Thermotropic Liquid Crystalline Behavior Research Articles

Synthesis and Thermotropic Liquid Crystalline Behavior of Copolymers Containing Ether Ketone and Ester Links

Copolymers containing ether ketone and ester links were synthesized by high temperature solution condensation and were characterized by Fourier transform infrared (FT/IR) spectroscopy, differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and polarized light microscopy (PLM). The melting behavior and liquid crystalline transition temperatures of the homopolymers and copolymers were dependent on the composition of trimer content. The transition temperatures could be observed to decrease at first and increase subsequently; i.e. surpass a minimum, with the increment of trimer content. Thermotropic liquid crystalline behaviors were observed in the copolymers containing 20, 40, 50 and 60 mol % trimer. But the further addition of the trimer content resulted in the gradual loss of liquid crystallinity. The crystalline to liquid crystalline transition (Tm) and liquid crystalline to isotropic transition (Ti) appeared in the DSC curves, whereas the trimer-based homopolymer had only a melting transition. The polymers were thermally stable up to 400 °C. WAXD results indicated that the copolymers showed a continuous change of the diffraction peaks from sharp main crystalline reflections for crystalline Homo-C to strong broad dispersed peak for liquid crystalline TLCP.

Thermal Properties and Crystallinity of Thermotropic Liquid Crystalline Copolyesters Prepared from Poly(ethylene terephtalate) (PET) and Rigid Aromatic Units

A series of copolyesters were synthesized by melt‐polycondensation reaction of poly(ethylene terephtalate) (PET) with various proportions of equimolar compositions of p‐acetoxybenzoic acid (p‐ABA), hydroquinone diacetate (HQDA) and terephtalic acid (TPA). Viscosity, liquid crystallinity, thermal properties, degree of crystallinity and thermal stabilitiy of these copolyesters were investigated by Ubbelohde viscometer, hot‐stage polarized light microscopy (PLM), differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD) and thermogravimetric analysis (TGA), respectively. On the basis of viscosity measurement, it was observed that intrinsic viscosity values of the copolyesters are increased regularly with increasing amounts of aromatic units (p‐ABA, HQDA and TPA) in the polymer chain. Thermotropic liquid crystalline behavior was observed in the copolyesters containing over 50 mol% of rigid p‐ABA/HQDA/TPA aromatic units. DSC analysis of the anisotropic copolyesters revealed broad and weak endotherms associated with the nematic phases, and the melting temperatures were found to be in the processable region. As the mol% of PET in the polymer chain increased, the specific enthalpies of fusion and the degree of crystallinity of the copolyesters were also increased regularly.

Comblike Liquid-Crystalline Polymers from Ionic Complexation of Dendronized Polymers and Lipids

This work describes the self-assembly behavior, the structure, the state, and phase diagrams of comblike liquid-crystalline polymers obtained by supramolecular ionic complexation of cationic dendronized polymers (PG1−PG3) and anionic sulfonated lipid surfactants. In order to characterize the influence of both the polymer and the surfactant on the microphase separation of these complexes, dendronized polymers with generation 1 ≤ n ≤ 3, carrying 2n positive charges per monomer, were complexed with a stoichiometric amount of anionic sodium alkyl monosulfate surfactants with hydrocarbon chain of C8, C12, C14, and C18 lengths. Supramolecular complexes were obtained in water, and the complexation process was monitored by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance. After drying and thermal annealing under high vacuum, the complexes showed thermotropic liquid-crystalline behavior as demonstrated by both cross-polarized optical microscopy and differential scanning calorimetry. Small-angle X-ray scattering allowed determining the respective lattice parameters and type of structures for all the complexes considered. Depending on both generation and lipid chain length, amorphous isotropic fluid, columnar rectangular, columnar hexagonal, columnar tetragonal, and lamellar phases were observed, each characterized by a specific order−disorder transition temperature (TODT).

