Polyelectrolyte Block Research Articles

Polyion Complex Nanomaterials from Block Polyelectrolyte Micelles and Linear Polyelectrolytes of Opposite Charge. 2. Dynamic Properties

The present study investigates the relationship between the aggregation state and dynamic properties of block ionomer complexes (BICs) based on amphiphilic ionic block copolymers. The polyion coupling of 4'-(aminomethyl)fluorescein (AMF)-labeled poly(sodium methacrylate) (PMANa) or polystyrene- block-poly(sodium carboxylates) with poly(N-ethyl-4-vinylpyridinium bromide), PEVP was studied at an excess of carboxylate groups [PEVP]/[COO(-)] TOTAL = 0.3 and detected by fluorescence quenching. The polyion interchange reactions included migration of PEVP between the following: (1) two linear polyanion chains, (2) linear polyanion chain and anionic polyion shell micelle, or (3) two anionic polyion shell micelles. Additionally, the interchange of AMF-labeled PMANa with unlabeled PMANa in the shell of polystyrene- block-PEVP micelles was studied. The interchange reactions were carried out at [PEVP]/[COO(-)] TOTAL = 0.15 and detected by fluorescence quenching (direct reaction) or ignition (reverse reaction). The rates of these reactions were compared using half-conversion times and, when possible, second-order reaction kinetic constants. The dependences of the rates on the ionic strength and polyion length observed for BICs were similar to those previously reported for regular interpolyelectrolyte complexes (IPECs) of linear polyions. However, the interchange reactions involving polyion shell micelles were much slower than those reactions observed in IPECs. The coupling reactions involving polyion shell micelles were also slower compared with the coupling of linear polyions. The observed phenomena were attributed to the aggregation state of polyion shell micelles and discussed using the collision model for polyion interchange reactions previously proposed for IPECs.

PH‐Switchable Complexation between Double Hydrophilic Heteroarm Star Copolymers and a Cationic Block Polyelectrolyte

AbstractDouble hydrophilic heteroarm star copolymers of poly(methacrylic acid) (PMAA) and poly(ethylene oxide) (PEO) were synthesized via atom‐transfer radical polymerization (ATRP) using the “in‐out” method. The synthesis consisted of three steps. Namely, ATRP was applied to the preparation of a star macroinitiator with PEO arms and a cross‐linked core resulting from the polymerization of divinylbenzene (DVB) in the first step, chain extension with tert‐butyl methacrylate (tBMA) under ATRP conditions, and subsequent hydrolysis of the tert‐butyl groups afforded (PEO)n‐PDVB‐(PMAA)n heteroarm star copolymers with a cross‐linked microgel core. This novel type of double hydrophilic heteroarm star copolymer can be considered as unimolecular micelles with hybrid coronas. The star copolymers exhibited pH‐dependent solubility in water, being soluble at high pH and insoluble at low pH, due to the formation of hydrogen‐bonded complexes between the PEO and PMAA arms. A mixed solution of the heteroarm star copolymer and a PEO‐b‐PQDMA diblock copolymer, where PQDMA is poly(2‐(dimethylamino)ethyl methacrylate) fully quaternized with methyl iodide, remained stable in the whole pH range, and exhibited an intriguing pH‐switchable complexation behavior accompanied with structural rearrangement.magnified image

The effect of PEO block lengths on the size and stability of complex coacervate core micelles

We report on a series of polyion complexes from mixtures of poly(ethylene oxide)- block-poly( N , N -diethylaminoethylmethacrylate) (PEO–PDEAMA) and poly(ethylene oxide)- block-poly(aspartic acid) (PEO–PAsp). As expected, the micelle size, polydispersity and stability are dependant on the relative and absolute lengths of the polyelectrolyte chains. However, we also demonstrate that whilst the length of the charged polyelectrolyte blocks is important, the length of the PEO chains is an equally relevant variable in determining both the size and stability of the final micelles as well as the degree of charge neutralisation at which micellisation occurs. We also show that the kinetics of formation can result in very different stability of the final micelles.

