Block Copolymer Blends Research Articles

One‐Step Spontaneous Formation of Dual Wrinkling on Uniform‐Sized Microparticles Induced by Surface

AbstractThis study demonstrates the wrinkle formation on biodegradable polymer‐blend microparticles prepared from an emulsion‐solvent evaporation method and investigates the formed patterns. A labyrinthine pattern is obtained for uniform‐sized microparticles, owing to the considerable size reduction during solvent evaporation. Changing the radius of the organic droplets dispersed in the aqueous solution switches the wrinkle pattern from labyrinth to bi‐phase. For the first time, the dual wrinkling structure is prepared; both labyrinthine texture and hexagonal dimple structures are spontaneously formed on the same microparticle surface. The former pattern is due to the surface instability from blends of hydrophobic polymer and amphiphilic block copolymer, while the latter is due to a mechanism similar that of the breath figure formed with organic phase change materials during solidification of microparticles. The general applicability of this approach is demonstrated on other pairs of polymer blends.

Self-Registered Self-Assembly of Block Copolymers.

Directed self-assembly (DSA) of block copolymer (BCP) thin films, especially with density multiplication, is one of the most promising options for further improving resolution and throughput in nanolithography. However, controlling defect density has been one of the major hurdles for many DSA applications. Both thermodynamically and kinetically, defect-free patterns favor the use of low density multiplication factors and thinner films, which undermine the promise of enhanced resolution and the formation of robust masks for pattern transfer. Here, we demonstrate a self-registered self-assembly method to enable nearly perfect DSA on loosely defined chemical patterns with high density multiplication factor. Self-registered self-assembly involves two DSA steps. In the first step, an ultrathin BCP blend film is used to obtain vanishingly low defect densities. Concurrently as the film is annealed, preloaded chemical markers separate into the different polymer blocks and graft to the substrate locking in a new chemical contrast pattern with 1:1 feature registration. After thorough removal of the blend film, the remaining self-registered chemical pattern can establish defect-free DSA of thick BCP films.

Shape memory properties of olefin block copolymer (OBC)/poly(ɛ‐caprolactone) (PCL) blends

ABSTRACTConventionally, the chemically crosslinked shape memory polymer (SMP) blends are hard to recycle due to their network structure. Herein, the environmental SMP blends of olefin block copolymer (OBC), a unique thermoplastic elastomer, and poly(ɛ‐caprolactone) (PCL) were physically crosslinked. Dicumyl peroxide was used as the compatibilizer to improve their miscibility, as evidenced by the reduced dispersed domain size of PCL in the OBC matrix and the increased complex viscosity. The peroxide modified OBC/PCL blend conferred enhanced tensile properties, increased dynamic storage modulus, increased crystallization temperature, and higher recovery stress. The shape memory behaviors of OBC/PCL blends predeformed under two different predeformation temperatures (30 and 65 °C) were investigated. The recovery stress showed respective maximum peak values corresponding to their predeformation temperatures. In addition, the modified blends gave the better shape memory performance at 65 °C. Besides the peroxide modification approach, a precycle training process via prestretching the samples and reducing the mechanical hysteresis was implemented to improve shape memory performance further. This is the first work on the OBC‐based SMP blends to enhance shape memory performance by combining the chemical modification using added peroxide compatibilizer and the process modification using a precycle training process. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45475.

Control of nanostructures in epoxy/acrylic block copolymer blends by the in situ generation of functional groups

The phase structures obtained from blends consisting of an epoxy resin, an aromatic amine and a PMMA-b-PnBA-b-PMMA triblock copolymer (BCP) were studied, in terms of the effect of the process used to blend the BCP into the epoxy/amine mixture. The thermal dissolution of the BCP in the amine was found to promote the in situ generation of carboxylic acids in the PMMA segments of the BCP. This enhanced the compatibility of the BCP with the cured epoxy/aromatic amine resin, allowing the self-assembly of the BCP to form nanophase structures in the polymeric matrix. This work also determined that modification of the heating conditions was an effective means of controlling the quantity of carboxyl groups generated (that is, the acid value). Such variations led to the formation of different types of micelle structures, such as curved lamellae, coexisting of worm-like micelles and vesicles and spheres, from epoxy/amine/BCP blends having the same composition. The blends of epoxy/amine/acrylic block copolymer (BCP) provided nanophase structures by optimizing the dissolution process of BCP. The thermal dissolution of the BCP in the amine promoted the in situ formation of carboxylic acids. Tuning the amount of carboxylic acids changed the phase structure, such variations led to the formation of different types of micelle structures, such as curved lamellae, coexisting of worm-like micelles and vesicles, and spherical micelles from epoxy/amine/BCP blends having the same composition.

