Synthesis, structure and mesomorphic properties of side-chain chiral liquid crystalline polysiloxanes based on (S)-(+)-2-methyl-1-butanol derivatives

The synthesis of five chiral liquid crystalline monomers (M₁-M₅), and their corresponding side-chain polymers (P₁-P₅) based on (S)-(+)-2-methyl-1-butanol derivatives is described. The chemical structures of the monomers were confirmed by FT-IR, ¹H NMR, and elemental analyses. The structure-property relationships of the monomers and polymers obtained are discussed. The mesomorphic properties were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), polarizing optical microscopy (POM), and X-ray diffraction (XRD) measurements. All monomers showed a cholesteric phase. For M₂, M₃, and M₅, besides a cholesteric phase and a smectic A (S_A) phase, M₂ also revealed an enantiotropic chiral smectic C phase and a monotropic smectic B (S_B) phase, and M₃ also showed a S_B phase. The polymers P₁-P₅ exhibited a S_A phase, moreover, P₂, P₃ and P₅ also revealed a phase. The experimental results demonstrated that a flexible siloxane backbone and a long flexible spacer tended to exhibit a low glass transition temperature, high thermal stability, and wide mesophase temperature range.     

Side-chain liquid crystalline polymers containing 4-[2-(S)-methyl-1-butoxy]-4′-(11-undecanyl-1-oxy)-α-methylstilbene side groups

The synthesis and characterization of polymethacrylate, polyacrylate, poly(methylsiloxane), and 1,3,5,7-tetramethylcyclotetrasiloxane containing chiral 4-[2-(S)-methyl-1- butoxy]-4′-(11-undecanyl-1-oxy)-α-methylstilbene side groups are described. All polymers exhibit an enantiotropic S_A mesophase and side-chain crystallization. The 1,3,5,7-tetramethylcyclotetrasiloxane containing mesogenic side groups represents a mixture of four stereoisomers and displays a monotropic S_A mesophase     

Synthesis by ATRP and effects of molecular weight on photomechanical properties of liquid crystalline polymers containing side-chain azobenzene chromophores

The synthesis of a series of azobenzene containing liquid crystalline methacrylic homopolymers, poly(4-ω-methacryloyloxy-hexyloxy-4′-ethoxyazobenzene) [Poly(M6A)], with distinct average chain lengths and low polydispersity has been achieved by Atom Transfer Radical Polymerization (ATRP) in THF solution using allyl 2-bromoisobutyrate as initiator and Cu(I)Br as catalyst. Under the adopted conditions the living centers concentration is found to be constant throughout the polymerization process and well defined chain end-groups are obtained. All the obtained polymeric samples, having average molecular mass ranging from 3300 to 14000 g/mol, exhibit smectic and nematic liquid-crystalline phases on heating, with transition temperatures strongly dependent on polymerization degree, as characterized by differential scanning calorimetry and polarized optical microscopy.The photomechanical effects (i.e. the dependence of volume and density) exhibited upon trans-to-cis and cis-to-trans photoisomerization of the azobenzene mesogenic groups have been investigated by ellipsometry and related to molecular weight, with particular attention to important parameters for potential applications such as the relative variation of total volume, response time, stability and reproducibility.     

Synthesis and properties of novel phosphorus‐containing thermotropic liquid crystalline copoly(ester imide)s

