PLURONIC x TETRONIC polyols: study of their properties and performance in the destabilization of emulsions formed in the petroleum industry

In this work, a new family of branched poly(ethylene oxide-propylene oxide) (PEO-PPO) block copolymers designed as TETRONIC polyols is evaluated and compared to linear PEO-PPO block copolymers designed as PLURONIC polyols. Additives have been employed as well in order to improve solubility of these materials in aqueous solution. Such additives include the sodium p-toluene sulfonate (NaPTS) hydrotrope and concentrated hydrochloric acid. Solubility tests and aqueous solution surface tension data showed consistent results: the structure of the block PEO-PPO copolymers exerts a huge influence on their solubility in water. The solubility of such copolymers is increased by the presence of the sodium toluene sulfonate (NaPTS) hydrotrope. The presence of HCl caused increased solubility for the copolymer TETRONIC polyol only, the effect being less than that observed for the hydrotrope. It is concluded that as regards emulsion stabilization, TETRONIC copolymer polyols perform better. Correlation between structure and properties leads to the optimization of block PEO-PPO copolymer selection aiming at using these materials for the separation of petroleum industry emulsions.     

Synthesis and Surface Tension Properties of Polyethyleneimine—Polyethylene Oxide Block Copolymers

IntroductionInrecentyearstherehavebeenincreasingactivitiesinblockcopolymersynthesisandcharacterization .Manystudieshaveshownthatblockcopolymersformmicellesofcloseasso ciationupondissolutionintoaselectivesolvent,whichactsthermodynamicallyasagoodsolventforoneblockandapoorsolventfortheotherblock .1Theimportanceofthesesyntheticactivitieshasbeenemphasizedbyblockcopolymermicelles ,whichhavebeendemonstratedaspotentialdrugcarriers,2 ,3andotherinvestigationshaverevealedtheirexcellentutilityincancerchem…     

Mechanism of gold metal ion reduction, nanoparticle growth and size control in aqueous amphiphilic block copolymer solutions at ambient conditions

Spontaneous formation and efficient stabilization of gold nanoparticles with an average diameter of 7 approximately 20 nm from hydrogen tetrachloroaureate(III) hydrate (HAuCl4.3H2O) were achieved in air-saturated aqueous poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymer solutions at ambient temperature in the absence of any other reducing agent. The particle formation mechanism is considered here on the basis of the block copolymer concentration dependence of absorption spectra, the time dependence (kinetics) of AuCl4- reduction, and the block copolymer concentration dependence of particle size. The effects of block copolymer characteristics such as molecular weight (MW), PEO block length, PPO block length, and critical micelle concentration (cmc) are explored by examining several PEO-PPO-PEO block copolymers. Our observations suggest that the formation of gold nanoparticles from AuCl4- comprises three main steps: (1) reduction of metal ions by block copolymer in solution, (2) absorption of block copolymer on gold clusters and reduction of metal ions on the surface of these gold clusters, and (3) growth of metal particles stabilized by block copolymers. While both PEO and PPO blocks contribute to the AuCl4- reduction (step 1), the PEO contribution appears to be dominant. In step 2, the adsorption of block copolymers on the surface of gold clusters takes place because of the amphiphilic character of the block copolymer (hydrophobicity of PPO). The much higher efficiency of particle formation attained in the PEO-PPO-PEO block copolymer systems as compared to PEO homopolymer systems can be attributed to the adsorption and growth processes (steps 2 and 3) facilitated by the block copolymers. The size of the gold nanoparticles produced is dictated by the above mechanism; the size increases with increasing reaction activity induced by the block copolymer overall molecular weight and is limited by adsorption due to the amphiphilic character of the block copolymers.     

A Morphological Transition of Inverse Mesophases of a Branched‐Linear Block Copolymer Guided by Using Cosolvents

We report here a strategy for influencing the phase and lattice of the inverse mesophases of a single branched‐linear block copolymer (BCP) in solution which does not require changing the structure of the BCP. The phase of the self‐assembled structures of the block copolymer can be controlled ranging from bilayer structures of positive curvature (polymersomes) to inverse mesophases (triply periodic minimal surfaces and inverse hexagonal structures) by adjusting the solvent used for self‐assembly. By using solvent mixtures to dissolve the block copolymer we were able to systematically change the affinity of the solvent toward the polystyrene block, which resulted in the formation of inverse mesophases with the desired lattice by self‐assembly of a single branched‐linear block copolymer. Our method was also applied to a new solution self‐assembly method for a branched‐linear block copolymer on a stationary substrate under humidity, which resulted in the formation of large mesoporous films. Our results constitute the first controlled transition of the inverse mesophases of block copolymers by adjusting the solvent composition.     

