Liquid Crystalline Copolymers Research Articles

Polarized Emission from Liquid-Crystalline Copolymers Prepared with Donor-Acceptor Monomers

Polarized Emission from Liquid-Crystalline Copolymers Prepared with Donor-Acceptor Monomers

Preparation and reflectance properties of new cholesteric liquid crystalline copolymers containing cholesteryl group

AbstractIn this study, a new family of side‐chain cholesteric liquid crystal copolymers derived from cholesterol substituents were synthesized. The chemical structures of the copolymers were validated by FTIR and 1H NMR. A wide‐band reflective polarizer from the above copolymers with stable optical properties was developed. The pitch gradient was formed by molecular diffusion between adjacent liquid crystal layers based on these cholesteric copolymers with different pitch lengths, and the pitch gradient was further stabilized by UV crosslinking of the polymerizable monomers during the diffusion process. The stability of these systems as a function of time was investigated. The polymer network was validated by scanning electron microscopy and this network played an important role in stabilizing the pitch gradient of the system. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

Effect of Recording Time on Grating Formation and Enhancement in an Amphiphilic Diblock Liquid-Crystalline Copolymer

To precisely control the first-order diffraction efficiency of holographic gratings recorded in an amphiphilic diblock liquid-crystalline copolymer P40A37, effect of recording time on grating formation and enhancement was studied systematically. Several parameters such as surface relief, the first-order diffraction efficiency, the maximum transmittance under an optical polarizing microscope and order parameters of grating samples were evaluated before and after annealing. Then the enhancement coefficient with recording time was estimated. The best enhancement effect was obtained at 10-s recording upon nano-scaled phase separation. By precisely adjusting the recording time, the diffraction efficiency of holographic gratings in P40A37 can be finely controlled from 0.13% to 10%.

Liquid Crystalline π-Conjugated Copolymers Bearing a Pyrimidine Type Mesogenic Group

Phenylene-thiophene-based liquid crystalline π-conjugated copolymers bearing mesogenic groups as side chains were synthesized via a Stille polycondensation reaction and confirmed to exhibit a nematic liquid crystal phase at appropriate temperatures. The formation of a nematic phase, but not a smectic phase indicates cooperation of the main chain and side chain in the formation of a nematic main-chain/side-chain liquid crystal phase. The generation of polarons in the main chain as charge carriers during in-situ vapor doping of iodine is confirmed to increase with a doping progresses, exhibiting Dysonian paramagnetic behavior typical of conductive polymers.

Photoinduced Orientation of Photo-Cross-Linkable Liquid Crystalline Copolymer Films Comprised of H-Bonded and Non-H-Bonded Mesogenic Side Groups

The cooperative molecular reorientation in methacrylate copolymer films with hexamethylene spacer groups terminated with photoreactive hydrogen (H) bonded 4-oxycinnamic acid (CA) and photoinactive 4-oxy-4′-methoxybiphenyl (MB) in their side chains was investigated by irradiating with linearly polarized ultraviolet light (LPUV) and subsequent annealing. A thermally enhanced cooperative in-plane orientation of both CA and MB side groups perpendicular to the polarization (E) of LPUV light was obtained when the annealing temperature was in the liquid crystalline temperature range of both mesogenic side group. On the other hand, thermal enhancement of the in-plane molecular reorientation did not occur when the annealing temperature was out of the LC temperature range of the MB. It was clarified that the amount of axis-selectively photoreacted H-bonded CA groups and the LC mesomorphism of the copolymer film play an important role in the thermally enhanced cooperative molecular reorientation.

Tuning surface interactions to control shape and array behavior of diblock copolymer micelles on a silicon substrate

The micellar shape of liquid crystalline diblock copolymers, PEO m - b-PMA(Az) n , consisting of high surface energy components was controlled by tuning surface interactions. On a fluorinated surface, the diblock copolymers formed ordered arrays of spherical micelles consisting of PEO cores surrounded by PMA(Az) coronas. Gold ions could be doped into the PEO cores by immersion in a solution of the gold ion. The Au 3+-doped micelles were subsequently etched and reduced by VUV radiation to form hexagonally ordered gold nanodots.

