Liquid Crystalline Diblock Copolymers Research Articles

Synthesis and Characterization of Side-Chain Liquid-Crystalline Block Copolymers Containing Cyano-Terminated Phenyl Benzoate Moieties

Block copolymers, known for their capacity to undergo microphase separation, spontaneously yield various periodic nanostructures. These precisely controlled nanostructures have attracted considerable interest due to their potential applications in microfabrication templates, conducting films, filter membranes, and other areas. However, it is crucial to acknowledge that microphase-separated structures typically exhibit random alignment, making alignment control a pivotal factor in functional material development. To address this challenge, researchers have explored the use of block copolymers containing liquid-crystalline (LC) polymers, which offer a promising technique for alignment control. The molecular structure and LC behavior of these polymers significantly impact the morphology and alignment of microphase-separated structures. In this study, we synthesized LC diblock copolymers with cyano-terminated phenyl benzoate moieties and evaluated the microphase-separated structures and molecular alignment behaviors. The LC diblock copolymers with a narrow molecular weight distribution were synthesized by atom transfer radical polymerization. Small angle X-ray scattering measurements revealed that the block copolymers exhibit smectic LC phases and form cylinder structures with a lattice period of about 18 nm by microphase separation. The examination of block copolymer films using polarized optical microscopy and polarized UV-visible absorption spectroscopy corroborated that the LC moieties were uniaxially aligned along the alignment treatment direction.

Properties and molecular self‐assembly of liquid crystalline hard–hard diblock and hard–soft–hard triblock copolymers influenced by Flory–Huggins interaction parameter and volume fraction of distinct segments

AbstractTwo series of hybrid liquid crystalline (LC) diblock copolymers (DBCs) and triblock copolymers (TBCs) composed of hard and soft blocks with great control over their molecular masses, dispersities (Mw/Mn = Đ ≤ 1.38) and compositions were prepared via reversible addition‐fragmentation chain transfer polymerization in anisole solvent using new p‐dodecylphenyl‐N‐acrylamide monomer, azobisisobutyronitrile initiator, poly(2‐[2‐(4‐cyano‐azobenzene‐4‐oxy)ethylene‐oxy]ethyl methacrylate) and poly(2‐[2‐(4‐cyano‐azobenzene‐4‐oxy)ethylene‐oxy]ethyl methacrylate)‐block‐poly(n‐butyl methacrylate) macroinitiators. Structures and properties of BCs were characterized by proton nuclear magnetic resonance, gel permeation chromatography, differential scanning calorimeter, optical polarizing microscope, atomic force microscope and grazing‐incidence small angle X‐ray scattering. Kinetic behavior indicated that block copolymerization proceeded with controlled/living characteristics. Every BCs revealed three endothermic transitions corresponding to glassy phase transition, smectic‐to‐nematic phase transition (TS‐N) and melting phase transition. DBC‐1, DBC‐2, TBC‐1 and TBC‐2 with high‐LC volume fractions exhibited strong TS‐N contrasted to DBC‐3, DBC‐4, TBC‐3 and TBC‐4 having low‐LC contents. DBC‐1, DBC‐2, DBC‐3, TBC‐1 and TBC‐2 evidenced smectic C structure while TBC‐3 containing low‐LC segment (39 wt%) showed nematic structure. Morphologies of block copolymer thin films in mixed solvent (Tetrahydrofuran/cyclohexane) vapor annealing system varied significantly, depending on the volume fractions of building blocks and the interactions between the blocks and solvents.

Formation of hierarchical platelets with morphological control by self-assembly of an azobenzene-containing liquid crystalline diblock copolymer

The diblock copolymer PEG-b-PAzoMA self-assembled into abundant assemblies through a heating-annealing approach, including leaf-type, macro-flower-type, and rectangular platelets by manipulating the concentration and the cooling rate of the solution.

