Linear Triblock Research Articles

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.

Cylindrical Micelles with “Patchy” Coronas from the Crystallization-Driven Self-Assembly of ABC Triblock Terpolymers with a Crystallizable Central Polyferrocenyldimethylsilane Segment

Solution self-assembly of a series of linear ABC triblock terpolymers with a central crystallizable poly(ferrocenyldimethylsilane) (PFS) core-forming “B” block and terminal polystyrene (PS) and poly(methyl methacrylate) (PMMA) “A” and “C” blocks has been investigated. Three PS-b-PFS-b-PMMA triblock terpolymers with different block ratios (1, 3.6:1.0:4.7; 2, 7.0:1.0:6.9; and 3, 1.1:1.0:1.4) but with similar degrees of polymerization for the central PFS block were prepared through a combination of living anionic and atom-transfer radical polymerization techniques, together with azide/alkyne “click” chemistry. Cylindrical micelles with a crystalline PFS core were formed in solvents selective for the terminal PS and PMMA blocks. In ethyl acetate, a slightly more selective solvent for the PS block, cylinders with significant microphase separation within the corona in the dry state were observed on the basis of TEM analysis. The use of acetone, which is slightly more selective for the PMMA block than the PS blo...

Morphology Reentry with a Change in Degree of Chain Asymmetry in Neat Asymmetric Linear A1BA2 Triblock Copolymers

We report experimental results on relationship between polymer chain architecture and morphology of microdomains of asymmetric linear triblock copolymers, S1BS2 (S: polystyrene; B: polybutadiene). For this purpose, we synthesized various asymmetric triblock copolymers having different lengths of two end-blocks. The morphology was examined by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Although total molecular weight, composition, and thermal annealing temperature were kept constant, the morphology was found to change with a degree of chain asymmetry. One typical example exhibits a morphological change as cylinder → lamella → cylinder with a decrease in length of the shorter S2 end-block chains, while keeping the total molecular weight and the total polystyrene composition constant. This curious morphological behavior exhibiting a re-entrant type change is qualitatively in accord with the self-consistent field theory (SCFT) results by Matsen [J. Chem. Phys. 2000, 113, 55...

Complex Self-Assembly Behavior of Bis-hydrophilic PEO-b-PCL-b-PMOXA Triblock Copolymers in Aqueous Solution

We report aqueous self-assembly of linear amphiphilic triblock copolymers poly(ethylene oxide)-block-polycaprolactone-block-poly(2-methyl-2-oxazoline) (PEO-b-PCL-b-PMOXA) and their PEO-b-PCL precursors with different PCL and PMOXA block lengths using three preparation methods: film rehydration, solvent evaporation, and cosolvent. For PEO-b-PCL, the self-assembled structures were ordinary spherical particles and polymersomes. For PEO-b-PCL-b-PMOXA, we observed polymersomes with asymmetric membrane, cloud-like aggregates, elongated particles, Y-shaped elongated particles, and 3D networks. All structures were of micrometer size and characterized using laser scanning microscopy (LSM). 3D networks were also characterized using z-stack confocal LSM, transmission electron microscopy (TEM), and cryogenic TEM. We demonstrated that film rehydration method results in pseudoequilibrium structures, whereas structures formed using solvent evaporation and cosolvent methods are under kinetic control. We showed how kineti...

Stable Superhydrophobic Porous Coatings from Hybrid ABC Triblock Copolymers and Their Anticorrosive Performance.

Superhydrophobic porous surfaces with ultralow water adhesion were successfully fabricated via micelle fusion-aggregation assembly of newly designed linear hybrid ABC triblock copolymers, where A, B, and C denote poly(dimethylsiloxane) (PDMS), polystyrene (PS), and poly(methacrylolsobutyl polyhedral oligomeric silsesquioxane) (PiBuPOSSMA), respectively. It was found that aggregation behavior in diluted solution and subsequent formation of nano-/microscale hierarchical surfaces in condensed state were affected by the molar mass of the triblock copolymers, which were evidenced by dynamic light scattering (DLS), SEM, and TEM studies. Increasing of PiBuPOSSMA content can significantly increase roughness of the resulting coatings, leading to an increase of apparent water contact angles from 145.7 ± 1° to 157.3 ± 1.1°. The optimized PDMS-PS-PiBuPOSSMA surface possesses unique nano/microscale hierarchical morphology, large apparent water contact angle (157.3 ± 1.1°), small roll-off angle (∼3°), low contact angle hysteresis (∼0.9°), long-term stability, and good chemical and thermal resistance. Moreover, it exhibits superior performance in preventing corrosive species such as ions and water in contact with the underlying metallic substrate (stainless steel) in 3.5 wt % NaCl aqueous solution with high inhibition efficiency and long-term preservability, which could be attributed to the synergistic effect of superhydrophobic surface and capillary action arising from the underlying porous structure.