A series of novel phosphorus‐containing polyesterimides were prepared from diols—a mixture of a new aromatic phosphorus‐containing bisphenol, namely 1,4‐bis[N‐(4‐hydroxyphenyl)phthalimidyl‐5‐carboxylate]‐2‐(6‐oxido‐6H‐dibenz<c,e><1,2>oxaphosphorin‐6‐yl)‐naphtalene, with aliphatic diols such as 1,3‐propanediol, 1,4‐butanediol, 1,5‐pentanediol, 1,6‐hexanediol, and 1,12‐dodecanediol—and an aromatic diacid chloride containing two preformed ester groups, namely terephthaloyl‐bis‐(4‐oxibenzoyl‐chloride), via high‐temperature polycondensation in o‐dichlorobenzene. The structures of monomers and polymers were verified by means of Fourier transform infrared (FTIR) spectroscopy and ¹H NMR spectroscopy. The molar ratio of aromatic bisphenol to aliphatic diol was varied to generate a series of copolyesterimides with tailored physicochemical properties, structure–properties relationships being established. The effect of the phosphorus content on the thermal properties and the flame retardancy was evaluated by means of thermogravimetric analysis (TGA), TGA–FTIR, and scanning electron microscopy. The polymers were stable up to 340 °C showing a 5% weight loss in the range of 340–395 °C and a 10% weight loss in the range of 370–415 °C. The char yields at 700 °C were in the range of 13.6–38% increasing with the content of phosphorus‐containing bisphenol. The effect of the aliphatic content on the liquid crystalline behavior was investigated by polarized light microscopy, differential scanning calorimetry, and X‐ray diffraction. The transition temperatures from crystal to liquid crystalline melt were in the range of 209–308 °C. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

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

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.     

Synthesis and mesomorphic properties of resorcyl di[4-(4-alkoxy-2,3-diflorophenyl)ethynyl] benzoate liquid crystals

Two resorcyl di[4-(4-alkoxy-2,3-difluorophenyl)ethynyl] benzoate liquid crystals (A10 and A12) were prepared and their mesomorphic properties were observed. A large polarisation value was obtained with longer terminal chains.     

Effect of the poly(oxytetramethylene)diol spacer length on some properties of liquid crystalline polyurethanes

Previous studies on liquid crystalline polyurethanes prepared from 4,4′-bis(2-hydroxyethoxy)biphenyl (BHBP) and 2,4-tolylene diisocyanate (TDI) were continued. In this article, a series of polyurethanes, which differ in the flexible spacer length and BHBP content is described. Poly(oxytetramethylene)diols of different molecular weights (PTMO, M _n = 250, 650, 1000, 2000) were used as flexible spacers. The polyurethanes were investigated by DSC, polarizing microscopy, x-ray diffractometry, and IR spectroscopy. The molecular weight distribution was determined by GPC. The morphology of the polyurethanes was investigated by the SALS method. Partial replacement of BHBP by 25–75 mol % PTMO and the flexible spacer length influence the liquid crystalline properties, the phase transition temperatures, and the range of mesophase occurrence. © 1993 John Wiley & Sons, Inc.     

Effect of smectogenicity of the ionic groups on the thermotropic liquid crystalline behavior of pyridinium and poly(4-vinylpyridinium) salts quaternized with mesogenic groups

In order to demonstrate the important smectic power of the ionic functions present in mesogenic molecules, a series of N-alkylpyridinium bromides ω-substituted with (4-cyanobiphenylyl)oxy or [4-(2-methyl-1-butoxy)biphenylyl]oxy mesogenic group and their analogous 4-vinylpyridinium polymers were synthesized and characterized. The liquid crystalline behavior was studied by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction. Smectic mesophases, namely A, B, and E, were identified for the low molecular weight compounds, whereas smectic A and E mesophases were identified for the analogous polymers. Both structures were found to be very similar. They consist of single layers of upright molecules laterally arranged head-to-tail; the polymer backbone is inserted in between the layers. The monolayer smectic ordering observed in spite of the presence of the interacting cyano and chiral groups demonstrates the prevailing effect of the electrical interactions upon the structural organization. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2569–2577, 1997     

Crystallization kinetics of a thermotropic liquid crystalline polyimide derived from 1,3-bis[4-(4′-aminophenoxy) cumyl] benzene

