Homopolymers as structure-driving agents in semicrystalline block copolymer micelles.

A simplified hierarchical self-assembly strategy is presented in which homopolymer additives are used to manipulate the crystallization-driven self-assembly of block copolymer micelles in selective media. By first incorporating the appropriate homopolymer chains within the micelle core, the system then evolves passively to yield crystalline platelets. These lamellae may be considered as self-assembled analogues of the traditional polymeric single crystal, which can be challenging or laborious to obtain otherwise. Used here as the test systems are micelles bearing polycaprolactone as the crystalline subphase in water and a mixed hydrophilic corona of poly(ethylene oxide) and poly(acrylic acid) the composition of which was varied methodically. Comicellization with homo-PCL has no influence at first; instead, the assemblies undergo morphological changes hierarchically, which were probed by electron microscopy and light scattering measurements. For all materials, the final product is consistently lamellar and micrometer-sized; however, lamellar shape variations are encountered as the stabilizing corona is altered. Such lamellae are unexpected based on the composition of most copolymers used here. The phenomenon also depends highly on the nature of the homo-PCL additive. A possible source for the activity of the homo-PCL is suggested, which also provides a strong basis to adapt the strategy for other crystalline materials.

Control of morphology and corona composition in aggregates of mixtures of PS-b-PAA and PS-b-P4VP diblock copolymers: effects of solvent, water content, and mixture composition.

The morphologies and corona compositions in aggregates of mixtures of PS-b-PAA and PS-b-P4VP diblock copolymers are influenced by controllable assembly parameters such as water content, block copolymer molar ratios, and solvent effects as well as the hydrophilic block lengths and block length ratios. All these factors can affect the morphology of the aggregates as well as their corona composition, the latter especially in vesicles, where two interfaces are involved. The morphologies and corona compositions of the aggregates were investigated by transmission electron microscopy and electrophoretic mobility, respectively. They depend, to a large extent, on the solubility of P4VP and PAA in the given organic solvent (e.g., DMF, THF, or dioxane), which influences the coil dimensions of the hydrophilic chains. The water content affects both the size and the shape of the block copolymer aggregates as well as the corona composition. Water acts as a precipitant for the hydrophobic block in the common solvent and, therefore, its progressive addition to the solution changes the interaction parameter with the hydrophobic block. The block copolymer molar ratio has an effect on both the morphology and the corona composition of the aggregates. With increasing PS-b-P4VP content in the mixture, the morphology transforms gradually from large compound micelles (LCMs), through coexistence of LCMs and small spherical micelles (SSMs), and eventually to vesicles. As expected, the corona composition of the aggregates is also affected by the block copolymer molar ratio, and changes progressively from pure PAA to a mixture of PAA and P4VP and to pure P4VP with increasing PS-b-P4VP content. It is clear that the use of mixtures of the soluble chains offers the opportunity of fine-tuning the corona composition in block copolymer aggregates under assembly conditions.

"Raft" formation by two-dimensional self-assembly of block copolymer rod micelles in aqueous solution.

Block copolymers can form a broad range of self-assembled aggregates. In solution, planar assemblies usually form closed structures such as vesicles; thus, free-standing sheet formation can be challenging. While most polymer single crystals are planar, their growth usually occurs by uptake of individual chains. Here we report a novel lamella formation mechanism: core-crystalline spherical micelles link up to form rods in solution, which then associate to yield planar arrays. For the system of poly(ethylene oxide)-block-polycaprolactone in water, co-assembly with homopolycaprolactone can induce a series of morphological changes that yield either rods or lamellae. The underlying lamella formation mechanism was elucidated by electron microscopy, while light scattering was used to probe the kinetics. The hierarchical growth of lamellae from one-dimensional rod subunits, which had been formed from spherical assemblies, is novel and controllable in terms of product size and aspect ratio.

Control of corona composition and morphology in aggregates of mixtures of PS-b-PAA and PS-b-P4VP diblock copolymers: effects of pH and block length.