Phase Behavior of Polyelectrolyte Block Copolymers in Mixed Solvents

We have studied the phase behavior of the poly(n-butyl acrylate)-b-poly(acrylic acid) block copolymer in a mixture of two miscible solvents, water and tetrahydrofuran (THF). The techniques used to examine the different polymers, structures and phases formed in mixed solvents were static and dynamic light scattering, small-angle neutron scattering, nuclear magnetic resonance and fluorescence microscopy. By lowering the water/THF mixing ratio X, the sequence unimers, micron-sized droplets, polymeric micelles was observed. The transition between unimers and the micron-sized droplets occurred at X = 0.75, whereas the microstructuration into core-shell polymeric micelles was effective below X = 0.4. At intermediate mixing ratios, a coexistence between the micron-sized droplets and the polymeric micelles was observed. Combining the different aforementioned techniques, it was concluded that the droplet dispersion resulted from a solvent partitioning that was induced by the hydrophobic blocks. Comparison of poly(n-butyl acrylate) homopolymers and poly(n-butyl acrylate)-b-poly(acrylic acid) block copolymers suggested that the droplets were rich in THF and concentrated in copolymers and that they were stabilized by the hydrophilic poly(acrylic acid) moieties.

Complex coacervate core micro-emulsions.

Complex coacervate core micelles form in aqueous solutions from poly(acrylic acid)-block-poly(acrylamide) (PAAxPAAmy, x and y denote degree of polymerization) and poly(N,N-dimethyl aminoethyl methacrylate) (PDMAEMA150) around the stoichiometric charge ratio of the two components. The hydrodynamic radius, Rh, can be increased by adding oppositely charged homopolyelectrolytes, PAA140 and PDMAEMA150, at the stoichiometric charge ratio. Mixing the components in NaNO3 gives particles in highly aggregated metastable states, whose Rh remain unchanged (less than 5% deviation) for at least 1 month. The Rh increases more strongly with increasing addition of oppositely charged homopolyelectrolytes than is predicted by a geometrical packing model, which relates surface and volume of the particles. Preparation in a phosphate buffer - known to weaken the electrostatic interactions between PAA and PDMAEMA - yields swollen particles called complex coacervate core micro-emulsions (C3-μEs) whose Rh increase is close to that predicted by the model. These are believed to be in the stable state (lowest free energy). A two-regime increase in Rh is observed, which is attributed to a transition from more star-like to crew-cut-like, as shown by self-consistent field calculations. Varying the length of the neutral and polyelectrolyte block in electrophoretic mobility measurements shows that for long neutral blocks (PAA26PAAm405 and PAA39PAAm381) the ζ-potential is nearly zero. For shorter neutral blocks the ζ-potential is around -10 mV. This shows that the C3-μEs have excess charge, which can be almost completely screened by long enough neutral blocks.

Polyisobutylene-block-poly(methacrylic acid) Diblock Copolymers: Self-Assembly in Aqueous Media

Ionic amphiphilic diblock copolymer polyisobutylene-block-poly(methacrylic acid) (PIBx-b-PMAAy), with various lengths of nonpolar (x=25-75) and polyelectrolyte (y=170-2600) blocks, spontaneously dissolve in aqueous media at pH>4, generating macromolecular assemblies, the aggregation number of which depends on external stimuli (pH and ionic strength). Spherical micellar morphology with a compact core formed by the PIB blocks and a swollen corona built up from the PMAA blocks was deduced by cryogenic transmission electron microscopy. The micelles were further characterized by means of dynamic and static light scattering as well as small-angle neutron scattering. The critical micellization concentration, estimated by means of fluorescence spectroscopy with the use of pyrene as a polarity probe, is decisively determined by the length of the PIB block and is insensitive to changes in the length of the PMAA block.

Field‐theoretic simulations of polyelectrolyte complexation

Field‐theoretic simulations of polyelectrolyte complexation

Broad-wavelength-range chemically tunable block-copolymer photonic gels

Responsive photonic crystals have been developed for chemical sensing using the variation of optical properties due to interaction with their environment. Photonic crystals with tunability in the visible or near-infrared region are of interest for controlling and processing light for active components of display, sensory or telecommunication devices. Here, we report a hydrophobic block-hydrophilic polyelectrolyte block polymer that forms a simple one-dimensional periodic lamellar structure. This results in a responsive photonic crystal that can be tuned via swelling of the hydrophilic layers by contact with a fluid reservoir. The glassy hydrophobic layer forces expansion of the hydrophilic layer along the layer normal, yielding extremely large optical tunability through changes in both layer thickness and index of refraction. Polyelectrolyte polymers are known to be highly responsive to a range of stimuli. We show very large reversible optical changes due to variation of the salt concentration of a water reservoir. These one-dimensional Bragg stacks reflect incident light from the ultraviolet-visible region to the near-infrared region (lambda(peak)=350-1,600 nm) with over a 575% change in the position of the stop band. Our work demonstrates the extremely high responsivity possible for polyelectrolyte-based photonic materials.

