Liquid Crystalline Polyesters Research Articles

Large spontaneous deformation of uniaxially oriented main-chain liquid–crystalline elastomers composed of BB-n mesogens

ABSTRACTWe observed the spontaneous shape change of a uniaxially oriented liquid–crystalline elastomer composed of smectic main-chain liquid–crystalline polyesters in a cyclic heating–cooling process. Although the elastomer contracted by about 650% on heating up to the isotropic phase, the sample length recovered by about 450% on cooling to room temperature in the first heating–cooling process. In contrast, the elastomer exhibited completely reversible deformation in the second heating–cooling process. The shape change occurred with almost no change in the orientational order of mesogens in the temperature region of the liquid–crystalline phase. The mechanism of the spontaneous thermotropic shape change is discussed.

Improving Stiffness, Strength, and Toughness of Poly(ω-pentadecalactone) Fibers through in Situ Reinforcement with a Vanillic Acid-Based Thermotropic Liquid Crystalline Polyester

We report on the morphology and performance of melt-drawn poly(ω-pentadecalactone) (PPDL) fibers reinforced with a vanillic acid-based thermotropic liquid crystalline polyester (LCP). The in situ reinforced PPDL/LCP fibers developed in this work are considered to be renewable in nature, given the fact that the feedstock for both polymers can be obtained from natural resources. To prepare these fibers, the polymers were mixed in a small scale twin-screw extruder, followed by melt-drawing of the extrudate. It is demonstrated that the tensile modulus and tensile strength of the fibers increase with increasing LCP orientation and concentration. Despite the brittle nature of the pure LCP component, melt-spun PPDL/LCP fibers maintain their ductile deformation for fibers containing up to 30 wt % LCP. The improved stiffness and strength of these PPDL/LCP fibers in combination with their ductile nature ensure improved energy absorption during deformation and effectively increases their toughness compared to the pu...

Annealing studies on a thermotropic liquid crystalline polyester meltblown fabric

Meltblown fabrics composed of a thermotropic liquid crystalline polyester were subjected to heat conditioning at various temperatures. Physical effect of the treatment was investigated by tensile testing of the fabrics and the individual fibers. The fabrics exhibited increased tensile strength by more than 100% after the heat conditioning due to inter-fiber bonding in the fabric structure and morphological reorganization of the thermotropic polymer. The calorimetric behavior of the polymer was further investigated to obtain information about the internal structure. Structural change during the annealing was also visually observed under a polarized light microscope.

Optical Behaviors of Cholesteric Liquid-Crystalline Polyester Composites with Various Chiral Photochromic Dopants.

New developments in the field of chiral nematic liquid crystals, such as color displays, are now being widely proposed. This article describes the tunable incident reflection band based on composite materials of low-molecular-weight chiroptical dopants and polymeric networks. These materials have advantages including easily manageable color according to a change in the helical pitch of the cholesteric liquid crystal upon exposure to light. A series of novel chiral dopants of isosorbide derivatives containing photochromic groups and three new main-chain liquid crystalline polyesters were synthesized and identified using nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), and elemental analyses. The phase-transition temperatures and the liquid-crystal phase determination of the synthesized polymers were estimated using DSC, WAXD, and POM analyses. The influence of the dopant concentrations and the solubility in a liquid crystalline polymer blend were also studied. The reflection band of the cholesteric liquid crystalline composites could be adjusted and tuned with a wide range of color variation across the entire visible region. A real image recording of the chiral photochromic liquid crystalline polymer blend was achieved by exposing it to UV light through a mask.

Thermotropic liquid crystalline polyesters derived from bis-(4-hydroxybenzoyloxy)-2-methyl-1,4-benzene and aliphatic dicarboxylic acid chlorides

A series of thermotropic liquid crystalline polyesters derived from bis-(4-hydroxybenzoyloxy)-2- methyl-1,4-benzene (BHBOMB) and aliphatic dicarboxylic acid chlorides were investigated. All these polyesters were synthesized by interfacial polycondensation method and characterized by differential scanning calorimetry and wide-angle X-ray diffractometer. These polyesters consist of BHBOMB as a mesogenic diol and aliphatic diacid chlorides were used as flexible spacers. The length of oligomethylene units in polymer was varied from the trimethylene to the dodecamethylene groups. The transition temperatures and thermodynamic properties were studied for all these polymers. All these polyesters were soluble in chlorinated solvents such as chloroform, dichloromethane, dichloroethane, etc. More importantly, all these polyesters exhibited very large mesophase stability.