The corona compositions and morphologies in aggregates of mixtures of amphiphilic polystyrene-block-poly(acrylic acid) (PS-b-PAA) and polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymers are influenced by controllable assembly parameters such as the hydrophilic block length and solution pH. The morphologies and corona compositions of the aggregates were investigated by transmission electron microscopy and electrophoretic mobility, respectively. When mineral acids or bases are present during aggregate formation, they can exert a strong influence on the corona composition. Morphology changes were also seen with changing pH, as well as changes in corona composition, specifically for vesicles. Because of complications introduced by the presence of ions, the general hypothesis that the external corona of the vesicles is composed of the longer chains, while the shorter chains form the inner corona, which is valid only in mixtures containing only nonionic chains without any additives (no acids or bases) or within a well-defined narrow pH range. In addition to the numerical block lengths and the pH, the solubility of the hydrophilic blocks can also influence the morphology and as well as the interfacial composition of vesicles; as the numerically longer chains become less soluble, they can contract and move to the interior, while the numerically shorter but more soluble chains go to the external corona. A remarkable morphological feature of the pH continuum is that for some compositions vesicles are observed in four distinct pH regions, separated by pH ranges in which other morphologies dominate. The effect of pH and microion content on coil dimensions of the PVP and PAA chains in the block copolymers is most likely responsible for the observed behavior.

Bacteria survival probability in bactericidal filter paper.

Bactericidal filter papers offer the simplicity of gravity filtration to simultaneously eradicate microbial contaminants and particulates. We previously detailed the development of biocidal block copolymer micelles that could be immobilized on a filter paper to actively eradicate bacteria. Despite the many advantages offered by this system, its widespread use is hindered by its unknown mechanism of action which can result in non-reproducible outcomes. In this work, we sought to investigate the mechanism by which a certain percentage of Escherichia coli cells survived when passing through the bactericidal filter paper. Through the process of elimination, the possibility that the bacterial survival probability was controlled by the initial bacterial load or the existence of resistant sub-populations of E. coli was dismissed. It was observed that increasing the thickness or the number of layers of the filter significantly decreased bacterial survival probability for the biocidal filter paper but did not affect the efficiency of the blank filter paper (no biocide). The survival probability of bacteria passing through the antibacterial filter paper appeared to depend strongly on the number of collision between each bacterium and the biocide-loaded micelles. It was thus hypothesized that during each collision a certain number of biocide molecules were directly transferred from the hydrophobic core of the micelle to the bacterial lipid bilayer membrane. Therefore, each bacterium must encounter a certain number of collisions to take up enough biocide to kill the cell and cells that do not undergo the threshold number of collisions are expected to survive.

Crystallinity-driven morphological ripening processes for poly(ethylene oxide)-block-polycaprolactone micelles in water.

A set of morphological transformations induced by core crystallization within spherical micelle-like aggregates of poly(ethylene oxide)-block-polycaprolactone (PEO-b-PCL) is described in the present article. The initial self-assembly step, in which individual copolymer chains associate to form the spheres, can be performed reproducibly; the stability of these spheres, however, seems to be limited, as both transmission electron microscopy and light scattering data suggest that the primary spheres transform slowly into elongated rod-like or ribbon-like aggregates when suspended in deionized water at room temperature. Although the sphere-to-rod transition takes place typically over a time scale of several days, the formation of individual rods from spheres is very rapid, as evidenced by the progressive increase in the number of long rods and the conspicuous absence of short rods.

Spherical blackberry-type capsules containing block copolymer aggregates.

The design, preparation, and properties of nanosized blackberry-like structures are described. These capsules are composed of two layers of individual block copolymer aggregates, relatively large core vesicles onto which is deposited a layer of smaller vesicles or micelles. The composition of the adjacent layers is such as to ensure strong electrostatic interactions between them. The core vesicles are typically composed of either PS-b-P4VP with a positively charged corona or of PS-b-PAA with a negatively charged corona, and are surrounded by a layer of smaller, oppositely charged block copolymer vesicles or micelles. These composite structures bear a strong resemblance to blackberries, hence the proposed name. The blackberry structures can be prepared in solution or on a flat surface, for example, a silicon wafer. Four compositional possibilities for the blackberries structures were studied, in which the positively or negatively charged core vesicles are covered either by a layer of oppositely charged micelles or by vesicles. These structures represent the earliest stage of a layer-by-layer approach of small spherical aggregates onto a larger spherical hollow core. The strong interaction between the contacting layers is achieved by electrostatic interactions or by complementary acid-base properties, for example, H-bonding. These multicompartmented capsules could be used potentially as delivery vehicles for multiple components; each layer of the capsules could be loaded with hydrophobic (in the core of the micelles or vesicle wall) or hydrophilic molecules (in the vesicle cavity). The overall size of such structures can vary, but in any case can be kept below 1 µm.

