Behavior Of Block Copolymers Research Articles

Reaction‐induced morphology control in block copolymers

AbstractControlling the self‐assembly behaviors of block copolymers (BCPs) is a focal point of many research thrusts due to their broad use in various applications. While BCP molecular weight, volume fraction, and chemical identities are key thermodynamic parameters to determine their morphology, an emergent method in this area is through reaction‐induced changes to the characteristics of a BCP in situ, which provides access to multiple morphologies and domain sizes from a single parent polymer, as well as enabling the formation of metastable morphologies which may be difficult to attain otherwise. This work provides a focused review about the current state of reaction‐induced morphology control in BCPs in both solution and solid states. Furthermore, we provide a forward‐looking perspective on the future opportunities of understanding and employing reaction engineering to manipulate and advance BCP self‐assembly. © 2023 Society of Industrial Chemistry.

Phase behavior of disk-coil block copolymers under cylindrical confinement: Curvature-induced structural frustrations.

In this paper, we explore the self-assembly behavior of disk-coil block copolymers (BCPs) confined within a cylinder using molecular dynamics simulations. As functions of the diameter of the confining cylinder and the number of coil beads, concentric lamellar structures are obtained with a different number of alternating disk-rich and coil-rich bilayers. Our paper focuses on the curvature-induced structural behavior in the disk-rich domain of a self-assembled structure, which is investigated by calculating the local density distribution P(r) and the orientational distribution G(r,θ). In the inner layers of cylinder-confined disk-coil BCPs, both P(r) and G(r,θ) show characteristic asymmetry within a bilayer which is directly contrasted with the bulk and slab-confined disk-coil BCPs. We successfully explain the structural frustration of disks arising from the curved structure due to packing frustration of disks and asymmetric stretching of coils to the regions with different curvatures in a bilayer. Our results are important to understand the self-assembly behavior of BCPs containing a rigid motif in a confined structure, such as a self-assembled structure of bacteriochlorophyll molecules confined by a lipid layer to form a chlorosome, the photosynthetic antennae complex found in nature.

Emergent symmetries in block copolymer epitaxy

The directed self-assembly (DSA) of block copolymers (BCPs) has shown promise in fabricating customized two-dimensional (2D) geometries at the nano- and meso-scale. Here, we discover spontaneous symmetry breaking and superlattice formation in DSA of BCP. We observe the emergence of low symmetry phases in high symmetry templates for BCPs that would otherwise not exhibit these phases in the bulk or thin films. The emergence phenomena are found to be a general behavior of BCP in various template layouts with square local geometry, such as 44 and 32434 Archimedean tilings and octagonal quasicrystals. To elucidate the origin of this phenomenon and confirm the stability of the emergent phases, we implement self-consistent field theory (SCFT) simulations and a strong-stretching theory (SST)-based analytical model. Our work demonstrates an emergent behavior of soft matter and draws an intriguing connection between 2-dimensional soft matter self-assembly at the mesoscale and inorganic epitaxy at the atomic scale.

Chiral expression in conjugated helical block copolymers

The organizational behaviour of block copolymers consisting of two helical blocks with opposite chiral expression is investigated.

Phase transition of block copolymer/homopolymer binary blends under 2D confinement

