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In recent years, π-conjugated liquid crystalline molecules with optoelectronic functionalities have garnered considerable attention, and integrating these molecules into side-chain liquid crystalline polymers (SCLCPs) holds potential for developing devices that are operational near room temperature. However, it is difficult to design SCLCPs with excellent processability because liquid crystalline mesogens are rigid rods, have low solubility in organic solvents, and have a high isotropization temperature. Recently, we developed near-room-temperature π-conjugated nematic liquid crystals based on "bridged stilbene". In this work, we synthesized a polyacrylate SCLCP incorporating a bridged stilbene that exhibited a nematic phase near room temperature and could maintain liquid crystallinity for more than three months. We conducted a thorough phase structure analysis and evaluated the optical properties. The birefringence values of the resulting polymers were higher than those of the corresponding monomers because of the enhanced order parameters due to the polymer effect. In addition, the synthesized polymers inherited mesogen-derived AIE properties, with high quantum yields (Φfl = 0.14–0.35) in the solid state. It is noteworthy that the maximum fluorescence wavelength exhibited a redshift of greater than 27 nm as a consequence of film formation. Thus, several unique characteristics of the SCLCPs are unattainable with small molecular systems. [ABSTRACT FROM AUTHOR]

To achieve all-organic polymer with high dielectric performances, we have designed a novel side-chain liquid crystalline polymer (P7) with strong polar mesogen of (Z)-4-(2-cyano-2-phenylvinyl)benzonitrile (CSCN) attached to polycyclooctene backbone. The bis-cyano-substituted CSCN is board-shaped and exhibits a large dipole moment (8.54 D) which tilts ∼34.2° away from its molecular long axis. Consequently, CSCN shows unique dual molecular anisotropy: one from biaxial shape anisotropy and the other from polarization anisotropy. The complex phase behaviors of P7 were investigated employing mainly the techniques of differential scanning calorimetry and X-ray diffraction. Four liquid crystal (LC) phases are identified as K0, K1, K2 and K3, which are SmA, highly-ordered biaxial SmA, B5-like and B7-like, respectively, with the thermal stability increased in sequence. The experimental results indicate that the different LC phases are arisen from the competition and balance between π-π stacking and dipole-dipole interaction. While the face-to-face π-π stacking is dominant in K0 and K1, optimizing the dipole-dipole interaction causes the CSCN mesogens within the smectic layer to tilt and rotate, resulting in K2 and K3. We further investigated the dielectric properties of P7 films using polarization-electric field loops test. The dielectric constant (εr) of P7 is found to be LC structure dependent, which is increased when the LC phase is varied from K0 to K3. With an average εr of 9.7 achieved in K3 and the low dielectric loss (tan δ = 0.001), P7 film offers a promising material in advanced applications like energy storage and electronic devices.

Cholesterol bearing side chain liquid crystal polymers (SCLCP) were prepared and the chemical structures of these polymers were determinated by Fourier Transform Infrared (FTIR), 1H Nuclear Magnetic Resonance Spectroscopy (1H NMR), and Gel Permeation Chromatography (GPC). Mesogenic properties of the polymers were examined by Wide- and Small-angle X-ray Scattering (WAXS and SAXS), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC) and Polarising Optical Microscopy (POM). The results revealed that all polymers have broken focal conic textures of the smectic liquid crystals, encouraging the mesomorphism. The conductivity mechanisms and dielectric properties were investigated, and the results showed that all polymers except 10% SCLCP can be used as insulators for OFET devices. [ABSTRACT FROM AUTHOR]

A series of side‐chain liquid crystal polymers (SCLCPs) without the spacer, named poly[ω‐(4′‐n‐alkyl oxybiphenyl‐4‐oxy)methacrylate (PMBiCm, m = 1, 2, 4, 6, 8, 10, 12, 14, 16, and 18), have been synthesized. The novel polymer organogels were prepared by introducing PMBiCm into common organic solvents. Solubility and gel properties of polymer organogelators differ widely according to the nature of the solvents. In aromatic solvents, PMBiCm completely dissolved in solvent due to good compatibility between biphenyl mesogen group and aromatic solvents. Poly[ω‐(4′‐n‐alkyl oxybiphenyl‐4‐oxy)methacrylate were still insoluble in polar solvents such as acetone, ethanol, DMF, ethylene glycol, and n‐butanol. This behavior resulted from mismatch of solubility parameter between PMBiCm and solvent. Considering the factors of solvent, we have systematically studied 3 organic solvents with different polarities (butyl acetate, n‐butyl amine, and n‐heptane). It is found that the length of the alkoxy tail chain of the SCLCPs has significant influence on gelability and gel thermal stability. In further studies discussed by UV‐Vis spectroscopy, the results revealed that the π‐π stacking interaction of the biphenyl mesogens might be the key factor for guiding the self‐assembly processes and the polymer gel formation. This work is useful to comprehending physical mechanism of polymer organogels. Meanwhile, those expand SCLCPs to a wide range of applications. [ABSTRACT FROM AUTHOR]

