Multicompartment Micelles Research Articles

Multicompartment Micelles from Polyester-Containing ABC Miktoarm Star Terpolymers

Well-defined μ-[poly(ethylethylene)][poly(ethylene oxide)][poly(γ-methyl-e-caprolactone)] (μ-EOC) miktoarm star terpolymers were prepared by a combination of two successive living anionic polymerizations and one controlled ring-opening polymerization (ROP). A mid-hydroxyl-functionalized poly(ethylethylene)-block-poly(ethylene oxide) (PEE−PEO) diblock copolymer served as a macroinitiator for the aluminum-mediated ROP of γ-methyl-e-caprolactone (MCL), leading to a family of μ-EOC triblock copolymers having monomodal molecular weight distributions and controlled PMCL weight fractions. Micelle structures formed in water from μ-EOC containing various lengths of PMCL were examined by cryogenic transmission electron microscopy (cryo-TEM) and dynamic light scattering. Increasing the fraction of hydrophobic PMCL resulted in a transition from spherical to wormlike to approximately spherical micelles. Although the multicompartment cores of the μ-EOC micelles could not be directly resolved by cryo-TEM, small-angle X-...

Effect of molecular architecture on the morphology diversity of the multicompartment micelles: A dissipative particle dynamics simulation study

Dissipative particle dynamics simulation is performed to study the sensitive influence of the molecular architecture and/or segment sequence on the morphology diversity of the multicompartment micelles. The multicompartment micelle morphologies formed by ABC triblock copolymers with various molecular architectures, such as the linear, the pentalinear, the cyclic, the star-like, the tetra-arm, and the π-shape are investigated, and different morphologies of the multicompartment micelles, for example, worm-like, “hamburger”, sheet-like with pores, “sweet potato” with alternating layers, sheet-like with cylinder-inclusion, and three-dimensional network are observed in this work. The density profiles and the radial distribution functions are calculated to characterize the structures of the multicompartment micelles. The preparation of complex multicompartment micelles can be fulfilled by simply changing the segment sequence and molecular architecture such as adding new bonds and grafting points.

Evolution of Multicompartment Micelles to Mixed Corona Micelles Using Solvent Mixtures

Miktoarm star triblock copolymers mu-[poly(ethylethylene)][poly(ethylene oxide)][poly(perfluoropropylene oxide)] self-assemble in dilute aqueous solution to give multicompartment micelles with the cores consisting of discrete poly(ethylethylene) and poly(perfluoropropylene oxide) domains. Tetrahydrofuran is a selective solvent for both the poly(ethylethylene) and poly(ethylene oxide) blocks, and thus in tetrahydrofuran mixed corona micelles are favored with poly(perfluoropropylene oxide) cores. The introduction of tetrahydrofuran into water induces an evolution from multicompartment micelles to mixed corona [poly(ethylethylene) + poly(ethylene oxide)] micelles, as verified by dynamic light scattering and nuclear magnetic resonance spectroscopy. A mixed solvent containing 60 wt % tetrahydrofuran corresponds to the transition point, as verified by analysis of a poly(ethylethylene)-poly(ethylene oxide) diblock copolymer in the same solvent mixtures. Furthermore, cryogenic transmission electron microscopy suggests that, as the poly(ethylethylene) block transitions from the core to the corona, the micelle morphologies evolve from disks to oblate ellipsoid micelles (with some vesicles), with worms and spheres evident at intermediate compositions.