Constraints imposed by nanometer scale confinement lead to the changes in bulk equilibrium behavior of block copolymers (BCPs). Cylindrical pores with diameter corresponding to the equivalent length of several copolymer chains have been employed to investigate the influence of two-dimensional (2D) confinement on the behavior of BCPs. Herein, we reported the microdomain transition behavior of block copolymer/homopolymer (AB/A) binary blends in cylindrical confinement. Lamellae forming poly(styrene-b-butadiene) (PS-b-PBD) and PS homopolymers (hPS) were drawn into the pores of anodized aluminum oxide (AAO) and isolated by selective etching of the AAO templates. Concentric ring morphologies of neat PS-b-PBD in the cylindrical confinement varied with on the addition of hPS. Given the volume fraction of homopolymers, the phase behavior of polymer blends was dependent on the molecular weight of homopolymers. When the ratio between the molecular weight of hPS and PS block was much lower than unity (α«1) (i.e., wet brush regime), the concentric ring structure was transformed into helical or spherical structure depending on the volume fraction of hPS. For α≈1 (i.e., dry brush regime), additional hPS chains were localized at the center of concentric ring where the entropic penalty of copolymer chains induced by confinement is maximized. Over the capability of hPS in the BCP domains in radial axis, the phase transition into microemulsions occurred in the dry brush regime. In both wet and dry brush regimes, the effect of hPS on the phase transition of BCP was significantly enhanced in the nanoscale 2D confinement compared to the bulk state due to the loss of conformational entropy of polymer chains.

Tuning the optoelectronic properties of P3EHT block copolymers by surface modification

P3AT-containing block copolymers (BCPs) have potential for use as electroactive polymer brushes for stimuli-responsive surfaces, with reversible tethering of the P3AT block. This kind of tethering is highly dependent on the P3AT block's affinity for the surface. We have investigated the effect of surface modification on P3EHT-b-PS and P3EHT-b-PtBA films deposited on ITO-coated glass substrates modified by electrodeposition of poly(terthiophene). Optical and electrochemical properties of the BCPs deposited both on PTTh films and on bare ITO were investigated by UV-Vis spectroscopy and cyclic voltammetry, respectively. These characterisations reveal interplay between deposition conditions and the optoelectronic behaviour of BCPs investigated, and also provide insight as to their morphology under various conditions as it impacts on such behaviour. Significantly, electrochemically-driven switches in the morphology of BCPs were observed, however polymer-solvent interactions dominated. Absorbance spectra revealed a strong interaction between BCPs and the poly(terthiophene) substrates, manifesting as disruptions in crystallinity in the BCPs.

Self-assembly behavior of ABC triblock copolymer in cylindrical pore: A Monte Carlo study

The spacially confined environment can greatly affect the self-assembly behavior of block copolymers, which provides an effective way for fabricating nanomaterials with novel structures and functionalities. Understanding the self-assembly behavior of block copolymers under various confined environments is of great importance for both fundamental studies and practical applications. In this work, the self-assembly behavior of tetragonal-packed cylinder-forming linear ABC triblock copolymers in cylindrical pore is studied using Monte Carlo simulation. Simulation results show that the self-assembly structures of the triblock copolymers depend on the pore size. In larger pore, the self-assembly structure is independent of the initial state of the system, only complex lariat structures are formed. While in smaller pore, the self-assembly structures depend on the initial state of the system. Double helices, parallel pillars and stacked disks can be obtained from different initial states. Further investigations indicate that when the pore size is incommensurate with the equilibrium period of the system in bulk, the occurring probability of the structure with higher interactive energy is high. However, when the pore size is commensurate with the equilibrium period, the occurring probability of the structure with higher interactive energy is low. Moreover, the statistical analysis at the level of micro-scale for the same double helices reveals that with the increase in the pore size, the mean-square end-to-end distance of the polymer chains in cylindrical pore increases, and the orientation of the polymer chains changes from the direction that is perpendicular to the pore axis to the direction that is parallel to the pore axis. The simulation results not only offer new insights into the self-assembly behavior of block copolymers under confined environment, but also provide a theoretical basis for corresponding experiments.

Photophysical behavior of block copolymers containing EDOT, thiophene, and benzodiathiazole units linked to fluorene

Photophysical behavior of block copolymers containing EDOT, thiophene, and benzodiathiazole units linked to fluorene

Effect of Knockout of Mdr1a and Mdr1b ABCB1 Genes on the Systemic Exposure of a Doxorubicin-Conjugated Block Copolymer in Mice.