Antimicrobial surfaces obtained from blends of block copolymers synthesized by simultaneous ATRP and click chemistry reactions

A series of amphiphilic block copolymers based on styrene (S) and a monomer bearing both thiazole and triazole groups (MTA) were synthesized by combination of ATRP and click chemistry. In particular, two approaches were followed; the direct ATRP from a PS macroinitiator of the pre-synthesized MTA antimicrobial monomer; and the simultaneous synthesis and polymerization of the MTA through a one-step ‘click chemistry’/ATRP process. Both strategies conduct to well-defined block copolymers with controlled molecular weight and low polydispersity. Subsequent quaternization of the thiazole and triazole groups of MTA units with butyl iodine renders systems with antimicrobial properties. Although these systems presented relatively low antimicrobial activity against bacteria and fungi in aqueous media, the preparation of surfaces functionalized with these copolymers leads to potent antimicrobial surfaces, especially against gram-positive bacteria.

Structure Formation of Binary Blends of Amphiphilic Block Copolymers in Solution and in Bulk

The self‐assembly and structure formation in binary blends of asymmetric polystyrene‐block‐poly(4‐vinylpyridine) diblock copolymers in different solvent systems and the bulk morphology of the blend films are studied by using dynamic light scattering, small‐angle X‐ray scattering, and transmission electron microscopy. In dilute solutions, the chains of pure diblock copolymers or binary blends of diblock copolymers having similar or different molecular weights remain as unimers, form common micelles in selective solvents or form unimers in coexistence with micelles in slightly selective solvents or solvent mixtures. The blends show mixing of the chemically similar blocks in the blend films and solutions at high concentrations. A single‐phase with common spherical morphology is formed in the blend films similar with the morphology of the individual components in the pure state. The characteristic length scale of the blends depends on the number average molecular weight following the typical scaling behavior of a strongly segregated block copolymer. image

Mix-and-Match Assembly of Block Copolymer Blends in Solution

The chemical structure of a block copolymer (BCP) dictates the size, shape, and function of its self-assembled structure in solution. This direct correspondence demands precision synthesis of a specific BCP with optimized structural parameters to obtain the desired nanostructures with structural and functional complexity by solution self-assembly. Here we show that the binary blends of BCPs self-assemble into the desired nanostructure in solution by adjusting the composition of the blend. By modifying the structural parameters of a binary BCP blend through control of the composition, two BCPs sharing the repeating units in both polymer blocks coassemble into the desired structures, which range from spherical micelles to inverse cubic and hexagonal mesophases. These BCP blends not only allow the direct creation of complex periodic mesoporous structures of the desired periodicity and pore size but also provide nanostructures of unprecedented morphology by simple solution self-assembly without relying on the synthesis of correspondingly designed BCPs.

Recovered Polypropylene Composites with High Impact Strength

This paper presents a modification study of recovered polypropylene by melt alloying with a styrene-isoprene block-copolymer blend, thus ensuring the optimum conditions to obtain polypropylene composites with performance impact strength.

Implications of Grain Size Variation in Magnetic Field Alignment of Block Copolymer Blends.