Synthesis of Novel Liquid Crystalline Polyesters of Cholesterol: Thermal, Electrical Conductivity and Dielectric Properties

Novel liquid crystalline polyesters of cholesterol, Polycholesteryl-3,3-dimethylacrylate (PCHDMA) and Polycholesterylcrotonate (PCHC) are synthesized by free radical polymerization and characterized by FT-IR, 1H-NMR, and GPC analysis. The thermal properties are studied by TGA and DSC techniques. The liquid crystalline phases are detected under hot stage optical microscope. Electronic conduction in the polymers is determined by Wagner polarization technique. There is about 5000 fold decrease in the impedance values of both PCHDMA and PCHC on increasing the frequencies from 40 Hz to 1 MHz at 30°C. Amperometric analysis of the polymers are also carried out at different temperatures and frequencies.

Ionic conductivity probed in main chain liquid crystalline azobenzene polyesters

ABSTRACTThree main chain thermotropic liquid crystalline (LC) azobenzene polymers were synthesized using the azobenzene twin molecule (P4P) having the structure Phenylazobenzene‐tetraethyleneglycol‐Phenylazobenzene as the AA monomer and diols like diethylene glycol, tetraethylene glycol (TEG), and hexaethylene glycol as the BB comonomer. Terminal C(O)OMe units on P4P facilitated transesterification with diols to form polyesters. All polymers exhibited stable smectic mesophases. One of the polymers, Poly(P4PTEG) was chosen to prepare composite polymer electrolytes with LiCF3SO3 and ionic conductivity was measured by ac impedance spectroscopy. The polymer/0.3 Li salt complex exhibited a maximum ionic conductivity in the range of 10−5 S cm−1 at room temperature (25 °C), which increased to 10−4 S cm−1 above 65 °C. The temperature dependence of ionic conductivity was compared with the phase transitions occurring in the sample and it was observed that the glass transition had a higher influence on the ionic conductivity compared to the ordered LC phase. Reversible ionic conductivity switching was observed upon irradiation of the polymer/0.3 Li salt complex with alternate UV and visible irradiation. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 629–641

Study on in situ reinforced composites of thermoplastic resins

Typical crystalline thermoplastic resin polypropylene (PP) and amorphous thermoplastic copolymer acrylonitrile–butadiene–styrene (ABS) were respectively blended with self-made novel low-melting point thermotropic liquid crystalline polyester (TLCP) that contained phosphorus and nitrogen elements (PN-TLCP). Then, the PP/PN-TLCP and ABS/PN-TLCP in situ-reinforced composites were prepared. The effects of PN-TLCP on mechanical property, microstructure, processability, and thermal stability of these two composites were investigated. The results showed that the strength and rigidity of matrix were improved, indicating that PN-TLCP played a role of enhancement. Meanwhile, PN-TLCP could form microfibrillar structure in PP and ABS matrix, which was the main reason of the formation of in situ composites. In the forming process, PN-TLCP could induce PP resin to form β-crystal, which was why the toughness of PP was improved. In addition, PP and ABS exhibited better processing flowability and their melt flow rates were respectively increased 18% and 56% after blending with PN-TLCP. Besides, PN-TLCP was highly beneficial to improving the thermal stabilities of matrix. Various tests showed that this kind of TLCP was suitable for crystalline thermoplastic resin PP and its composites would have more outstanding comprehensive properties.

Liquid Crystalline PET/60HBA-MWNTs Composite: Synthesis, Characterization, and Properties

PET/60HBA-MWNTs Liquid Crystalline Polyester (LCP) composite was synthesis by melting polymerization process with a novel method of reacting in acetic anhydride solution. FTIR, XRD, POM, TGA and mechanical properties tests were applied for the characterization of modification of nanotube, crystallization property, thermal and mechanical properties. The results indicate that thermal and mechanical properties of LCP polyester are all enhanced with 0.3wt% MWNTs addition. The degradation temperature (Td) increased for 8°C and the modules, strength and breaking elongation are increased by 39.0%, 62.3% and 46.4% respectively.