Interaction of amphiphilic block copolymer micelles with surfactants

An out line and summary of literature studies on interactions between different types of amphiphilic copolymer micelles with surfactants has been given. This field of research is still emerging and it is difficult presently to make generalisations on the effects of surfactants on the copolymer association. The effects are found to be varied depending upon the nature and type of hydrophobic (hp) core and molecular architecture of the copolymers and the hydrocarbon chain length and head group of surfactants. The information available on limited studies shows that both anionic and cationic surfactants (in micellar or molecular form) equally interact strongly with the associated and unassociated forms of copolymers. The beginning of the interaction is typically displayed as critical aggregation concentration (CAC), which lies always below the critical micelle concentration of the respective surfactant. The surfactants first bind to the hydrophobic core of the copolymer micelles followed by their interaction with the hydrophilic (hl) corona parts. The extent of binding highly depends upon the nature, hydropobicity of the copolymer molecules, length of the hydrocarbon tail and nature of the head group of the surfactant. The micellization of poly(ethylene oxide) (PEO)–poly(propylene oxide) (PPO)–poly(ethylene oxide) was found to be suppressed by the added surfactants and at higher surfactant concentrations, the block copolymer micelles get completely demicellized. This effect was manifested itself in the melting of liquid crystalline phases in the high copolymer concentrations. However, no such destabilization was found for the micelles of polystyrene (PS)–poly(ethylene oxide) copolymers in water. On the contrary, the presence of micellar bound surfactant associates resulted in to large super micellar aggregates through induced intra micellar interactions. But with the change in the hydrophobic part from polystyrene to poly(butadiene) (PB) in the copolymer, the added surfactants not only reduced the micellar size but also transformed cylindrical micelles to spherical ones. The mixtures in general exhibited synergistic effects. So varied association responses were noted in the mixed solutions of surfactants and copolymers.     

Preparation and characterization of biodegradable poly(l-lactide)/poly(ethylene glycol) microcapsules containing erythromycin by emulsion solvent evaporation technique

In this work, the producing of a biodegradable poly(l-lactide) (PLA)/poly(ethylene glycol) (PEG) microcapsule by emulsion solvent evaporation method was investigated. The effect of PEG segments added to the PLA microcapsules on the degradation, size distribution, and release behavior was studied. According to the results, PLA/PEG copolymer was more hydrophilic than PLA homopolymer, and with lower glass transition temperature. The surface of PLA/PEG microcapsules was not as smooth as that of PLA microcapsules, the mean diameters of prepared PLA and PLA/PEG microcapsules were 40 and 57 microm, respectively. And spherical forms were observed by the image analyzer and the scanning electron microscope (SEM). Drug release from microcapsules was affected by the properties of PLA/PEG copolymers determined by UV-vis spectra. It was found that the drug release rates of the microcapsules were significantly increased with adding of PEG, which explained by increasing hydrophilic groups.     

Synthesis of vesicles on polymer template

Reactive single-tail cationic surfactants self-assemble on the anionic block copolymer templates. These systems spontaneously arrange in small vesicles of nanoscale size. The vesicles are further stabilized by dimerization of the assembled surfactant monomers forming double-tail surfactants bound to the block copolymer. The resulting systems are resistant to changes in environmental characteristics such as pH, ionic strength, and temperature variations. Hydrophilic macromolecules can be encapsulated in the internal aqueous volume of these vesicles. The simplicity of the preparation makes these systems promising as drug and gene delivery carriers.     

Cytotoxicity of nonionic amphiphilic copolymers

The purpose of this study is to ascertain the relationship between the structure of an amphiphilic nonionic polymer and its toxicity for cells (cytotoxicity) growing in a culture. To this end, 16 polymers of different architectures and chemical structures are tested, namely, linear triblock copolymers of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (Pluronics); diblock copolymers of propylene oxide, ethylene oxide, and hyperbranched polyglycerol; alternating and diblock copolymers of ethylene oxide and dimethylsiloxane; and two surfactants containing linear (Brij-35) or branched (Triton X-100) aliphatic chains. Polymer-cell interaction is assayed in a culture medium in the absence of serum. Effective concentrations of the polymers causing 50% cell death, EC₅₀, vary within three orders of magnitude. Toxic concentrations of the alternating copolymer, Triton X-100, and Brij-35 are lower than their CMC values. In contrast, all block copolymers, regardless of their chemical structures, become toxic at concentrations above the CMC; that is, they acquire cytotoxicity only in the micellar form. The EC₅₀ values of the copolymers depend on their hydrophilic-liphophilic balance (HLB) through the following empirical formula: EC₅₀ × 10⁶ = 8.71 × HLB^2.1. This relationship makes it possible to predict the cytotoxic concentration region of a block copolymer of a known structure.     

