Triblock Copolymers In Selective Solvent Research Articles

Synthesis and self-assembly behavior of polyhedral oligomeric silsesquioxane-based triblock copolymers in selective solvents by dissipative particle dynamics simulation

A polyhedral oligomeric silsesquioxane (POSS)-based hybrid triblock copolymer - methyl methacrylate-b-perfluoroalkylethyl methacrylate-b-methacrylisobutyl polyhedral oligomeric silsesquioxane (PMMA-b-PFMA-b-PMAPOSS) was synthesized via an atom transfer radical polymerization (ATRP) method. The self-assembly behavior of triblock copolymers in selective solvents of tetrahydrofuran (THF) and trichlorotrifluoroethane (F113) was studied using dissipative particle dynamics (DPD) simulation. The effects of the block sequence and volume ratio of F113/THF were discussed. The aggregate morphology and size were also characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS). The simulation results showed that the spherical micelle with core-shell-corona or core-mixed shell structure could be formed and the micelle size increased with the F113 content, which was in qualitative agreement with the experimental results. The DPD simulation revealed the dynamic process of the formation of aggregates at the mesoscopic scale, which can be considered as an adjunct to experiments and provides other valuable information for the experiments.

Effect of solvophobicity on the phase behavior of linear ABC triblock copolymers in selective solvents: a Monte Carlo study.

The microphase separation behavior of linear ABC triblock copolymers in A-selective solvents are studied using Monte Carlo simulation. The ABC triblock copolymer used in this study has a short solvophilic block A and two long solvophobic blocks B and C. The effects of the solvophobicity difference and the incompatibility between solvophobic blocks B and C on the micelle morphologies formed by linear ABC triblock copolymers are investigated, and phase diagrams as a function of the solvophobicity of blocks B and C are given at different repulsions between blocks B and C, respectively. A series of multicompartment micelles with distinct solvophobic parts is obtained, such as pupa-like multi-layered micelles, hamburger-like micelles and bumpy disks. Remarkably, when the solvophobicity of blocks B is much stronger than that of blocks C, a novel reverse core–shell–corona micelle with solvophilic blocks A located in the center of the micelle is obtained. Moreover, the results indicate that the competition between the effects of the incompatibility and solvophobicity difference between blocks B and C determines the microphase separation structures in the multicompartment micelles. These simulation results elucidate the mechanism of the formation of ABC triblock copolymer nanostructures and provide theoretical guidance for experimental studies.

Vesicles from the self-assembly of coil–rod–coil triblock copolymers in selective solvents

Self-assembled vesicles formed by symmetrical coil–rod–coil triblock copolymer in selective solvents are investigated by dissipative particle dynamics method. With varying the coil length Lc and the rod length Lr, five kinds of typically ordered micelles are observed, including the special vesicles formed in the range of the rod block ratio fr ≈ 30% ∼ 50% and the rod length Lr ≤ 9. The kinetic process of vesicle formation is also observed. The aggregates firstly experience the fusion, elongation, and deformation, and then encompass the solvents, and finally close up to a vesicle membrane, where the bilayer disc is observed as an intermediate phase transited from solid micelles to hollow vesicles. A scaling behavior of the average aggregate size with time is also obtained during the process of the self-assembly. Furthermore, the effects of polymer concentration fp and solvent property are discussed. Vesicle structure only appears in the range of fp = 6% ∼ 25%, where vesicle size exhibits a well linear increase with polymer concentration. Meanwhile, vesicle size decreases with an increase in the interactions aCS between coil blocks and solvents. Due to the interfacial energy increased with aCS, the system minimizes interfacial energy by compressing the vesicle size.