Thermally Recordable Cholesteric Liquid Crystalline Copolymers Containing Pendant Menthyl and Cholesteryl Groups

In order to investigate the effect of spacer length and linkages between the rigid mesogenic core and the terminal group on the molecular interaction and physical properties of polymers, a series of novel side chain liquid crystalline polymers were synthesized. These were composed of liquid crystalline monomers with six or eleven methylene segments as spacers, and chiral monomers end capped with menthyl or cholesteryl groups. Liquid crystalline phases of the polymers were investigated using differential scanning calorimetry and polarized optical microscopy, and confirmed with X-ray diffractometry. Color image recording of the synthesized polymer films was achieved using a thermal treatment, and then fixed by quenching. This investigation demonstrates that the introduction of carbonate linking groups between the rigid mesogenic core and terminal group decreases both the lateral molecular interaction and thermal stability of the liquid crystalline polymers. The RGB reflection colors of the cholesteric composite film could be tuned by varying the film temperature and applying an external field. The results of this investigation present significant scientific and practical contributions with respect to the development of unique cholesteric polymer materials.

Synthesis and thermal properties of side‐chain liquid crystalline poly[1‐({(4‐methoxyazobenzene‐4′‐oxy)alkyl}thio)‐2.3‐epoxypropane

A novel series of side‐chain liquid crystalline copolymers, i.e. poly‐[1‐({(4‐methoxyazobenzene‐4′‐oxy)alkyl}thio)‐2.3‐epoxypropane]s, were synthesised in which the number of methylene units in the alkyl group of the side chain varies from 3 to 6. The structures of compounds obtained were characterised by elemental analysis and 1H NMR spectroscopy. Thermal properties were investigated using polarising optical microscopy, differential scanning calorimetry and X‐ray diffraction analysis. The synthesised thiols and corresponding polyepichlorohydrin‐based copolymers exhibited thermotropic liquid crystalline behaviour and nematic phases with schlieren textures. The thiols have lower transition temperatures than the corresponding copolymers. In addition, the degree of substitution of the copolymers synthesised increased with an increase in number of methylenes in the side chain. The phase transition temperatures increased and the mesomorphic temperature ranges widened with the increasing degree of substitution of the copolymers.

Double Ordered Layers within Microphase-separated Lamellar Structure of Double Liquid Crystalline Side-chain Type Block Copolymer

Abstract A new hierarchical nanostructure was created by self-assembly of a double liquid crystalline side-chain type block copolymer. The block copolymer was successfully prepared via a nitroxide-mediated living free radical polymerization and formed double ordered layers within a phase-separated lamellar structure of the cast film.

Synthesis and characterization of liquid crystalline copolymers with dual photochromic pendant groups

In order to study the photoreactivity and the optical properties of liquid crystalline copolymers with multiple photochromic groups, a series of novel liquid crystalline binary and ternary polyacrylates consisting of one (CC or NN) or dual (CC and NN) photochromic segments were synthesized and characterized considering their liquid crystalline, optical, and photochromic properties and their thermal stability. Achiral homopolymer P1 shows a smectic A phase (fan-shaped texture), and all chiral copolymers CP1–CP6 exhibit chiral nematic phases (cholesteric, oily streaks textures). The polymers show excellent solubility in common organic solvents such as chloroform, toluene, and THF. These polymers also exhibit good thermal stability, with decomposition temperatures (Tds) greater than 373°C at 5% weight loss, and beyond 440°C at 50% weight loss under nitrogen atmosphere. UV irradiation caused E/Z photoisomerization at NN and CC segments of the synthesized photochromic copolymers leading to reversible and irreversible isomerizations, respectively. The synthesized liquid crystalline ternary copolymer CP6, containing two different photochromic NN and CC groups, is sensitive to different UV wavelengths and is notably interesting from the viewpoint of photochromic copolymers.

Photoorientation in hydrogen-bonded blends of liquid-crystalline polymers with a low-molecular photochromic dopant

A series of hydrogen-bonded blends of nematic liquid-crystalline copolymers with a low-molecular photochromic dopant and their covalent analogs were prepared. Their phase behavior and photooptical properties were studied. The introduction of a dopant increases considerably the isotropization temperatures of the systems. A comparative study of photoorientation processes in the blends and copolymers analogous to them was carried out. The induced dichroism in covalent systems is more pronounced than in similar hydrogen-bonded blends.

Synthesis and characterization of H-type amphiphilic liquid crystalline block copolymers by ATRP

H-type amphiphilic liquid crystalline block copolymers containing azobenzene were synthesized by atom transfer radical polymerization (ATRP). Macroinitiators prepared by the esterification between poly(ethylene oxide) (PEG) and 2,2-dichloroacetyl chloride were utilized to initiate the polymerization of 6-[4-(4-ethoxyphenylazo)phenoxy]hexyl methacrylate (M6C). The resulting macroinitiators and block copolymers were characterized by 1H NMR, gel permeation chromatography (GPC). Polarizing optical microscopy (POM) and differential scanning calorimetry (DSC) preliminarily revealed the liquid crystalline property of these block copolymers. This series of liquid crystalline block copolymers are promising in some areas, such as optical data storage, optical switch, and molecular devices.