Experimental understanding of the viscosity reduction ability of TLCPs with different PEs

In this study, two thermotropic liquid crystalline polyesters (TLCPs) synthesized by polycondensation of phydroxybenzoic acid /hydroquinone/ poly dicarboxylic acid were used as viscosity reduction agents for polyethylene (PE). The TLCPs had different thermal, rheological and other physical properties that were quantitatively characterized. The two TLCPs were blended with high density PE (HDPE) and high molecular mass PE (HMMPE) by simple twin screw extrusion under the same weight ratio of 1.0 wt% and were each rheologically characterized at 190 o C. The TLCPs acted as processing modifiers for the PEs and the bulk viscosity of the blends decreased dramatically. However, the viscosity reduction ability was not identical: one TLCP had obviously higher viscosity reduction ability on the HDPE, with a maximum viscosity reduction ratio of 68.1%, whereas the other TLCP had higher viscosity reduction ability on the HMMPE, with a maximum viscosity reduction ratio of 98.7%. Proposed explanations for these differences are evaluated.

Chain folding in main-chain liquid crystalline polyesters: from π–π stacking toward shape memory

A series of main-chain thermotropic liquid crystalline polyesters were synthesized by polycondensation from mesogenic dial such as 4,4′-bis(6-hydroxyhexyloxy)biphenyl (BHHBP) and various diacids with different substituents such as succinic acid (no side group), 2-methylsuccinic acid (aliphatic side group) and 2-phenylsuccinic acid (aromatic side group), named poly(4,4′-bis(6-hydroxyhexyloxy)biphenyl succinate) (PBDS), poly(4,4′-bis(6-hydroxyhexyloxy)biphenyl methylsuccinate) (PBDMS), and poly(4,4′-bis(6-hydroxyhexyloxy)biphenyl phenylsuccinate) (PBDPS), respectively. Liquid crystalline behaviours were investigated through differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and small angle X-ray scattering (SAXS) and the thermal stability of the polyesters was determined via thermogravimetric analysis (TGA). PBDS, PBDMS and PBDPS showed a SmF, SmB and SmA phase, respectively. On enlarging the side group, the d-spacing of the smectic layer increased, indicating folding packing of the polymer chains. Therefore, the adjacent phenyl rings in side groups stacked well together and formed strong π–π interactions even when the temperature was higher than Ti. The special structure of PBDPS could provide good mechanical properties. Thus, PBDPS exhibited the maximum tensile stress (28.6 MPa) and the highest elongation at break (1060%). Furthermore, the strong π–π interaction can act as netpoints; therefore, PBDPS exhibited excellent shape fixing (>99%) and shape recovery ratio (>99%) with large strain (>220%).

주사슬에 X-자 모양의 메소젠기를 갖는 액정폴리에스터의 합성 및 성질

주사슬에 X-모양의 메소젠기를 갖는 액정폴리에스터 시리즈가 단위체인 2,5-디(4-치환된 벤조에이트)하이드로퀴논과 4,4'-디카르복시-1,8-디페녹시옥테인으로부터 용액중합에 의해 합성되었다. 합성된 중합체의 구조와 물성들은 <TEX>$^1H$</TEX>-NMR, FT-IR, DSC, TGA, POM, WXRD를 이용하여 조사되었다. 1,1,2,2-테트라클로로에탄 내에서 측정된 중합체의 고유점성도(<TEX>${\eta}_{inh}$</TEX>)는 0.35~0.66 dL/g로 측정되었으며, 본 실험에서 용해도 조사에 사용된 대부분의 유기용매에 잘 용해되었다. 모든 중합체들은 비교적 낮은 용융전이온도(<TEX>$T_m$</TEX>)와 결정성을 나타내었으며, <TEX>$T_m$</TEX> 이상으로 가열했을 때 열방성 네마틱 액정성을 보였다. 중합체의 이러한 특성은 주사슬에 결합되어 있는 벌키한 4-치환된 벤조에이트기에 때문인 것으로 보인다. A series of liquid crystalline polyesters containing X-shaped mesogenic groups in main chain were synthesized through the solution polymerization of 2,5-di(4-substituted benzoate)hydroquinones and 4,4'-dicarboxy-1,8-diphenoxyoctane. The structures and properties of synthesized polymers were investigated by <TEX>$^1H$</TEX>-NMR, FT-IR, differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), polarized optical microscopy (POM) and wide angel X-ray diffraction (WXRD). Inherent viscosities (<TEX>${\eta}_{inh}$</TEX>) of polymers were measured between 0.35 and 0.66 dL/g in 1,1,2,2-tetrachloroethane, and they were easily soluble in most of organic solvents used for this experiment. All polymers revealed relatively low melting transition temperature (<TEX>$T_m$</TEX>) and crystallinity, and also showed thermotropic nematic liquid crystallinity when they were heated to their melting temperatures. These properties of polymers were presumably due to the presence of the bulky substituting groups on the hydroquinone unit in mesogenic group.