A classical side-chain liquid crystalline polymer (SCLCP) named poly [ω-(4′- n -octadecyloxybiphenyl-4-oxy) hexyl methacrylate (PM6BiC18) have been synthesized. The polymer and its monomer (M6BiC18) organogels were prepared by introducing PM6BiC18 or M6BiC18 into common organic solvents. The minimum gelation concentration (MGC) and gel-to-sol transition temperature (T GS ) were tested by the “tube-testing method”. In the same organic solvent, it was found that the T GS of gels based on PM6BiC18 was higher than the gels formed by M6BiC18. The microscopic morphology of the gels was carefully investigated by SEM and polarizing microscope. Experimental results revealed that the M6BiC18 gels are formed by the crystallization of fibers. However, the polymer gels are formed by uniform spherical self-assembly structures. Further studies discussed by UV–vis spectroscopy, the results implied that the π–π stacking interaction of the biphenyl mesogens might be the key factor for guiding the self-assembly processes and the polymer gel formation. [ABSTRACT FROM AUTHOR]

Three sets of novel side-chain liquid crystalline polymers with monosubstituted azobenzene moieties in the side-chain have been studied. These are poly(p-(4'-methoxy-4-oxyhexyloxy azobenzene) benzyl methacrylate) (PPHABM), poly(m-(4'-methoxy-4-oxyhexyloxy azobenzene) benzyl methacrylate) (PMHABM) and poly(o-(4'-methoxy-4-oxyhexyloxy azobenzene) benzyl methacrylate) (POHABM). The chemical structure of the monomers was confirmed by 1H NMR, 13C NMR spectroscopy and elemental analysis. The structural characterisation of the polymers was performed by 1H NMR spectroscopy and gel permeation chromatography, and their phase behaviour and liquid crystalline properties were studied using differential scanning calorimetry, polarised optical microscopy and wide-angle X-ray diffraction. The results show that the transitional behaviour of side-chain liquid crystalline polymers containing monosubstituted azobenzene moieties depends strongly on the position of the substituent on the azobenzene moiety; for example, the ortho-monosubstituted polymers do not form liquid crystalline phases, but all the para- and meta-monosubstituted polymers exhibit a smectic A phase. Furthermore, the glass transition temperature (Tg) of the polymers decreases in the order, para > meta > ortho. For the PPHABM and PMHABM polymers the isotropic temperature (Ti) and liquid crystalline range (ΔT, from Tg to Ti) are found to be in the order, para > meta, although it is surprising that the associated enthalpy changes in these polymers is the opposite order, meta > para. [ABSTRACT FROM AUTHOR]

Abstract: The phase structures and transition behaviors of a series of side-chain liquid crystalline (LC) polymethacrylates based on p-methoxyazobenzene (PMnAzs, n =6, 8, 10, 12) were studied using differential scanning calorimetry, one- and two-dimensional (1D and 2D) wide-angle X-ray diffraction, and Fourier transform infrared spectroscopic experiments. The LC phase transition of PMnAz follows the sequence of smectic A (SmA)↔nematic (N)↔isotropic (I). For PM10Az and PM12Az, the transition of SmA-to-N is not complete upon heating. In the low-temperature SmA phase, the polymers adopt a fully interdigitated side-chain packing with the smectic layer period almost identical to the side-chain length. For all the four samples, the first-order diffraction of the SmA structure only renders when the temperature approaches the transition of SmA ↔ N, with the intensity much lower than that of the second-order diffraction. The absence of the first-order diffraction at low temperatures is ascribed to the possible matching of the electron densities between the center portion of the side-chain sublayer and the main-chain sublayer of the SmA structure. Since only the mesogens from the same main-chain sublayer can stack parallel together, the distribution of the azobenzene domains may cause some sort of density undulation within the smectic layer. Among the samples, PM6Az presents the strongest undulation with some additional orders. We also examined the annealing effect on the H-aggregation of PMnAzs. It is found that isothermal annealing at a temperature slightly higher than the T g of PM8Az and PM10Az can significantly enhance the UV absorption at 326nm, indicating a further development of H-aggregation. However, for PM6Az and PM12Az, the UV–vis spectrum of the annealed sample is nearly identical to that without annealing. [Copyright &y& Elsevier]