Disperse cyclic diblock copolymer: another promising candidate for fabricating irregular bicontinuous structure

In this work, dissipative particle dynamics simulations are carried out to investigate the phase behaviour of cyclic c-AB diblock copolymers with different designed dispersities in molecular weight distribution. Phase diagrams are constructed and detailed comparisons are carried out for monodisperse, one-component and two components disperse systems. For monodisperse system, our simulation results show a good agreement with self-consistent field theory. For one-component disperse system, the symmetry of the phase diagram centred at is found broken and the order–order transition boundaries are shifted towards larger volume fraction of disperse component. We also find that in one-component disperse c-AB system, an irregular bicontinuous (BIC) structure can be formed by monodisperse minority component in a 10% wide composition window where the majority component is disperse. Results are also compared with those of linear l-AB diblock and l-ABA triblock copolymers. Very similar to l-ABA system, both A and B blocks in two-components disperse c-AB system can form BIC structure, each of them occupies 10% wide composition window that flanks the lamellar window in the phase diagram. Further analyses show that for a given chain length, A blocks in cyclic c-AB system will form BIC structure at larger volume fraction of A block and therefore such BIC structure will have thicker internal network pipes than that in linear triblock l-ABA system. Consequently, BIC structure formed by c-AB diblock copolymer will have a larger specific surface area than that formed by l-ABA triblock copolymer. These results indicate that disperse c-AB diblock copolymer can be another promising candidate for fabricating irregular bicontinuous structure for better material performances.

Rheological characterization of nanostructured material based on Polystyrene-b-poly(ethylene-butylene)-b-polystyrene (SEBS) block copolymer: Effect of block copolymer composition and nanoparticle geometry

Block copolymer (BCP) nanocomposite systems are of broad interest; however, reports on the role of nanoparticles on microphase separation behavior are rare. The goal of present study is to investigate the preparation of composite nanostructured materials containing Multi-Walled Carbon Nanotubes (MWCNTs) or graphene nanoplates. BCP nanocomposites based on the linear triblock copolymer, Polystyrene-b-poly(ethylene-butylene)-b-polystyrene (SEBS), with different morphological structure were prepared by melt mixing. The results of temperature sweep experiments showed an enhancing effect of both MWCNT and graphene nanosheets on increasing the microphase separation temperature as well as accelerating its kinetic, resulting from the confinement of BCP segments, with graphene nanosheets providing a more severely confined geometry for polystyrene segments in contrast to MWCNTs. Additionally, DMTA results indicated a promotion of the BCP microphase separation by incorporation of nanoparticles. Transient flow measurements followed by time sweep test suggested the existence of a special 3D network microstructure caused by nanoparticles/domain interactions.

Tuning the self-assembly of EO-PO block copolymers and quercetin solubilization in the presence of some common pharmacuetical excipients: A comparative study on a linear triblock and a starblock copolymer

Here we report, the effect of biologically important additives such as glucose, glycine, sodium chloride, urea and ethanol on the clouding and micellar behaviour of two commercially available ethylene oxide-propylene oxide (EO-PO) block copolymers (one linear triblock, Pluronic® P104 and other branched, starblock Tetronic® T1304) in aqueous environment. The cloud point (CP), viscosity, and dynamic light scattering (DLS) were measured. The solubilization of poorly water soluble drug, quercetin (QN) was also checked for the copolymer micelles in the presence of these additives using UV–visible spectroscopy. These additives depending upon their structure either decrease or increase CP and hydrodynamic diameter (Dh). Salt, glucose and glycine favoured micellization while urea and ethanol showed opposite behaviour. Markedly enhanced solubilization of QN was observed by the copolymer micelles which further improved in the presence of salt, glucose and glycine but decreased in the presence of ethanol and urea. The conclusions derived from this work will be highly useful in optimizing the performance of the copolymers in different pharmaceutical applications and in drug delivery systems as drug carriers.