Controlled Synthesis and Photophysical Properties of Liquid Crystalline Diblock Copolymers with Side⁃Chain Discotic Triphylene and Calamitic Azobenzene Mesogens

Controlled Synthesis and Photophysical Properties of Liquid Crystalline Diblock Copolymers with Side⁃Chain Discotic Triphylene and Calamitic Azobenzene Mesogens

Optimization of Chemical Structure of Compatibilizers Based on Liquid Crystalline Diblock Copolymers for Reconciliation Between Inorganic Quantum Dots and Organic Cholesteric Liquid Crystals

Optimization of Chemical Structure of Compatibilizers Based on Liquid Crystalline Diblock Copolymers for Reconciliation Between Inorganic Quantum Dots and Organic Cholesteric Liquid Crystals

Cooperative and Independent Effect of Modular Functionalization on Mesomorphic Performances and Microphase Separation of Well-Designed Liquid Crystalline Diblock Copolymers.

Liquid crystalline block copolymers (LCBCPs) are promising for developing functional materials owing to an assembly of better functionalities. Taking advantage of differences in reactivity between alkynyl and vinyl over temperature during hydrosilylation, a series of LCBCPs with modular functionalization of the block copolymers (BCPs) are reported by independently and site-selectively attaching azobenzene moieties containing alkynyl (LC1 ) and Si-H (LC2 ) terminals into well-designed poly(styrene)-block-polybutadienes (PS-b-PBs) and poly(4-vinylphenyldimethylsilane)-block-polybutadienes (PVPDMS-b-PBs) produced from living anionic polymerization (LAP). By the principle of modular functionalization, it is demonstrated that mono-functionalized (PVPDMS-g-LC1 )-b-PB and PS-b-(PB-g-LC2 ) not only maintain independence but also have cooperative contributions to bi-functionalized (PVPDMS-g-LC1 )-b-(PB-g-LC2 ) in terms of mesomorphic performances and microphase separation, which is evident from differential scanning calorimetry (DSC) and polarized optical morphologies (POM) and identified by powder X-ray diffractions. With the application of the new principle of modular functionalization, local-crosslinked liquid crystalline networks (LCNs) with controlled functionality are successfully synthesized, which show well-controlled phase behaviors over molecular compositions.

The Effects of Magnetic Field Alignment on Lithium Ion Transport in a Polymer Electrolyte Membrane with Lamellar Morphology.

The transport properties of block copolymer-derived polymer electrolyte membranes (PEMs) are sensitive to microstructural disorder originating in the randomly oriented microdomains produced during uncontrolled self-assembly by microphase separation. This microstructural disorder can negatively impact performance due to the presence of conductivity-impeding grain boundaries and the resulting tortuosity of transport pathways. We use magnetic fields to control the orientational order of Li-doped lamellar polyethylene oxide (PEO) microdomains in a liquid crystalline diblock copolymer over large length scales (>3 mm). Microdomain alignment results in an increase in the conductivity of the membrane, but the improvement relative to non-aligned samples is modest, and limited to roughly 50% in the best cases. This limited increase is in stark contrast to the order of magnitude improvement observed for magnetically aligned cylindrical microdomains of PEO. Further, the temperature dependence of the conductivity of lamellar microdomains is seemingly insensitive to the order-disorder phase transition, again in marked contrast to the behavior of cylinder-forming materials. The data are confronted with theoretical predictions of the microstructural model developed by Sax and Ottino. The disparity between the conductivity enhancements obtained by domain alignment of cylindrical and lamellar systems is rationalized in terms of the comparative ease of percolation due to the intersection of randomly oriented lamellar domains (2D sheets) versus the quasi-1D cylindrical domains. These results have important implications for the development of methods to maximize PEM conductivity in electrochemical devices, including batteries.

Synthesis and self-assembling of diblock copolymers containing a side-on liquid crystalline block and a pseudo-stilbene azobenzene block

Liquid crystalline (LC) diblock copolymers containing a side-on LC block and a pseudo-stilbene azobenzene block were synthesized, and their self-assembling in water/tetrahydrofuran (THF) was investigated. Side-on LC monomer 4’’-methylacryloyloxybutyl 2,5-di(4’-butyloxybenzoyloxy) benzoate (4-MDBB) was synthesized, and then polymerized into P4MDBB through reversible addition-fragmentation chain transfer (RAFT) polymerization. A pseudo-stilbene azobenzene monomer 6-(N-methyl-N-(4-(4’-cyanophenylazo)phenyl)amino)hexyl methacrylate (6-NCN) was also synthesized. The diblock copolymers P4MDBBm-b-P6NCNn were obtained through the RAFT polymerization of 6-NCN by using P4MDBB as the chain transfer agent. The copolymers and the intermediates were confirmed by 1H and 13C NMR spectra, FT-IR spectra, UV-Vis spectra, mass spectra, DSC analysis, POM observations, GPC tests and contact angle measurements. The diblock copolymers self-assembled upon adding water slowly into their THF solutions. The self-assembling and the corresponding assemblies were characterized by fluorescence spectra, laser light scattering experiments as well as TEM measurements. Results demonstrated that these diblock copolymers form spherical aggregates in water/THF, but the aggregates are un-stretchable upon irradiation with polarized light.