Poly(ethylene oxide)-b-Poly(propylene oxide) Amphiphilic Block Copolymer-Mediated Growth of Silver Nanoparticles and Their Antibacterial Behavior

Silver nanoparticles were grown in self-assembled amphiphilic poly(ethylene oxide)/poly(propylene oxide) (PEO/PPO) triblock copolymers in selective solvents. Ternary systems of block copolymer, water, and p-xylene were used, forming a dispersion of water droplets in oil (reverse micellar) as well as binary water/block copolymer solutions. Besides its stabilizing affect, the role of the copolymer as a reducing agent for the metal salt precursors was examined. It was found that block copolymer-enabled reduction, carried out mainly by the PEO blocks, could take place only under particular conditions mostly related to the metal precursor, the block copolymer concentration, and the self-assembled micellar configuration. The effect of the triblock copolymers on growth and stabilization of gold nanoparticles was also examined. The antibacterial effect of the silver nanoparticles was investigated against Escherichia coli cells, and their performance was evaluated through a series of parametrization experiments, including the effect of the metal concentration, stability, activity over time, and dosage, while particular emphasis was given on the role of ions versus nanoparticles on the antibacterial performance.

Core–Shell–Corona Polymeric Micelles as a Versatile Template for Synthesis of Inorganic Hollow Nanospheres

Hollow, inorganic nanoscale capsules have many applications, from the delivery of encapsulated products for cosmetic and medicinal purposes to use as lightweight composite materials. Early methods for producing inorganic hollow nanospheres using hard templates suffered from low product yield and shell weakness upon template removal. In the past decade, researchers have turned to amphiphilic copolymers to synthesize hollow nanostructures and ordered mesoporous materials. Amphiphilic molecules self-assemble into well-defined nanostructures including spherical micelles. Micelles formed from simple, two-component AB diblock and ABA triblock copolymers, however, have been difficult to work with to construct inorganic hollow nanoparticles, because the corona of the micelle, which serves as the template for the shell, becomes unstable as it absorbs inorganic shell precursors, causing aggregates to form. Newly developed, three-component ABC triblock copolymers may solve this problem. They provide nanoassemblies with more diverse morphological and functional features than AB diblock and ABA triblock copolymers. Micelles formed from ABC triblock copolymers in selective solvents that dissolve only one or two of the blocks provide templates for these improved nanoassemblies. By manipulating individual polymer blocks, one can "encode" additional features at the molecular level. For instance, modifying the functional groups or substitution patterns of the blocks allows better morphological and size control. Insights into polymer self-assembly gained over years of work in our group have set the stage to systematically engineer inorganic spherical hollow nanoparticles using ABC triblock copolymers. In this Account, we report our recent progress in producing diverse, inorganic hollow spherical nanospheres from asymmetric triblock copolymeric micelles with core-shell-corona architecture as templates. We discuss three classes of polymeric micelles-with neutral, cationic, and anionic shell structures-that allow fabrication of a variety of hollow nanoparticles. Importantly, we synthesized all of these particles in water, avoiding use of hazardous organic solvents. We have designed the precursor of the inorganic material to be selectively sorbed into the shell domain, leaving the corona free from the inorganic precursors that would destabilize the micelle. The core, meanwhile, is the template for the formation of the hollow void. By rationally tailoring experimental parameters, we readily and selectively obtained a variety of hollow nanoparticles including silica, hybrid silicas, metal-oxides, metal-carbonates, metal-sulfates, metal-borates, and metal-phosphates. Finally, we highlight the state-of-the-art techniques we used to characterize these nanoparticles, and describe experiments that demonstrate the potential of these hollow particles in drug delivery, and as anode and cathode materials for lithium-ion batteries.

Structural Evolution of Multicompartment Micelles Self-Assembled from Linear ABC Triblock Copolymer in Selective Solvents

Using dissipative particle dynamics simulation, structural evolution from concentric multicompartment micelles to raspberry-like multicompartment micelles self-assembled from linear ABC triblock copolymers in selective solvents was investigated. The structural transformation from concentric micelles to raspberry-like micelles can be controlled by changing either the length of B blocks or the solubility of B block. It was found that the structures with B bumps on C surface (B-bump-C) are formed at shorter B block length and the structures with C bumps on B surface (C-bump-B) are formed at relative lower solubility of B blocks. The formation of B-bump-C is entropy-driven, while the formation of C-bump-B is enthalpy-dominated. Furthermore, when the length of C blocks is much lower than that of B blocks, an inner-penetrating vesicle was discovered. The results gained through the simulations provide an insight into the mechanism behind the formation of raspberry-like micelles.

