Micelle-polymer complexes as studied by the ESR spin probe technique

Complexes between sodium dodecyl sulfate micelles and the water-soluble polymers poly(N-vinylpyrrolidone), poly(ethylene oxide) and a copolymer of poly (vinyl alcohol) and poly(vinyl acetate) have been studied in aqueous solution by the electron spin resonance (ESR) technique using di-tert-butyl nitroxide as a spin probe. The effective rotational correlation times reveal lowering of the critical micelle concentration and decreased headgroup packing in the micelle upon interaction with the polymers.     

In situ polymerization and morphology of polypyrrole obtained in water‐soluble polymer templates

Several water‐soluble polymers were used as templates for the in situ polymerization of pyrrole to determine their effect on the generation of nanosized polypyrrole (PPy) particles. The polymers used include: polyvinyl alcohol (PVA), polyethylene oxide (PEO), poly(vinyl butyral), polystyrene sulfonic acid, poly(ethylene‐alt‐maleic anhydride) (PEMA), poly(octadecene‐alt‐maleic anhydride), poly(N‐vinyl pyrrolidone), poly(vinyl butyral‐co‐vinyl alcohol‐co‐vinyl acetate), poly(N‐isopropyl acrylamide), poly(ethylene oxide‐block‐propylene oxide), hydroxypropyl methyl cellulose, and guar gum. The oxidative polymerization of pyrrole was carried out with FeCl₃ as an oxidant. The morphology of PPy particles obtained after drying the resulting aqueous dispersions was examined by optical microscopy, and selected samples were further analyzed via atomic force microscopy. Among the template polymers, PVA was the most efficient in generating stable dispersions of PPy nanospheres in water, followed by PEO and PEMA. The average size of PPy nanospheres was in the range of 160 nm and found to depend on the molecular weight and concentration of PVA. Model reactions and kinetics of the polymerization reaction of pyrrole in PVA were carried out by hydrogen ¹H NMR spectroscopy using ammonium persulfate as an oxidant. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Syntheses of ordered mesoporous silica by new hybrid template

Ordered mesoporous silica with macroscopic shape has been prepared with a hybrid template of gel and poly(ethylene oxide)₁₀₆–poly(propylene oxide)₇₀–poly(ethylene oxide)₁₀₆ (pluronic F127) surfactant, where both water-soluble agar gel and pluronic F127 significantly affect the mesoporous structure and morphology of silica. The thermal analysis revealed the noticeable interaction between agar and F127, which contributes to the formation of homogenous hybrid template. In the hybrid template, agar gel contributed to the maintenance of morphology structure, while F127 was responsible for the formation of ordered porous structure in silica solids.     

The effect of Pluronics on the photocatalytic activity of water-soluble porphyrins

Solubilization of hydrophilic porphyrins, 2,7,12,18-tetramethyl-3,8-di(1-methoxyethyl)-13,17-di(2-oxycarbonylethyl) porphyrin disodium salt (dimegin) and N-methyl-di-D-glucose amine salt of chlorine e ₆ (photoditazine), as well water-insoluble meso-tetraphenylorphyrin in the micelles of Pluronics (triblock copolymers and propylene oxide and ethylene oxide), increases the photocatalytic activity of porphyrins in the course of the oxidation of L-tryptophan in aqueous salt-containing solutions. The maximum photocatalytic activity is attained for the photocatalysts based on the Pluronics P85 and F127 containing 50–70% ethylene oxide units. As a result of solubilization, the activity of tetraphenylporphyrin increases by a factor of 50, while the activities of hydrophilic dimegin and photoditazine increase by factors of 1.5 and 6, respectively. The increased activity of tetraphenylporphyrin is due to the dissolution and dissociation of aggregates in the presence of Pluronics. The increased activity of dimegin, which is known to aggregate in water, is primarily provided by disaggregation. In the case of photoditazine, which does not form aggregates in aqueous solutions and is likely to be localized in the polar micellar “crown,” the effect of a polymer is due to the local concentration of both a substrate and a catalyst in the micellar pseudophase.     