Changes in Grain Structures Upon Blending of a Homopolymer to a Liquid-Crystalline Diblock Copolymer Which Forms Perpendicularly-Oriented Cylinders

Changes in Grain Structures Upon Blending of a Homopolymer to a Liquid-Crystalline Diblock Copolymer Which Forms Perpendicularly-Oriented Cylinders

Synthesis of amphiphilic comb-like liquid crystalline diblock polyethers and their self-assembly in solution

We have designed and synthesized a series of novel polyether based amphiphilic liquid crystalline (LC) diblock copolymers composed of pendent hydrophobic LC mesogens and hydrophilic ethylene oxide (EO) oligomers by using sequential anionic polymerization. The majority of this comb-like diblock copolymer is constituted by EO segments except the mesogenic groups which generate the chemical dissimilarity and drive the phase segregation. We have investigated the morphology evolution of the diblock copolymers in dioxane/water co-solvent with continuous tuning of the quality of the solvent, and discovered a systematic morphological transformation from a spherical micelle to a spherical vesicle, and finally to a faceted vesicle with increase of the water content above a critical value. The formation of the structured vesicle is related to the emerging of LC order within the membranes as revealed by in situ wide-angle X-ray diffraction experiments on the polymer solution. The elastic instability imparted from collective LC interactions which is incommensurate with the global topological geometry dictates this unique behavior. This type of faceted capsules on the tens of nanometer scale are expected to be potentially useful in biotechnological applications or drug delivery.

Design, synthesis, and phase behaviors of a novel triphenylene-based side chain liquid crystalline diblock copolymer

Influence of the weight fraction of PMT6S on the phase behaviors of diblock copolymers.

Thermotropic and Lyotropic Transitions of Concentrated Solutions of Liquid Crystalline Block Copolymers in a Liquid Crystalline Solvent

Rich phase structures and evolutions of the blends of smectic–nematic (S–N) liquid crystalline (LC) diblock copolymers and a nematic solvent (5CB) are investigated in a concentrated regime. These types of fully LC systems are macroscopically homogeneous with ordered phase-separated structures on the nanometer scale. By varying the temperature as well as the content of 5CB, the phase diagram of the blends is constructed, where the order-to-order transition (OOT) between lamellar and cylindrical nanostructures can be induced either lyotropically or thermotropically. The temperature and concentration dual-responsive properties are found to be closely related to the selectivity and distribution of 5CB, in addition to its phase transformation at the nematic–isotropic transition. As inferred from the miscibility and phase behaviors of its blends with the respective smectic and nematic homopolymers, the partition of 5CB in the S–N diblock copolymers and its influence on the phase structures reveal the important ...

Vertical Orientation of Nanocylinders in Liquid-Crystalline Block Copolymers Directed by Light.

The microphase-separated nanostructures of block copolymers are ideal nanotemplates for advanced fabrication, but they are greatly limited by the rapid and precise manipulation especially at room temperature. Here we report one method of light-directed regulation of nanostructures in thin films of liquid-crystalline diblock copolymers containing azobenzene units as photoresponsive mesogens. The in-plane orientated nanocylinders in thin film can be light-directed into out-of-plane on a time scale of seconds at room temperature. This fast regulation is beneficial from the fast process of photoinduced phase transition of the mesogenic block from liquid crystal to disordered isotropic phase. Several influence factors like the molecular weight of polymer, film thickness, light intensity, and relative humidity were studied in the light-directed processes. In addition, the photoregulated nanostructures demonstrate their capability of being photopatterned and further used as nanotemplates for fabrication of nanoparticles. The light-directed method shows noncontact, precise, and reversible features, enabling it to find further applications in fast control of nanostructures for nanofabrication and nanoengineering.