Self-assembling of star-like amphiphilic block copolymers with polyelectrolyte blocks. Effect of pH

The self-assembling behaviour of a four-arm amphiphilic star block copolymer, (PMMA73-b-PAA143)4, with poly(methyl methacrylate) inner blocks and poly(acrylic acid) outer blocks in ratio 1:2 (PMMA:PAA) has been investigated in aqueous solutions as a function of pH by dynamic light scattering and cryo-transmission electron microscopy. At low pH (pH≤5) the amphiphile forms in the presence of salt both spherical and worm-like micellar aggregates that coexist in solution. At high pH (pH>12) the solution contains mainly spherical micelles and a small number of larger aggregates that have ‘pearl-necklace’ structure, indicating the disintegration of the worm-like species. In addition to the experiments, computer simulations of the four-arm amphiphilic star block copolymer with the same ratio of the blocks as above were conducted using a coarse-grained model. The simulations predict the formation of the worm-like micellar aggregates at low pH and the spherical ones at high pH. The changes in the morphology of the aggregates are related to the higher degree of ionization of poly(acrylic acid) blocks at high pH and to the swelling of the corona of the micelles by the higher osmotic pressure due to trapped counterions.

Electrostatic Self-Assembly of Neutral and Polyelectrolyte Block Copolymers and Oppositely Charged Surfactant

We investigated the phase behavior and the microscopic structure of the colloidal complexes constituted from neutral/polyelectrolyte diblock copolymers and oppositely charged surfactant by dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The neutral block is poly(N-isopropylacrylamide) (PNIPAM), and the polyelectrolyte block is negatively charged poly(acrylic acid) (PAA). In aqueous solution with neutral pH, PAA behaves as a weak polyelectrolyte, whereas PNIPAM is neutral and in good-solvent condition at ambient temperature, but in poor-solvent condition above approximately 32 degrees C. This block copolymer, PNIPAM-b-PAA with a narrow polydispersity, is studied in aqueous solution with an anionic surfactant, dodecyltrimethylammonium bromide (DTAB). For a low surfactant-to-polymer charge ratio Z lower than the critical value ZC, the colloidal complexes are single DTAB micelles dressed by a few PNIPAM-b-PAA. Above ZC, the colloidal complexes form a core-shell microstructure. The core of the complex consists of densely packed DTA+ micelles, most likely connected between them by PAA blocks. The intermicellar distance of the DTA+ micelles is approximately 39 A, which is independent of the charge ratio Z as well as the temperature. The corona of the complex is constituted from the thermosensitive PNIPAM. At lower temperature the macroscopic phase separation is hindered by the swollen PNIPAM chains. Above the critical temperature TC, the PNIPAM corona collapses leading to hydrophobic aggregates of the colloidal complexes.

Polyion Complex Nanomaterials from Block Polyelectrolyte Micelles and Linear Polyelectrolytes of Opposite Charge: 1. Solution Behavior

The present study investigates whether block polyelectrolyte micelles can form soluble complexes upon interaction with oppositely charged linear polyelectrolytes. The phase behavior and molecular characteristics of the complexes were examined by turbidimetry, phase analysis, dynamic light scattering, and sedimentation velocity techniques. At an excess of polyelectrolyte micelles, soluble complexes were formed either independently on the route of preparation or, for select linear polyelectrolytes, through routes that avoided macrophase separation. Such soluble complexes are in a thermodynamic equilibrium state for all polyion pairs. The hydrodynamic sizes and sedimentation coefficients did not depend on the chemical nature of the linear polyelectrolyte, but were determined by the charge ratios and the hydrodynamic properties of the initial micelles. At an excess of linear polyelectrolyte, complex solubility and molecular characteristics depended on the chemical nature of the linear polyelectrolyte. In this region, linear polyelectrolytes formed soluble complexes with micelles if soluble complexes could be formed with the corresponding linear analogues of the block polyelectrolyte.

Complexes of Polyelectrolyte-Neutral Double Hydrophilic Block Copolymers with Oppositely Charged Surfactant and Polyelectrolyte

Complexes between sodium (sulfamate-carboxylate)isoprene/ethylene oxide double hydrophilic diblock copolymers (SCIEO) and dodecyltrimethylammonium bromide (DTMAB), as well as quaternized poly(2-vinylpyridine) (QP2VP), were studied in aqueous solutions, at pH 7. The complexes are formed due to electrostatic interactions between the anionic groups of the polyelectrolyte block of the copolymers and the cationic groups of the surfactant or the homopolyelectrolyte. The structure of the complexes was investigated as a function of the mixing ratio of the two components in solution and ionic strength by static, dynamic, and electrophoretic light scattering, atomic force microscopy, and fluorescence spectroscopy. The mass and size of the complexes depend on the mixing ratio between the components. A transition from intrachain to an interchain association was observed for block copolymer/ surfactant complexes. SCIEO/QP2VP complexes were found to respond to increasing concentrations of added salt. Spherical and ellipsoid shaped complexes with a core-shell micellar like structure were formed in the systems studied.