Surface Effect of Silica Nano-Particles with Different Size on Thermotropic Liquid Crystalline Polyester Composites

Interface properties of nano-silica/thermotropic liquid crystalline polyesters (TLCP) composites were investigated by X-ray diffraction analysis and differential scanning calorimetory. The crystallinity of TLCP in the composites drastically decreased with an increase of nano-silica content, depending on the surface area of the silica particles. Little size effects (40 - 400 nm) in the particles and strong interaction between silica surface and the C=O moieties of TLCP were observed by IR analysis. The glass transition temperature of TLCP (。C higher than that in bulk.

Improved thermal and mechanical properties of poly(butylene succinate) by polymer blending with a thermotropic liquid crystalline polyester

ABSTRACTA novel polymer blending system consisting of poly(butylene succinate) (PBS) and a thermotropic liquid crystalline polyester [LCP: a poly(4‐hydroxybenzoate)‐based polymer] was investigated in the presence and absence of a polycarbodiimide (PCD) and/or 1,1′‐carbonyl biscaprolactam (CBC) as chain extenders. Although the LCP was immiscible with PBS, it formed elongated fibrous domains having an orientation in the flowing direction when an extensional flow was applied during the processing. Scanning electron micrograph (SEM) of the injection‐molded polymer blends supported the distribution of micro fibrils of LCP in the PBS matrix by which the efficient toughening was provided. These blend specimens showed highly improved mechanical properties along with retaining high dynamic storage‐moduli (E′) up to the melting temperature of PBS. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39952.

Influence of molecular orientation direction on the in‐plane thermal conductivity of polymer/hexagonal boron nitride composites

ABSTRACTThe effect of the molecular orientation direction of a polymer matrix on the in‐plane thermal conductivity (TC) of injection‐molded polymer/hexagonal boron nitride (h‐BN) composites is investigated. In this system, the h‐BN platelets align in the in‐plane direction owing to injection shear flow. Three molecular orientations (perpendicular, random, and parallel to the h‐BN plane) are achieved using liquid crystalline polyesters and the in‐plane TCs are compared. Although a parallel orientation of the polymer chains provides the highest TC of the matrix in the injection direction, the TC of the composites is the lowest of the three systems for this orientation. The highest in‐plane TC is found in the perpendicularly oriented system, irrespective of the in‐plane direction. These results reveal that perpendicularly oriented molecular chains serve as effective heat paths between h‐BN platelets that are arranged one above the other, and consequently, a continuous thermal network is created in the in‐plane direction. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39768.

Synthesis and characterization of a new family of photoactive liquid crystalline polyesters based on α‐methylstilbene

AbstractA liquid crystal polyester and two liquid crystal copolyesters containing α‐methylstilbene moieties and aliphatic or aromatic spacers in the backbone were synthesized in good yields, with the aim of using them for photosensitive microcapsule preparation. The synthesized polymers were fully characterized with respect to thermal stability, type of mesophase, molecular weight and E–Z photoisomerization. Combination of monomers with different structures allowed adjustment of the polymer characteristics such as degree of crystallinity and glass transition temperature, as verified using X‐ray diffraction, polarized optical microscopy and differential scanning calorimetry. Quantitative 1H NMR and UV‐visible experiments were performed in order to investigate E–Z photoisomerization after photoirradiation at 364 nm. Finally, a membrane based on one of these polymers was prepared and it was found that its wettability increased on photoirradiation. © 2013 Society of Chemical Industry

Synthesis and characterization of segmented copolymers of polystyrene and thermotropic liquid crystalline poly(4-oxybenzoate-co-2,6-oxynaphthoate)