We have studied the nonisothermal and isothermal crystallization kinetics of an aromatic thermotropic liquid crystalline polyimide synthesized from 1,2,4,5-benzenetetracarboxylic dianhydride (PMDA) and 1,3-bis[4-(4′-aminophenoxy) cumyl] benzene (BACB) by means of differential scanning calorimetry (DSC). Polarized light microscopy (PLM) and wide-angle X-ray diffraction (WAXD) results confirm that this polyimide exhibits a smectic texture. Nonisothermal crystallization showed two strong and one weak exothermic peaks during cooling. The phase transition from isotropic melt to liquid crystalline state is extremely fast which completes in several seconds. The mesophase transition has a small Avrami parameter, n, of approximate 1. The isothermal crystallization of 253–258°C has been examined. The average value n is about 2.6 and the temperature-dependent rate constant k changes about two orders of magnitude in the crystallization temperature range of 6°C. The slope of ln k versus 1/(T_cΔT) is calculated to be −2.4 × 10⁵, which suggests nucleation control, via primary and/or secondary nucleation for the crystallization process. During the annealing process, a new phase (slow transition) is induced, which grows gradually with annealing time. At lower annealing temperatures (220–230°C), the slow transition process seems not to be influenced by the crystals formed during cooling process and its Avrami parameter n is ca. 0.3–0.4. However, the slow transition was hindered by the crystals formed during cooling process when annealed at higher temperature (230–240°C). © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1679–1694, 1998     

Synthesis and liquid crystalline properties of poly(1‐alkyne)s carrying triphenylene discogens

Triphenylene‐containing 1‐decynes with different alkyl chain lengths and their polymers are synthesized and the effects of the structural variables on their mesomorphic properties are investigated. The monomers [HC?C(CH₂)₈CO₂C₁₈H₆ (OC_mH_2m+1)₅; m = 4–9] are prepared by consecutive etherization, coupling, and esterification reactions. The monomers form columnar phases at room temperature. The polymerizations of the monomers are effected by [Rh(nbd)Cl]₂, producing soluble polymers in high yields (up to 84%). The structures and properties of the polymers are characterized and evaluated by IR, NMR, TGA, DSC, POM, and XRD analyses. All the polymers are thermally stable, losing little of their weights when heated to 300 °C. The isotropization temperature of the polymers increases initially with the length of alkyl chain but decreases on further extension. Although the polymers with shorter and longer alkyl chain lengths adopt a homogeneous hexagonal columnar structure, those with intermediate ones form mesophases with mixed structures. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2960–2974, 2008     

Synthesis, characterization and photolysis studies on liquid crystalline poly[4-(4′-x-biphenyl)yl-4″-(m-methacryloyloxyalkyloxy) cinnamate]’s

Three series of side chain liquid crystalline polymers containing terminally substituted biphenyl cinnamoyl esters were synthesized and characterized. The para position in the cinnamoyl group was connected with polymer backbone through various even numbers of methylene spacers. The terminal electron acceptor and donor substituted biphenyl groups were linked to cinnamoyl group through ester linkages. Polarizing microscopic and DSC studies confirm the formation of thermotropic mesophase up on heating. All the polymers exhibited nematic/grainy mesophases. The TGA and DSC studies showed that the nature of the terminal substituents have significant effect on mesophase temperatures as well as in thermal stability of these liquid crystalline polymers. UV light promoted photocrosslinking studies reveal that the clear involvement on photocrosslinking efficiency, although they are linked to the olefinic bond of cinnamoyl group through their ester linkage. It is observed that electron-donating group accelerate the photocrosslinking rate, while acceptor group retard the phase of the reaction on the other hand, the unsubstituted polymers show an intermediate rate.     

Synthesis and mesomorphic properties on the series of 2-(4-alkylphenyl)-6-methylquinolines and 2-(4-alkoxyphenyl)-6-methylquinolines

Two homologous series of quinoline-containing liquid crystalline compounds were synthesised. Preparation of these compounds was completed in a short two-step reaction. Fair to good two-step overall yields of 63%–68%?and 50%–60%?were obtained respectively for the liquid crystalline compounds of 2-(4-alkylphenyl)-6-methylquinolines (nPQMe, n?=?4–8) and 2-(4-alkoxyphenyl)-6-methylquinolines (mOPQMe, m?=?3–7). Spectral analyses were in accordance with the expected structures. Polarising optical microscopy showed both series of compounds only display a nematic phase. Their thermotropic behaviours were further confirmed by differential scanning calorimetry.     