Synthesis and Solution Behavior of Carbon Nanotubes Decorated with Amphiphilic Block Polyelectrolytes

The aqueous solubilization of carbon nanotubes (CNTs) with the aid of a block copolymer possessing one polyelectrolyte block (namely polystyrene-b-sodium (sulfamate/carboxylate polyisoprene)) is reported. The solubilization protocol, based on the co-dissolution of the copolymer and the CNTs, leads to the formation of supramolecular assemblies on the side walls of the tubes. Electron microscopy as well as infrared spectroscopy and thermogravimetric analysis were employed as meaningful probes to identify the adsorption of the polymer onto the surface of CNTs and the composition of the final hybrid material. Viscosity measurements on solutions of the copolymer decorated CNTs indicate that the polyelectrolyte effect, which is observed in the case of net polymers, is preserved in a lesser extent in the case of the copolymer/CNTs dispersions.

Irreversible Structural Transitions in Mixed Micelles of Oppositely Charged Diblock Copolymers in Aqueous Solution

Using light scattering (titration) measurements, we have shown that micelles can be formed in aqueous solutions of a mixture of poly(4-(2-amino hydrochloride-ethylthio)butylene)-block-poly(ethylene oxide), PAETB49-b-PEO212, and poly(4-(2-sodium carboxylate-ethylthio)butylene)-block-poly(ethylene oxide), PCETB47-b-PEO212. The driving force is not only electrostatic attraction between the oppositely charged polyelectrolyte blocks, but also hydrophobic interaction contributes. For pH < 5.3 or pH > 9.7 the single acid or alkaline diblock copolymer also forms micelles due to absence of electrostatic repulsion and the presence of only hydrophobic interaction. The mixed micelles formed under so-called optimal conditions (pH = 7.2, 10 mM NaNO3, T = 25.0 °C) irreversibly shrink upon an increase in pH, ionic strength, and temperature and upon a decrease in pH. Restoring pH or temperature to the critical value has no effect on the hydrodynamic radius. We propose to relate these changes to an irreversible transition of the micellar core from a metastable fluidlike state (complex coacervate like) to a more stable glasslike state, triggered by a shift in the balance between electrostatic and hydrophobic interactions.

Novel double hydrophilic block copolymers based on poly(p-hydroxystyrene) derivatives and poly(ethylene oxide)

The synthesis of three series of double hydrophilic block copolymers (DHBCs), consisting of poly(ethylene oxide) as the neutral water soluble block and a second polyelectrolyte block of variable chemistry, is described. The synthetic scheme involves the anionic polymerization of poly(p-tert-butoxystyrene-b-ethylene oxide) (PtBOS-PEO) amphiphilic block copolymer precursors followed by the acidic hydrolysis of the hydrophobic poly(p-tert-butoxystyrene) (PtBOS) block to an annealed anionic polyelectrolyte poly(p-hydroxystyrene) (PHOS) block. The PHOS block was subsequently transformed into a high charge density annealed cationic polyelectrolyte namely poly[3,5-bis(dimethylaminomethylene) hydroxystyrene] (NPHOS), via amino-methylation. Finally, the NPHOS block was transformed into a quenched polyelectrolyte, namely quaternized poly[3,5-bis(dimethylaminomethylene) hydroxystyrene] (QNPHOS) block by reaction with CH 3 I. The solution properties of the different series of the above block polyelectrolyte copolymers have been investigated using static, dynamic and electrophoretic light scattering, turbidimetry, and fluorescence spectroscopy.

Block Polyelectrolyte Networks from Poly(acrylic acid) and Poly(ethylene oxide): Sorption and Release of Cytochrome C

A new family of block polyelectrolyte networks containing cross-linked poly(acrylic acid) (PAA) and poly(ethylene oxide) (PEO) was synthesized by copolymerization of acrylic acid and bisacrylated PEO (10 kDa). Two materials with different PEO/PAA ratios were compared with a weakly cross-linked PAA homopolymer network. The networks bound a cationic protein, cytochrome C, due to the polyion coupling, leading to the network contraction. After binding the protein the block polyelectrolyte networks were more porous compared to a homopolymer network, facilitating protein absorption within the gel. The protein was released by adding Ca2+ ions or a polycation. Ca2+ ions migrated within the gels and reacted with PAA chains, thus displacing the protein. The polycation transfer into hydrogels, as a result of polyion substitution reactions, was inhibited by the excess of PEO chains in the block polyelectrolyte networks. Overall, these findings advance development of functional polyelectrolyte networks for immobilization and controlled release of proteins.

