Side-chain Liquid Crystalline Copolymers Research Articles

Polymerization-induced self-assembly of side-chain liquid crystalline copolymers by dissipative particle dynamics simulation

Side-chain liquid crystal copolymers can self-assemble into dispersed assemblies effectively with the polymerization-induced self-assembly (PISA) technique. However, the synergy of polymerization and self-assembly result in undefined self-assembly behavior and polymerization kinetics. We explored the PISA behavior of side-chain liquid crystal copolymers in selective solvents by combining dissipative particle dynamics simulation and a probability-based reaction model. It was found that the morphologies of assemblies depend on the PISA time, copolymer concentrations, and various structural parameters. The polymerization exhibits three stages with different reaction constants during the PISA, achieving low polydispersity of the produced copolymers. The comparison with experiments demonstrated that the simulation could capture the essential characteristics of PISA. This study can help fundamentally understand the PISA behavior of side-chain liquid crystal copolymers.

Synthesis and Phase Behavior of (Semifluorinated Alkane)-Based Side-Chain Liquid Crystalline Copolymers.

Side-chain liquid crystalline polymer (SCLCP) usually contains a simple and flexible homopolymer as main chain, while its effect on the self-assembly behavior is often ignored. In this work, in order to increase the structural complexity and investigate the interaction between the main chain and mesogens, perfluorinated segments are introduced into the main chain using a photoinduced Step Transfer-Addition & Radical-Termination polymerization method, producing a novel series of SCLCPs containing 4-methoxyphenyl benzoate mesogens, soft hydrocarbon spacers, and a strictly alternating perfluoroalkyl and alkyl backbone. By adjusting the length of spacers or perfluoroalkyl segments, several mesophases with complex chain packing structures are achieved. This design strategy that constructing highly ordered liquid crystalline (LC) structures from SCLCPs with precise chemical structure provides a facile way toward novel LC nanomaterials.

Membranes for Cation Transport Based on Dendronized Poly(Epichlorohydrin-Co-Ethylene Oxide). Part 2: Membrane Characterization and Transport Properties.

In this paper, we report on the preparation and characterization of membranes out of two side-chain liquid crystalline copolymers, dendronized at two different extents (20 and 40%, CP20 and CP40, respectively). The membranes were characterized by atomic force microscopy (AFM), field-emission scanning electron microscopy (FESEM), contact angle (CA) analysis, and water uptake. Moreover, transport properties were studied by methanol and proton conductivity experiment and by linear sweep voltammetry (LSV). For the sake of comparison, the behavior of the grafted copolymers was compared with the unmodified copolyether CP0 and with Nafion 117. Results demonstrated that in CP20 and CP40, cation transport depends on the presence of defined cationic channels, not affected by water presence; the comparison between LSV experiments performed with different alkaline cations suggests that CP40 possesses channels with larger diameters and better-defined inner structures.

Composition-dependent phase transformation in side-chain liquid crystalline copolymers with mesogenic groups at different substituent positions.

Copolymerization is an effective approach to tailor the thermal and structural properties of liquid crystalline polymer materials, which is essential for various applications. In this work, two series of polynorbornene copolymers, A-r-B and A-r-C, with the biphenyl mesogenic side group at different substituent positions were synthesized via ring-opening metathesis polymerization in various compositions. The corresponding homopolymers A and C are liquid crystalline polymers, exhibiting an oblique columnar structure (Colob/p2) and lamellar structure, respectively, while homopolymer B is amorphous. The composition-dependent phase behaviors of copolymers were systematically studied with the combination of SAXS, GISAXS, AFM, DSC and POM techniques. With increasing molar content of A (xA), the self-organzied structure of copolymer A-r-B follows the sequence from amorphous to lamellar, undulated lamellar, and Colob/p2 structures, and that of A-r-C follows the sequence of lamellar, undulated lamellar, and Colob/p2 structures. Then, copolymers with undulated lamellar or Colob/p2 structures tend to enter lamellar phase first at higher temperature and then change to the isotropic state during heating. The composition-induced transition from lamellar to supramolecular columnar organization is somewhat reminiscent of block copolymers and other soft matter systems that can form ordered structures. Furthermore, the subsitituent number and position of rigid mesogenic units in the side chain can further modify the morphologies of self-organized phases.