Kinetics of hexagonal cylinders to face-centered cubic spheres transition of triblock copolymer in selective solvent: Brownian dynamics simulation

The kinetics of the transformation from the hexagonal packed cylinder (hex) phase to the face-centered-cubic (fcc) phase was simulated using Brownian dynamics for an ABA triblock copolymer in a selective solvent for the A block. The kinetics was obtained by instantaneously changing either the temperature of the system or the well-depth of the Lennard-Jones potential. Detailed analysis showed that the transformation occurred via a rippling mechanism. The simulation results indicated that the order-order transformation was a nucleation and growth process when the temperature of the system instantly jumped from 0.8 to 0.5. The time evolution of the structure factor obtained by Fourier transformation showed that the peak intensities of the hex and fcc phases could be fit well by an Avrami equation.

Vesicle Formation and Microphase Behavior of Amphiphilic ABC Triblock Copolymers in Selective Solvents: A Monte Carlo Study

Using Monte Carlo simulation, we studied the vesicle formation and microphase behavior of ABC triblock copolymers in selective solvent for A and C blocks. Simulation results show that the hydrophilicity of Blocks A and C determines not only the vesicle formation but also the microphase behavior. If Blocks A and C are of equal length, then Block A (with lower hydrophilicity) is likely to aggregate on the inner surface, whereas Block C (with higher hydrophilicity) tends to move to the outer surface, forming the ABC (from inside to outside) three-layer vesicle. Simulation results reveal that if the hydrophilicity difference between the two blocks is sufficiently low, then the ABC three layers are formed after the membrane closes (i.e., after the formation of vesicle profile). Otherwise, the ABC three layers are formed before the membrane closes. Furthermore, the effect of chain length and incompatibility between the two amphiphilic blocks (i.e., A and C) is studied and discussed in this article. The shorter block A is much more likely to aggregate on the inner surface, and the incompatibility between A and C must be sufficiently strong to ensure that the ABC copolymer forms an ABC (from inside to outside) three-layer vesicle.

Complex micelles from the self-assembly of amphiphilic triblock copolymers in selective solvents

The self-assembled microstructures of amphiphilic block copolymers depend on the selectivity of solvents for each block. By changing the selectivity of solvents, defined in terms of the repulsive interactions between the solvent and the hydrophilic/hydrophobic particles, an extensive simulation study on the spontaneous formation of complex micelles from amphiphilic triblock copolymers in a dilute solution is presented. The dynamic pathways in the formation of these assemblies have been investigated using a particle-based dissipative particle dynamics approach. In addition, the potential mechanism behind the formation of these microstructures has also been studied, which may be helpful in explaining how these aggregates are formed and in understanding the general principle of amphiphilic molecules.

Effect of shear flow on the self-assembly of ABC triblock copolymers in selective solvent

We have studied the effect of shear flow on the self-assembly of ABC amphiphilic copolymers in dilute selective solutions by changing the stirring rate and the composition of the triblock copolymer. The results revealed that the self-assembled morphology strongly depends on the stirring rate and the composition of the copolymer. The self-assembled morphology formed by the ABC triblock copolymer in selective solvent is the result in a competition between the shear flow and the interfacial tension of the micelles.

Complex micelles from the self-assembly of coil-rod-coil amphiphilic triblock copolymers in selective solvents

Download options Please wait... Article information DOI https://doi.org/10.1039/B926370E Article type Paper Submitted 15 Dec 2009 Accepted 11 Jan 2010 First published 11 Feb 2010 Download Citation Soft Matter, 2010,6, 1539-1546 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Complex micelles from the self-assembly of coil-rod-coil amphiphilic triblock copolymers in selective solvents P. He, X. Li, M. Deng, T. Chen and H. Liang, Soft Matter, 2010, 6, 1539 DOI: 10.1039/B926370E To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Social activity Tweet Share Search articles by author Pengtao He Xuejin Li Mingge Deng Tao Chen Haojun Liang