Planar multilayer assemblies containing block copolymer aggregates.

The design, preparation, and properties of planar multilayer structures composed of various combinations of sequentially deposited polyelectrolyte (PE) chains and self-assembled layers of individual block copolymer aggregates (vesicles, micelles, or large compound micelles (LCMs)) are described. The aggregates contain negatively or positively charged corona chains while the PE multilayers contain alternating polyanionic or polycationic chains deposited on silicon wafers. The final structures consist of combinations of layers of various charged species: multilayers of alternating PEs of poly(allyl hydrochloride) (PAH) and poly(acrylic acid) (PAA) as well as vesicles, micelles, or large compound micelles of ionized poly(styrene)-b-poly(4-vinylpyridine) (PS-b-P4VP) or of poly(styrene)-b-poly(acrylic acid) (PS-b-PAA). Two types of layer-by-layer (LbL) multilayer structures were studied: individual aggregate layers sandwiched between PE multilayers and layers of individual aggregates of various morphologies and of different corona chain charges, deposited on top of each other without intermediate multilayers or individual layers of PEs. The strong interactions between the successive layers are achieved mainly by electrostatic attraction between the oppositely charged layers. The planar LbL multilayers containing block copolymer aggregates could, potentially, be used as carriers for multiple functional components; each aggregate layer could be loaded with hydrophobic (in the core of the micelles, LCMs, or vesicle walls) or hydrophilic functional molecules (in the vesicular cavities). The overall thickness of such planar LbL multilayers can be controlled precisely and can vary from tens of nanometers to several micrometers depending on the number of layers, the sizes of the aggregates, and the complexity of the structure.

Binder-block copolymer micelle interactions in bactericidal filter paper.

We previously produced a bactericidal filter paper loaded with PAA47-b-PS214 block copolymer micelles containing the biocide triclosan (TCN), using cationic polyacryamide (cPAM) as a binder. However, we encountered a very slow filtration, resulting in long bacteria deactivation times. Slow drainage occurred only when the filter paper was left to dry. It appears that the filter paper with cPAM and micelles develops hydrophobic properties responsible for this very slow filtration. Three approaches were taken to accelerate the very slow drainage all based on modification of binder-micelle interactions: (i) keeping the micelles wet, (ii) modification of the corona, and (iii) replacing cPAM with smaller and more highly charged cationic poly(isopropanol dimethylammonium) chloride (PIDMAC). In all cases, the drainage time of bactericidal filter paper became close to that of untreated filter paper, without decreasing its efficiency. Moreover, replacing cPAM with PIDMAC led to a much more efficient bactericidal filter paper that reduced bacteria viability by more than 6 orders of magnitude. In addition to resolving the hydrophobic drainage hurdle, the three solutions also offer a better understanding of the interaction between cPAM and micelles in the filter paper.

Selective localization of preformed nanoparticles in morphologically controllable block copolymer aggregates in solution.

The development of nanodevices currently requires the formation of morphologically controlled or highly ordered arrays of metal, semiconducting, or magnetic nanoparticles. In this context, polymer self-assembly provides a powerful bottom-up approach for constructing these materials. The self-assembly of block copolymers (BCPs) in solution is a facile and popular method for the preparation of aggregates of controllable morphologies, including spherical micelles, cylindrical micelles, vesicles (or polymersomes), thin films, and other complex structures that range from zero to three dimensions. Researchers can generally control the morphology of the aggregates by varying copolymer composition or environmental parameters, including the copolymer concentration, the common solvent, the content of the precipitant, or the presence of additives such as ions, among others. For example, as the content of the hydrophilic block in amphiphilic copolymers decreases, the aggregates formed from the copolymers can change from spherical micelles to cylindrical micelles and to vesicles. The aggregates of various morphologies provide excellent templates for the organization of the nanoparticles. The presence of various domains, such as cores, interfaces, and coronas, in BCP aggregates allows for selective localization of nanoparticles in different regions, which may critically affect the resulting properties and applications of the nanoparticles. For example, the incorporation of quantum dots (QDs) into micelle cores solves many problems encountered in the utilization of QDs in biological environments, including enhancement of water solubility, aggregation prevention, increases in circulation or retention time, and toxicity clearance. Simultaneously it preserves the unique optical performance of QDs compared with those of organic fluorophores, such as size-tunable light emission, improved signal brightness, resistance against photobleaching, and simultaneous excitation of multiple fluorescence colors. Therefore, many studies have focused on the selective localization of nanoparticles in BCP aggregates. This Account describes the selective localization of preformed spherical nanoparticles in different domains of BCP aggregates of controllable morphologies in solution, including spherical micelles, cylindrical micelles, and vesicles. These structures offer many potential applications in biotechnology, biomedicine, catalysis, etc. We also introduce other types of control, including interparticle spacing, particle number density, or aggregate size control. We highlight examples in which the surface coating, volume fraction, or size of the particles was tailored to precisely control incorporation. These examples build on the thermodynamic considerations of particle-polymer interactions, such as hydrophobic interactions, hydrogen bonding, electrostatic interactions, and ligand replacement, among others.