Properties of polyethylene glycol supported tetraarylporphyrin in aqueous solution and its interaction with liposomal membranes

5,10,15,20-Tetrakis(4-hydroxyphenyl)porphyrin was functionalized by covalent attachment of poly(ethylene glycol) (PEG) chains of various molecular weights, 350, 2000, and 5000 Da. The properties of PEG-functionalized tetraarylporphyrins in aqueous solution and their interactions with liposomes have been studied. Electronic absorption spectroscopy, dynamic light scattering, atomic force microscopy, and fluorescence quenching were used to monitor aggregation of porphyrin chromophores and behavior of the attached PEG chains in the aqueous solution. The tendency for aggregation of porphyrin chromophores in aqueous solution and the efficiency of fluorescence quenching by KI decrease with increasing length of PEG chain linked to the porphyrin ring. The experimental results indicate that polymer clusters are present in aqueous solution of all pegylated porphyrins. The interactions between the pegylated porphyrins and phosphatidylcholine liposomes in the aqueous solution were studied using the fluorescence methods. The apparent binding constants of porphyrin chromophores to liposomes were determined. The degree of binding was found to be dependent on the molecular weight of the attached polymer.     

Porphyrin photosensitizers solubilized with pluronics in the oxidation of tryptophan

It was shown that water-insoluble porphyrins solubilized with pluronics (ternary block copolymers of ethylene oxide and propylene oxide) efficiently transfer photoexcitation energy to molecular oxygen dissolved in aqueous media to excite it into the singlet state, which is active in oxidizing organic substrates. It was established that the degree of solubilization of porphyrin photosensitizers (PPSs) γ defined as the proportion of PPS molecules passed into the aqueous phase in the dissolution of formed films depends on a single parameter, the initial ratio between the porphyrin and pluronic molar concentrations q. γ = γ(q) dependences for the solubilization of dissimilar water-insoluble porphyrins were analyzed. It was shown that the behavior of all the obtained γ = γ(q) dependences is changed at a characteristic value q _max: when q ? q _max, γ ～ 1, and, when q ≥ ?q_max, the degree of solubilization decreases. It was concluded that solubilized porphyrins are efficient photosensitizers in the oxidation of organic substrates (tryptophan).     

Synthesis and Characterization of Uncharged Water‐Soluble Star Polymers Containing a Porphyrin Core

Uncharged water‐soluble porphyrins were prepared by reaction between tetrakis(p‐hydroxyphenyl)porphyrin and chlorinated poly(ethylene glycol) methyl ethers of different molecular weights. Water‐solubility was achieved by binding four poly(ethylene glycol) branches to a porphyrin core to give star polymers with molecular weights in the range 2000–21 000 Da. Structural characterization of these star polymers was performed by means of gel permeation chromatography, NMR spectroscopy, and MALDI‐TOF analysis.     

Effect of bovine serum albumin on the micellization of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers in aqueous solutions by fluorescence spectroscopy

Effect of bovine serum albumin (BSA) on the temperature-dependent association behavior of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers was investigated using pyrene fluorescence spectroscopy. The critical micellization temperature (CMT) of pluronics in aqueous solution was increased by the addition of BSA. A closed association model was used to obtain the standard free energies (△G0), enthalpies (△H 0), and entropies (△S 0) of micellization. The standard enthalpy and entropy of micellization for pluronic polymers in water were decreased with an increase of the BSA content. The more PPO component in the pluronic polymer, the higher the changed values of micellization enthalpy and entropy. The hydrophobic part of the pluronics, PPO, was responsible for the interaction between pluronics and BSA. Hydrophobic interaction between PPO and BSA was correlated to the alternation of the PPO-PPO interaction by the addition of BSA, which would shift the CMT toward higher temperature and alter the thermodynamic parameters of micellization for pluronics in aqueous solutions.     