A series of segmented copolymers containing a thermotropic liquid crystalline poly(4-oxybenzoate-co-2,6-oxynaphthoate) and an amorphous polystyrene were created and analyzed. The segmented copolymers were prepared by solution polycondensation of α,ω-dicarboxylic acid-terminated polystyrene with 4-hydroxybenzoic acid and 2-hydroxy-6-naphtholic acid in a mixture of triphenylphosphine, hexachloroethane, and pyridine. The obtained polymers were fractionated to isolate the pure segmented copolymers. The segmented copolymers were characterized by FT-IR spectroscopy, differential scanning calorimetry, thermogravimetric analysis, optical polarizing microscopy (OPM), and X-ray diffraction measurement. OPM and X-ray diffraction measurements verified the presence of a nematic liquid crystalline phase for the segmented copolymers. The experimental results indicate that the segmented copolymers have a microphase-separated morphology, that is both amorphous and liquid crystalline properties were shown by the polystyrene and liquid crystalline polyester segments respectively.

Preparation and Characterization of Light-Sensitive Microcapsules Based on a Liquid Crystalline Polyester

Photosensitive microcapsules and membranes based on poly(α-methylstilbenesebacoate-co-α-methylstilbeneisophthalate), containing the photosensitive α-methylstilbene moiety, were prepared by a phase-inversion precipitation process. In order to simulate the morphology and behavior of the microcapsule shell under UV irradiation, an exhaustive characterization of a membrane was first performed by ESEM, POM, AFM, and contact angle measurements. The prepared microcapsules contained either chloroform or a concentrated solution of vanillin in chloroform as the core; in all cases, before UV irradiation, their outer surface appeared smooth and dense. The influence of vanillin on microcapsule cross-section morphology was observed by ESEM microscopy. Release of vanillin in water, at room temperature, was markedly influenced by UV irradiation: in the absence of irradiation, it was practically negligible, while when microcapsules were submitted to continuous irradiation with UV light, the surface morphology of the capsules changed drastically and vanillin started to be released after ca. 20 min of irradiation.

Well-Ordered Lamellar Microphase-Separated Morphology of an ABA Triblock Copolymer Containing a Main-Chain Liquid Crystalline Polyester as the Middle Segment 2: Influence of Amorphous Segment Molecular Weight

A series of an ABA triblock copolymer with amorphous polymethacrylate A blocks and a main-chain liquid-crystal (LC) polyester center block were prepared with the molecular weight of the amorphous blocks (Mn am) ranging from 2300 to 10 000 and that of the LC block kept constant at 10 000. Irrespective of asymmetric compositions, all block copolymers invariably formed lamellar microstructures. The LC segments were more extended perpendicular to the interface to form smectic layers parallel to the lamellae and folded to be accommodated in lamellae, whereas the amorphous segments had dimensions similar to those of segments in amorphous block copolymer microdomains. Increases in Mn,am enlarge the interfacial area between the amorphous and LC segments and increase the number of folds in LC segments. Thus, LC lamellar thickness decreases and counterbalances the increase in amorphous lamellar thickness so as to suppress the lamellar spacing increase. When the LC segment was in the isotropic phase, the lamellae in the copolymers at asymmetric fractions were disordered and developed on cooling simultaneously with LC formation. The lamellar formation is attributed to the smectic layers that prefer a flat microdomain interface from an energetic perspective.

Preparation of new supramolecular liquid-crystalline polyesters containing 3-chloro-4-(alkoxy)benzoic acids

Supramolecular liquid-crystalline polyester complexes based on intermolecular hydrogen bonds between the carboxylic group and the pyridyl moieties was prepared by using non-liquid-crystalline H-donors, [3-chloro-4-(butyloxy)benzoic acid (2a), 3-chloro-4-(octyloxy)benzoic acid (2b), 3-chloro-4-(dodecyloxy)benzoic acid (2c) and 3-chloro-4-(tetradecyloxy)benzoic acid (2d)] and H-acceptor-polyester containing pyridyl units. Intermolecular hydrogen bond formation was confirmed by Fourier transform infrared spectroscopy. The liquid-crystalline behavior of the complex formed was established by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). The polyester complexes containing 2c and 2d donor components exhibit liquid crystalline mesophase and behave as side-chain liquid-crystalline polymers. Compared with unsubstituted parent acid, the presence of chloro group as a lateral substituent has a little negative effect on the induction of liquid crystallinity on the polyester complexes systems. The results show that the more stability of the obtained H-bonded complexes in comparison with analogues without 3-Cl substituents is due to the increased acidity of benzoic acid moiety.