Molecular engineering of stimuli-responsive, functional, side-chain liquid crystalline copolymers: synthesis, properties and applications

This review describes recent progress made in designing stimuli-responsive, functional, side-chain, end-on mesogen attached liquid crystalline polymers (LCPs).

Responsive Smart Windows Enabled by the Azobenzene Copolymer Brush with Photothermal Effect.

An azobenzene side chain liquid crystalline copolymer (MAzo-co-GMA) is successfully synthesized through copolymerizing the monomer 6-(4-((4-butylphenyl)diazenyl)phenoxy)hexyl methacrylate (MAzo) with glycidyl methacrylate (GMA). The obtained MAzo-co-GMA copolymer can form stabilized polymer brush on the surface after thermal annealing. The obtained polymer brush not only induces the alignment of liquid crystals but also shows a photothermal effect under UV light irradiation due to the azobenzene side group. On basis of these results, the LC cell with this polymer brush as the substrate is further used to fabricate the polymer-stabilized liquid crystal (PSLC) smart window. The resultant PSLC smart window shows the transparent state because the homeotropic alignment in the SmA* phase of PSLC is induced by the polymer brush on the surface of the LC cell. The opaque state can be achieved in the scattering N* phase by UV light irradiation or heating. The response time of the PSLC smart window can be regulated by adjusting the concentration of MAzo-co-GMA copolymer brush and the intensity of UV light. This kind of PSLC smart window with both thermal and UV response shows good reversibility and stability, which endows enormous promising applications in energy-saving devices.

Sequencing of Side-Chain Liquid Crystalline Copolymers by Matrix-Assisted Laser Desorption/Ionization Tandem Mass Spectrometry.

Polyether based side-chain liquid crystalline (SCLC) copolymers with distinct microstructures were prepared using living anionic polymerization techniques. The composition, end groups, purity, and sequence of the resulting copolymers were elucidated by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) and tandem mass spectrometry (MS/MS). MALDI-MS analysis confirmed the presence of (CH3)3CO– and –H end groups at the initiating (α) and terminating (ω) chain end, respectively, and allowed determination of the molecular weight distribution and comonomer content of the copolymers. The comonomer positions along the polymer chain were identified by MS/MS, from the fragments formed via C–O and C–C bond cleavages in the polyether backbone. Random and block architectures could readily be distinguished by the contiguous fragment series formed in these reactions. Notably, backbone C–C bond scission was promoted by a radical formed via initial C–O bond cleavage in the mesogenic side chain. This result documents the ability of a properly substituted side chain to induce sequence indicative bond cleavages in the polyether backbone.

Self-assembly and stimuli-responsive behaviours of side-chain liquid crystalline copolymers: a dissipative particle dynamics simulation approach.

We conducted a dissipative particle dynamics simulation to explore the self-assembly behaviours of side-chain liquid crystalline copolymers in solvents poor for comb blocks. Our results show that the copolymers are able to self-assemble into various aggregates such as micelles and vesicles, and especially into deformed structures such as rectangle cylinders. The morphology of the aggregates depends on the concentration of copolymers and a series of structural parameters such as the length of the coil blocks. Three kinds of morphology diagrams are mapped out to gain insight into the effect of these parameters on the self-assembly behaviours. Moreover, the aggregate structures such as the spatial arrangement of the rigid side chain are analysed, and it was found that the interfaces of the aggregates are greatly influenced by the packing of the side chains. We also investigated the influence of the rod-to-coil conformation transition of side chains on the self-assembly, motivated by stimuli-responsive polymer systems. A transformation from a disk-like structure to a vesicle was observed as the rod-to-coil conformation transition occurs. A comparison between the available experimental observations and the simulation results is made, and agreement is achieved.

Cholesteric–azobenzene liquid crystalline copolymers: design, structure and thermally responsive optical properties

We report the synthesis of new functional cholesteric–azobenzene side-chain liquid crystalline copolymers and terpolymers, their temperature-responsive mesophase behavior, and stimuli responsive photonic properties from 400 nm to the near infra-red region of the electromagnetic spectra.