Tuning the Polarization Along Linear Polyaromatic Strands for Rationally Inducing Mesomorphism in Lanthanide Nitrate Complexes

The opposite orientation of the ester spacers in the rodlike ligands L 4C12 (benzimidazole-OOC-phenyl) and L 5C12 (benzimidazole-COO-phenyl) drastically changes the electronic structure of the aromatic systems, without affecting their meridional tricoordination to trivalent lanthanides, Ln(III), and their thermotropic liquid crystalline (i.e., mesomorphic) behaviors. However, the rich mesomorphism exhibited by the complexes [Ln(L 4C12)(NO3)3] (Ln=La-Lu) vanishes in [Ln(L 5C12)(NO3)3], despite superimposable molecular structures and comparable photophysical properties. Density functional theory (DFT) and time-dependant DFT calculations performed in the gas phase show that the inversion of the ester spacers has considerable effects on the electronic structure and polarization of the aromatic groups along the strands, which control residual intermolecular interactions responsible for the formation of thermotropic liquid-crystalline phases. As a rule of thumb, an alternation of electron-poor and electron-rich aromatic rings favors intermolecular interactions between the rigid cores and consequently mesomorphism, a situation encountered for L 4C12, L 5C12, [Ln(L 4C12)(NO3)3], but not for [Ln(L 5C12)(NO3)3]. The intercalation of an additional electron-rich diphenol ring on going from [Ln(L 5C12)(NO3)3] to [Ln(L 6C12)(NO3)3] restores mesomorphism despite an unfavorable orientation of the ester spacers, in agreement with our simple predictive model.

Side-Chain Liquid Crystalline Poly(meth)acrylates with Bent-Core Mesogens

We report the design, synthesis, and characterization of side-chain liquid crystalline (LC) poly(meth)acrylates with end-on bent-core liquid crystalline (BCLC) mesogens. Both conventional free radical polymerization and atom transfer radical polymerization have been used to synthesize these liquid crystalline polymers (LCP). The resulting polymers exhibit thermotropic LC behavior. Differential scanning calorimetry, thermopolarized light microscopy, wide-angle X-ray diffraction, and small-angle X-ray scattering were used to characterize the LC structure of both monomers and polymers. The electro-optic (EO) measurement was carried out by applying a triangular wave and measuring the LC EO response. SmCP (Smectic C indicates the LC molecules are tilted with respect to the layer normal; P denotes polar ordering) phases were observed for both monomers and polymers. In LC monomers, typical antiferroelectric switching was observed. In the ground state, SmCPA (A denotes antiferroelectric) was observed which switched to SmCPF (F denotes ferroelectric) upon applying an electric field. In the corresponding LCP, a unique bilayer structure was observed, which is different from the reported BCLC bilayer SmCG (G denotes generated) phase. Most of the LCPs did not switch upon applying electric field while weak AF switching was observed in a low molecular weight poly{(3‘-[4-(4-n-dodecyloxybenzoyloxy)benzoyloxy]-4-(12-acryloyloxydodecyloxy)benzoyloxybiphenyl} sample.

Synthesis and properties of new phosphorus‐containing poly(ester‐imide)s

AbstractNew phosphorous‐containing poly(ester‐imide)s have been prepared by polycondensation in solution at high temperature of a p‐hydroxyphenol containing phosphorus, namely 2‐(6‐oxid‐6H‐dibenz<c,e><1,2>oxaphosphorin‐6‐yl)‐1,4‐benzenediol, with various aromatic diacide chlorides containing preformed imide rings. The polymers were easily soluble in polar organic solvents, such as N‐methylpyrrolidone, N,N‐dimethylformamide, tetrahydrofuran and chloroform. They showed high thermal stability, the decomposition temperature being above 360°C and the glass transition in the temperature range 142–223°C. One of these polymers exhibited thermotropic liquid crystalline behavior. Solutions of the phosphorous‐containing poly(ester‐imide)s in N,N‐dimethylformamide showed fluorescence having a maximum emission wavelength in the range 376–378 nm. Due to the presence of phosphorus the polymers gave high char yield in thermogravimetric analysis. Copyright © 2006 John Wiley & Sons, Ltd.

