Micellar Polymers with Hydrocarbon and Fluorocarbon Hydrophobic Chains. A Strategy to Multicompartment Micelles

Multicompartment Micelles by Aqueous Self-Assembly of μ-A(BC) n Miktobrush Terpolymers

The aqueous self-assembly of μ-A(BC) _n miktobrush terpolymers has been studied using dynamic light scattering and cryogenic transmission electron microscopy. In this system, the A block is hydrophilic poly(ethylene oxide), "O", the B block is hydrophobic poly(methylcaprolactone), "C", and the C block is hydrophobic and oleophobic poly(perfluoropropylene oxide), "F". Two terpolymers were examined: one with an average of about two C blocks and two F blocks and another with an average of about three C blocks and two F blocks. In both cases, the total molar mass is near 40 kg mol^-1, and the volume fraction of the single O block is greater than 50% of the whole. Both samples form multicompartment micelle structures with subdivided solvophobic cores of C and F domains. The morphologies observed are generally analogous to those previously observed for the self-assembly of μ-ABC miktoarm star terpolymers, namely, "raspberry" and "hamburger" micelles; however, an intriguing multicompartment polymersome morphology with compartmentalized solvophobic bilayers is also observed. These results are interpreted in terms of the relative strengths of the competing interactions among the three blocks and the solvent and in terms of the constraints imposed by the miktobrush architecture.

Probing the Role of Side-Chain Interconnecting Groups in the Structural Hydrophobicity of Comblike Fluorinated Polystyrene by Solid-State NMR Spectroscopy

In order to probe the role of side-chain interconnecting groups (-O-, -S-, and -SO2- linkages between the polystyrene (PST) main chain and fluorooctyl side chain) in the hydrophobicity of the comblike fluorinated polystyrenes, the molecular motion and structure of polymers are explored using the spin-lattice relaxation times (T1 and T1ρ) by solid-state (1)H and (19)F nuclear magnetic resonance spectroscopy. The chain-end motions of the polystyrene main chain and the fluorooctyl side chain are homogeneous, regardless of the interconnecting groups, which means that the chain-end motions of the main chain and the side chain maintain consistency, and these are irrelevant to each other. However, the local dynamic of the main chain shows the structural heterogeneity composed of the mobile and rigid regions, attributed to the rigidity of the side chain. The mobile dynamic portions of the main chain for PST-O and PST-S increase, and their rigid dynamic portions decrease as the temperature increases, whereas the ratio of structural heterogeneity for PST-SO2 is maintained despite increasing temperature. The activation energies (Ea) corresponding to the local motion of fluorooctyl side chains for PST-O and PST-S are drastically increased on the fast motion side compared to the slow motion side, suggesting the motional transformation of side chains for PST-O and PST-S from the small local motion into the large-scale movements related to a cooperative segmental motion when heated. Also, the local motion of the fluorooctyl side chain for PST-SO2 has similar Ea values on both sides, indicating that the relaxation time of PST-SO2 does not change with temperature. Therefore, PST-SO2 is structurally more stable than PST-O or PST-S, which can be attributed to the densely packed fluorooctyl side chain structure caused by the large dipole moment of the sulfone interconnecting group.

Polyelectrolyte multilayers with perfluorinated phthalocyanine selectively entrapped inside the perfluorinated nanocompartments

A novel perfluorinated magnesium phthalocyanine (MgPcF64) was synthesized and employed to probe nanodomains in hydrophobically modified, amphiphilic cationic polyelectrolytes bearing alkyl and/or fluoroalkyl side chains. MgPcF64 was found to be solubilized exclusively in the aqueous solutions of the fluorocarbon modified polycations, occupying the perfluorinated nanocompartments provided, while analogous polyelectrolytes with alkyl side chains forming hydrocarbon nanocompartments could not host the MgPcF64 dye. Multilayer films were fabricated by means of the layer-by-layer (LbL) deposition method using sodium poly(styrene sulfonate) as a polyanion. Linear multilayer growth was confirmed by UV-Vis spectroscopy and spectroscopic ellipsometry. Atomic force microscopy studies indicated that the micellar conformation of the polycations is preserved in the multilayer films. Fluorescence spectroscopy measurements confirmed that MgPcF64 stays embedded inside the fluorocarbon domains after the deposition process. This facile way of selectively incorporating water-insoluble, photoactive molecules into the structure of polyelectrolyte multilayers may be utilized for nanoengineering of ultrathin film-based optoelectronic devices.