Structure of pluronic F-127 and its tetraphenylporphyrin complexes: X-ray diffraction study

The structure of pluronic F-127 and its complexes with tetraphenylporphyrin has been studied by SAXS and WAXS techniques. It has been shown that the samples prepared via evaporation of chloroform and aqueous solutions of pluronic and its mixtures with tetraphenylporphyrin have a semicrystalline layered structure with the crystalline phase composed of poly(ethylene oxide). The identity period of layers in the samples prepared from the aqueous solution of pluronic has been found to be larger than that in the samples prepared from chloroform solutions of the polymer. This result may apparently be explained by a more pronounced hydration of the samples prepared by the former method. The presence of tetraphenylporphyrin in the samples has an insignificant effect on the parameters of the crystalline and layered structures of pluronic. When the tetraphenylporphyrin content is not larger than its solubilization limit with pluronic, tetraphenylporphyrin concentrates in the amorphous layers of pluronic in the noncrystalline finely dispersed state.     

Microenvironment in the corona region of triblock copolymer micelles: temperature dependent solvation and rotational relaxation dynamics of coumarin dyes

Dynamic Stokes' shift and fluorescence anisotropy measurements using coumarin-153 (C153) and coumarin-151 (C151) as the fluorescence probes have been carried out in aqueous poly(ethylene oxide)20-poly(propylene oxide)70-poly(ethylene oxide)20 (P123) and poly(ethylene oxide)100-poly(propylene oxide)70-poly(ethylene oxide)100 (F127) block copolymer micelles with an aim to understand the water structures and dynamics in the micellar corona region. It has been established that the probes reside in the micellar corona region. It is indicated that the corona regions of P123 and F127 micelles are relatively less hydrated than the Palisade layers of neutral micelles like Triton-X-100 and Brij-35. From the appraisal of total Stokes' shift values for the probes in the two block copolymer micelles, it is inferred that the F127 micelle is more hydrated than the P123 micelle. It is observed that the dynamic Stokes' shift values for both of the probes remain more or less similar at all the temperatures studied in the P123 micelle. For C153 in F127, however, the observed Stokes' shift is seen to decrease quite sharply with temperature, though it remains quite similar for C151. Moreover, the fraction of the unobserved initial dynamic Stokes' shift is appreciably higher for both the probes in the F127 micelle compared to that in P123. Over the studied temperature range of 293-313 K, the spectral shift correlation function is described adequately by a bi-exponential function. Rotational relaxation times for C153 in both the micelles show a kind of transition at around 303 K. These results have been rationalized assuming collapse of the poly(ethylene oxide) (PEO) blocks and formation of water clusters in the corona region due to dehydration of poly(ethylene oxide) blocks with an increase in temperature. A dissimilar probe location has been inferred for the differences in the results with C153 and C151 probes in F127. Comparison of the microviscosity and the hydration of the block copolymer micelles has also been made with those of the other commonly used neutral micelles, for a better understanding of the results in the block copolymer micelles.     

Effect of laponite clay particles on thermal and rheological properties of Pluronic triblock copolymer

The high concentration 17 wt% triblock copolymer poly(ethylene oxide)₁₀₀–poly(propylene oxide)₆₅–poly(ethylene oxide)₁₀₀ Pluronic F127 aqueous solutions with the addition of laponite is investigated as a novel temperature-sensitive hydrogel system. The critical micelle temperature (cmt) and the sol-to-gel transition were characterized by rheological experiments and differential scanning calorimetry. Experimental results showed that laponite particles have no significant influence on the cmt. On the other hand, viscoelastic measurements have highlighted an increase of the sol-to-gel transition temperature for mixtures with 2 and 3 wt% of laponite particles. This additive can be used to adjust the gelation temperature close to physiological temperature in medical applications.     