Interaction studies of styrene—ethylene oxide block copolymers with ionic surfactants in aqueous solution

The interaction of styrene—ethylene oxide block copolymers with four anionic surfactants (sodium dodecyl sulfate, sodium dodecanoate, sodium dodecylbenzenesulfonate, and sodium dodecanoyl sarcosinate), and two cationic surfactants (tetradecyl- and hexadecyl-trimethylammonium bromide), was studied and each surfactant showed a distinct interaction with the copolymer in aqueous solution. Usually two transitions, one below and one above the critical micelle concentration, CMC, of the surfactants, were observed from conductance, surface tension, and dye solubilization measurements. These transitions indicate the beginning and completion of polymer—surfactant interaction. The viscometric results showed the formation of a polyelectrolyte complex. The interaction between copolymer and sodium dodecyl sulfate was also examined by ¹H NMR. The influence of the molecular characteristics of the block copolymers, the nature and type of surfactants, temperature and added salt on the interaction is described. A possible mechanism for such an interaction is proposed.     

New amphiphilic diblock copolymers: surfactant properties and solubilization in their micelles

Several series of amphiphilic diblock copolymers are investigated as macrosurfactants in comparison to reference low-molar-mass and polymeric surfactants. The various copolymers share poly(butyl acrylate) as a common hydrophobic block but are distinguished by six different hydrophilic blocks (one anionic, one cationic, and four nonionic hydrophilic blocks) with various compositions. Dynamic light scattering experiments indicate the presence of micelles over the whole concentration range from 10(-4) to 10 g x L(-1). Accordingly, the critical micellization concentrations are very low. Still, the surface tension of aqueous solutions of block copolymers decreases slowly but continuously with increasing concentration, without exhibiting a plateau. The longer the hydrophobic block, the shorter the hydrophilic block, and the less hydrophilic the monomer of the hydrophilic block is, the lower the surface tension is. However, the effects are small, and the copolymers reduce the surface tension much less than standard low-molar-mass surfactants. Also, the copolymers foam much less and even act as anti-foaming agents in classical foaming systems composed of standard surfactants. The copolymers stabilize O/W emulsions made of methyl palmitate as equally well as standard surfactants but are less efficient for O/W emulsions made of tributyrine. However, the copolymer micelles exhibit a high solubilization power for hydrophobic dyes, probably at their core-corona interface, in dependence on the initial geometry of the micelles and the composition of the block copolymers. Whereas micelles of copolymers with strongly hydrophilic blocks are stable upon solubilization, solubilization-induced micellar growth is observed for copolymers with moderately hydrophilic blocks.     

Rheology of linear and branched styrene–acrylonitrile copolymers. Similarities and differences

A comprehensive investigation of rheological properties of linear and branched styrene-acrylonitrile copolymer specimens with similar molecular characteristics has been carried out. During the steady-state shear flow, the viscosity properties of both specimens are described by the Cross equation. In this case, the branched copolymer is characterized by a higher viscosity and shear thinning degree as well as by substantially lower shear rate values corresponding to transition to the non-Newtonian flow region. The elasticity of the branched copolymer melt (estimated from the value of the first normal stress difference) is considerably higher than that of the linear. This is reflected on the characteristics of occurrence of unstable flow at high shear rates. Rougher extrudate surface distortions are characteristic for the branched copolymer, and the shear rate corresponding to their occurrence is noticeably lower than for the linear copolymer. The dynamic characteristics of the copolymers being compared also attest to a greater elasticity of the branched specimen. An investigation of the viscoelastic properties in a wide temperature range allowed constructing a generalized frequency dependence of dynamic moduli encompassing various regions of the relaxation states of the copolymer specimens. Continuous relaxation spectra were calculated by means of the Mellin transform. It is shown that relaxation phenomena caused by segmental mobility doesn’t depend on the presence of branchings, whereas branching of the chain has a substantial effect on translation mobility of the chain as a whole. Branching leads to a noticeable increase of transient elongation viscosity but has almost no effect of strain hardening of the melt.     