Self-assembly of block copolymers.

Block copolymer (BCP) self-assembly has attracted considerable attention for many decades because it can yield ordered structures in a wide range of morphologies, including spheres, cylinders, bicontinuous structures, lamellae, vesicles, and many other complex or hierarchical assemblies. These aggregates provide potential or practical applications in many fields. The present tutorial review introduces the primary principles of BCP self-assembly in bulk and in solution, by describing experiments, theories, accessible morphologies and morphological transitions, factors affecting the morphology, thermodynamics and kinetics, among others. As one specific example at a more advanced level, BCP vesicles (polymersomes) and their potential applications are discussed in some detail.

Deactivation efficiency of stabilized bactericidal emulsions.

Biocide emulsions stabilized with various stabilizing agents were prepared and characterized, and their efficiency in bacteria deactivation was evaluated. A number of stabilizing agents were tested for their stabilizing effect on emulsions of thiocyanomethylthiobenzothiazole (TCMTB) biocide. Two agents, the most successful in stabilizing the biocide, were chosen for further studies: high molecular weight polyethyleneimine (PEI) and an amphiphilic block copolymer of poly(caprolactone)-b-poly(acrylic acid) (PCL(33)-b-PAA(33)). The emulsion droplet sizes varied between 325 and 500 nm. Deactivation of bacteria was studied by exposing E. coli ATCC 11229 bacteria dispersions to emulsions stabilized by positively charged PEI or negatively charged PCL-b-PAA micelles and by measuring their absorbance; E. coli do not grow with time in the presence of biocide emulsions. PEI molecules alone act as biocide and deactivate the bacteria. PCL-b-PAA micelles as stabilizing agent do not affect the growth of the E. coli ; bacteria are deactivated by TCMTB released from the emulsion droplets. The kinetics of emulsion dissolution studies revealed for both stabilizing agents a decrease in droplet size with time while the emulsions were subjected to dialysis. The biocide was released from the emulsions within ∼250 min; the droplet shells consist mostly of PEI or PCL-b-PAA insoluble complexes with the biocide, which do not dissolve during dialysis. SEM images confirm the presence of residual crumbled shells with holes after 24 h of dialysis.

Bactericidal block copolymer micelles.

Block copolymer micelles with bactericidal properties were designed to deactivate pathogens such as E. coli bacteria. The micelles of PS-b-PAA and PS-b-P4VP block copolymers were loaded with biocides TCMTB or TCN up to 20 or 30 wt.-%, depending on the type of antibacterial agent. Bacteria were exposed to loaded micelles and bacterial deactivation was evaluated. The micelles loaded with TCN are bactericidal; bacteria are killed in less than two minutes of exposure. The most likely interpretation of the data is that the biocide is transferred to the bacteria by repeated micelle/bacteria contacts, and not via the solution.

Controlled incorporation of particles into the central portion of vesicle walls.

Vesicles have attracted considerable attention recently because of many potential applications as well as intrinsic interest in the structures. The incorporation of various particles into vesicle walls has also received attention. One of the unsolved problems, in this context, is the controlled incorporation of particles into only the central portion of the vesicle walls, i.e. approximately halfway between the external and internal interfaces. In this paper, we describe a general method for the incorporation of particles into only the central portion, i.e. central 10-20%, of the vesicle walls. The strategy involves the use, as coatings on the particles, of diblock copolymers of a structure similar to that of the vesicle formers, which allows the particles to be preferentially localized in the central portion of the walls.