Stimuli responsive associative polyampholytes based on ABCBA pentablock terpolymer architecture

A poly(methyl methacrylate)–poly(acrylic acid)–poly(2-vinyl pyridine)–poly(acrylic acid)–poly(methyl methacrylate) (PMMA–PAA–P2VP–PAA–PMMA), ABCBA pentablock terpolymer was synthesized by “living” anionic polymerization and was studied in aqueous media at different pH conditions in the presence of MeOH. By tuning the pH and/or the solvent selectivity and dielectric constant of the medium, reversible hydrogels of different nature were formed. At low pH the hydrogel is based on a three dimensional network comprising PMMA hydrophobic cores (physical crosslinks) interconnected by complex bridging (elastically active) chains constituted of positively charged P2VP and non-ionic PAA segments. At high pH the hydrogel is transformed reversibly to a negatively charged network the bridging chains of which comprise ionized PAA segments interrupted by hydrophobic P2VP blocks, swellable on MeOH addition. Furthermore, we found conditions for the formation of flower-like micelles of different topologies and nature like core–shell–corona micelles with positively charged corona (pH<2), multicompartment micelles comprising P2VP and PMMA hydrophobic domains (pH 8.3, low MeOH content), micelles constituted of a centrosymmetric compartmentalized core and PAA negatively charged corona (pH 8.3, 30%, 40% MeOH), and core–shell micelles of PMMA cores (pH 8.3, 50% MeOH).

Novel Fluoroalkyl End-Capped Amphiphilic Diblock Copolymers with pH/Temperature Response and Self-Assembly Behavior

A series of fluoroalkyl end-capped diblock copolymers of poly[2-(N,N-dimethylamino)ethyl methacrylate] (PDMAEMA or PDMA) and poly[2-(N,N-diethylamino)ethyl methacrylate] (PDEAEMA or PDEA) have been synthesized via oxyanion-initiated polymerization, in which a potassium alcoholate of 4,4,5,5,6,6,7,7,7-nonafluoro-1-heptanol (NFHOK) was used as an initiator. The chemical structures of the NFHO-PDMA-b-PDEA and NFHO-PDEA-b-PDMA depended on the addition sequence of the two monomers and the feeding molar ratios of [DMA] to [DEA] during the polymerization process. These copolymers have been characterized by (1)H NMR and (19)F NMR spectroscopy and gel permeation chromatography (GPC). The aggregation behavior of these copolymers in aqueous solutions at different pH media was studied using a combination of surface tension, fluorescence probe, and transmission electron microscopy (TEM). Both diblock copolymers exhibited distinct pH/temperature-responsive properties. The critical aggregation concentrations (cacs) of these copolymers have been investigated, and the results showed that these copolymers possess excellent surface activity. Besides, these fluoroalkyl end-capped diblock copolymers showed pH-induced lower critical solution temperatures (LCSTs) in water. TEM analysis indicated that the NFHO-PDMA(30)-b-PDEA(10) diblock copolymers can self-assemble into the multicompartment micelles in aqueous solutions under basic conditions, in which the pH value is higher than the pKa values of both PDMA and PDEA homopolymers, while the NFHO-PDEA(10)-b-PDMA(30) diblock copolymers can form flowerlike micelles in basic aqueous solution.

Multicompartment micelles formed from star-dendritic triblock copolymers in selective solvents: A dissipative particle dynamics study

Dissipative particle dynamics method was used to study the multicompartment micelles formed from star-dendritic triblock copolymers in selective solvents, in which particular attention was paid to the effects of dendritic structure. The simulations show that the dendritic structure not only influences the morphology and the formation process of multicompartment micelles formed, but also the response of the micelle structure to solvent quality. The information obtained is useful for the future design of multicompartment micelles for practical applications, especially in the field of drug delivery.

Multicompartment Micelles from Star and Linear Triblock Copolymer Blends

Dissipative particle dynamics simulations were performed on multicompartment micelles formed by blending star and linear triblock copolymers, in which the influences of blending options and blending ratio as well as copolymer chain compositions were studied systematically. The results show that blending of copolymers with different architectures is a promising strategy to control the morphology and structure of multicompartment micelles. This work revealed several new morphologies of multicompartment micelles by blending star and linear triblock copolymers, and the dynamic processes were elucidated at the molecular level by tracing the motions of copolymer chains. The results of this work provide deep insight into micro/mesoscopic details of the underlying mechanisms, contributing to a more complete understanding of multicompartment micelle formation and structural control.