Block Copolymers in Emulsion and Dispersion Polymerization

Summary: This article deals with recent progress including the authors' work concerning the application of block copolymers as polymeric surfactants in heterophase polymerizations. The synthesis methods for preparing block copolymers by emulsion and dispersion techniques are outlined, with emphasis on recently developed controlled free radical polymerizations in aqueous media. Specific characteristics of amphiphilic block copolymers are described, for example, micellization and emulsifying effects. A general overview of emulsion and dispersion polymerization in an aqueous and organic medium with ionic and nonionic block copolymers is presented for the preparation of electrosteric and sterically stabilized latex particles. Typical examples of microemulsion, miniemulsion, oil‐in‐oil emulsion, and micellar polymerizations are provided. Current and potential developments of so‐called “hairy latexes”, inverse‐, multiple‐, and solid emulsions, as well as of nonaqueous polymeric dispersions are also discussed.

PS foam obtained by free radical polymerization of water‐in‐styrene, stabilized with a PS–PEO diblock copolymer.     

Polymeric surfactants in latex technology: polystyrene–poly(ethylene oxide) block copolymers as stabilizers in emulsion polymerization

Polystyrene–poly(ethylene oxide) PS–PEO di- and triblock copolymers have been used as stabilizers in the emulsion polymerization of styrene and styrene–butylacrylate for the preparation of “hairy latexes”. The polymerization kinetics and the efficiency of these polymeric surfactants were correlated with the molecular characteristics of the block copolymer. It was shown that the efficiency decreased with increasing molecular weight and PS content of the block copolymer. The PEO frige, with a thickness of 4–25 nm, on the latex particle surface could be characterized and it was shown by differential scanning calorimetry (DSC) that water is strucured in that PEO layer. Film formation with “hairy latexes” was also examined both by DSC and thermomechanical analysis. The properties and application possibilities, such as in controlled latex flocculation, have been reviewed.     

Synthesis and MALDI‐TOF analysis of dendritic‐linear block copolymers of lactides: Influence of architecture on stereocomplexation

Formation of a stereocomplex from polylactide copolymers can be tuned by changing the size and the chain topology of the second block in the copolymer. In particular, the use of a dendritic instead of linear architecture is expected to destabilize the cocrystallisation of polylactide blocks. With this idea in mind, dendritic‐linear block copolymers were synthesized by ring‐opening polymerization (ROP) of lactides using benzyl alcohol dendrons of generation 1–3 as macroinitiators and stannous octoate as catalyst. Polymers with controlled and narrow molar mass distribution were obtained. The MALDI‐TOF mass spectra of these dendritic‐linear block copolymers show well‐resolved signals. Remarkably, 10% or less of odd‐membered polymers are present, indicating that ester‐exchange reactions which occur classically parallel to the polymerization process, were in these conditions, very limited. Thermal analysis of polyenantiomers of generation 1–3 and the corresponding blends were examined. The blend of a pair of enantiomeric dendritic‐linear block copolymers exhibit a higher melting temperature than each copolymer, characteristic for the formation of a stereocomplex. Melting temperatures are strongly dependent on the dendron generation. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6782–6789, 2006     

Surface properties of styrene–ethylene oxide block copolymers

Hydrophobic–hydrophilic block copolymers were prepared by “living” anionic polymerization. They consist of polystyrene and poly(ethylene oxide) blocks, and are soluble in water. Their interfacial properties were investigated, employing aqueous solutions. The block copolymers lowered the surface tension of water in analogy with the low molecular weight surfactants such as sodium lauryl sulfate and heptaethylene oxide n-dodecyl ether. Their aqueous solutions exhibited solubilization properties differing from those of polyethylene glycol. Therefore, it is thought that the polystyrene blocks produce solubilization phenomena. In samples of the same styrene content, the precipitation temperature of a high molecular weight copolymer in water was lower than that of a low molecular weight copolymer at the same concentration in the same solvent. The surface tension and precipitation temperature of aqueous solutions seem to be influenced by molecular weight and composition.     

Coupling reaction of poly(α-methylstyryl) anion with (MMA–α-methylstyrene) block copolymer

(MMA–α-methylstyrene)block copolymer was reacted with poly(α-methylstyryl)anion at ?78°C in a mixture of good tetrahydrofuran (THF) and poor methylcyclohexane solvents. The reaction conditions were chosen so as to produce graft copolymers made up of a backbone (AB-type block copolymer) and a single branched chain (1:2 graft copolymer). Gel permeation chromatograph (GPC), osmotic pressure measurement, and elemental analysis were used for the characterization of 1:2 graft copolymer. It appeared that poly(α-methylstyryl)anion reacted with the end pendant groups located farthest away from the branched point of AB-type block copolymer, when the dimensions of AB-type block copolymer molecule are small.     