Simulation study of aggregate morphologies formed by ABC linear triblock copolymers in a selective solvent through the self‐consistent field theory

AbstractThe effect of the hydrophobic properties of blocks B and C on the aggregate morphologies formed by ABC linear triblock copolymers in selective solvent was studied through the self‐consistent field theory. Five typical micelles, such as core‐shell‐corona, hamburger‐like, segmented‐wormlike, were obtained by changing the hydrophobic properties of blocks B and C. The simulation results indicate that the shape and size of micelle are basically controlled by the hydrophobic degree of the middle block B, whereas the type of micelle is mainly determined by the hydrophobic degree of the end block C. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 484–492, 2009

ABC Triblock Copolymer Micelle-Like Aggregates in Selective Solvents for A and C

Interesting self-assembly behavior of an ABC triblock copolymer in selective solvents for the terminal A and C blocks is reported. The triblock copolymer consists of poly(tert-butyl acrylate)-block-poly(2-cinnamoyloxyethyl methacrylate)-block-poly(glyceryl monomethacrylate) or PtBA-b-PCEMA-b-PGMA, with 107 tBA units, 193 CEMA units, and 115 GMA units. The solvents used are pyridine/methanol with methanol volume fraction fMeOH between 80 and 100%. While pyridine is a good solvent for all of the three blocks, methanol is selective for PtBA and PGMA. At fMeOH = 80% and fMeOH = 90% and at 50 °C, spherical and cylindrical micelles with PtBA and PGMA coronal chains are formed. At fMeOH = 95%, vesicles are formed. Grafted on the outer surface of the vesicles are mostly the PGMA chains and some PtBA chains. The PtBA chains are found by atomic force microscopy and transmission electron microscopy to segregate from the PGMA chains to form circular patches. At fMeOH = 100%, tubular micelle-like aggregates (MAs) coexisted with vesicular MAs. While there have been many reports on morphologies of block copolymer MAs, reports on MAs of ABC triblock copolymers in selective solvents for A and C are rare. Also, there have been very few reports on tubular MAs and MAs with segregated surface chains. These combinations make results of this study unique.

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.

Association and physical gelation of ABA triblock copolymer in selective solvent

Association behavior and physical gelation mechanism of ABA triblock copolymer dissolved in B-selective solvent have been studied systematically from dilute to moderately concentrated solutions. Static and dynamic light scattering and nuclear magnetic resonance measurements for dilute solutions of poly(methyl methacrylate)- block-poly( tert-butyl acrylate)- block-poly(methyl methacrylate) (PMMA–P tBuA–PMMA) in 1-butanol (P tBuA selective solvent) indicated that PMMA–P tBuA–PMMA chains are molecularly dissolved above 50 °C. With decreasing temperature, the triblock copolymers form associated micelles consisting PMMA associated core and P tBuA shell. Linear dynamic viscoelastic measurements for solutions with moderate concentration (3.9–12.0 wt%) revealed that the system was viscous sol state at 60 °C. Drastic increase of shear storage modulus ( G′) occurred with decreasing temperature, and at 25 °C, G′ showed rubbery plateau with weak frequency dependency, means the formation of elastic physical gel. The consistency between the temperature for micelle formation and that at the increase in G′ indicates that the physical gelation is owing to the network formation as the result of the association of PMMA chains and the bridging P tBuA chains connecting the PMMA cores. Master curves for the dynamic moduli were derived by time–temperature superposition along the frequency axis. Just above sol–gel transition concentration ( C gel), the master curves suggest the existence of fairy amount of aggregate that is not incorporated in the macroscopic network. With the increase in polymer concentration, the master curves become to reveal Maxwell-type viscoelasticity with narrow relaxation time distribution, suggesting the formation of transient network with easily generation and destruction of crosslinks. Concentration dependency of the plateau modulus is stronger than the theoretically expected, means the macroscopic transient network grows with polymer concentration by increasing the fraction of elastically effective bridging P tBuA chain above C gel.