New Phosphorus‐Containing Copolyesters

A series of phosphorus‐containing copolyesters was prepared by polycondensation of 2‐(6‐oxido‐6H‐dibenzo<c,e><1,2>oxaphosphorin‐6‐yl)1,4‐benzenediol, 1 , or of an equimoleculare amount of 1 and different bisphenols 2 , such as: hydroquinone, 4,4′‐(hexafluoroisopropylidene)diphenol, 4,4′‐isopropylidenediphenol, 4,4′‐(1,4‐phenylene‐diisopropylidene)bisphenol, 2,7‐dihydroxynaphthalene, 4,4′‐dihydroxybiphenyl, 9,9‐bis‐(p‐hydroxyphenyl)fluorene, with an aromatic diacid chloride containing two preformed ester groups 3 , namely terephthaloyl‐bis‐(4‐oxybenzoyl‐chloride). The copolyesters exhibited thermal stability having the decomposition temperature above 350°C and char yield at 700°C in the range of 19–41%. The glass transition temperature was in the range of 131–164°C. Some of the polymers exhibited thermotropic liquid crystalline behavior.

Synthesis and Properties of some Phosphorus-containing Polyesters

Phosphorus-containing polyesters were prepared by polycondensation of 2-(6-oxido-6H-dibenz &gt;c,e&lt; &gt;1,2&lt; oxaphosphorin-6-yl)-1,4-benzenediol with different aromatic dicarboxylic acids using a SOCl2/pyridine condensing agent. The polymers were soluble in polar organic solvents such as N-methylpyrrolidone, N, N-dimethylformamide, tetrahydrofuran and chloroform. They showed high thermal stability having a decomposition temperature above 360°C and char yield at 700°C in the range of 19-32%. The glass transition temperature was in the range of 180-194°C. Solutions of the polymers in N, N-dimethylformamide showed fluorescence having maximum emission wavelength around 362 nm. One of the polymers exhibited thermotropic liquid crystalline behavior

Synthesis and characterization of thermotropic liquid crystalline poly(aryl ether ketone) copolymers with pendant 3‐(trifluoromethyl) phenyl groups

AbstractNovel poly(aryl ether ketone) copolymers with pendant 3‐(trifluoromethyl)phenyl groups were synthesized by the reaction of a crystal‐disrupting monomer, 3‐(trifluoromethyl)phenylhydroquinone (FH) and a mesogenic monomer, 4,4′‐biphenol (BP) with 1,4‐bis(p‐fluorobenzoyl)benzene (BF). Thermotropic liquid crystalline behavior of the copolymers was investigated by means of differential scanning calorimetry, polarized optical microscope and wide‐angle X‐ray diffraction. As a result, the copolymers with the respective molar ratios of FH/BP/BF of 0/100/100–10/90/100 and 80/20/100–100/0/100 were semi‐crystalline without liquid crystalline properties, and amorphous polymers, respectively. In contrast, copolymers with the molar ratio of FH/BP/BF of 20/80/100–70/30/100 had liquid crystalline characteristics. Interestingly, the formation of a highly ordered smectic phase was confirmed for copolymers with the molar ratio of FH/BP/BF of 20/80/100–50/50/100, respectively. All the liquid crystalline copolymers had a wide liquid crystalline temperature range (57–75 °C). Copyright © 2006 Society of Chemical Industry

PREPARATION AND PROPERTIES OF COMPOSITES OF THERMOTROPIC LIQUID CRYSTALLINE COPOLYESTERS AND POLYESTER THERMOPLASTIC ELASTOMER