Rheological Properties of Hydrophobically Associative Copolymers Prepared in a Mixed Micellar Method Based on Methacryloxyethyl-dimethyl Cetyl Ammonium Chloride as Surfmer

A novel cationic surfmer, methacryloxyethyl-dimethyl cetyl ammonium chloride (DMDCC), is synthesized. The micellar properties, including critical micelle concentration and aggregation number, of DMDCC-SDS mixed micelle system are studied using conductivity measurement and a steady-state fluorescence technique. A series of water-soluble associative copolymers with acrylamide and DMDCC are prepared using the mixed micellar polymerization. Compared to conventional micellar polymerization, this new method could not only reasonably adjust the length of the hydrophobic microblock, that is,NH, but also sharply reduce the amount of surfactant. Their rheological properties related to hydrophobic microblock and stickers are studied by the combination of steady flow and linear viscoelasticity experiments. The results indicate that both the hydrophobic content and, especially the length of the hydrophobic microblock are the dominating factors effecting the intermolecular hydrophobic association. The presence of salt influences the dynamics of copolymers, resulting in the variation of solution characters. Viscosity measurement indicates that mixed micelles between the copolymer chain and SDS molecules serving as junction bridges for transitional network remarkably enhance the viscosity. Moreover, the microscopic structures of copolymers at different experimental conditions are conducted by ESEM. This method gives us an insight into the preparation of hydrophobically associative water-soluble copolymers by cationic surfmer-anionic surfactant mixed micellar polymerization with good performance.

Facile access to cytocompatible multicompartment micelles with adjustable Janus-cores from A-block-B-graft-C terpolymers prepared by combination of ROP and ATRP

The architecture of hydrophobic segments can determine the specific morphology of multicompartment micelles (MCMs) that are generated from aqueous assembly of amphiphilic terpolymers. In this study, we aimed to design and generate poly(ɛ-caprolactone)-based multicompartment micelles with adjustable Janus-cores. Well-defined terpolymers with a novel A-block-B-graft-C architecture composed of biologically compatible polymers, methoxy poly(ethylene glycol) (PEG), poly(ɛ-caprolactone) (PCL) and poly(2-(perfluorobutyl)ethyl methacrylate) (PPFEMA), were prepared by the stepwise use of ring-opening polymerization and atom transfer radical polymerization. Characterization of the obtained terpolymers was carried out by (1)H NMR and gel permeation chromatography. Results from differential scanning calorimetry and X-ray diffraction studies indicated that within the terpolymer structure, the PCL segments are in the crystalline state, while fluorocarbon segments belong to the amorphous domains. Due to the thermodynamic incompatibility of PCL and PPFEMA, MCMs could be obtained upon aqueous self-assembly of the terpolymer. The well-segregated Janus-cores with adjustable compartment balance were revealed by transmission electron microscopy. In vitro cell viability assays further demonstrated an excellent cytocompatibility of the MCMs both in mouse embryonic fibroblasts (3T3) and human acute monocytic leukemia (THP-1) cells.

Polymeric Surfactants: Novel Agents with Exceptional Properties

This article presents recent progress in the field of polymeric surfactants made of permanently amphiphilic block copolymers or of stimulus-sensitive ones. We highlight key points in the design of amphiphilic macromolecules, to yield polymer surfactants with tailor-made properties, as well as recently developed and still challenging application fields for this new class of surfactants. The efficiency boosting of amphiphilic block copolymers as co-surfactants in microemulsions is discussed, as are surface modification by polymer surfactants, and stabilization of dispersions. Moreover, the use of block copolymers in nanosciences is presented, for instance as a tool for nanomaterial fabrication, or for biomedical and cosmetic applications in bio-nanotechnology. Finally, self-assembly and applications of some newly developed “exotic” amphiphilic block copolymer structures as new surface-active materials will be highlighted.