Comicellization of Diblock and Triblock Copolymers in Selective Solvents

Comicellization of a diblock block copolymer polystyrene-block-hydrogenated polyisoprene, PS−HPI (Mw 1.05 × 105 g mol-1, the weight fraction of styrene wPS 0.34), and triblock copolymer polystyrene-block-hydrogenated polybutadiene-block-polystyrene, PS−HPB−PS (Mw 7.0 × 104 g mol-1, wPS 0.28), in selective solvents was investigated by static and dynamic light scattering methods at 25−70 °C. Decane was a selective solvent for HPI and HPB blocks and 1,4-dioxane for PS blocks. HPI and HPB blocks are incompatible. Only the diblock copolymer formed micelles in decane while the triblock was molecularly dissolved at low concentrations and the measurement temperatures. Both the copolymers formed micelles of different sizes in 1,4-dioxane solutions. Comicellization was observed at all weight fraction of PS−HPB−PS, X, in solutions of copolymer mixtures in both solvents. In contrast to mixtures of chemically identical diblock copolymers with different molecular weights of the constituent blocks in selective solvents, small changes of micellar parameters resulting from comicellization were found in the copolymer mixtures under study. This is due to different constitution of the copolymers and their partial incompatibility. The X dependence of the molecular weight and size of comicelles in decane at low values of X was successfully described by adsorption of the PS−HPB−PS copolymers on micelles of the PS−HPI copolymer. The large PS−HPI copolymers were accommodated in small micelles of the PS−HPB−PS copolymer in 1,4-dioxane solutions with an excess of the PS−HPI.

Phase behavior and structure of an ABC triblock copolymer dissolved in selective solvent.

A mean-field lattice theory is applied to predict the self-assembly into ordered structures of an ABC triblock copolymer in selective solvent. More specifically, the composition-temperature phase diagram has been constructed for the system (C)14(PO)12(EO)17/water, where C stands for methylene, PO for propylene oxide and EO for ethylene oxide. The model predicts thermotropic phase transitions between the ordered hexagonal, lamellar, reverse hexagonal, and reverse cubic phases, as well as the disordered phase. The thermotropic behavior is a result of the temperature dependence of water interaction with EO- and PO-segments. The lyotropic effect (caused by changing the solvent concentration) on the formation of different structures has been found weak. The structure in the ordered phases is described by analyzing the species volume fraction profiles and the end segment and junction distributions. A "triple-layer" structure has been found for each of the ordered phases, with each layer rich in C-, PO-, and EO-segments, respectively. The blocks forming the layers are not stretched. The dependence of the domain spacing on polymer volume fraction and temperature is also considered.

Thermodynamic and Conformational Properties of Styrene–Methyl Methacrylate Block Copolymers in Dilute Solution. IV. Behavior of Diblock and Triblock Copolymers in Selective Solvents

Solution properties of nearly equimolar AB-diblock and BAB-triblock copolymers, wherein A is polystyrene (PST) and B poly(methyl methacrylate) (PMMA), were examined in various selective solvents. In either type of selective solvents the diblock copolymers usually underwent intermolecular association and formed micelles, in which domains of PST- and PMMA-subchains were presumably segragated (intramolecular phase separation). The stability and size of such micelles depended on their molecular weight and composition as well as on the nature of solvents. The behavior of the triblock copolymers appeared to be more critically influenced by the solubility of the PMMA than that of the PST. In selective solvents having preferential solvency towards PMMA rather than PST, their behavior was more or less similar to that of the diblock copolymers whilst in selective solvents preferential to PST, they were usually unstable and liable to precipitate. In the transition region between the stable solution and precipitation states, the individual triblock copolymer chains often showed conformational anomalies without forming micelles, as shown by the intrinsic viscosity anomaly in p-xylene at 30°C. The possibility of intramolecular association of two PMMA subchains within a single triblock copolymer molecule was suggested as a hypothesis. However the hydrodynamic properties alone cannot provide decisive evidence for this possibility.