Recent experiments have highlighted the intrinsic magnetic anisotropy in coil-coil diblock copolymers, specifically in poly(styrene-block-4-vinylpyridine) (PS-b-P4VP), that enables magnetic field alignment at field strengths of a few tesla. We consider here the alignment response of two low molecular weight (MW) lamallae-forming PS-b-P4VP systems. Cooling across the disorder-order transition temperature (Todt) results in strong alignment for the higher MW sample (5.5K), whereas little alignment is discernible for the lower MW system (3.6K). This disparity under otherwise identical conditions of field strength and cooling rate suggests that different average grain sizes are produced during slow cooling of these materials, with larger grains formed in the higher MW material. Blending the block copolymers results in homogeneous samples which display Todt, d-spacings, and grain sizes that are intermediate between the two neat diblocks. Similarly, the alignment quality displays a smooth variation with the concentration of the higher MW diblock in the blends, and the size of grains likewise interpolates between limits set by the neat diblocks, with a factor of 3.5× difference in the grain size observed in high vs low MW neat diblocks. These results highlight the importance of grain growth kinetics in dictating the field response in block copolymers and suggests an unconventional route for the manipulation of such kinetics.

Interference lithography with functional block copolymer blends: Hierarchical structuration and anisotropic wetting

This manuscript describes the preparation of hierarchically, i.e. micro and nanometer scale ordered surfaces with variable functionality by simultaneously combining the microfabrication using Laser Interference Lithography (LIL) and the self-assembly of block copolymers occurring at the nanometer scale. The block copolymers employed in this study are a double hydrophobic poly(2,3,4,5,6-pentafuorostyrene)-block-polystyrene (P5FS31-b-PS21) and an amphiphilic polystyrene-block-poly(acrylic acid) (PS20-b-PAA9) diblock copolymer. The incorporation of these block copolymers in the photosensitive mixture resulted in surfaces with hierarchically micro and nanostructured interfaces with either hydrophobic or hydrophilic surface chemical composition. Moreover, in comparison with microstructured surfaces prepared using statistical copolymer with similar composition, the use of block copolymers enhanced both the surface wettability changes and the final anisotropic wetting. We evidenced herein that by preparing unidirectional micrometer size patterns with either P5FS31-b-PS21 or PS20-b-PAA9 the wetting anisotropy increases with the hydrophobicity or the hydrophilicity of the surface.

Multiple phase transitions in block copolymer blends and pressure effects on these transitions

We sought to identify an evident enthalpic-driven transition below an entropic-driven closed-loop phase transition by studying the phase behavior in miscible binary block copolymer (BCP) blends of a polystyrene-b-poly (n-butyl methacrylate) (PS-b-PnBMA) and a deuterated polystyrene-b-poly (n-hexyl methacrylate) (dPS-b-PnHMA), using small-angle x-ray scattering (SAXS) and depolarized light scattering (DPLS). Intriguingly, an order-to-disorder transition (ODT) below the closed-loop transition consisting of a lower disorder-to-order transition (LDOT) and an upper order-to-disorder transition (UODT) was observed in the BCP blends of an asymmetric (PS-rich) PS-b-PnBMA and a symmetric dPS-b-PnHMA. Multiple phase transitions, previously undiscovered in BCP system, were attributed to a delicate balance in the free energy of the dispersive intermolecular interactions, the entropic compressibility, and the combinatorial entropy of mixing at an experimental temperature range between the glass transition temperature (Tg) and degradation temperature (Td). We also characterized the effects of hydrostatic pressure on the transition temperatures to determine the thermodynamic origins of each phase transition.

Effect of block composition on the morphology and transport properties of sulfonated fluoroblock copolymer blend membranes

This study focuses on the relationship between the transport properties and the morphological changes of ionic block copolymer blend membranes, as a function of the fluoroblock chemical composition and loading. Poly(styrene‐b‐isobutylene‐b‐styrene) was sulfonated and blended with three different fluoropolymers: Poly(styrene)‐b‐poly(2,3,4,5,6‐pentafluorostyrene)‐b‐poly(2,2,3,4,4,4‐hexafluorobutyl methacrylate) [PS‐b‐PFS‐b‐PHFBMA], a difluoroblock copolymer composed of PS‐b‐PHFBMA and a homopolymer composed of PHFBMA. Equilibrium and transport properties (e.g., ion exchange capacity, water uptake, water content, proton conductivity, and methanol permeability), were shown to be significantly influenced by the chemical nature of the fluoroblock copolymer, the fluoropolymer content, and their resulting morphology. Proton conductivity and methanol permeability were very sensitive to the incorporation of PHFBMA. Polymer blends composed of sulfonated poly(styrene‐b‐isobutylene‐b‐styrene) (SIBS SO3H) and PHFBMA above 9 wt% showed interconnected ionic domains that have a shorter correlation length and high water content, which results in improved transport properties for direct methanol fuel cell (DMFC) applications. POLYM. ENG. SCI., 57:1262–1272, 2017. © 2017 Society of Plastics Engineers