MULTI-SCALES RELAXATION PROCESSES OF SHORT FIBER OF NEMATIC LIQUID CRYSTALLINE COPOLYMER IN POLYCARBONATE MATRIX

Multi-scales relaxation processes of short fiber of a nematic liquid crystalline copolymer (LCP) in polycarbonate matrix were investigated. First, the structure relaxation of LCP was studied by rheology. The relaxation spectrum of the nematic liquid crystalline copolymer at 295°C was calculated from the combined dynamic modulus. There are three kinds of relaxation mechanisms for nematic liquid crystalline copolymer: the relaxation of chain orientation, the relaxation of deformed polydomains and the coalescence of polydomains (or the relaxation of textures). As the relaxation of chain orientation is very fast, we have not obtained the accurate relaxation time by rheological measurements. The relaxation of deformed polydomains takes about 50 s. Domain coalescence occurs after a much longer relaxation time (> 2400 s). Secondly, the shape relaxation of LCP short fiber in matrix was studied. During shape relaxation of short fiber in matrix, changes of inner structure in short fiber take place, which is characterized by the application of power spectrum of discrete Fourier transform (DFT). The aspect ratio b/a increases during shape relaxation of short fiber in matrix.

Synthesis and characterization of side-chain liquid crystalline ABC triblock copolymers withp-methoxyazobenzene moieties by atom transfer radical polymerization

A series of novel side-chain liquid crystalline ABC triblock copolymers composed of poly(ethylene oxide) (PEO), polystyrene (PS), and poly[6-(4-methoxy-4′-oxy-azobenzene) hexyl methacrylate] (PMMAZO) were synthesized by atom transfer radical polymerization (ATRP) using CuBr/1,1,4,7,7-pentamethyldiethylenetriamine (PMDETA) as a catalyst system. First, the bromine-terminated diblock copolymer poly(ethylene oxide)-block-polystyrene (PEO-PS-Br) was prepared by the ATRP of styrene initiated with the macro-initiator PEO-Br, which was obtained from the esterification of PEO and 2-bromo-2-methylpropionyl bromide. An azobenzene-containing block of PMMAZO with different molecular weights was then introduced into the diblock copolymer by a second ATRP to synthesize the novel side-chain liquid crystalline ABC triblock copolymer poly(ethylene oxide)-block-polystyrene-block-poly[6-(4-methoxy-4′-oxy-azobenzene) hexyl methacrylate] (PEO-PS-PMMAZO). These block copolymers were characterized using proton nuclear magnetic resonance (1H NMR) and gel permeation chromatograph (GPC). Their thermotropic phase behaviors were investigated using differential scanning calorimetry (DSC) and polarized optical microscope (POM). These triblock copolymers exhibited a smectic phase and a nematic phase over a relatively wide temperature range. At the same time, the photoresponsive properties of these triblock copolymers in chloroform solution were preliminarily studied. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4442–4450, 2008

ABA type liquid crystalline triblock copolymers by combination of living cationic polymerizaition and ATRP: synthesis and self-assembly.

Lamellar and hexagonal-coil-cylinder self-assembled structures of ABA type triblock copolymers containing mesogen-jacketed liquid crystalline polymer (MJLCP) as the rod block, and polyisobutylene (PIB) as the coil middle block were discovered. PIB was synthesized by living cationic polymerization of isobutylene initiated by 1,4-bis(2-chloro-2-propyl)benzene (p-DCC), and then a small amount of styrene was introduced at the end of the PIB chains to form the difunctional PIB macroinitiator with -CH2CH(C6H5)Cl end groups for further atom transfer radical polymerization (ATRP). 2,5-Bis[(4-methoxyphenyl)oxycarbonyl]styrene (MPCS) was block-copolymerized from the difunctional PIB macroinitiators at 110 °C. The molecular characterization of the triblock copolymers was performed with 1H NMR, 13C NMR, gel permeation chromatography (GPC), and thermogravimetric analysis (TGA). Their phase structures and transitions were investigated by differential scanning calorimetry (DSC), small angle X-ray scattering (SAXS), and polarized optical microscopy experiments. It was demonstrated that the triblock copolymers formed lamellar structures at moderate rod fractions and hexagonal coil cylinders in the rod matrix at high rod fractions. The d-spacing of the microphase-separated structures was influenced by the liquid crystalline phase of rod-like PMPCS blocks.

Influence of variations in liquid-crystalline content upon the self-assembly behavior of -based block copolymers.

