Self‐organized liquid‐crystalline polyethers obtained by grafting tapered mesogenic groups onto poly(epichlorohydrin): Toward biomimetic ion channels

A set of high‐molecular‐weight new side‐chain liquid‐crystalline polyethers was obtained by chemical modification of poly(epichlorohydrin) with potassium 3,4,5‐tris(dodecyloxy)benzoate. The degree of modification ranged from 48 to 70% depending on the reaction conditions, and the upper value was an apparent modification plateau. NMR characterization indicated that no side reactions of any kind occurred (e.g., deshydrohalogenation). All copolymers had a nematic columnar mesophase whose range of stability depended on the modification degree. X‐ray diffraction experiments performed on mechanically oriented samples showed that tapered groups were tilted with respect to the column axes. Also X‐ray experiments and density measurements demonstrated that the number of disks per unit cell decreased as the modification degree increased. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2918–2929, 2003     

High‐molecular‐weight side‐chain liquid‐crystalline polyethers based on 4′‐cyanobiphenyl‐4‐oxy mesogenic groups

A set of poly[ω‐(4′‐cyano‐4‐biphenyloxy)alkyl‐1‐glycidylether]s were synthesized by the chemical modification of the corresponding poly(ω‐bromoalkyl‐1‐glycidylether)s with the sodium salt of 4‐cyano‐4′‐hydroxybiphenyl. New high‐molecular‐weight side‐chain liquid‐crystalline polymers were obtained with excellent yield and almost quantitative degree of modification. All side‐chain liquid‐crystalline polymers were rubbers soluble in tetrahydrofuran. The characterization by ¹H and ¹³C NMR revealed no changes in the regioregular isotactic microstructure of the starting polymer and the absence of undesirable side reactions such as deshydrobromination. The liquid crystalline behavior was analyzed by DSC and polarized optical microscopy, and mesophase assignments were confirmed by X‐ray diffraction. Polymers that had alkyl spacers with n = 2 and 4 were nematic, those that had spacers with n = 6 and 8 were nematic cybotactic, and those that had longer spacers (n = 10 and 12) were smectic C and showed some crystallization of the side alkyl chains. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3002–3012, 2004     

Main‐chain,thermotropic, liquid‐crystalline,hydrogen‐bonded polymers of 4,4′‐bipyridyl with aliphatic dicarboxylic acids

A series of main‐chain, thermotropic, liquid‐crystalline (LC), hydrogen‐bonded polymers or self‐assembled structures based on 4,4′‐bipyridyl as a hydrogen‐bond acceptor and aliphatic dicarboxylic acids, such as adipic and sebacic acids, as hydrogen‐bond donors were prepared by a slow evaporation technique from a pyridine solution and were characterized for their thermotropic, LC properties with a number of experimental techniques. The homopolymer of 4,4′‐bipyridyl with adipic acid exhibited high‐order and low‐order smectic phases, and that with sebacic acid exhibited only a high‐order smectic phase. Like the homopolymer with adipic acid, the two copolymers of 4,4′‐bipyridyl with adipic and sebacic acids (75/25 and 25/75) also exhibited two types of smectic phases. In contrast, the copolymer of 4,4′‐bipyridyl with adipic and sebacic acids (50/50), like the homopolymer with sebacic acid, exhibited only one high‐order smectic phase. Each of them, including the copolymers, had a broad temperature range of LC phases (36–51 °C). The effect of copolymerization for these hydrogen‐bonded polymers on the thermotropic properties was examined. Generally, copolymerization increased the temperature range of LC phases for these polymers, as expected, with a larger decrease in the crystal‐to‐LC transition than in the LC‐to‐isotropic transition. Additionally, it neither suppressed the formation of smectic phases nor promoted the formation of a nematic phase in these hydrogen‐bonded polymers, as usually observed in many thermotropic LC polymers. The thermal transitions for all of them, measured by differential scanning calorimetry, were well below their decomposition temperatures, as measured by thermogravimetric analysis, which were in the temperature range of 193–210 °C. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1282–1295, 2003     