Multicompartment Micelles From π‐Shaped ABC Block Copolymers

AbstractDissipative particle dynamics simulations were performed on the morphology and structure of multicompartment micelles formed from π‐shaped ABC block copolymers in water. The influences of chain architectures were studied in a systematic way, and a rich variety of morphologies were observed, such as spherical, wormlike, X‐shaped, Y‐shaped, ribbon‐like, layered rod‐like, layered disk‐like, as well as network morphologies. The simulations show that the distance between the two grafts plays an important role in control of the morphology. Since π‐shaped ABC block copolymers can be reduced to linear ABC and star ABC block copolymers, they are good model copolymers for studying the self‐assembly of complex block copolymers into micelles. The knowledge obtained in this work as well as the new morphologies identified provide useful information for future rational design and synthesis of novel multicompartment micelles.

Multicompartment Micelles from Hyperbranched Star-Block Copolymers Containing Polycations and Fluoropolymer Segment

In this Article, we have investigated the self-assembly of a series of amphiphilic hyperbranched star-block copolymers to form multicompartment micelles in acidic aqueous solution (pH 3.0) or in a dimethylformamide/water (pH 3.0) mixture. These hyperbranched star-block copolymers were prepared via oxyanion-initiated polymerization process, using hydroxyl-terminated hyperbranched poly[3-ethyl-3-(hydroxymethyl)oxetane] (HP) as a macroinitiator precursor with multi-reactive sites. It was turned into oxyanion end-capped macroinitiator through the reaction with potassium hydride, and followed by a sequential addition of 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA) and 2,2,3,3,4,4,5,5-octafluoropentyl methacrylate (OFPMA). The resultant HP-star-PDMAEMA-b-POFPMA copolymers were characterized via 1H NMR, 19F NMR, and gel permeation chromatography (GPC). The analyses of transmission electron microscopy (TEM), dynamic light scattering (DLS), and microelectrophoresis confirmed that these copolymers could directly self-organize into supramolecular multicompartment micelles with different diameters, depending on the length of the PDMAEMA segment, which can be protonated in acidic aqueous medium. The measurement of the zeta potential gave further evidence of the aggregating structures for the multicompartment micelles.

Synthesis and Aqueous Micellization of Amphiphilic Tetrablock Ter- and Quarterpoly(2-oxazoline)s

The aqueous self-assembly of block copolymer systems is of major interest to prepare well-defined nanosized structures. Recently, the self-assembly of well-defined triblock and tetrablock ter- and quarterpolymers into sophisticated multicompartment micelles was reported. Inspired by these examples, the sequential one-pot synthesis of tetrablock ter- and quarterpolymers via living cationic ring-opening polymerization of 2-oxazolines was investigated under microwave irradiation, leading to well-defined tetrablock ter- and quarterpoly(2-oxazoline)s for the first time. The resulting tetrablock ter- and quarterpolymers were analyzed using both size exclusion chromatography and H-1 NMR spectroscopy, revealing their successful preparation. In addition, the surface energy of the polymers was determined to investigate the effect of block order on the surface properties. The last part of the paper discusses the aqueous self-assembly of the tetrablock ter- and quarterpolymers. Atomic force microscopy, transmission electron microscopy, and dynamic light scattering revealed the presence of spherical micellar aggregates.

Understanding Multicompartment Micelles Using Dissipative Particle Dynamics Simulation

AbstractMulticompartment micelles are a new class of nanomaterials that may find wide applications in the fields of drug delivery, nanotechnology and catalysis. Due to their structural complexity, as well as the wide parameter space to explore, experimental investigations are a difficult task, to which molecular simulation may contribute greatly. In this paper, the application of the dissipative particle dynamics simulation technique to the understanding of multicompartment micelles is introduced, illustrating that DPD is a powerful tool for identifying new morphologies by varying block length, block ratio and solvent quality in a systematic way. The formation process of multicompartment micelles, as well as shear effects and the self‐assembly of nanoparticle mixtures in multicompartment micelles, can also be studied well by DPD simulation. The present work shows that DPD, as well as other simulation techniques and theories, can complement experiments greatly, not only in exploring properties in a wider parameter space, but also by giving a preview of phenomena prior to experiments. DPD, as a mesoscopic dynamic simulation technique, is particularly useful for understanding the dynamic processes of multicompartment micelles at a microscopic level.magnified image