Synthesis and mesophase characterization of methacrylate based three phenyl ring core side chain liquid crystalline copolymers

A new series of side chain liquid crystalline copolymers consisting of a mesogenic monomer and a non-mesogenic n-butyl methacrylate are prepared by free radical solution polymerization. The mesogenic monomer is synthesized by a multistep route and is built with side arm core consisting of three phenyl rings linked by an ester and a terminal alkoxy chain at one end and hexamethylene spacer between methacyrlate unit and the phenyl ring core. The copolymers are synthesized with different feed ratios of liquid crystalline monomer and n-butyl methacrylate to realize composition dependent copolymers. The mesogenic monomers are characterized by FT-IR, 1H and 13C NMR while for a representative mesogen solution two-dimensional (2D) NMR experiments are also carried out. The hot-stage optical polarized microscopy, differential scanning calorimetry and variable temperature powder X-ray diffraction investigations revealed the existence of enantiotropic nematic (N) and smectic C (SC) mesophases for the copolymers. The weight average and number average molecular weight of the copolymers are found to be in the range 1.6×104 to 3.7×104g/mol from gel permeation chromatography. Thermal degradation profile of mesogenic copolymers investigated by thermogravimetric analysis revealed that the copolymers are stable till 335°C in nitrogen atmosphere. The copolymer compositions were determined using 1H NMR analysis.

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.

Influence of the spacer on the phase behaviors of side-chain liquid crystalline copolymers based on triphenylene discotic mesogen unit

Based on two analogous triphenylene liquid crystalline monomers (MTS and MT6S), a novel series of binary copolymers poly{[3,6,7,10,11-pentakis(hexyloxy)-2-oxytriphenylene]methacrylate-co-6-[3,6,7,10,11-pentakis(hexyloxy)-2-oxytriphenylene]hexyl methacrylate} (poly(MTSx-co-MT6Sy)) were prepared by free radical polymerization using AIBN as initiator. The random nature of the copolymers was expected on the basis of the assumed similar reactivities due to the analogous triphenylene monomers. The phase behaviors of copolymers were studied by DSC, POM and 1D WAXD. The results showed that the content of PMT6S has a significant effect on the liquid crystalline (LC) phase behaviors and phase structures of copolymers. The comparison between PMTS and PMT6S indicates that the content of the spacer was crucial to determine the LC structures. The PMTS formed a stable columnar nematic phase (ΦN) and the PMT6S exhibited a stable hexagonal columnar phase (ΦH). After copolymerization, the glass transition temperature and the phase transition temperature of the copolymers from the LC phase to isotropic phase both decreased with the molar fraction of PMT6S in the feed. The samples whose molar content of PMT6S was below 75% formed stable ΦN, similar to the property of PMTS. The samples whose molar content of PMT6S was above 80% presented the symmetry ΦH, similar to the property of PMT6S. Through copolymerization, one can better understand the interrelation of microstructures and how Tp mesogenic orders constitute the key basis for various applications.

Preparation of poly (N-vinylcarbazole)-co-poly(2-(dimethylamino)ethyl methacrylate) based hydrogen bonded side-chain liquid crystal copolymer

In this study, new side chain liquid crystalline copolymers were prepared from N-vinyl carbazole (NVC) and 2-(Dimethylamino)ethyl methacrylate) (DMAEM) as a hydrogen bond acceptor copolymer and 8-(4-cyanobiphenyl-4′-oxy)octan-1-ol (LC8) by molecular self-assembly processes via hydrogen bond formation between nitrogen of (DMAEM) and hydroxyl group of the LC8. The formation of H bond was confirmed by using FTIR spectroscopy. The liquid crystalline behavior of the copolymers and homopolymer of the (DMAEM) was investigated using a differential scanning calorimeter (DSC) and polarized optical microscopy. The dielectric relaxation properties of H-bonded Side Chain LC Copolymers (HB-LCP) doped 8-(4-cyanobiphenyl-4′-oxy)octan-1-ol (LC8) and pure LC8 liquid crystals have been investigated by the dielectric spectroscopy (DS) method. The dielectric behavior of the LCs shows a dielectric relaxation process. The relaxation frequency of the LCs was changed by the addition of HB-PLC. It is evaluated that the dielectric strength and relaxation properties of LC8 and LC8/HB-PLC LCs can be controlled by 1% HB-PLC dopant.