Fully collapsed (kippah) vesicles: preparation and characterization.

A study is presented of the formation of a kippah or hemispherical dome structure, a new morphology generated when a vesicle completely collapses to a hollow hemisphere. Justification for the new name is given in the Introduction. Relatively large vesicles of ca. approximately 500 nm in diameter were prepared from poly(acrylic acid)-block-polystyrene (PAA-b-PS) amphiphilic copolymer in the dioxane/water system. The vesicle specimens for transmission electron microscopy (TEM) were prepared using four different methods: drying under ambient conditions, freeze-drying, freeze-drying and subsequent resuspension in water, and drying under vacuum. The formation of the kippah was found to be strongly influenced by the method of preparation. When the vesicles were allowed to dry on the grid, either by drying under ambient conditions or by direct freeze-drying, "normal" vesicles (i.e., not kippah) with the classical indentation pattern were the only structures to be observed. Kippah vesicles, on the other hand, were obtained only by freeze-drying and subsequent rehydration in water or by direct drying under vacuum where no freezing is involved. The cause of the kippah vesicle formation is not yet completely understood for all methods of preparation; however, it was postulated to be strongly influenced by one or more of the following parameters: the relative flexibility of the vesicle wall, pressure gradient, and surface tension. Unlike "normal" vesicles, which exhibit, in TEM, a classical indentation pattern, kippah vesicles appear nearly round but with average wall thickness twice as large as in the "normal" vesicles. The study illustrates also the usefulness of specimen tilting in the analysis of the kippah. In addition, specimen tilting was found to allow the unambiguous determination of the orientation of the kippah on the surface (i.e., open-side-up or open-side-down).

"Breathing" vesicles.

A vesicle system is described that possesses a pH-induced "breathing" feature and consists of a three-layered wall structure. The "breathing" feature consists of a highly reversible vesicle volume change by a factor of ca. 7, accompanied by diffusion of species into and out of the vesicles with a relaxation time of ca. 1 min. The triblock copolymer poly(ethylene oxide)(45)-block-polystyrene(130)-block-poly(2-diethylaminoethyl methacrylate)(120) (PEO(45)-b-PS(130)-b-PDEA(120)) was synthesized via ATRP. Self-assembly into vesicles was carried out at a pH of ca.10.4. The vesicle wall was shown by cryo-TEM to consist of a sandwich of two external ca. 4 nm thick continuous PS layers and one ca. 17 nm thick PDEA layer in the middle. As the pH decreases, both the vesicle size and the thickness of all three layers increase. The increase of the thickness of the intermediate PDEA layer arises from the protonation and hydration, but the swelling is constrained by the PS layers. The increase of the thickness of the two PS layers is a result of an increasing incompatibility and an accompanying sharpening of the interface between the PS layers and the PDEA layer. Starting at a pH slightly below 6, progressive swelling of the PDEA layer with decreasing pH induces a cracking of the two PS layers and also a sharp increase of the vesicle size and the wall thickness. By pH 3.4, the vesicle size has increased by a factor of approximately 1.9 and the wall shows a cracked surface. These changes between pH 10.4 and 3.4 are highly reversible with the relaxation time of ca. 1 min and can be performed repeatedly. The change in the wall structure not only increases dramatically the wall permeability to water but also greatly expands the rate of proton diffusion from practically zero to extremely rapid.

Relationship between wall thickness and size in block copolymer vesicles.

