethylene oxide) triblock copolymers and complexation with poly(acrylic acid) at low pH

The self-organization of the double hydrophilic triblock copolymer poly(ethylene oxide)-b-poly(2-vinylpyridine)-b-poly(ethylene oxide), PEO-b-P2VP-b-PEO, was investigated in dilute aqueous solution under several experimental conditions using turbidimetry, as well as static and dynamic light scattering. As a result of the temperature-sensitive properties of the end PEO blocks and the p H-responsive properties of the middle P2VP block, the formation of large star-like micellar nanostructures is observed at high p H, while at low p H, but in the presence of salt and at high temperature, flower-like micelles are formed. Moreover, the viscosimetric and dynamic light scattering studies at low p H revealed that micelle-like nanostructures are formed upon mixing the triblock copolymer with poly(acrylic acid), PAA, due to hydrogen bonding interpolymer complexation.     

Crystallization Behavior of PEO in Nano‐Structured PEO‐b‐PS/PPO Blends

Blends of poly (ethylene oxide)‐b‐polystyrene (PEO‐b‐PS) diblock copolymer and poly (2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) homopolymer were obtained by solution blending, and the morphologies of PEO dispersed nanoparticles in PPO/PS matrix were observed by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The isothermal crystallization kinetics was studied using differential scanning calorimetry (DSC) and polarized optical microscopy (POM). Nonisothermal crystallization kinetics was studied using DSC. The results showed that PEO segments were easier to crystallize in the blend than in the copolymer probably due to the interfaces of PPO acting as nucleation sites to promote the crystallization of PEO. The crystallization of PEO blocks destroyed the pre‐existing microdomain structure even though the glass transition temperature of the matrix was much higher than the crystallization temperature.     

A small angle neutron scattering study on the mixtures of pluronic L121 and anionic surfactant AOT

Small angle neutron scattering (SANS) experiments have been carried out on the micellar solutions containing mixtures of a hydrophobic triblock copolymer (L121, EO₅PO₆₈EO₅) and a hydrophobic anionic surfactant (AOT, sodium bis(2-ethylhexyl)sulphosuccinate) in water with varying ratio (R) of AOT to L121 for R = 0.15, 0.2, 0.3, 0.5 and 0.6. It is known that either L121 or AOT alone forms vesicles in water, but in the mixture with appropriate ratio of the two components a thermodynamically stable, isotropic solution of apparently small micelle-like aggregates is formed. We find that these micelles are prolate ellipsoidal.      

Correlation between the viscoelastic properties of a soft crystal and its microstructure

We investigate the rheological properties of a cubic fcc phase of micelles obtained by aggregation of a triblock copolymer (PEO)₁₂₇(PPO)₄₈(PEO)₁₂₇ in water as selective solvent. The resulting soft solid is submitted to a range of stresses varying from 20 to 800Pa in Couette geometry. Creep and flow behaviour can be distinguished and interpreted in terms of structural changes previously observed by SAXS under flow. Contrasting with other systems, no discontinuity in the flow behaviour is associated with the structural changes. The strong shear thinning is interpreted from the scattering data, as resulting from the nucleation of a new structure of hexagonal compact planes parallel to the Couette walls. This creates a lubricating domain in the gap, whose size grows with the applied shear rate. We argue moreover that the very existence of flow (as a steady state opposed to creep) is associated with this so-called layer-sliding structure in a fraction, however small, of the sample. Received on 4 June 1999 and Received in final form 6 September 1999     

Development of novel formulations for photodynamic therapy on the basis of amphiphilic polymers and porphyrin photosensitizers. Porphyrin-polymer complexes in model photosensitized processes

We have studied the effect of amphiphilic polymers with different structure (polyvinylpyrrolidone, polyethyleneoxide and a triblock copolymer of ethylene- and propyleneoxide—(Pluronic F127)) on the photoactivity of a hematoporphyrin derivative (dimegin). It has been shown that such polymers can cause a considerable increase in the porphyrin photosensitizer (PPS) activity both in the process of singlet oxygen photogeneration and in the reaction of a substrate photooxidation in D2O and water. Among the studied polymers, polyvinylpyrrolidone appeared to have a most significant influence onto the photoactivity of dimegin. We attribute the observed effect of the amphiphilic polymers on the photoactivity of dimegin to the presence of polymer-porphyrin interactions resulting in the porphyrin disaggregation in aqueous phase. Using 1H NMR spectroscopy, we have found that dimegin binds to the polymers via the PPS interaction mainly with the hydrophobic fragments of polymeric macromolecules. However, in the case of polyvinylpyrrolidone we observed also PPS interactions with the hydrophilic fragments of macromolecules.     