Relationship between the mechanical properties of epoxy/PMMA-b-PnBA-b-PMMA block copolymer blends and their three-dimensional nanostructures

Relationship between the mechanical properties of epoxy/PMMA-b-PnBA-b-PMMA block copolymer blends and their three-dimensional nanostructures

Stabilizing the Frank-Kasper Phases via Binary Blends of AB Diblock Copolymers.

The emergence of the complex Frank-Kasper phases from binary mixtures of AB diblock copolymers is studied using the self-consistent field theory. The relative stability of different ordered phases, including the Frank-Kasper σ and A15 phases containing nonspherical minority domains with different sizes, is examined by a comparison of their free energy. The resulting phase diagrams reveal that the σ phase occupies a large region in the phase space of the system. The formation mechanism of the σ phase is elucidated by the distribution of the two diblock copolymers with different lengths and compositions. In particular, the segregation of the two types of copolymers, occurring among different domains and within each domain, provides a mechanism to regulate the size and shape of the minority domains, thus enhancing the stability of the Frank-Kasper phases. These findings provide insight into understanding the formation of the Frank-Kasper phases in soft matter systems and a simple route to obtain complex ordered phases using block copolymer blends.

Selective directed self-assembly of coexisting morphologies using block copolymer blends.

Directed self-assembly (DSA) of block copolymers is an emergent technique for nano-lithography, but is limited in the range of structures possible in a single fabrication step. Here we expand on traditional DSA chemical patterning. A blend of lamellar- and cylinder-forming block copolymers assembles on specially designed surface chemical line gratings, leading to the simultaneous formation of coexisting ordered morphologies in separate areas of the substrate. The competing energetics of polymer chain distortions and chemical mismatch with the substrate grating bias the system towards either line/space or dot array patterns, depending on the pitch and linewidth of the prepattern. This is in contrast to the typical DSA, wherein assembly of a single-component block copolymer on chemical templates generates patterns of either lines/spaces (lamellar) or hexagonal dot arrays (cylinders). In our approach, the chemical template encodes desired local spatial arrangements of coexisting design motifs, self-assembled from a single, sophisticated resist.

Thermodynamic and Morphological Behavior of Block Copolymer Blends with Thermal Polymer Additives

Block copolymer (BCP) blends offer a facile route toward customizable nanomaterials. To better understand these systems, the thermodynamics of polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) and poly(vinylphenol) (PVPH) blends were examined using scattering measurements and self-consistent field theory (SCFT). PVPH hydrogen bonds to the PMMA block, resulting in the selective infusion into the PMMA layer. Measurements on initially disordered blends show that this interaction can induce an order–disorder transition (ODT). The ODT was observed to be a continuous transition, unlike the first-order thermal ODT typically observed in BCPs. Free energy curves extracted from SCFT simulations also observed a lack of a discontinuity in the first-order derivative. Lamellar systems underwent a greater increase in BCP period compared to identical athermal systems due to the extension of the PMMA chains away from the interface. Comparison with the SCFT models finds good agreement in the predicted behavior of the ble...