New liquid crystalline 3-methyl-6-(4-substituted phenyl)-4,5-dihydrobenzo [ d ] isoxazoles and 3,5-disubstituted 4,5-dihydroisoxazoles: synthesis and mesomorphic properties

The synthesis and mesomorphic properties of new liquid crystalline 3-methyl-6-(4-substituted phenyl)-4,5-dihydrobenzo [ d ] isoxazoles and 3,5-disubstituted 4,5-dihydroisoxazoles are reported. These compounds have been synthesized by the reaction of 6-(4-substituted phenyl)-3-acetyl cyclohex-2-enones with hydroxylamine hydrochloride and of the corresponding oximes with unsaturated compounds in the presence of N -chlorosuccinimide and triethylamine, respectively.     

Synthesis and properties of azobenzene‐containing poly(1‐alkyne)s with different functional pendant groups

1‐Alkynes containing azobenzene mesogenic moieties [HC?C(CH₂)₉? O? ph? N?N? ph? O? R; R = ethyl ( 1 ), octyl ( 2 ), decyl ( 3 ), (S)‐2‐methylbutyl ( 4 ), or (S)‐1‐ethoxy‐1‐oxopropan‐2‐yl ( 5 ); ph = 1,4‐phenyl] were synthesized and polymerized in the presence of a Rh catalyst {(nbd)Rh⁺[B(C₆H5)₄]^?; nbd = 2,5‐norbornadiene} to yield a series of liquid‐crystalline polymers in high yields (e.g., >75%). These polymers had moderate molecular weights (number‐average molecular weight ≥ 12,000), high cis contents in the main chain (up to 83%), good thermal stability, and good solubility in common organic solvents, such as tetrahydrofuran, chloroform, and dichloromethane. These polymers were thoroughly characterized by a combination of infrared, nuclear magnetic resonance, thermogravimetric analysis, differential scanning calorimetry, polarized optical microscopy, and two‐dimensional wide‐angle X‐ray diffraction techniques. The liquid‐crystalline behavior of these polymers was dependent on the tail group attached to the azobenzene structure. Poly‐ 1 , which had the shortest tail group, that is, an ethyl group, showed a smectic A mesophase, whereas poly‐ 2 , poly‐ 3 , and poly‐ 5 , which had longer or chiral tail groups, formed smectic C mesophases, and poly‐ 4 , which had another chiral group attached to the azobenzene structure, showed a chiral smectic C mesophase in both the heating and cooling processes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4532–4545, 2006     

Preparation of poly(2‐anilinoethanol) containing azobenzene group under electrical field and its liquid crystalline properties investigation

In this project, 2‐[N‐ethyl‐N‐[4‐[(4′‐nitrophenyl)azo]‐phenyl]amino]ethanol (Disperse Red‐I) was prepared by adding of (N‐ethyl‐2‐anilinoethanol) with the salt diazonium p‐nitroaniline. The main mesogenic liquid crystalline (LC) 2‐[N‐ethyl‐N‐[4‐[4′‐nitrophenyl)azo]‐phenyl]amino]ethyl‐3‐chloro propionate (Disperse Red‐II) was synthesized by reaction of disperse Red I and 3‐chloropropanoeic acid at the alkaline condition. Then 2‐anilinoethyl‐3‐chloropropionate‐{2‐[ethyl[4‐[(4′‐nitrophenyl)azo]phenyl]amino] ethanol}, (2AECP‐Red‐I) was prepared via reaction of disperse red‐II and 2‐anilinoethanol. On the other hand, poly 2‐anilinoethyl‐3‐chloropropionate‐{2‐[ethyl[4‐[(4′‐nitrophenyl)azo]phenyl]amino]ethanol} and poly(2AECP‐Red‐I) have been synthesized by polymerization of 2AECP‐Red‐I in two separate schemes. These include polymerization in the absence of electric field (EF) and polymerization under different EFs. A comparison of the results reveals that the polymer produced under electric field is more linear, regular in shape with high electrical conductivity, as well as good LC behavior with semectic texture. The resulted monomer and poly(2AECP‐Red‐I) are characterized by using Fourier transform infrared and ultraviolet–visible and were studied by thermogravimetric analysis and differential scanning calorimetry. Scanning electron microscopy images supported the formation of poly(2AECP‐Red‐I) and showed morphology feature and homogeneous structure on poly(2AECP‐Red‐I). Electrical conductivity of poly(2AECP‐Red‐I) has been studied by four‐point probe method. Copyright © 2014 John Wiley & Sons, Ltd.     