Giant brainlike aggregates from new fluorocarbon/hydrocarbon hybrid cationic surfactants

A rapid synthetic procedure in two steps from perfluoroalkylethyl iodide derivatives led to 18 novel ammonium type hybrid surfactants of the general formula: R(F)(CH(2))(2)S(CH(2))(2)N(+)(CH(3))(2)R(H)Br(-) (R(F) = C(4)F(9), C(6)F(13), C(8)F(17); R(H) = C(4)H(9), C(6)H(13), C(8)H(17), C(10)H(21), C(12)H(25), C(14)H(29)). These hybrid surfactants exhibited very low surface tension (from 16 to 25 mN/m) as well as low critical micellar concentration until 1.5 × 10(-5) mol/L. A special focus was made on aggregation phenomenon as giant multilamellar "brainlike" vesicles were observed via cryogenic scanning electron microscopy (cryoSEM) and transmission electron microscopy (TEM; with a contrast agent) suggesting a high encapsulation ability and a very important specific surface of these particular organizations.

Multicompartment micelles from a metallo-supramolecular tetrablock quatercopolymer

Multicompartment micelles with tunable compartment solubility have been prepared in alcohols from a metallo-supramolecular poly(p-tetrafluoromethylstyrene)-block-poly(tert-butylacrylate)-block-poly(styrene)-[Ru]-poly(ethylene glycol) tetrablock quaterpolymer.

A new strategy to form multicompartment micelles: fluorocarbon-hydrocarbon ion-pair surfactant

The hydrophobic core of the multicompartment micelles consists of incompatible and clearly separated distinct subdomains which make them different from the classical micelles. Owing to these properties multicompartment micelles have a great potential to be used as solubilization agents and carriers for a wide variety of applications where it is important to prevent the uncontrolled interaction of the solubilizates before reaching the target and to convey them to the specified point simultaneously. Here we show that effective compartmentalization inside the micelle and high solubilization capacity for the two immiscible water-insoluble materials in cases of both simultaneous and separate solubilization can be achieved by newly designed ion-pair hybrid surfactant CH(3)(CH(2))(11)(OCH(2)CH(2))(23)N(+)(C(2)H(5))(3)SO(3)(-)(CF(2))(7)CF(3) (C(12)E(23)N(+)SO(3)(-)F(8)) through the agency of favorable molecular design. Molecular structure is tailored by the approach of using a balance of forces to obtain compartmentalization, which is without precedent. This new molecule also has the properties of quite low critical micelle concentration and an extensive surfactant concentration range for solubilization which are additional important advantageous features.

Synthesis and micellar self-assembly of ternary hydrophilic-lipophilic-fluorophilic block copolymers with a linear PEO chain

Linear amphiphilic diblock and ternary triblock copolymers were synthesized by the RAFT method in two successive steps using a poly(ethylene oxide) (PEO) macrochain transfer agent, butyl or 2-ethylhexyl acrylate, and 1H,1H,2H,2H-perfluorodecyl acrylate. The diblock and the triblock copolymers, which consist of a hydrophilic, a lipophilic, and a short fluorophilic block, self-assemble in water into spherical micellar aggregates. Imaging by cryogenic transmission electron microscopy (cryo-TEM) revealed that the micellar cores of the aggregates made from these "triphilic" copolymers can undergo local phase separation to form a unique ultrastructure. In these multicompartment micelles, it appears that extended nonspherical domains, presumably made of nanocrystallites of the fluorocarbon block, are embedded in the hydrocarbon matrix forming the spherical micellar core. This novel internal structure of a micellar core is attributed to the mutual incompatibility of the fluorocarbon and hydrocarbon side chains in combination with the tendency of the used fluorocarbon acrylate monomer to undergo side-chain crystallization.