The composites of thermotropic liquid crystalline copolyesters((p-hydroxy benzoic acid)-terephthalic acid-resorcin)(HB-TA-RES) and poly(butylene terephthalate)-poly(tetramethylene glycol) thermoplastic elastomer(PBT-PTMG) with different copolyester content or copolyester composition were prepared by in-situ polycondensation method.The obtained(HB-TA-RES)/PBT-PTMG were characterized by POM,TGA,WAXD,SEM and rheological analysis.Liquid crystalline behavior of the composites was observed when the HB content in copolyester was 40 mol% and copolyester content in composite was 30?wt%～70?wt% or copolyester content in composite was around 50?wt% and HB content in copolyester was 20 mol%～80 mol%.When the copolyester content in composites ≤50?wt% or HB content in copolyester≤60 mol%,no obvious phase separation happened.The molecular structure of copolyester in composites was more homogeneous and the crystallization of HB was limited.The good thermal stability of(HB-TA-RES)/PBT-PTMG composites with thermotropic liquid crystalline behavior was obtained as compared with the corresponding homocopolyester and the viscosity of the composites was lower than that of the matrix PBT-PTMG especially when the copolyester content was more than 30?wt%.Good processability of the composite is expected in the application.

Side-chain liquid-crystalline polymers with a limonene-co-methyl methacrylate main chain: Synthesis and characterization of polymers with phenyl benzoate mesogenic groups

A new series of liquid-crystalline polymers with a polymer backbone of limonene-co-methyl methacrylate were synthesized and characterized, and the spacer length was taken to be nine methylene units. The chemical structures of the obtained olefinic compound and polymers were confirmed with elemental analysis and proton nuclear magnetic resonance spectroscopy. The thermal behavior and liquid crystallinity of the polymers were characterized with differential scanning calorimetry and polarized optical microscopy. The polymers exhibited thermotropic liquid-crystalline behavior and displayed a glass-transition temperature at 48°C. The appearance of the characteristic schlieren texture confirmed the presence of a nematic phase, which was observed under polarized optical microscopy. These liquid-crystalline polymers exhibited optical activity. A comparison was also made with polyacrylates and polymethacrylate-based materials. This revealed that the nature of the polymer backbone had a major effect on the liquid-crystalline properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4595–4600, 2006

Carbohydrate Rod Conjugates: Ternary Rod−Coil Molecules Forming Complex Liquid Crystal Structures

T-shaped polyphilic triblock molecules, consisting of a rodlike p-terphenyl unit, a hydrophilic and flexible laterally attached oligo(oxyethylene) chain terminated by an 1-acylamino-1-deoxy-D-sorbitol unit, and two end-attached lipophilic alkyl chains, have been synthesized by palladium-catalyzed cross-coupling reactions as the key steps. The thermotropic liquid crystalline behavior of these compounds was investigated by polarized light microscopy, differential scanning calorimetry (DSC), and X-ray scattering. We investigated the mode of self-organization as a function of the length and position of the lateral polar chain and the length of the terminal alkyl chains. Depending on the size of the polar and lipophilic segments, a series of unusual liquid crystalline phases was detected. In three of these phases, the space is divided into three distinct periodic subspaces. In addition to a hexagonal channeled layer phase (ChL(hex)) consisting of layers that are penetrated by polar columns, there are also two honeycomb-like network structures formed by square (Col(squ)/p4mm) or pentagonal cylinders (Col(squ)/p4gm). The cylinder walls consist of the terphenyl units fused by columns of alkyl chains, and the interior contains the polar side chains. In addition, a hexagonal columnar phase was observed in which the polar columns are organized in a continuum of terphenyls and alkyl chains with an organization of the terphenyl cores tangentially around the columns with the long axis perpendicular to the columns. For one compound, a reversal of birefringence was observed, which is explained by a reorientation of the terphenyl cores. The addition of protic solvents induces lamellar phases.