Chain exchange kinetics between linear ABA-type triblock copolymer micelles

Chain exchange kinetics between triblock block copolymers of ABA-type with end block being soluble in solvent is investigated using dissipative particle dynamics simulations for the first time. In such micelles, the polymer conformation is believed to play an important role. Our simulations find that a majority of polymer chains take loop (bend) conformations within the micelle, and unimer expulsion is the dominant mechanism for exchange. The chain exchange follows a first-order kinetic process, for which the characteristic time τ increases with both core and corona block lengths, showing a qualitative agreement with the literature. While the strong effect of core block length is due to an increase in activation energy, the marginal effect of corona block length is attributable to the re-insertion of an escaping chain into the same micelle. Re-insertion is favored because of greater resistance for a chain to escape a thicker corona.

Self-Assembled Morphologies of Linear and Miktoarm Star Triblock Copolymer Monolayers.

Monolayers of linear and miktoarm star ABC triblock copolymers with equal A and C blocks were investigated using self-consistent field theory. Monolayers of ABC triblock copolymers were formed between two parallel surfaces that were attractive to the A and C blocks. The repulsive interaction parameter χACN between the A and C blocks was chosen to be weaker than the A/B and B/C interactions, quantified by χABN and χBCN, respectively, such that the B blocks were confined at the A/C interface, resulting in various B domains with different geometries and arrangements. It was observed that two variables, namely, the strength of the surface fields and the film thickness, were dominant factors controlling the self-assembly of the B blocks into various morphologies. For the linear triblock copolymers, the morphologies of the B domains included disks, stripes (parallel cylinders), and hexagonal networks (inverse disks). For the miktoarm star triblock copolymers, the competition between the tendency to align the junction points along a straight line and the constraint on their arrangement from the surface interactions led to richer ordered morphologies. As a result of the packing of the junction points of the ABC miktoarm star copolymers, a counterintuitive phase sequence from low-curvature phases to high-curvature phases with increasing length of B block was predicted. The study indicates that the self-assembly of monolayers of ABC triblock copolymers provides an interesting platform for engineering novel morphologies.

Synthesis of Multicompartment Nanoparticles of ABC Triblock Copolymers through Intramolecular Interactions of Two Solvophilic Blocks

A new strategy to synthesize multicompartment block copolymer nanoparticles (MCBNs) of poly(4-vinylpyridine)-block-polystyrene-block-poly(4-hydroxystyrene) (P4VP-b-PS-b-P4HS) combining the polymerization-induced self-assembly (PISA) of linear ABC triblock copolymers and the intramolecular complexation through hydrogen bonding between the poly(4-vinylpyridine) (P4VP) and poly(4-hydroxystyrene) (P4HS) blocks is proposed. These MCBNs contain a polystyrene (PS) core of about 30 nm and the dispersed 3–5 nm microdomains of the P4VP/P4HS complexes on the solvophobic PS core, in which the size of the dispersed P4VP/P4HS microdomains increases with the polymerization degree (DP) of the P4HS block. The successful synthesis of MCBNs is ascribed to the intramolecular interactions via hydrogen bonding between the P4HS and P4VP blocks confined within the triblock copolymer nanoparticles. The strategy affords the efficient synthesis of MCBNs and avoids the application of the ABC miktoarm terpolymers and the fluorinated ...

Process-Accessible States of Block Copolymers.

Process-directed self-assembly of block copolymers refers to thermodynamic processes that reproducibly direct the kinetics of structure formation from a starting, unstable state into a selected, metastable mesostructure. We investigate the kinetics of self-assembly of linear ACB triblock copolymers after a rapid transformation of the middle C block from B to A. This prototypical process (e.g., photochemical transformation) converts the initial, equilibrium mesophase of the ABB copolymer into a well-defined but unstable, starting state of the AAB copolymer. The spontaneous structure formation that ensues from this unstable state becomes trapped in a metastable mesostructure, and we systematically explore which metastable mesostructures can be fabricated by varying the block copolymer composition of the initial and final states. In addition to the equilibrium mesophases of linear AB diblock copolymers, this diagram of process-accessible states includes 7 metastable periodic mesostructures, inter alia, Schoen's F-RD periodic minimal surface. Generally, we observe that the final, metastable mesostructure of the AAB copolymer possesses the same symmetry as the initial, equilibrium mesophase of the ABB copolymer.