Binding of hexadecylammonium surfactants to water-soluble neutral polymers

The binding of hexadecyltrimethylammonium bromide and hexadecyldimethyl-2-hydroxyethylammonium bromide to neutral polymers was measured by a potentiometric titration method using surfactant selective electrodes. Binding to poly(vinyl alcohol) was slightly cooperative, while that to poly(ethylene oxide) lacked the co-operativity. Poly(vinyl pyrrolidone) did not bind them at all. Binding affinity as estimated by a distribution coefficient of the cationic surfactants between the bulk and polymer phases is about 2 orders of magnitude smaller than that of anionic sodium dodecyl sulfate. The heat of binding was estimated from the temperature dependence of the distribution coefficient and found to be endothermic. It is imagined that the cationic surfactants are simply partitioned between the aqueous bulk phase and the polymer coil phase which is regarded as aqueous organic mixed solvent.     

Photostability of pseudoisocyanine J aggregates in polymer films and ways of its improvement

The photostability of J aggregates of the pseudoisocyanine dye in polyvinylpyrrolidone (PVP) and poly(vinyl alcohol) (PVA) polymer films under continuous irradiation with visible light was investigated. The decay of J aggregates in PVP is predominantly due to the reaction of photooxidation with singlet oxygen generated by triplet-state pseudoisocyanine dimers. Unlike the case of PVP, J aggregates in PVA demonstrate significantly higher photostability because of a lower PVP permeability for oxygen. A significant improvement in the photostability of J aggregates is achieved by the introduction of scavengers of singlet oxygen into the polymer films.     

Stabilization of two-phase octanol/water flows inside poly(dimethylsiloxane) microchannels using polymer coatings

In this paper we present our first results on the realization of stable water/octanol, two-phase flows inside poly(dimethylsiloxane) (PDMS) microchannels. Native PDMS microchannels were coated with high molecular weight polymers to change the surface properties of the microchannels and thus stabilize the laminar flow profile. The polymers poly(2-hydroxyethyl methacrylate), poly(vinyl pyrrolidone), poly(ethylene oxide), poly(ethylene glycol), and poly(vinyl alcohol) were assessed for their quality as stabilization coatings after deposition from flowing and stationary solutions. Additionally, the influence of coating the microchannels homogeneously with a single kind of polymer or heterogeneously with two different polymers was investigated. From the experimental observations, it can be concluded that homogeneous polymer coatings with poly(2-hydroxyethyl methacrylate) and poly(vinyl pyrrolidone) led to the effective stabilization of laminar water/octanol flows. Furthermore, heterogeneous coatings led to two-phase flows which had a better-defined and more stable interface over long distances (i.e., 40-mm-long microchannels). Finally, the partitioning of fuchsin dye in the coated microchannels was demonstrated, establishing the feasibility of the use of the polymer-coated PDMS microchannels for determination of logP values in laminar octanol/water flows.     

A viscosity-tunable polymer for DNA separation by microchip electrophoresis

A thermo-responsive separation matrix, consisting of Pluronic F127 tri-block copolymers of poly(ethylene oxide) and poly(propylene oxide), was used to separate DNA fragments by microchip electrophoresis. At low temperature, the polymer matrix was low in viscosity and allowed rapid loading into a microchannel under low pressure. With increasing temperatures above 25°C, the Pluronic F127 solution forms a liquid crystalline phase consisting of spherical micelles with diameters of 17–19 nm. The solution can be used to separate DNA fragments from 100 bp to 1500 bp on poly(methyl methacrylate) (PMMA) chips. This temperature-sensitive and viscosity-tunable polymer provided excellent resolution over a wide range of DNA sizes. Separation is based on a different mechanism compared with conventional matrices such as methylcellulose. To illustrate the separation mechanism of DNA in a Pluronic F127 solution, DNA molecular imaging was performed by fluorescence microscopy with F127 polymer as the separation matrix in microchip electrophoresis. Figure Temperature dependence of the viscosity of 20% w/w Pluronic F127 solution in 1xTBE buffer. Dotted approximates resultant curve.     