Spherical Compound Micelles with Lamellar Stripes Self‐Assembled from Star Liquid Crystalline Diblock Copolymers in Solution

Detailed investigations on the self‐assembly of amphiphilic star block copolymers composed of three‐arm poly(ethylene oxide) (PEO) and poly(methacrylate) (PMAAz) with an azobenzene side chain (denoted as 3PEO‐b‐PMAAz) into stable spherical aggregates with clear lamellar stripes in solution are demonstrated. Four block copolymers, 3PEO12‐b‐PMA(Az)33, 3PEO22‐b‐PMA(Az)31, 3PEO22‐b‐PMA(Az)62, and linear PEO68‐b‐PMA(Az)31, are synthesized. The liquid crystalline properties of the block copolymers are studied by differential scanning calorimetry, polarized optical microscopy techniques, and wide‐angle X‐ray diffraction. The morphologies of the compound micelles self‐assembled in tetrahydrofuran (THF)/water mixtures are observed by means of transmission electron microscopy and scanning electron microscopy. The size of the spherical micelles is influenced by the self‐assembly conditions and the lengths of two blocks. The well‐defined three‐arm architecture of the hydrophilic blocks is a key structural element to the formation of stable spherical compound micelles. The micelle surface integrity is affected by the lengths of PEO blocks. The lamellar stripes are clearly observed on these micelles. This work provides a promising strategy to prepare functional stable spherical compound micelles self‐assembled by amphiphilic block copolymers in solution.

Photoalignment of Vertically Oriented Microphase Separated Lamellae in LC-LC Diblock Copolymer Thin Film.

The microphase separation and photoalignment behavior of a diblock copolymer consisting of two kinds of side chain liquid crystalline (LC) polymers are investigated. Here, the mesogens of photoresponsive azobenzene and non-photoresponsive cyanobiphenyl are introduced in the side chains. The azobenzene and cyanobiphenyl mesogens orient homeotropically and planarly, respectively, in a thin film state. The combination of these contrasting orienting properties leads to a formation of vertically oriented lamella in the microphase separation structure. Irradiation with linearly polarized light onto this polymer film induces a highly oriented microphase separation structure having regularly elongated stripe morphology with 30 nm periodicity. The nearly defect-free morphology of this LC-LC diblock copolymer after the photoalignment is a distinct feature when compared with those of coil (amorphous)-LC diblock copolymer films possessing the same azobenzene side chain.

Synthesis, liquid crystalline mesophases and morphologies of diblock copolymers composed of a poly(dimethylsiloxane) block and a nematic liquid crystalline block

ABSTRACTIn this study, a series of liquid crystalline diblock copolymers, composed of a soft poly(dimethylsiloxane) (PDMS) block with a defined length and a side-on liquid crystalline poly(3ʹʹ-acryloyloxypropyl 2,5-di(4ʹ-butyloxybenzoyloxy) benzoate) (P3ADBB) block with different lengths, are synthesised by the atom transfer radical polymerisation. The macromolecular structures, liquid crystalline properties and the microphase-separated morphologies of the diblock copolymer are investigated by 1H NMR, FT-IR, GPC, POM, DSC and TEM. The results show that the well-defined diblock copolymers (PDMSn-b-P3ADBBm) possess four different soft/rigid ratios (n = 58, m = 10, 25, 42, 66) and relatively narrow molecular distributions (PDI ≤ 1.30). P3ADBB blocks of the copolymers show nematic sub-phases, which are identical to the mesomorphic behaviour of the homopolymer P3ADBB. After being annealed at 90°C in a vacuum oven for 48 h, the copolymers form a lamellar morphology when m = 10 and morphologies of PDMS spheres embedded in P3ADBB matrix when m = 25, 42 and 66.