Dissipative particle dynamics simulation on the self-assembly of linear ABC triblock copolymers under rigid spherical confinements

AbstractAlthough a great deal of unique nanostructures were already obtained from polymer self-assemblies in terms of conventional parameters, the self-assembly under the confinement is still not well understood. Here, dissipative particle dynamics simulations were used to explore the self-assemble behaviors of linear ABC triblock copolymers under rigid spherical confinements. First several unusual morphologies, such as multilayer onion, coupled helix, and stacked lamella, were distinguished from the total 210 simulations. Second, the influences of three important parameters (block sequence, wall selectivity, and spherical radius) on the morphologies were discussed in detail. Finally, the dynamics evolution of several typical aggregates was examined. This simulation enriches micelle morphologies for the self-assembly of linear ABC triblock copolymers under rigid spherical confinements and is helpful to understand the formation of valuable nanostructures from linear ABC terpolymers.

Robust & thermosensitive poly(ethylene glycol)-poly(ε-caprolactone) star block copolymer hydrogels

Novel 8-armed poly(ethylene glycol)-poly(ε-caprolactone) (PEG-PCL) star block copolymers, possessing an amide or an ester group between the PEG core and the PCL arms (PEG20K-(NHCO)-(PCL9)8 and PEG20K-(OCO)-(PCL9)8), are synthesized by ring opening polymerization of ε-caprolactone in toluene at 110 °C initiated by 8-armed star PEG20K-(NH2)8 and PEG20K-(OH)8, respectively. Compared to linear triblock copolymers with a similar hydrophilic/hydrophobic balance and molecular weight, star block copolymers show better aqueous solubility and yield more homogeneous and transparent hydrogels. PEG20K-(NHCO)-(PCL9)8 hydrogels exhibit a significantly higher storage modulus and in vitro stability in comparison with PEG20K-(OCO)-(PCL9)8 hydrogels of similar concentration and molecular weight. 1H NMR analysis of degrading hydrogel samples clearly demonstrates different degradation mechanisms for the ester and amide type star block copolymers. Their robust mechanical properties, the possibility to be formed in situ and their excellent resistance against hydrolytic degradation make these PEG-PCL star block copolymer hydrogels, especially those based on PEG20K-(NHCO)-(PCL9)8, appealing for various biomedical applications.

Mechanical Properties of Star Block Polymer Thermoplastic Elastomers with Glassy and Crystalline End Blocks

The mechanical properties of thermoplastic elastomers (TPEs) consisting of 6-arm star block polymers with glassy, crystalline, or composite crystalline–glassy physical cross-linking (hard) domains were investigated and compared to the analogous linear triblock or pentablock polymers. The 6-arm stars exhibited qualitatively similar solid-state morphologies and phase behavior to their linear counterparts, as demonstrated by small-angle X-ray scattering and differential scanning calorimetry. Consequently, the architecture had minimal impact on the small-strain behavior in uniaxial extension at room temperature. As the applied strain increased, the star polymers exhibited more pronounced strain hardening than the corresponding linear TPEs, resulting in an increase in the ultimate strength of 20% for the polymers with crystalline end blocks and 30% when the end blocks were glassy. Each of the three star polymers exhibited superior recovery (i.e., lower residual strain) and lower hysteresis than the correspondi...

Complex liquid-crystal nanostructures in semiflexible ABC linear triblock copolymers: A self-consistent field theory.

We show that two series of ABC linear triblock copolymers possess sequences of order-to-order phase transitions between microphase-separated states, as the degree of flexibility of the semiflexible middle B-blocks varies. The spatial and orientational symmetries of these phases, some of them containing liquid-crystal ordering, are analysed in comparison with related structures previously determined experimentally and theoretically. A theoretical framework based on the self-consistent field treatment of the wormlike-chain model, which incorporates the Flory-Huggins and Maier-Saupe interactions in the free energy, is used here as a basic foundation for numerical calculations. We suggest that tuning the flexibility parameter, which reduces to the concept of degree of polymerization in the coil-like limit and characterizes the chain-persistency in the rod-like limit, provides a promising approach that can be used to design the resulting microphase-separated structures in semiflexible copolymer melts.

Well-Defined Cyclic Triblock Terpolymers: A Missing Piece of the Morphology Puzzle.