Synthesis of azobenzene‐containing side chain liquid crystalline diblock copolymers using RAFT polymerization and photo‐responsive behavior

ABSTRACTWell‐defined azobenzene‐containing side chain liquid crystalline diblock copolymers composed of poly[6‐[4‐(4‐methoxyphenylazo)phenoxy]hexyl methacrylate] (PAzoMA) and poly(glycidyl methacrylate) (PGMA) were synthesized by a two‐step reversible addition–fragmentation chain transfer polymerization (RAFT). The thermal liquid‐crystalline phase behavior of the PGMA‐b‐PAzoMA diblock copolymers in bulk were measured by differential scanning calorimetry (DSC) and polarized light microscopy (POM). The synthesized diblock copolymers exhibited a smectic and nematic liquid crystalline phase over a relatively wide temperature range. With increasing the weight fraction of the PAzoMA block, the phase transition temperatures, and corresponding enthalpy changes increased. Atomic force microscope (AFM) measurements confirmed the formation of the microphase separation in PGMA‐b‐PAzoMA diblock copolymer thin films and the microphase separation became more obvious after cross‐linking the PGMA block. The photochemical transition behavior of the PGMA‐b‐PAzoMA diblock copolymers in solution and in thin films were investigated by UV–vis spectrometry. It was found that the trans–cis isomerization of diblock copolymers was slower than that of the corresponding PAzoMA homopolymer and the photoisomerization rates decreased with increasing either the length of PAzoMA block or PGMA block. The photo‐induced isomerization in solid films was quite different with that in CHCl3 solution due to the aggregation of the azobenzene chromophore. The cross‐linking structures severely suppressed the photoisomerization of azobenzene chromophore. These results may provide guidelines for the design of effective photo‐responsive anisotropic materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2165–2175, 2013

Carbon dioxide as a porogen on self-organized nano-structure of amphiphilic side-chain type liquid crystalline di-block copolymers

Liquid and supercritical carbon dioxide (LCO2, SCCO2) have been used as a porogen to swell self-organized nano-structure of an amphiphilic side-chain type liquid crystalline PEO–b-PMA(Az) copolymer. Carbon dioxide interacts with the hydrophilic PEO domain rather than the PMA matrix. The preferential interactions of PEO component with carbon dioxide result in a solvent-induced surface topology changes and the generation of a nano-porous template. The area density of the nano-pores is identical to that of the original copolymer film while keeping the hexagonally packed PEO nano-scale organization. Since the process is based on the gases diffusion on solid surfaces under controlled temperature and since neither polymer block is fundamentally altered by the sorption effect, the process is fully reversible. The supercritical condition of CO2 treatment gives rise to the highest expansion of pre-patterned PEO cylinders and consecutively induces the retardation of PEO crystallization. This versatile thermo-diffuso approach would be applied to a wide variety of pre-patterned copolymers systems for nano-templating applications requiring nano-scale features sizes and/or area feature densities.

Study on side-chain liquid–crystalline copolymer as a new β-nucleating agent to induce phase behavior of isotactic polypropylene

The nucleating activity of side-chain liquid–crystalline copolymer, as new β-nucleating agent (LCP-NA3), towards isotactic polypropylene (iPP) was investigated by differential scanning calorimetry, wide-angle X-ray diffraction, and polarized optical microscopy. The effect of LCP-NA3 content, crystallization temperature, and time on the phase behavior of the iPP has been discussed. The results indicate that the relative content of β-crystal mainly depends on LCP-NA3 content, crystallization temperature, and time. A high content of β-crystal can be obtained by the combined effect of the optimum LCP-NA3 concentration, crystallization temperature, and time. The maximum content of β-crystal reaches 0.63 when the LCP-NA3 content, crystallization temperature, and time are 0.8 wt%, 130 °C, and 1 h, respectively. In addition, LCP-NA3 is identified to have dual nucleating ability for α- and β-crystals under appropriate kinetic conditions.