Synthesis and crosslinking of vinyl‐terminated biphenyl and naphthalene liquid‐crystalline poly(epichlorohydrin) derivatives: Effect of nonmesogenic nonvinylic units on the mesogenic properties

Two series of vinyl‐terminated side‐chain liquid‐crystalline polyethers containing ethylene oxide or glycidyl aromatic carboxylates as spacers were synthesized. The mesogenic cores were 4,4′‐biphenyl or 2,6‐naphthalene moieties. The polymers were synthesized by chemically modifying poly(epichlorohydrin) or poly(epichlorohydrin)‐poly(ethylene oxide) with the corresponding mesogenic carboxylic acids or with mixtures of these acids and the nonmesogenic non‐crosslinkable analogous 4‐biphenyl‐ and 2‐naphthalenecarboxylic acids. In most cases the degree of modification achieved was higher than 90%. The polymers were characterized by chlorine analysis, IR, and ¹H and ¹³C NMR spectroscopies; viscosimetry; size exclusion chromatography; multi‐angle laser light scattering; and thermogravimetric analysis. The liquid‐crystal behavior, shown by most polymers, was examined by differential scanning calorimetry, polarized optical microscopy (POM), and X‐ray diffraction on mechanically oriented samples. The crosslinking of most polymers was done by peroxide‐type initiators that led to liquid‐crystal thermosets or elastomers. The freezing of the mesophase organization on the crosslinked materials was confirmed by POM and X‐ray diffraction. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3893–3908, 2002     

Crosslinking of vinyl‐terminated biphenyl and naphthalene side‐chain liquid‐crystalline poly(epichlorohydrin) derivatives

We performed the crosslinking of vinyl‐terminated biphenyl and naphthalene side‐chain liquid‐crystalline polyethers using peroxide‐type initiators with and without the addition of tertiary amine promoters. The crosslinking temperatures were chosen in the range of mesophase stability to allow the mesophase order to be frozen. The biphenyl derivatives, with a high isotropization temperature, were crosslinked to a large extent. This led to anisotropic thermosets. To crosslink naphthalene derivatives, amine promoters were needed, but degrees of crosslinking were lower, and anisotropic elastomers were obtained. Crosslinking processes were studied by differential scanning calorimetry, polarized optical microscopy, and Fourier transform infrared spectroscopy. The nature of the frozen mesophase was confirmed by X‐ray diffraction studies on mechanically oriented samples. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2237–2244, 2002     

New liquid‐crystalline poly(ester amide)s: The role of nitro groups in the phase behavior

New hydrogen‐bonded liquid‐crystalline poly(ester amide)s (PEA)s were obtained from 1,4‐terephthaloyl[bis‐(3‐nitro‐N‐anthranilic acid)] (5) or 1,4‐terephthaloyl[bis‐(N‐anthranilic acid)] (6), with or without nitro groups, respectively, through the separate condensation of each with hydroquinone or dihydroxynaphthalene. The dicarboxylic monomers were synthesized from 2‐aminobenzoic acid. The phase behavior of the monomers and polymers were studied with differential scanning calorimetry, polarized light microscopy, and wide‐angle X‐ray diffraction methods. Monomer 5, containing nitro groups, exhibited a smectic liquid‐crystalline phase, whereas the texture of monomer 6 without nitro groups appeared to be nematic. The PEAs containing nitro groups exhibited polymorphism (smectic and nematic), whereas those without nitro groups exhibited only one phase transition (a nematic threaded texture). The changes occurring in the phase behavior of the polymers were explained by the introduction of nitro groups. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1289–1298, 2004     

Synthesis and properties of mesogen‐jacketed liquid crystalline polymers containing biphenyl mesogen with asymmetric substitutions