Abstract: The structure of a side-chain liquid crystalline polysiloxane containing two oligo(oxyethylene) units and (R)-1-methylheptyl 4-(4-hydroxybiphenyl-4′-carbonyloxy) benzoate mesogens (PS221B) has been studied using X-ray diffraction patterns and molecular modeling. Ten periodic simulated cells with equilibrated structures are generated, each containing 35 mesogenic groups and a polysiloxane backbone. The simulated X-ray diffraction patterns are in agreement with those obtained experimentally. The calculated width of the sublayers of the polysiloxane backbone is about 5.63Å along the z-axis. The distributions of the dihedral angles of the polysiloxane backbone in the equilibrated structures indicate that the backbone has a higher probability distribution in the trans state. The distributions of the dihedral angles at the bonds in the aromatic core of the mesogenic groups reveal high probabilities of the trans and cis placements. The local order due to the interactions between the aromatic cores is in the range of 3–5Å. The order of the radial distribution function vanishes beyond this range. [Copyright &y& Elsevier]

The liquid crystal (LC) block copolymers composed of side-chain LC polymer (LCP) and polystyrene (PS) segments with various molecular weights and block contents were prepared by atom transfer radical polymerization, and their microsegregated structures were examined for magnetic alignment. Well-aligned samples have been prepared only for the low molecular weight block copolymers with cylindrical microdomains of PS dispersed in the LCP matrix. The prerequisites for perfect alignment of the microdomain structure are (1) coincidence of the disorder-order transition of the microdomain with the isotropic to nematic transition of the LCP segment, and (2) anchoring of the LC mesogen parallel to the microdomain interface. Well-oriented cylindrical and/or anisotropic microsegregated structures are also observed for the mixtures of a LC homopolymer and a LC block copolymer irrespective of extremely low PS segment content of 12-2%. Such persistent formation of anisotropic PS microdomains in the LC field indicates a significant interplay between the microdomain and liquid crystalline structures. [ABSTRACT FROM AUTHOR]

Electro optical properties of a side-chain liquid crystalline polymer (SLCP) are investigated by concerning the laser induced effects on molecular reorientation. In the scope of this work, various measurements were performed to see the effect of laser illumination on the system including a polymer component mixed in E7 coded nematic host. Experimental results exhibit dependency on laser illumination at the level of switching voltage in reorientation process and electro optical parameters are investigated by the dependency of dissipation factor in dark and laser induced circumstances for polymer doped and no-polymered samples. Dielectric anisotropy dependency is also studied for the mentioned conditions and its dependency is quantitatively estimated by capacitive measurements. [Copyright &y& Elsevier]

We synthesized two kinds of side chain type polymers containing chalconyl moieties to investigate the alignment's capability of photo-crosslinked polymer films. One is methacrylate type polymer having the chalconyl moiety in the side chain, and the other is imide type polymer. A smectic phase was exhibited for the methacrylate type polymers, while no mesophases were observed for the imide type polymer. These polymer films were irradiated with linearly polarized UV (LPUV) light (350  nm) under different conditions. The liquid crystalline (LC) cell was fabricated from the polymer film irradiated with LPUV light to examine the alignment properties of low molecular liquid crystal on the film. A mixture of a low molecular liquid crystal and a dichroic dye was filled in the LC cells. Alignment behavior of the low molecular liquid crystal was discussed by the dichroic ratio of the dichroic dye in the LC cell. [ABSTRACT FROM AUTHOR]

We synthesized two types of photocrosslinkable side-chain liquid crystalline polymers (SLCPs) with a chalcone derivative in the side chain. One is a polymer having the chalconyl moiety directly connected to the benzoate component, the other is a polymer with a spacer group introduced between the cyanobiphenyl and the chalconyl moiety. The thermal properties of these polymers were investigated by polarizing optical microscopy measurements and differential scanning calorimetry measurements. Mesophase structures of these polymers were examined by X-ray measurements. A smectic phase was exhibited for the polymers. [ABSTRACT FROM AUTHOR]