Synthesis of side-on liquid crystalline diblock copolymers through macromolecular azo coupling reaction

We report a strategy for the synthesis of side-on liquid crystalline diblock copolymers by a combination of atom transfer radical polymerization (ATRP) method and a macromolecular azo coupling reaction. The liquid crystalline block, with a terminus suitable for azo coupling reaction, was obtained by ATRP using a synthesized ATRP initiator with the designed functional group and a side-on liquid crystalline monomer. The other block, with a diazonium salt terminus, was obtained by the diazotization of aniline-functionalized PEG. The macromolecular azo coupling reactions between above two polymer blocks were carried out in DMF. The products and intermediates were characterized by GPC, 1H NMR, FT-IR, POM and DSC.

Hierarchical Nanostructures and Self-Assemblies in Smectic-Nematic Liquid Crystalline Diblock Copolymers.

Coexistence of smectic and nematic orders in 3D curvaceous bicontineous cubic or hexagonal hierarchical structures is observed in a novel class of nanophase separated, flexible double liquid crystalline (LC) diblock copolymers of different molecular weights (MWs) but similar compositions, obtained via sequential anionic polymerization. The diblock copolymer of higher MW exhibits an exceptional order-order transition (OOT) from lamellae (Lam) to hexagonal-packed cylinder (HPC) upon nematic ordering. In contrast, the polymer with lower MW forms a thermodynamically stable, ordered gyroid structure, interwining with LC defects on nanoscale. Delicate balance of collective LC interactions and geometric frustration dictates this unique behavior, which offers a genuine way to fine-tune 2D and 3D complex structures with sub-10 nm feature sizes.

Directed self-assembly of nematic liquid crystalline polymers on a rubbed polyimide alignment layer

Amphiphilic diblock copolymers PEO-b-PMA(4OPB) comprising hydrophilic poly(ethylene oxide) (PEO) and hydrophobic nematic liquid crystalline polymethacrylate [PMA(4OPB)] subunits were synthesized by atom transfer radical polymerization. The liquid crystalline property and microphase-separated structure were investigated by differential scanning calorimetry, polarized optical microscopy, atomic force microscopy, and X-ray diffraction analysis. Unimodal PEO-b-PMA(4OPB) with 114 ethylene oxide repeating units and phenylbenzoate moieties as methacrylate side chain mesogens showed a nematic phase when the methacrylate repeating unit was around 57. Hexagonal cylinders of the PEO subunits were formed in nematic phase and supercooling states. The thin film on a rubbed polyimide alignment layer showed a microphase-separated structure independent of the rubbing direction, while horizontally aligned cylinders were observed in the presence of small nematic liquid crystalline molecules of 4-cyano-4′-pentyloxybiphenyl (5OCB). The assistance of nematic liquid crystalline molecules was necessary for directed self-assembly of the nematic liquid crystalline diblock copolymer in accordance with the rubbing direction of the polyimide alignment layer.

Enormously Wide Range Cylinder Phase of Liquid Crystalline PEO-b-PMA(Az) Block Copolymer

A series of amphiphilic liquid crystalline diblock copolymers, PEOm-b-PMA(Az)n, consisting of hydrophilic poly(ethylene oxide) and hydrophobic poly(methacrylate) moieties with side chains containing liquid crystalline (LC) azobenzene moieties, produced highly ordered microphase-separated films with PEO cylinders aligned perpendicular to the smectic LC layer of azobenzene in the PMA(Az) matrix. In this paper, morphological phase diagrams of PEOm-b-PMA(Az)n diblock copolymers above and below the isotropic transition temperature of LC azobenzene (Tiso) are presented. The diagrams are based on small-angle X-ray scattering (SAXS) measurements of approximately 70 kinds of polymers with varying degrees of polymerization in each block. An asymmetric phase diagram described against the volume fraction of PEO (fPEO) was obtained at temperatures above and below Tiso. The lamellar phase appears in the fPEO window 0.52 ≤ fPEO ≤ 0.78 above and below Tiso. Besides, the wide window, 0.087 ≤ fPEO < 0.52, allows the PEO cylinder phase to form below Tiso. In particular, the PEO sphere phase, observed above Tiso, was completely eliminated through an order–order transition (OOT) to the PEO cylinder phase in the window 0.087 ≤ fPEO ≤ 0.23. Such a large expansion in the PEO-cylinder-phase window could be attributed to the main chain of LC PMA(Az) being shorter than that of the flexible PEO chain, and LC azobenzene forming a smectic layer in the microphase separated system.