Interaction of ethylene oxide-propylene oxide copolymers with ionic surfactants studied by calorimetry: random versus block copolymers

The present study used calorimetric techniques to follow the interaction of random and block ethylene oxide (EO)-propylene oxide (PO) copolymers with ionic surfactants. Features such as the intensity of the interaction (evaluated through their critical aggregation concentrations) and the profile of the isothermal titration calorimetry (ITC) curves were comparatively analyzed for random and block copolymers with similar composition (number of EO and PO units). Random copolymers displayed an interaction similar to that observed with other hydrophilic homopolymers with the additional characteristic that the intensity of the interaction increased with the increase in the copolymer hydrophobicity (as determined by its PO content), revealing that these copolymers display an intermediate behavior between PEO and PPO. For nonaggregated block copolymers (unimers) with large enough EO blocks (molar mass above 2000 g mol-1), ITC curves revealed that the anionic surfactant sodium dodecylsulfate (SDS) interacts with the PO and EO blocks almost independently, being more favorable with the PO block, which controls the critical aggregation concentration (cac) value. Effects of temperature and of the nature of the ionic surfactants on their interaction with these copolymers were found to agree with the previously reported trends.     

Comparison of surface properties of random, block, and graft copolymers having perfluoroalkyl and silicone-containing side chains

Fluorosilicone copolymers of random, block, and graft with both perfluoroalkyl and silicone-containing side chains were synthesized, and their surface properties and surface modification effects on PVC film were compared. It can be confirmed that the fluorosilicone copolymers of random, block, and graft exhibit very low surface free energies of 9-13 dyn/cm, depending on the perfluoroalkyl group content and their molecular structure. The inherent surface free energies of the fluorosilicone copolymers are significantly influenced by their molecular structure and perfluoroalkyl group content. It can also be found that the fluorosilicone copolymers are very effective for lowering surface free energy. The surface free energy of a copolymer/PVC blend strongly varies with perfluoroalkyl group content as well as molecular structure. The molecular structure of a fluorosilicone copolymer is as important as the perfluoroalkyl group content for their inherent surface free energies and surface modification of other polymers.     

Biocompatible surfactants for water-in-fluorocarbon emulsions

Drops of water-in-fluorocarbon emulsions have great potential for compartmentalizing both in vitro and in vivo biological systems; however, surfactants to stabilize such emulsions are scarce. Here we present a novel class of fluorosurfactants that we synthesize by coupling oligomeric perfluorinated polyethers (PFPE) with polyethyleneglycol (PEG). We demonstrate that these block copolymer surfactants stabilize water-in-fluorocarbon oil emulsions during all necessary steps of a drop-based experiment including drop formation, incubation, and reinjection into a second microfluidic device. Furthermore, we show that aqueous drops stabilized with these surfactants can be used for in vitro translation (IVT), as well as encapsulation and incubation of single cells. The compatability of this emulsion system with both biological systems and polydimethylsiloxane (PDMS) microfluidic devices makes these surfactants ideal for a broad range of high-throughput, drop-based applications.     

The dramatic effect of architecture on the self-assembly of block copolymers at interfaces

Dramatic morphological changes are observed in the Langmuir-Blodgett (LB) film assemblies of poly(ethylene glycol)-b-(styrene-r-benzocyclobutene) block copolymer (PEG-b-(S-r-BCB)) after intramolecular cross-linking of the S-r-BCB block to form a linear-nanoparticle structure. To isolate architectural effects and allow direct comparison, the linear block copolymer precursor and the linear-nanoparticle block copolymer resulting from selective intramolecular cross-linking of the BCB units were designed to have exactly the same molecular weight and chemical composition but different architecture. It was found that the effect of architecture is pronounced with these macromolecular isomers, which self-assemble into dramatically different surface aggregates. The linear block copolymer forms disklike surface assemblies over the range of compression states, while the linear-nanoparticle block copolymer exhibits long (>10 microm) wormlike aggregates whose length increases as a function of increasing cross-linking density. It is shown that the driving force behind the morphological change is a combination of the altered molecular geometry and the restricted degree of stretching of the nanoparticle block because of the intramolecular cross-linking. A modified approach to interpret the pi-A isotherm, which includes presence of the block copolymer aggregates, is also presented, while the surface rheological properties of the block copolymers at the air-water interface provide in-situ evidence of the aggregates' presence at the air-water interface.