In this study, we report a new phenomenon dealing with the size-dependent behavior of the wall thickness of block copolymer vesicles, especially the decrease in wall thickness with decreasing vesicle size. Four vesicle-forming copolymers from the polystyrene-b-poly-(acrylic acid) (PS-b-PAA) family (i.e., PS(500)-b-PAA(50), PS(310)-b-PAA(28), PS(240)-b-PAA(15), and PS(412)-b-PAA(46)) were chosen for study. The sizes and wall thicknesses of the vesicles after quenching were determined from the TEM micrographs, and plots were made of the wall thickness versus size for each family of vesicles made from each of the various blocks. First, the effect of the length of the PAA block on the relationship between the wall thickness and the size was examined. In the vesicles prepared from PS(500)-b-PAA(50), the copolymer with the longest PAA block that yields the smallest vesicles, the wall thickness decreases strongly with decreasing size. By contrast, in the case of vesicles made from PS(240)-b-PAA(15), for which a wide size distribution is obtained, only a weak size dependence of the wall thickness is seen. For vesicles made from the copolymer with intermediate PAA block length (i.e., PS(310)-b-PAA(28)), both strong and weak behavior regions are observed depending on the vesicle size range. We suggest that this new phenomenon of the size dependence of the wall thickness can be considered to be another stabilization mechanism for very small vesicles, under conditions where chain segregation is insufficient to stabilize the size. The vesicles can be stabilized by decreasing the wall thickness for very small vesicles, resulting in the increase in area per corona chain, thus decreasing the corona repulsion on the inside. The effects of additives such as NaCl, HCl, or NaOH on the relationship between the wall thickness and the size were also investigated. By shielding the electrostatic repulsion among corona chains in the presence of NaCl, the strong behavior of the vesicles prepared from PS(412)-b-PAA(46) changes to a weak one as the width of the vesicle size distribution increases. In a NaCl concentration region around 10 mM, an opposite effect is seen relative to that observed in small vesicles in that the wall thickness decreases with increasing vesicle size for vesicles larger than ca. 300 nm, an effect ascribed to corona repulsion among the external corona chains. The addition of HCl also drives the relationship to be weaker through the protonation of the carboxylate groups of PAA chains, in an effect similar to that of NaCl. The presence of NaOH is expected to strengthen the relationship via the deprotonation of PAA, which increases the corona repulsion. However, because of the very short length of PAA chains in the system where a weak effect is seen, no significant effect of NaOH addition was observed because the size distribution remained broad.

Block-copolymer micelles as carriers of cell signaling modulators for the inhibition of JNK in human islets of Langerhans.

Here we investigate the potential of PCL-b-PEO micelles in preventing the cell death of isolated human islets of Langerhans. PCL-b-PEO micelles were loaded with c-Jun NH2-terminal kinases inhibitor SP600125 to rescue the isolated islets. Mechanistic studies of the uptake were conducted in PC12 cells. Incorporation of SP600125 afforded 8.2 fold greater solubility of SP600125 in micelle suspension. To investigate the effectiveness of micelle-incorporated SP600125 in preventing the islet cell death, we challenged the islets with TNF-alpha, IL-1, and IFN gamma. Micelle-incorporated SP600125 did not lose its inhibitory activity during incorporation into micelles, and it protected the islets against cytokine-induced loss of viability to the same extent as control SP600125. Moreover, the concentration of micelle-incorporated SP600125 used was 13-fold lower, demonstrating the greater efficacy of micelle delivered SP600125. Micelles maintained their cytoplasmic distribution without detectable nuclear localization in islets. The inhibition of JNK was confirmed by western blots. This study suggests that micelle-based intracellular delivery of potent, poorly water soluble, cell-death-pathway inhibitors may represent a valuable addition to established delivery of cytocidal block-copolymer micelle-incorporated bioactives.

Loading and release mechanisms of a biocide in polystyrene-block-poly(acrylic acid) block copolymer micelles.

The kinetics of loading of polystyrene197-block-poly(acrylic acid)47 (PS197-b-PAA47) micelles, suspended in water, with thiocyanomethylthiobenzothiazole biocide and its subsequent release were investigated. Loading of the micelles was found to be a two-step process. First, the surface of the PS core of the micelles is saturated with biocide, with a rate determined by the transfer of solid biocide to micelles during transient micelle-biocide contacts. Next, the biocide penetrates as a front into the micelles, lowering the Tg in the process (non-Fickian case II diffusion). The slow rate of release is governed by the height of the energy barrier that a biocide molecule must overcome to pass from PS into water, resulting in a uniform biocide concentration within the micelle, until Tg is increased to the point that diffusion inside the micelles becomes very slow. Maximum loading of biocide into micelles is approximately 30% (w/w) and is achieved in 1 h. From partition experiments, it can be concluded that the biocide has a similar preference for polystyrene as for ethylbenzene over water, implying that the maximum loading is governed by thermodynamics.

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.