Cover Picture: Macromol. Theory Simul. 2/2007

Cover: The picture on the cover shows the structures of copolymer chains and the morphologies of multicompartment micelles formed from them in a selective solvent, illustrating that various morphologies can be formed by changing chain architecture, composition, and/or solvent quality. Further details can be found in the article by C. Zhong* and D. Liu on page 141.

Novel Two‐Compartment Micelles Formed by Self‐Assembly of Linear Pentablock Copolymers in Selective Solvents

AbstractIn this work, the formation of two‐compartment micelles from symmetric pentablock copolymers in selective solvents was studied using the dissipative particle dynamics simulation technique, and the effects of block lengths and solvent quality were investigated. The simulations revealed several new morphologies and their formation mechanisms were elucidated at the molecular level, providing useful information that may contribute to the future rational design and synthesis of novel multicompartment micelles with tailored structures.magnified image

Multicompartment micelles and vesicles from π-shaped ABC block copolymers: a dissipative particle dynamics study

Dissipative particle dynamics simulations were performed on the morphology and structure of multicompartment micelles and vesicles formed from pi-shaped ABC block copolymers in water. By varying the chain architecture and the composition of copolymers, a rich variety of morphologies were observed, such as oblate vesicles, trumpet vesicles, layered ribbon-like micelles and Y-shaped micelles. The simulations show that the hydrophilic block length and the distance between the two grafts play important roles in the control of the morphology. Since pi-shaped ABC block copolymers can reduce to linear ABC and star ABC block copolymers, they are good model copolymers for studying the self-assembly of complex block copolymers into micelles or vesicles. Thus, the knowledge obtained in this work as well as the new morphologies identified provides useful information for future rational design and synthesis of novel multicompartment micelles and vesicles.

Morphologies of multicompartment micelles formed by triblock copolymers

Multicompartment micelles are desirable for advanced applications such as drug delivery. Recently, core-shell-corona (CSC) and segmented-worm (SW) micelles formed by ABC triblock terpolymers with three mutually immiscible blocks are observed in experiments. We have performed dissipative particle dynamics simulations to study the effects of molecular architecture, block length, and solution concentration on the morphologies of ABC triblock terpolymers. The formation of CSC and SW micelles for linear and miktoarm star ABC terpolymers is confirmed in this work. In addition, we predict that different multicompartment micellar morphologies (e.g., incomplete skin-layered micelles and segmented worms) can be formed by linear copolymer with different arrangements of the three blocks.

Self‐Assembly of Two Agents in a Core‐Shell‐Corona Multicompartment Micelle Studied by Dissipative Particle Dynamics Simulations

AbstractSummary: Dissipative particle dynamics simulations are performed on the distributions of two agents in a core‐shell‐corona multicompartment micelle. The simulated results show that when the agents are weakly hydrophobic, their distributions in the multicompartment micelle are largely affected by the interactions between the agents and the blocks; while for strongly hydrophobic agents, the self‐assembly of solubilized species in the micelle is also affected largely by the interactions between the species. This work confirms that a multicompartment micelle can store two agents within separate nanoscopic compartments simultaneously, and shows that the distributions of the agents can be tailored easily by changing the interactions presented. This provides molecular‐level information that is useful for the future rational design of new micellar systems with tailored properties.Simulated cross sections of the multicompartment micelles with strongly hydrophobic solubilized agents (the solvent and block A are omitted for clarity, block B is dark gray, block C is light gray, agent P is white, and agent Q is black).imageSimulated cross sections of the multicompartment micelles with strongly hydrophobic solubilized agents (the solvent and block A are omitted for clarity, block B is dark gray, block C is light gray, agent P is white, and agent Q is black).