嵌段共聚物傅里叶变换拉曼光谱

用傅里叶变换拉曼光谱(FT-Paman)研究了聚环氧乙烷-聚环氧丙烷-聚环氧乙烷(PEO-PPO-PEO)嵌段共聚物的无水样品,发现某些谱带对PEO0-PPO-PEO嵌段共聚物的结构和构象变化敏感,其中某些峰的相对强度的PPO/PEO比率和共聚物的构象有关,研究表明PluronicF68和F88具有一些反式构象的螺旋结构,PluronicP103(P123)是无规则结构,其它的嵌段共聚物处于二者之间.     

Effect of temperature on the intrinsic viscosity of poly(ethylene glycol)/poly(vinyl pyrrolidone) blends in aqueous solutions

In this work the intrinsic viscosity of poly(ethylene glycol)/poly(vinyl pyrrolidone) blends in aqueous solutions were measured at 283.1–313.1 K. The expansion factor of polymer chain was calculated by use of the intrinsic viscosities data. The thermodynamic parameters of polymer solution (the entropy of dilution parameter, the heat of dilution parameter, theta temperature, polymer–solvent interaction parameter and second osmotic virial coefficient) were evaluated by temperature dependence of polymer chain expansion factor. The obtained thermodynamic parameters indicate that quality of water was decreased for solutions of poly(ethylene oxide), poly(vinyl pyrrolidone) and poly(ethylene oxide)/poly(vinyl pyrrolidone) blends by increasing temperature. Compatibility of poly(ethylene oxide)/poly(vinyl pyrrolidone) blends were explained in terms of difference between experimental and ideal intrinsic viscosity and solvent–polymer interaction parameter. The results indicate that the poly(ethylene glycol)/poly(vinyl pyrrolidone) blends were incompatible.     

Effect of metal-free porphyrins on the thermal–oxidative breakdown of biocompatible polymers

The inhibitory effect of metal-free porphyrins on the thermal–oxidative breakdown of several biocompatible polymers is observed for the first time. Differential thermal analysis shows that the thermal stability of poly(ethylene oxide) and triblock copolymers of ethylene oxide and propylene oxide increases by 80–100 K, compared to the initial breakdown temperatures of these polymers in the presence of metal-free porphyrins (up to 3 wt %).     

Reaction of chlorine-containing polymers with living polymers

A graft polymer was prepared by means of the coupling reaction of chlorinated ethylene–propylene terpolymer with living polystyrene, obtained with a sodium–naphthalene complex as initiator, under various conditions; the grafting efficiency and the percentage of grafting are discussed. Poly(chloroprene), chlorinated butyl rubber, poly(vinyl chloride), poly(epichlorohydrin), and epichlorohydrin–ethylene oxide copolymer were also used as chlorine-containing polymers. The grafting efficiencies were found to be in the following order: chlorinated butyl rubber > poly(epichlorohydrin) > epichlorohydrin-ethylene oxide copolymer > chlorinated ethylene-propylene terpolymer > poly(chloroprene) > poly(vinyl chloride). A graft polymer was obtained from the reaction between chlorinated ethylene–propylene terpolymer and living poly(isoprene), with butyllithium in benzene. The undesirable metal–halogen interchange reaction was considerable.     

Preparation of Ultrafine Water-soluble Polymers Nanofiber Mats via Electrospinning

A series of water-soluble polymers such as poly(ethylene oxide)(PEO),polyacrylamide(PAM) and poly(vinyl pyrrilidone)(PVP) was successfully prepared via the electrospinning of their aqueous solutions without the use of a surfactant.The effects of solution properties on the electrospinning of PEO,PAM and PVP solutions were investigated.The viscosity of the solution,charge density carried by the jet,and the surface tension of the solution are the key factors that influence the morphology and diameter size of t...