New side chain ferroelectric liquid crystalline polymers based on (2S, 3S)-2-chloro-3-methylpentanoic acid: synthesis and phase behaviour

The synthesis of four new chiral mesogenic monomers (M₁–M₄) and side chain ferroelectric liquid crystalline polymers containing (2S, 3S)-2-chloro-3-methylpentanoate is described. The chemical structures and phase behaviour of the monomers and polymers obtained in this study were characterised by Fourier transform infrared, proton nuclear magnetic resonance, polarising optical microscopy, differential scanning calorimetry, thermogravimetric analysis and X-ray diffraction. The selective reflection of light was investigated with ultraviolet/visible (UV/Vis). Their structure–mesomorphism relationships were discussed. M₁ and P₁ all showed a chiral smectic C (SmC*) phase. M₂ and M₃ revealed a SmC* phase and cholesteric phase, while their corresponding polymers P₂ and P₃ revealed a SmC* phase and smectic A (SmA) phase. M₄ only exhibited a cholesteric phase, whereas the corresponding polymers P₄ showed a SmA phase. Moreover, the selective reflection of light shifted to the long-wavelength region at the SmC* phase range and to the short-wavelength region at the cholesteric range with increasing temperature, respectively. The results seemed to demonstrate that the tendency towards melting temperature (T_m), glass transition temperature (T_g), isotropic temperature (T_i) and mesophase range for the monomers and polymers increased by increasing the mesogenic core rigidity or the number of phenyl ring. The polymerisation effect could lead to higher liquid crystalline to isotropic phase transition temperature, wider mesophase range and more ordered smectic phase formed. In addition, all the obtained polymers had a very good thermal stability and the corresponding T_d increased by increasing the number of phenyl ring.     

Synthesis and properties of 2-(2-furyl)-1-methyl-1H-acenaphtho[9,10-d]imidazole

2-(2-Furyl)-1-methyl-1H-acenaphtho[9,10-d]imidazole was obtained by the condensation of 9,1-acenaphthenequinone with furfural in the presence of ammonium acetate followed by N-methylation of the obtained 2-(2-furyl)-1H-acenaphtho[9,10-d]imidazole with methyl iodide in N-methylpyrrolid-2-one in the presence of potassium hydroxide. It was established that its electrophilic substitution in an acidic medium only takes place at position 2 of the furan ring while in a neutral medium both position 2 and position 7 of the aromatic part of the molecule undergo electrophilic attack. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 191–196, February, 2006.     

A novel synthetic approach to very late antigen-4 antagonist trans-4-[1-[[2,5-dichloro-4-(1-methyl-3-indolylcarboxyamide)phenyl]acetyl]-(4S)-methoxy-(2S)-pyrrolidinylmethoxy]cyclohexanecarboxylic acid via tert-butyl trans-[(4S)-Methoxy-(2S)-pyrrolidinylmethoxy]cyclohexanecarboxylate as a key intermediate

This contribution describes a novel synthetic approach to very late antigen-4 (VLA-4) antagonist trans-4-[1-[[2,5-dichloro-4-(1-methyl-3-indolylcarboxyamide)phenyl]acetyl]-(4S)-methoxy-(2S)-pyrrolidinylmethoxy]cyclohexanecarboxylic acid (1) via tert-butyl trans-[(4S)-methoxy-(2S)-pyrrolidinylmethoxy]cyclohexanecarboxylate (2b) as a key intermediate. The synthesis, which includes n-Bu?NSO?H that catalyzed basic etherification of 12 and iodine-mediated cyclization to provide the 2,4-disubstituted pyrrolidine frame of 2b, is designed to utilize trans-4-hydroxycyclohexanecarboxylic acid (9) as a commercially available starting material.