Self-Assembled Blends of AB/BAB Block Copolymers Prepared through Dispersion RAFT Polymerization

Synthesis of ingenious nanoassemblies is pursued in materials science. Herein, the in situ synthesis of the self-assembled blends of AB/BAB block copolymers of poly(ethylene glycol)-block-polystyrene/polystyrene-block-poly(ethylene glycol)-block-polystyrene (PEG-b-PS/PS-b-PEG-b-PS) via two-macro-RAFT agent comediated dispersion polymerization is reported. The synthesis strategy combines the advantages of polymer blending and polymerization-induced self-assembly. Following this strategy, various nanoassemblies of PEG-b-PS/PS-b-PEG-b-PS blends such as high-genus compartmentalized vesicles, multilayer and bicontinuous nanoassemblies, and porous nanospheres are prepared. The parameters, such as PEG-b-PS/PS-b-PEG-b-PS molar ratio, polymerization degree of the PS block, and fed monomer concentration, affecting morphology/structure of PEG-b-PS/PS-b-PEG-b-PS self-assembled blends are revealed. Computer simulations of self-assembly of the AB/BAB blends are performed, and nanoassemblies similar to those observed in our experiments are obtained, indicating that these morphologies are close to thermodynamical equilibrium. The formation mechanism of compartmentalized vesicles is investigated. The proposed strategy of two-macro-RAFT agent comediated dispersion polymerization is considered to be an efficient approach to construct self-assembled blends of block copolymers.

Promoting effect of crystallization on the foaming behavior in polypropylene homopolymer/polypropylene block copolymer blends

Polypropylene (PP) is a kind of semi-crystalline polymer so it is hard to foam with supercritical carbon dioxide (SCCO2). We used polypropylene block (PP-B) copolymer as a modifier to improve the crystallization behaviors and foaming performance of polypropylene homo polymer (HPP). HPP, PP-B, and a series of HPP/PP-B blends were characterized by differential scanning calorimeter (DSC), X-ray diffraction, and polarized optical microscope. Results show that both the crystallization behaviors and melt strength have influence on the cell structure. The crystallization temperature of PP-B is about 7°C higher than that of HPP and that the crystallization behavior of HPP/PP-B blends is similar to that of PP-B. Much denser and smaller size spherulites are observed in PP-B and HPP/PP-B blends than in HPP, and the crystal structure is unchanged after blending. Scanning electron microscope results show that much more uniform, smaller cells can be obtained for the HPP/PP-B blends. The crystal nuclei formed earlier can act as physical cross-link points, increasing the melt strength and improving dramatically the cell structure and morphology of the HPP/PP-B blends. Furthermore, the best cell structure and morphology was achieved for HPP/PP-B blends with the ratio of 70/30 under the same foaming conditions. POLYM. ENG. SCI., 2016. © 2016 Society of Plastics Engineers

Uniform patchy and hollow rectangular platelet micelles from crystallizable polymer blends.

The preparation of colloidally stable, self-assembled materials with tailorable solid or hollow two-dimensional (2D) structures represents a major challenge. We describe the formation of uniform, monodisperse rectangular platelet micelles of controlled size by means of seeded-growth methods that involve the addition of blends of crystalline-coil block copolymers and the corresponding crystalline homopolymer to cylindrical micelle seeds. Sequential addition of different blends yields solid platelet block comicelles with concentric rectangular patches with distinct coronal chemistries. These complex nano-objects can be subject to spatially selective processing that allows their disassembly to form perforated platelets, such as well-defined hollow rectangular rings. The solid and hollow 2D micelles provide a tunable platform for further functionalization and potential for a variety of applications.

Confinement effects on the miscibility of block copolymer blends.

Thin films of long and short symmetric AB diblock copolymers are examined using self-consistent field theory (SCFT). We focus on hard confining walls with a preference for the A component, such that the lamellar domains orient parallel to the film with an even number ν of monolayers. For neat melts, confinement causes the lamellar period, D, to deviate from its bulk value, Db, in order to be commensurate with the film thickness, i.e., L = νD/2. For blends, however, the melt also has the option of macrophase separating into ν(l) large and ν((s)) small monolayers so as to provide a better fit, where L = ν(l)D(l)/2 + ν(s)D((s))/2. In addition to performing full SCFT calculations of the entire film, we develop a semi-analytical calculation for the coexistence of thick and thin monolayers that helps explain the complicated interplay between miscibility and commensurability.