Two well-defined cyclic triblock terpolymers, missing pieces of the terpolymer morphology puzzle, consisting of poly(isoprene), polystyrene, and poly(2-vinylpyridine), were synthesized by combining the Glaser coupling reaction with anionic polymerization. An α,ω-dihydroxy linear triblock terpolymer (OH-PI1,4-b-PS-b-P2VP-OH) was first synthesized followed by transformation of the OH to alkyne groups by esterification with pentynoic acid and cyclization by Glaser coupling. The size exclusion chromatography (SEC) trace of the linear terpolymer precursor was shifted to lower elution time after cyclization, indicating the successful synthesis of the cyclic terpolymer. Additionally, the SEC trace of the cyclic terpolymer produced, after cleavage of the ester groups, shifted again practically to the position corresponding to the linear precursor. The first exploratory results on morphology showed the tremendous influence of the cyclic structure on the morphology of terpolymers.

Thermoresponsive (star) block copolymers from one-pot sequential RAFT polymerizations and their self-assembly in aqueous solution

A series of hydrophobically end-capped linear triblock copolymers as well as of three-arm and four-arm star block copolymers was synthesized in a one-pot procedure from N,N-dimethylacrylamide (DMA) and N,N-diethylacrylamide (DEA). The sequential reversible addition-fragmentation chain transfer (RAFT) polymerization of these monomers via the R-approach using bi-, tri- and tetrafunctional chain transfer agents (CTAs) bearing hydrophobic dodecyl moieties proceeded in a well-controlled manner up to almost quantitative conversion. Polymers with molar masses up to 150 kDa, narrow molar mass distribution (PDI ≤ 1.3) and high end group functionality were obtained, which are thermoresponsive in aqueous solution showing a LCST (lower critical solution temperature) transition. The temperature-dependent associative behavior of the polymers was examined using turbidimetry, static and dynamic light scattering (SLS, DLS), and small angle neutron scattering (SANS) for structural analysis. At 25 °C, the polymers form weak transient networks, and rather small hydrophobic domains are already present for polymer concentrations of 5 wt%. However, when heating above the LCST transition (35–40 °C) of the PDEA blocks, the enhanced formation of hydrophobic domains is observed by means of light and neutron scattering. These domains have a size of about 12–15 nm and must be effectively physically cross-linked as they induce high viscosity for the more concentrated samples. SANS shows that these domains are ordered as evidenced by the appearance of a correlation peak. The copolymer architecture affects in particular the extent of ordering as the four-arm star block copolymer shows much more repulsive interactions compared to the analogous copolymers with a lower number of arms.

Controlling Multicompartment Morphologies Using Solvent Conditions and Chemical Modification.

The solution self-assembly of amphiphilic diblock copolymers into spheres, cylinders, and vesicles (polymersomes) has been intensely studied over the past two decades, and their morphological behavior is well understood. Linear ABC triblock terpolymers with two insoluble blocks A/B, on the other hand, display a richer and more complex morphological spectrum that has been recently explored by synthetic block length variations. Here, we describe facile postpolymerization routes to tailor ABC triblock terpolymer solution morphologies by altering block solubility (solvent mixtures), blending with homopolymers, and block-selective chemical reactions. The feasibility of these processes is demonstrated on polystyrene-block-polybutadiene-block-poly(methyl methacrylate) (SBM) that assembles to patchy spherical micelles, which can be modified to evolve into double and triple helices or patchy and striped vesicles. These results demonstrate that postpolymerization treatments give access to a broad range of morphologies from single triblock terpolymers without the need for multiple polymer syntheses.

Swarm Intelligence Platform for Multiblock Polymer Inverse Formulation Design.

Multiblock polymers (MBPs) show great promise as a platform for synthesizing materials with highly customized nanostructures. In these systems, the subtle balance of chain configurational entropy and interactions between dissimilar block chemistries emerge a rich palette of self-assembled structural motifs that may be leveraged to impart novel functional, mechanical, or optical properties to the final material. Unfortunately, extensive study of MBP self-assembly has yielded few reliable heuristics for intuitively navigating the enormous molecular design space made available by modern polymer synthesis techniques. In order to make progress, new methods must be developed that allow researchers to efficiently screen molecular designs for achieving a desired state of self-assembly. Here, we introduce a platform for the automated discovery of tailored MBP formulations based on the Particle Swarm Optimization (PSO) method and a linear multiblock chain parametrization that enables continuous optimization of chain architecture. We apply the method to thin-film blends of linear ABC triblock polymers subject to lateral confinement, allowing all polymer and blend parameters to freely optimize in search of a prespecified, nontrivial target morphology. While we focus on pattern selection as a proof of principle, any computable equilibrium property can be optimized using the methods described here.