Morphologies of Multicompartment Micelles Formed by ABC Miktoarm Star Terpolymers

Several new multicompartment micellar structures have been identified by cryogenic transmission electron microscopy (cryoTEM) from the aqueous self-assembly of mu-[poly(ethylethylene)][poly(ethylene oxide)][poly(perfluoropropylene oxide)] (mu-EOF) miktoarm star terpolymers. This work extends our previous studies, in which it was found that, upon decreasing the length of the hydrophilic block (O), the resulting micelles evolved from "hamburger" micelles to segmented worms and ultimately to nanostructured bilayers and vesicles. In the terpolymers examined here segmented ribbons and bilayers were found at an intermediate composition between segmented worms and nanostructured bilayers, provided that the fluoropolymer (F) was the minority component in the micelle core. On the other hand, when the F block exceeded the chain length of the hydrocarbon block (E), the superhydrophobic F block imposed a "double frustration" on the self-assembly of the mu-EOF(2-9-5) terpolymer; while F prefers to minimize its interfacial contact with the O corona, it must occupy the majority of the micellar core. Therefore, a richer variety of multicompartment micelles, including well-defined segmented worms, raspberry-like micelles, and multicompartmentalized worms, were formed from one terpolymer, as revealed by cryoTEM. Despite the complexity and variety of the observed aggregate morphologies, a small number of common structural elements can be invoked to interpret the observed micelles and to relate a given structure to the terpolymer composition.

Multicompartment Micellar Solutions in Shear: A Dissipative Particle Dynamics Study

AbstractSummary: Dissipative particle dynamics simulations were performed to study the effect of shear on the rheological behavior of multicompartment micellar solutions, demonstrating that both shear thickening and thinning can occur, and the macroscopic behavior was elucidated at a molecular level. In addition, a novel shear‐induced morphology of “sphere‐on‐rod” was observed. This work provides useful information towards a complete understanding of the properties and morphologies of multicompartment micelles that is useful for future rational synthesis of novel micelles.Shear‐induced morphological transitions and rheological behavior in multicompartment micellar solutions formed from star triblock copolymers.magnified imageShear‐induced morphological transitions and rheological behavior in multicompartment micellar solutions formed from star triblock copolymers.

Dissipative Particle Dynamics Study of the Formation of Multicompartment Micelles from ABC Star Triblock Copolymers in Water

AbstractSummary: Dissipative particle dynamics simulation was performed to study the formation of multicompartment micelles from ABC star triblock copolymers in water. The study revealed some new morphologies that had not been observed before and also provided a direct visualization of the evolution of wormlike multicompartment micelles that follows the fusion process. Thus, this work provides molecular understanding of multicompartment micelles which will be useful for the future rational synthesis of novel micelles.Multicompartment micelles formed from ABC star triblock copolymers in water by DPD simulations.magnified imageMulticompartment micelles formed from ABC star triblock copolymers in water by DPD simulations.

Solution self‐assembly of tailor‐made macromolecular building blocks prepared by controlled radical polymerization techniques

AbstractThis review describes the preparation of colloidal aggregates (spherical micelles, cylindrical micelles, polymer vesicles, multicompartment micelles, polyion complexes, schizophrenic micelles) using bottom‐up self‐assembly approaches. In particular, it focuses primarily on the self‐organization of well‐defined macromolecular building blocks (macrosurfactants, polysoaps, polyelectrolytes) synthesized by controlled radical polymerization techniques such as atom transfer radical polymerization, reversible addition fragmentation transfer polymerization and nitroxide‐mediated polymerization. The goal of this review is to highlight that these versatile techniques of polymer synthesis allow the preparation of unprecedented nanostructures in dilute solutions. Copyright © 2006 Society of Chemical Industry