We previously elucidated that ATP-binding cassette subfamily B member 1 (ABCB1) mediates the efflux of doxorubicin-conjugated block copolymers from HeLa cells. Here, we investigated the role of ABCB1 in the in vivo behavior of a doxorubicin-conjugated polymer in Mdr1a/1b(-/-) mice. The area under the curve for intravenously administered polymer in Mdr1a/1b(-/-) mice was 2.2-fold greater than that in wild-type mice. The polymer was mostly distributed in the liver followed by spleen and less so in the brain, heart, kidney, and lung. The amount of polymer excreted in the urine was significantly decreased in Mdr1a/1b(-/-) mice. The amounts of polymers excreted in the feces were similar in both groups despite the higher systemic exposure in Mdr1a/1b(-/-) mice. Confocal microscopy images showed polymer localized in CD68(+) macrophages in the liver. These results show that knockout of ABCB1 prolonged systemic exposure of the doxorubicin-conjugated polymer in mice. Our results suggest that ABCB1 mediated the excretion of doxorubicin-conjugated polymer in urine and feces. Our results provide valuable information about the behavior of block copolymers in vivo, which is important for evaluating the pharmacokinetics of active substances conjugated to block copolymers or the accumulation of block copolymers in vivo.

Synthesis, characterization, and temperature‐responsive behaviors of novel hybrid amphiphilic block copolymers containing polyhedral oligomeric silsesquioxane

Organic/inorganic hybrid amphiphilic block copolymer poly(methacrylate isobutyl POSS)‐b‐poly(N‐isopropylacrylamide‐co‐oligo(ethylene glycol) methyl ether methacrylate) (PMAPOSS‐b‐P(NIPAM‐co‐OEGMA)) was synthesized via reversible addition–fragmentation chain transfer polymerization. The self‐assembly behavior of this block copolymer in aqueous solution was investigated by dynamic light scattering (DLS) and transmission electron microscopy. The results indicate that the novel block copolymer can self‐assemble into spherical micelles with PMAPOSS segment as the hydrophobic part and P(NIPAM‐co‐OEGMA) segment as the hydrophilic part. The temperature‐responsive characteristics of the assemblies were tested by UV–Vis spectra and DLS. Some factors such as the concentration, molecular weight, and copolymer generation that may affect the cloud point were studied systematically. The results reveal that this copolymer exhibits a sharp and intensive lower critical solution temperature (LCST). The essentially predetermined LCST can be conveniently achieved by adjusting the content of NIPAM or OEGMA domain. In addition, these novel hybrid micelles can undergo an association/disassociation cycle with the heating and cooling of solution and the degree of reversibility displaying a tremendous concentration dependence, as a novel organic/inorganic hybrid material with distinctive virtues can be potentially used in biological and medical fields, especially in drug nanocarriers for targeted therapy. Copyright © 2014 John Wiley & Sons, Ltd.

Features of the phase behavior of block copolymers related to their polydispersity

To calculate cloud points of a melt of block copolymers, at which its microphase separation occurs, for the first time in the theory of polymers, a spectral method is used in a model that takes into account the compressibility of the melt and the polydispersity of its macromolecules. A particular case of this calculation for a copolymer whose macromolecules consist of two blocks is described, and the polydispersity of each of them is defined through the exponential Flory distribution.

Controlling the phase behavior of block copolymers via sequential block growth

Block copolymers remain one of the most extensively investigated classes of polymers due to their abilities to self-organize into various nanostructures and modify polymer/polymer interfaces. Despite fundamental and technological interest in these materials, only a handful of experimental phase diagrams exist due to the laborious task of preparing such diagrams. In this work, two copolymer series are each synthesized from a single macromolecule via sequential living anionic polymerization to yield molecularly asymmetric diblock and triblock copolymers systematically varying in composition. The phase behavior and morphology of these copolymers are experimentally interrogated and quantitatively compared with predictions from mean-field theories, which probe copolymer phase behavior beyond current experimental conditions.