Mesostructures and properties of transparent block copolymer/silica nanocomposite monoliths

In this work, three different block copolymer/silica hybrid nanocomposite monoliths that possess mesostructured domains (hexagonal, cubic, and disordered) were prepared through the micellization of the block copolymer during the sol-gel process of a silica precursor. Transparent block copolymer/silica nanocomposite monoliths were obtained from the amphiphilic triblock copolymer poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (EO₁₀₆PO₇₀EO₁₀₆, Pluronic F127), which we used to organize the polymerizing silica networks; the ratio between the block copolymer and silica was fixed at 60:40 (wt%). Small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) were used to observe the mesostructural ordering. Temperature-dependent SAXS patterns of the cubic structured nanocomposites showed that the calcination process takes place at 210°C. The transmittances of the nanocomposite monoliths over the range of wavelengths from 400 to 800 nm was >85%. From rheological measurements at low frequency, it was found that the hexagonally structured monoliths had higher storage and loss moduli relative to the monoliths possessing cubic and disordered structures.     

An isothermal titration calorimetry study of the interactions between an oxyphenylethylene/oxyethylene diblock copolymer and sodium dodecyl sulfate

Interactions between the diblock copolymer S₁₅E₆₃ and the surfactant sodium dodecyl sulfate (SDS) have been investigated by isothermal titration calorimetry (ITC) in the temperature range 10–40°C. At 20°C, the block copolymer is associated into micelles with a hydrodynamic radius of 11.6?nm, which is composed of a hydrophobic styrene oxide (S) core and a water-swollen oxypolyethylene (PEO) corona. The copolymer/surfactant system has been studied at a constant copolymer concentration of 0.25?wt% and over a wide range of surfactant concentration, from 7.5?×?10^?6 up to 0.3?M. The titration calorimetric data for SDS in the temperature range 10–20°C presents a first endothermic increase indicating the formation of mixed copolymer rich-surfactant micelles. From that point, important differences in the ITC plots for surfactant titrations in the presence and in the absence of the copolymer are present. A shallow second endothermic peak is assigned to the interaction between SDS molecules and copolymer molecules resulting from the beginning of micelle disruption. An exothermic peak indicates the end of this disruption where only SDS micelles attached to single copolymer monomers are present, as shown by DLS in a previous paper. At higher temperatures in the range 25–40°C, the first endothermic maximum is not totally shown because interactions between surfactant and block copolymer start at very low SDS concentrations. Moreover, the second endothermic peak is absent and the exothermic minimum is less pronounced as a consequence of the increased micellization of the block copolymer.     

Microphase separation behavior on the surfaces of PEG-MDI-PDMS multiblock copolymer coatings

A series of poly(ethylene glycol)(PEG)-4,4′-diphenylmethanediisocyanate(MDI)-poly(dimethylsiloxane) (PDMS) multiblock copolymers were synthesized by employing two-step growth polymerization technique. Atomic force microscopy (AFM) observed nanoscopically well-organized phase-separated surfaces consisting of hydrophilic domain from PEG and MDI segments and hydrophobic domain from PDMS segments even with 50 wt.% PDMS in the copolymer, and the multiblock copolymer coatings presented a surface free energy of as low as 6-8 mN m⁻¹.     

Nanostructured Thermosetting Blends of Phenolic Thermosets and Poly(ethylene oxide)‐block‐poly(propylene oxide)‐block‐poly(ethylene oxide) Triblock Copolymer

The amphiphilic triblock copolymer, poly(ethylene oxide)‐block‐poly(propylene oxide)‐block‐poly(ethylene oxide) (PEO‐b‐PPO‐b‐PEO) was incorporated into novolac resin to prepare thermosetting blends. The morphology of the thermosetting blends was investigated by means of atomic force microscopy (AFM) and small‐angle x‐ray scattering (SAXS) and the nanostructures were obtained. It was identified that the reaction‐induced phase separation occurred in the blends of phenolic thermosets with the model poly(propylene oxide) (PPO), whereas poly(ethylene oxide) (PEO) was miscible with novolac resin after and before the curing reaction. In terms of miscibility and phase behavior of the subchains of the triblock copolymer with novolac resin, it was demonstrated that the formation of nanostructures in the thermosets followed a mechanism of reaction‐induced microphase separation.