Complexes of lysozyme with sodium (sulfamate‐carboxylate)isoprene/ethylene oxide double hydrophilic block copolymers

AbstractComplexes between sodium (sulfamate‐carboxylate)isoprene/ethylene oxide double hydrophilic block copolymers and lysozyme, a globular protein, were formed in aqueous solutions, at pH 7, because of electrostatic interactions between the anionic groups of the polyelectrolyte block of the copolymers and the cationic groups of lysozyme. The structure of the complexes was investigated as a function of the anionic/cationic charge ratio of the two components in solution and ionic strength by static, dynamic, and electrophoretic light scattering, atomic force microscopy, and fluorescence spectroscopy. The mass and size of the micellar‐like complexes depend on the mixing ratio and the molecular characteristics (molecular weight, composition, and architecture) of the copolymer used. Complexation persists at 0.15M NaCl, the value for physiological saline, as a result of additional hydrophobic interactions between the copolymers and the enzyme. Fluorescence spectroscopy measurements indicate that the secondary structure of lysozyme does not change substantially after complex formation. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 509–520, 2007

Stimuli-Responsive Polyelectrolyte Block Copolymer Brushes Synthesized from the Si Wafer via Atom-Transfer Radical Polymerization

Surface-tethered oppositely charged weak polyelectrolyte block copolymer brushes composed of poly(2-vinyl pyridine) (P2VP) and poly(acrylic acid) (PAA) were grown from the Si wafer by atom-transfer radical polymerization. The P2VP-b-PAA brushes were prepared through hydrolysis of the second PtBA block to the corresponding acrylic acid. The P2VP-b-PAA brushes with different PAA block length were obtained. The P2VP-b-PAA brushes revealed a unique reversible wetting behavior with pH. The difference between the solubility parameters for P2VP and PAA, the changes of surface chemical composition and surface roughness, and the reversible wetting behavior illustrated that the surface rearrangement occurred during treatment of the P2VP-b-PAA brushes by aqueous solution with different pH value. The reversible properties of the P2VP-b-PAA brushes can be used to regulate the adsorption of the sulfonated PS nanoparticles.

Coexistence of Crew-Cut and Starlike Spherical Micelles Composed of Copolymers with an Annealed Polyelectrolyte Block

The self-assembly of block copolymer AmBn into spherical micelles is analyzed using a numerical self-consistent-field theory. A is the hydrophilic annealed polyacid and B the hydrophobic part. The degree of polymerization for the polar moiety is fixed (m = 100), whereas that of the tail is varied (n = 100, 200, and 300). The charge in the annealed A block depends on both the pH and the added 1:1 electrolyte concentration φs. Beyond the cmc, the diblock copolymers form either low aggregation number starlike or large aggregation number crew-cut micelles. A nonmonotonic behavior of the micellar properties as a function of φs for fixed pH is found. For starlike micelles, the scaling of the aggregation number Nagg with φs is in fair agreement with analytical predictions, i.e., Nagg ∼ φs0.7-0.9. For the core radius, we find that Rcore ∼ φs0.24-0.3, and for the corona thickness Tcorona ∼ φs-0.08. For crew-cut micelles, the scaling exponents deviate significantly from analytical predictions. Upon increasing pH, a...

Rheology of Block Polyelectrolyte Solutions and Gels: A Review

We review recent experimental results on the rheology of block polyelectrolyte solutions, focusing mainly on diblock and triblock architectures and the effects of block polyelectrolyte concentration, block composition, solution pH, and ionic strength. Micellar solutions of diblock polyelectrolytes are typically viscoelastic liquids at a low concentration; however, gel formation can occur at higher concentrations when micelle corona chains begin to interpenetrate or interact. The rheology can be tuned by varying pH or ionic strength or through the addition of hydrophobic groups along the corona chain. Triblock architectures form elastic gels, analogous to neutral telechelic associative polymers. However, the charged nature of the backbone promotes the formation of a highly networked structure, enabling gel formation at lower concentrations than those observed with neutral telechelics. Finally, we briefly describe recent work on creating block copolypeptide gels with unique rheological and self-assembly characteristics and new architectures for creating thermoreversible block polyelectrolyte gels.