A series of well-defined smectic side chain liquid-crystalline (LC) block copolymers with a low glass transition (Tg) siloxane block has been synthesized via anionic polymerization; these systems consist of a glassy polystyrene block and a unique low glass transition temperature LC block based on poly(vinylmethylsiloxane) to which six different LCs have been synthesized and attached. The synthesis techniques used provide systematic control over covalent LC side chain content, allowing for a range of morphologies to be obtained from a single block copolymer backbone during a one-step LC attachment reaction. Variations in the LC structure and content significantly affect the morphology of the LC mesophase, allowing the smectic-to-isotropic transition temperature to be tuned from room temperature up to 150 °C. There are two key driving forces in the self-assembly behavior of these materials that are significantly affected by the LC content. The first is the segmental interaction parameter (χ) between the blocks, which is a function of the amount of LC attached to the siloxane block. The attachment percent of the LCs to the siloxane block determines the packing density, which affects the stability of the LC mesophase and its interactions with the inter-material dividing surface. The self-assembled morphologies are characterized as a function of LC content and the mechanisms for the observed behavior are detailed. Additional insights into the interactions between the LC and block copolymer mesophases are gained by investigating the morphologies in response to mechanical deformation. The elastic modulus of this system can be tailored over several orders of magnitude by controlling the LC content, and the thermo-mechanical behavior is also highly dependent. The ability to precisely control the degree of LC functionalization enables the custom design and tailoring of material properties for specific applications such as electro-mechanical, damping, and mechano-optical devices.

Control of Regular Nanostructures Self-Assembled in an Amphiphilic Diblock Liquid-Crystalline Copolymer

An amphiphilic diblock liquid-crystalline copolymer consisting of poly(ethylene oxide) (PEO) and polymethacrylate containing an azobenzene moiety in the side chain was prepared by atom transfer radical polymerization (ATRP). The specifically-designed chemical constitution and the low molecular-weight polydispersity enable the block copolymer to form a regular microphase-separated nanostructure self-assembled in its bulk films, in which a hexagonal packing of the PEO cylinders normal to the substrates was dispersed in a continuous phase of azobenzene mesogens with out-of-plane alignment. Then a commerically available rubbing technique was first used to control the microphase-separated domains in the copolymer films. By introducing novel supramolecular cooperative motions between ordered azobenzene mesogens and PEO microphase domains, macroscopic array of PEO nanocylinders was regularlly formed along the rubbing direction. Both the dotted and parrallel stripe patterns of PEO nanocylinders were successfully obtained in the same block copolymer.

Photochromic liquid-crystalline copolymers containing crown ether groups

An approach was developed for the synthesis of new multifunctional photosensitive liquid-crystalline copolymers of the acryl series containing azobenzene, ionophoric, and mesogenic groups in the same macromolecule. The phase behavior of the copolymers was studied. Most of these copolymers were demonstrated to form nematic mesophases. An increase in the concentration of crown-containing groups to 26 mol.% leads to amorphization of the copolymers. The influence of complexation of the crown ether groups of the copolymers with potassium perchlorate on the mesomorphic properties of the systems was investigated. A comparative study of the photooptical properties of the copolymers in solution and thin films was performed.

ABA‐type liquid crystalline triblock copolymers via nitroxide‐mediated radical polymerization: Design, synthesis, and morphologies

AbstractWe have designed and synthesized rod–coil–rod triblock copolymers of controlled molecular weight by two‐step nitroxide‐mediated radical polymerization, where the rod part consists of “mesogen‐jacketed liquid crystalline polymer” (MJLCP). The MJLCP segment examined in our studies is poly{2,5‐bis[(4‐methoxyphenyl)oxycarbonyl]styrene} (MPCS) while the coil part is polyisoprene (PI). Characterization of the triblock copolymers by GPC, 1H and 13C NMR spectroscopies, TGA, DSC confirmed that the triblock copolymers were comprised of microphase‐separated low Tg amorphous PI and high Tg PMPCS blocks. Analysis of POM and 1D, 2D‐WAXD demonstrated that the triblock copolymers formed nematic liquid crystal phase. Morphological studies using TEM indicated the sample formed lamellar structure. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5949–5956, 2007

Structure analysis of amphiphilic di-block copolymer monolayer by X-ray reflectivity

Monolayer of liquid crystalline amphiphilic di-block copolymer, PEO40-b-PMA(Az)n, was investigated by a grazing incidence X-ray diffraction (GIXRD) and X-ray reflectivity. GIXRD results indicated the condensed ordered state of azobenzene moieties in the monolayer. The four-layer model considering the chemical structure and the Fourier transform analysis, and the five-layer model considering the molecular mobility of PEO40-b-PMA(Az)nwere used to analyze the X-ray reflectivity profiles. Both models gave the condensed state of trans azobenzene moieties, which aligned perpendicular to the silicon wafer surface.