Principles of Hierarchical Meso- and Macropore Architectures by Liquid Crystalline and Polymer Colloid Templating

The generation of porous silica with hierarchically organized bimodal mesoporosity of adjustable size and well-defined shape was investigated by using surfactant mixtures and the nanocasting procedure (liquid crystalline templating). A systematic study of combinations of various block copolymers (Pluronics F127, KLE (poly(omega-hydroxypoly(ethylene-co-butylene)-co-poly(ethylene oxide))) and SE (PS-co-PEO)) with smaller surfactants (Pluronics P123, C16mimCl, and CTAB) revealed that hierarchical bimodal mesopore architectures could only be obtained by the usage of block copolymers with a strong hydrophilic-hydrophobic contrast, such as KLE and SE, giving rise to pores between 6 and 22 nm. Furthermore, the ionic liquid (IL) C16mimCl appeared to have advantageous templating properties, resulting in 2-3-nm pores being located between the block copolymer mesopores, whereas phase separation was observed for Pluronics and CTAB as small templates. Thereby, the study provided also general insights into the mixing and co-self-assembly behavior of block copolymers and ionic surfactants in water and confirmed the special templating properties of ILs, as recently proposed. In addition to the bimodal mesoporosity, additional tunable macroporosity was created by the presence of poly(styrene) or poly(methyl methacrylate) spheres, leading to well-defined trimodal hierarchical pore architectures with the small pores being located in the walls of the respective larger pores. As a major improvement, due to the pore hierarchy, these large-pore materials showed relatively large surface areas and pore volumes, and the size of densely packed macropores could even be decreased down to 90 nm. The materials were characterized by electron microscopy, small-angle X-ray scattering, and nitrogen sorption using a proper NLDFT (nonlocal density functional theory) approach for calculations of the pore size distribution in the entire range of micro- and mesopores.

Poly(styrene‐block‐isoprene) nanocomposites: Kinetics of intercalation and effects of copolymer on intercalation behaviors

AbstractIn addition to phase morphology, diffusion, and dynamics in the bulk, the behavior of block copolymers in the confined state has been of great interest. Although random and graft copolymers have been used in polymer‐layered silicate nanocomposites, well‐defined block copolymers have received relatively little attention. In this study, the kinetics of intercalation of a series of poly(styrene‐b‐isoprene) block copolymers into a layered silicate were examined via X‐ray diffraction. Intercalation was observed even when the copolymer was in the ordered state, with no discontinuity around the order–disorder transition of the copolymer. As the size of the polystyrene block was increased, slower intercalation kinetics were observed, possibly because of the increased glass‐transition temperature of the polystyrene segment. Finally, the clearing temperature of the copolymer in the nanocomposites as measured by small‐angle X‐ray scattering showed a large heating‐rate dependence suggesting that the nanoparticles act as kinetics barriers to the disordering of the copolymer. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3264–3271, 2003

Physical Properties of Polyurethane Modified with Poly(m-Phenylene Isophthalamide)

A segment of block copolymers with poly(m-phenylene isophthalamide) (PmIA) length was prepared. The block copolymers were prepared using various molecular weights of polytetramethylene glycols (PTMG) as the soft segment, and 4,4′-diphenylmethane diisocyanate (MDI), 1,4-butane diol (BD), and aromatic diamineterminated PmIA as the hard segment. The block copolymers exhibited soft-segment crystallization when a PTMG greater than 2000M, was used. The glass transition temperature, Tgs , of these block copolymers progressively shift to lower temperatures (below 0°C) as the chain length of the soft segment was increased and the glass transition temperature. Tgh , of these block copolymers shift to higher temperatures (up 0°C) as the chain length of hard segment was increased. The stress-strain and stress-relaxation behaviors of block copolymers were studied. The determined values of Young's modulus, E, the Mooney-Rivlin elastic parameters C 1 and C 2, relaxation moduli, E(10 sec) and E(100 sec), as well as relaxation speed, Vr , and relaxation time T1, T2, and T3 were used to estimate the effect of the length of PmIA molecules segments on the mechanical behavior of block copolymers. It was found that block copolymers still displayed good elastic properties (especially using the molecular weight 2900 of PTMG which exhibited a more elastic behavior).