Synthesis and tuning of bimodal mesoporous silica by combined hydrocarbon/fluorocarbon surfactant templating

Hydrocarbon and fluorocarbon surfactants show highly nonideal mixing that under some conditions results in demixing of the two types of surfactants into distinct populations of fluorocarbon-rich and hydrocarbon-rich aggregates. This also occurs in materials prepared by cooperative assembly of hydrolyzed tetraethoxysilane with mixtures of cetyltrimethylammonium chloride (CTAC) and 1,1,2,2-tetrahydro-perfluorodecylpyridinium chloride (HFDePC). Here, we report conditions under which demixed micelles lead to bimodal mesoporous materials (including specific concentrations of ammonia and salt in the synthesis solution) and show that the sizes of the hydrocarbon-templated and fluorocarbon-templated pores can be finely and independently controlled by adding lipophilic or fluorophilic oils, respectively. Nitrogen sorption isotherms and transmission electron microscopy provide clear evidence for a single phase of demixed but disordered wormhole-like pores.

Complex domain architecture of multicompartment micelles from a linear ABC triblock copolymer revealed by cryogenic electron tomography

Cryo-electron tomography of raspberry-like multicompartment micelles formed by a linear ABC triblock copolymer in water revealed that the fluorocarbon domains may be dispersed all over the hydrocarbon core.

Investigation of a dual set of driving forces (hydrophobic + electrostatic) for the two-step fabrication of defined block copolymer micelles

The aqueous complexation of an amphiphilic block copolymer AB containing a hydrophobic segment A and a polyanionic segment B, with a double hydrophilic block copolymer CD containing a polycationic block C and a non-ionic block D was studied. Defined A(BC)D aggregates ( spherical micelles and vesicles) were obtained by this novel sequential pathway superposing both hydrophobic and electrostatic forces. This proof of concept indicates that this straightforward strategy could be further applied for preparing compartmented polymer-based nanostructures.

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.

Laterally nanostructured vesicles, polygonal bilayer sheets, and segmented wormlike micelles

We report the formation of vesicles with a laterally nanostructured membrane by self-assembly of "miktoarm" star terpolymers, that is, macromolecules with three chemically distinct arms. The lateral structure consists of approximately hexagonally packed fluorocarbon channels with 4.1 nm radii, immersed in a continuous, two-dimensional hydrocarbon bilayer. We also show that the assembly of these vesicles proceeds via metastable polygonal, faceted bilayer sheets.

Self-assembly of block copolymer micelles in an ionic liquid

Four amphiphilic poly((1,2-butadiene)-block-ethylene oxide) (PB-PEO) diblock copolymers were shown to aggregate strongly and form micelles in an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF(6)]). The universal micellar structures (spherical micelle, wormlike micelle, and bilayered vesicle) were all accessed by varying the length of the corona block while holding the core block constant. The nanostructures of the PB-PEO micelles formed in an ionic liquid were directly visualized by cryogenic transmission electron microscopy (cryo-TEM). Detailed micelle structural information was extracted from both cryo-TEM and dynamic light scattering measurements, with excellent agreement between the two techniques. Compared to aqueous solutions of the same copolymers, [BMIM][PF(6)] solutions exhibit some distinct features, such as temperature-independent micellar morphologies between 25 and 100 degrees C. As in aqueous solutions, significant nonergodicity effects were also observed. This work demonstrates the flexibility of amphiphilic block copolymers for controlling nanostructure in an ionic liquid, with potential applications in many arenas.

Two-compartment micellar assemblies obtained via aqueous self-organization of synthetic polymer building blocks

We synthesized a symmetric linear ABCBA pentablock copolymer consisting of poly(ethylene oxide), poly(gamma-benzyl l-glutamate), and a poly(perfluoro ether) (fluorolink). The different blocks are highly immiscible with each other and form two-compartment micelles of mainly cylindrical shape in aqueous solution with lengths in the range of 100 to 200 nm and diameters of about 24 nm. The poly(perfluoro ether) (C blocks) forms the liquidlike center of the micelles (d = 6 nm). This is surrounded by a first shell of ca. 2 nm thickness consisting of beta-sheets of poly(gamma-benzyl l-glutamate) (B blocks) and a second 7 nm shell of poly(ethylene oxide) (A blocks). The A blocks provide water solubility, and the B and C blocks form separated hydrophobic compartments. This work is a contribution to the development of multicompartment micelles devoted to mimic transport proteins such as serum albumins in long-term development.