Benzylation of cellulose in the solvent dimethylsulfoxide/tetrabutylammonium fluoride trihydrate

The cellulose solvent dimethylsulfoxide/tetrabutylammonium fluoride trihydrate (TBAF·3 H2O) was studied as reaction medium for the synthesis of benzyl cellulose (BC) by treating the dissolved polymer with benzyl chloride in the presence of solid NaOH or aqueous NaOH solution. BC samples with degree of substitution (DS) between 0.40 and 2.85 were accessible applying different molar ratios. The studies show that both the TBAF·3 H2O concentration and the molar ratio of the reagents to repeating unit influence the DS. The solubility of the BC synthesized in a different way, however, of comparable DS is different. Structural analyses were carried out by means of FTIR-, 1H- and 13C NMR spectroscopy. SEC measurements revealed polymer aggregation in samples of low DS synthesized in a solvent containing 9.0% TBAF·3 H2O. At higher concentration of TBAF·3 H2O in the solvent, the BC samples obtained do not form aggregates. BC of high DS is crystalline and shows thermotropic liquid crystalline behavior as analyzed by means of DSC. Melting point and degradation temperature are not related to the DS.

Synthesis and characterization of diblock copolymers based on crystallizable poly(ε-caprolactone) and mesogen-jacketed liquid crystalline polymer block

Diblock copolymers comprising crystallizable poly(ε-caprolactone) and poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PMPCS) were synthesized by ring-opening polymerization of ε-caprolactone and subsequent atom transfer radical polymerization (ATRP) of MPCS. The molecular structure of the copolymers was confirmed by 1H NMR spectroscopy and GPC. Kinetic study of ATRP showed that the polymerization proceeded in a controlled way up to high conversions. Three series of diblock copolymers were obtained with relatively narrow polydispersity indices (PDI≤1.11) and PCL blocks of 8000, 12,900, and 22,800 molecular weights, respectively. The existence of microphase separation was identified by differential scanning calorimetry (DSC) and directly observed through transmission electron microscopy (TEM). The melting behavior of PCL block was significantly affected by the length of PCL block and composition of PMPCS. The thermotropic liquid crystalline behavior was examined by polarized optical microscopy (POM) and DSC. The result showed that the diblock copolymer exhibited liquid crystalline behavior when the degree of polymerization (DP) of PMPCS block was not less than 44.

The synthesis and thermal properties of polyepichlorohydrin side-chain liquid crystal polymers

The synthesis and characterization of a new series of side-chain liquid crystal polyepichlorohydrin (PECH) polymers are described. The structures and thermal properties of the synthesized polymers were investigated using IR, NMR, polarized optical microscopy and differential scanning calorimetry. A substantial increase of the glass transition temperature with the degree of substitution of side-chain groups was observed. Polymers with a degree of substitution of side groups, of at least 60%, exhibited thermotropic liquid crystalline behaviour. The polymers present thermal liquid crystalline behaviour and form Schlieren and thread texture upon cooling from the isotropic phase, after annealing for 120 min at different temperatures. In addition, the thermal decomposition of PECHOPhPhCN was studied by thermogravimetry under both nitrogen and air environments. The temperature of the maximum decomposition rate was about 340 °C. Weight loss decreased considerably after 350 °C and was approximately 98% at 700 °C. Chemical modification of functional polymers offers a simple method for obtaining liquid crystalline polymers whose transition temperature can be tailored by varying the amount of substitution, however complete substitution cannot be achieved.

A surfactant-encapsulated polyoxometalate complex towards a thermotropic liquid crystal

A novel surfactant-encapsulated terbium-substituted heteropolyoxotungstate complex [L1]13[Tb(SiW11O39)2].30H2O (SEC-1) bearing mesomorphous groups was successfully prepared by the ionic self-assembling route, exhibiting characteristic thermotropic liquid-crystalline behavior.