Normally Oriented Cylindrical Nanostructures in Amphiphilic PEO–LC Diblock Copolymers Films

The amphiphilic diblock copolymers consist of poly(ethylene oxide) (PEO) and poly(methacrylate) (PMA) having azobenzenes as mesogen units in the side chain afford highly ordered phase-segregated nanostructures, in which PEO cylindrical domains are hexagonally arranged and normally oriented in PMA matrix in the thin films. The liquid crystalline ordering in the strongly segregated block copolymers plays one of the most important roles to attain such an excellent arrangement of the nanostructure, potentially leading to practical use. In order to elucidate the role of the mesogen units in the side chain of the PMA segment, a new series of amphiphilic liquid crystalline diblock copolymers were synthesized to tune molecular interaction between mesogen units in liquid crystalline segments by using azobenzene, benzylideneaniline, and stilbene as mesogen cores. All the side-chain liquid crystalline diblock copolymers exhibited smectic phase and gave hexagonally arranged cylindrical nanostructures in the bulk pell...

Synthesis and characterization of novel near-infrared electrochromic cholesteric liquid crystalline polymers with chiroptical switching properties

The side-chain liquid crystalline copolymers(PC5A10,PC5A20CB,PC5A30CB) bearing near-infrared electrochromic chromophores were synthesized by hydrosilylation reactions between 4'-methoxyphenyl 4-(allyloxy)benzoate(M1),(S)-(-)-N-(hex-6-enyl)-6-(4'-(2-methylbutoxy)phenyl)-anthraquinone-2,3-dicarboxylic imide(M2) and poly(methylhydrosiloxane).The thermotropic liquid crystalline properties,redox activities,and spectroelectrochemical behaviors of these polymers were characterized.The copolymers containing 10 mol% and 20 mol% M2 exibited cholesteric liquid crystalline phases,whereas the polymer with 30 mol% of M2 formed a smectic A phase.Two reversible redox peaks appeared in the cyclic voltammograms of the copolymers,corresponding to the radical anions and the dianions after two successive one-electron reductions,respectively.In the neutral state,the copolymers showed absorption peaked at 420 nm,while a new strong absorption peaked at 840 nm appeared when reduced to radical anions.Optical modulation at 800 nm was carried out in an all-solid state electrochromic device consisting of the copolymers as the cathodic electrochiromic layer and an additional layer of Prussian blue as the ion storage layer.Furthermore,the redox triggered chiroptical switching property of this device was discussed.

Synthesis and Thermal Properties of Poly(2-Chloroethyl Glycidyl Ether)-Based Side-Chain Liquid-Crystalline Polymers

A novel series of poly(2-chloroethyl glycidyl ether)-based side-chain liquid-crystalline copolymers has been synthesized in which the mesogenic units are biphenyl 4-methoxybiphenyl, 4-methoxyazobenzene, and N-benzylidene-4-methoxyaniline, respectively (corresponding polymers are referred to as PCBH, PCMB, PCMA, and PCBM). The structures of the compounds obtained are characterized by infrared (IR) and 1H nuclear magnetic resonance (NMR). The thermal properties were investigated using polarized optical microscopy, differential scanning calorimetry, and X-ray diffraction analysis. The results indicate that PCMA, PCMB, and PCBM exhibit thermotropic liquid-crystalline behavior and present nematic phases with Schlieren textures. However, PCBH does not display a mesogenic phase. The decomposition temperatures of copolymers begin at 290°C.

Directing the Smectic Layer Orientation by Shear Flow in Hierarchical Lamellar‐within‐lamellar Liquid Crystalline Diblock Copolymers

AbstractA self‐assembled lamellar‐within‐lamellar structure of a side chain liquid crystalline diblock copolymer was shear aligned to induce overall alignment and to direct the smectic layer orientation within the copolymer lamellae. The copolymer consisted of a polystyrene block and a poly(methyl methacrylate) block bearing cholesteryl mesogens with only short oxycarbonyloxyethyl spacers separating the mesogens from the backbone. Upon shearing, the copolymer lamellae exhibited uniaxial alignment whereas the smectic layers of the mesogens showed coexisting perpendicular and parallel orientations with respect to the copolymer lamellae. The fraction of the parallel oriented domains could be systematically increased by tuning the oscillation frequency and strain amplitude.magnified image