Tem‐ and neutron reflection studies on surfaces and interfaces with block copolymers

AbstractThe behavior of block copolymers at various interfaces is studied by transmission electron microscopy and neutron reflection. A thin film of a symmetric diblock copolymer of styrene and methyl methacrylate forms layer structures when in contact with air and a random copolymer of styrene and acrylonitrile containing 35 wt% acrylonitrile. When the random copolymer has an acrylonitrile content of 25 wt%, a competition between layer formation and diffusion of disordered micelles takes place. Driving force for these processes are different interfacial tensions and a changing miscibility behavior as a function of acrylonitrile contents of the random copolymers. The ordering behavior of a symmetric diblock copolymer of deuterated styrene and isoprene in contact with poly(3,5‐dimethyl phenylene ether) is studied by neutron reflection. Polystyrene‐block‐poly(ethene‐co‐but‐1‐ene)‐block‐polystyrene with cylindrical PS microdomains shows an interfacial phase transition to lamellae near to the interface with different polymers. The morphological studies are in agreement with adhesion data obtained by peel tests on different bilayer specimens.

Mechanical behaviour of block copolymers of polyurethane with poly (4,4′-diphenylsulphone terephthalamide)

Two poly (tetramethylene glycols) (PTMG), molecular weight of 650 and 2000, with 4,4′-diphenylmethane diisocyanate (MDI) and poly(4, 4′-diphenylsulphone terephthalamide) (PSA) prepolymer were polycondensated. Four different molar ratios of PTMG, MDI and PSA prepolymer were synthesized to form eight PU-PSA block copolymers. The mechanical properties including stress-strain and stress-relaxation measurements of each copolymer were discussed. The determined values of Young's modulus E, Mooney-Rivlin relation elastic parameters C1 and C2, relaxation moduli E1(0) and E2(0), relaxation time τ1 and τ2 were used to estimate the effect of hard segment and soft segment domains on the mechanical behaviour of copolymers. It was found that PU-PSA block copolymers apparently displayed elastic properties, especially using the molecular weight 2000 of PTMG which exhibited more elastic behaviour.

Behavior of Block Copolymers in Thin Films

The uses of polymeric materials in today's world are vast. Polymers are finding applications in the microelectronics industry as dielectric insulators and photoresists, in the aerospace and automobile industry as lightweight substitutes for metals, and in biotechnology as replacement components for bone, heart, and other organs. These are just a few of the many end uses of polymers.Often, a polymer may have a particular, desirable property but processing of the polymer is difficult or the polymer's surface characteristics are undesirable. To circumvent such shortcomings there are several options. The first is to synthesize a new material, which is quite costly and time consuming. Alternatively, two polymers with complimentary properties can be mixed. Unfortunately, most polymer pairs are immiscible unless there are specific interactions (e.g., hydrogen bonding) between the two components. Consequently, coarse phase separation is often observed, leading to an ill-defined material. Finally, two chemically distinct homopolymers can be joined together at one point, forming a block copolymer. While phase separation may occur, the scale of the domains is restricted to the sizes of the individual homopolymers, which is typically on the tens of nanometers scale. The added advantage of this approach is that the size of the different blocks can be altered, varying the concentration of the different components. For copolymers that “microphase” separate, this variation in composition leads to a variation of the morphology of the microdomains ranging from spherical to cylindrical to lamellar.

Investigation of the behaviour of random and block copolymers of styrene and methacrylic acid

For the first time hydrophilic-hydrophobic block copolymers of styrene and methacrylic acid have been obtained through a radical mechanism. It is shown that the behaviour of the block copolymers in dioxan-ethyl alcohol solution differs from that of random copolymers of like composition. Curling of the individual blocks into globules in the block copolymer molecules is dependent solely on solvent composition, whereas curling of the random copolymer molecule is also dependent on the styrene content of the copolymer.