Liquid Crystalline Properties of Polyguanidines

Modified polyguanidines were prepared, and their liquid crystalline properties were studied using optical polarizing microscopy and X-ray diffraction. Parameters examined include chirality, the uniformity of the lengths of side chains, and attached side-chain mesogens. If the side chains on the repeat units are identical, then polymer has a more ordered structure in both solution and the solid state. Uniform lengths of the side chains are also important. Poly(N,N'-di-n-hexylguanidine), poly-I, exhibited a lyotropic smectic texture in contrast to a nematic texture of poly(N-(rac)-2-phenylethyl)-N'- methylguanidine) (poly-(rac-II)). Optically pure poly(N-((R)-2-phenylethyl)-N'-methylguanidine) (poly- (R-II)) formed a cholesteric texture, whereas the corresponding racemic polyguanidine, poly-(rac-II), formed a nematic texture. Additionally, poly-(R-II) displayed a mesophase at a lower critical concentration than either poly-I or poly-(rac-II), implying that poly-(R-II) is stiffer than these two other derivatives. Poly(N-6-((4'-methoxyphenylazo)phenyl-4-oxy)hexyl-N'-n-hexylguanidine) (poly-IV), one of combined liquid crystalline structures (liquid crystalline backbone plus liquid crystalline side chains), displayed a lyotropic nematic texture presumably due to the strong dipolar-dipolar interaction between the main chain and side chains that folds the appendages parallel to the molecular axis. Poly(N-12-((4'-methoxybiphenyl-4- oxy)dodecyl-N'-n-dodecylguanidine) (poly-V) and poly(N,N'-di-n-dodecylguanidine) (poly-VI) exhibited thermotropic liquid crystalline behavior.

Liquid crystalline bolaamphiphiles with semiperfluorinated lateral chains: competition between layerlike and honeycomb-like organization.

Novel bolaamphiphilic triblockmolecules consisting of a rigid biphenyl unit, with a polar 2,3-dihydroxypropyloxy group and a phenolic OH group at opposite ends, as well as a semiperfluorinated chain in a lateral position have been synthesized via palladium catalyzed cross coupling reactions as the key steps. The thermotropic liquid crystalline behavior of these compounds was investigated by polarized light microscopy, DSC and X-ray scattering, and the influence of the length of the lateral chain on the mesomorphic properties was studied. The compound with the shortest chain as well as the long chain derivatives form lamellar mesophases composed of segregated layers of the bolaamphiphilic moieties and sublayers comprising the fluid lateral chains. The layers within the lamellar phases of the short chain compound adopt a positional correlation, leading to a 2D lattice (Col(r)/p2mm), whereas the layers of the lamellar phases of the long chain derivatives are noncorrelated (Lam). Compounds with a medium chain length organize into columnar phases, where the nonpolar lateral chains segregate into columns, which are embedded in networks of regular (Col(h)) or stretched (Col(r)/c2mm) hexagonal cylinder shells consisting of the bolaamphiphilic units. In total, an unusual phase sequence was found, where, with respect to the chain length, columnar mesophases occur between two mesophases with layer organization.

Amphiphilic and mesogenic carbohydrates XIII. Perfluoroalkylated amphiphilic liquid crystals with inositol and carbohydrate head groups†

New perfluoroalkylated amphiphiles based on carbohydrates (D-xylose, D-ribose, D-glucose) and on myo-inositol were synthesized and their thermotropic liquid crystalline behaviour was investigated. The introduction of perfluoroalkyl groups was carried out by radical addition of 1-iodoperfluoroalkanes to O- and C-allyl-substituted sugar and inositol derivatives.

An Ia3¯d thermotropic cubic phase from N-alkylpyridinium tetrahalocuprates

The thermotropic liquid crystalline behaviour of two N-alkylpyridinium tetrahalocuprates was investigated. The n-pentadecyl tetrachloro and tetrabromo derivatives (CU15-CL and CU15-BR, respectively) exhibit very similar behaviour on cooling, and specifically, a high temperature smectic phase followed by a cubic phase. We fully elucidated the Ia3¯d space group for the cubic phase from X-ray diffraction on single crystals. The type of cubic phase is still under discussion, but we suggest that it is a direct type of structure based on the known phase sequence of lower and higher homologues. A model for the local organization of CU15-CL and CU15-BR in the cubic and smectic mesophases is also proposed.