This work focuses on the design, synthesis, and characterization of a series of mesogen‐jacketed liquid crystalline polymers (MJLCPs), poly(alkyl 4′‐(octyloxy)‐2‐vinylbiphenyl‐4‐carboxylate) (pVBP(m,8), m = 1, 2, 4, 6, 8, 10, 12). For the first time, we realized asymmetric substitutions in the mesogens of MJLCPs. The polymers obtained by conventional free radical polymerization were investigated in detail by a combination of various techniques, such as differential scanning calorimetry, wide‐angle X‐ray diffraction, and polarized light microscopy. Our results showed that all the polymers were thermally stable, and their glass transition temperatures decreased when m increased. The liquid crystalline (LC) phases that developed at high temperatures and disappeared at low temperatures were strongly dependent on the difference in lengths of alkyl groups on the 4 and 4′ substitution positions of the side‐chain biphenyl. While polymer pVBP(1,8) was not liquid crystalline, columnar liquid crystalline phases were observed for all other pVBP(m,8) (m = 2, 4, 6, 8, 10, 12) polymers. Polymer pVBP(8,8) showed a tetragonal columnar nematic liquid crystalline phase, and the other LC polymers exhibited columnar nematic phases. In additions, the smaller the difference in the lengths of the terminal alkyls, the easier the development of the liquid crystalline phase. Birefringence measurements showed that solution‐cast polymer films exhibited moderately high positive birefringence values, indicating potential applications as optical compensation films for liquid crystal displays. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and phase behavior of side‐chain liquid‐crystalline polymers containing malachite green lactone groups

New side‐chain liquid‐crystalline polymers containing both cholesteric and thermochromic side groups were synthesized. Their chemical structures were confirmed with elemental analyses and Fourier transform infrared, proton nuclear magnetic resonance, and carbon‐13 nuclear magnetic resonance spectra. The mesogenic properties and phase behavior were investigated with differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X‐ray diffraction measurements. The effect of the concentration of dye side groups on the phase behavior of the polymers was examined. The polymers showed smectic or cholesteric phases. Those polymers containing less than 20 mol % dye groups had good solubility, reversible phase transitions, wider mesophase temperature ranges, and higher thermal stability. The experimental results demonstrated that the isotropization temperature and mesophase temperature ranges decreased with an increasing concentration of dye groups. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3870–3878, 2004     

Amphiphilic mesogen‐jacketed liquid crystalline polymers: Design,synthesis, and self‐assembly behaviors

We synthesized a series of amphiphilic mesogen‐jacketed liquid crystalline (LC) polymers with a biphenyl side‐chain mesogen containing a carboxylic acid group on one side and an octyloxy group on the other, and the number of methylene units between the biphenyl core and the exterior carboxylic acid group was varied to adjust the mesophases and the amphiphilic nature. The polymers were obtained through conventional radical polymerizations and characterized by a combination of different techniques such as thermogravimetric analysis, differential scanning calorimetry, polarized light microscopy, and X‐ray scattering. The results revealed that the polymer without any methylene spacer, POBP‐0C, did not exhibit LC properties while POBP‐1C (n = 1) and POBP‐7C (n = 7) formed double layer smectic A (S_A) phases. The hydrogen bonding among the carboxylic acid groups and the segregation between the carboxylic acid groups and the alky chains played important roles in forming the mesophases. In addition, the solution self‐assembly behaviors were also preliminarily investigated through the fluorescent probe technique and transmission electron microscopy, and vesicles with uniform sizes were observed. The weak hydrophilicity and large degree of freedom of the carboxylic acid group and the relative rigidity of the polymer chain due to the “jacketing” effect were responsible for the formation of the structures. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Lyotropic liquid‐crystalline behavior of polyisocyanodipeptides

Rigid, helical polyisocyanodipeptides derived from alanine (PIAAs) that form lyotropic liquid‐crystalline (LC) phases in tetrachloroethane are presented. An investigation by optical microscopy between crossed polarizers demonstrated that PIAAs prepared by the polymerization of isocyanodipeptide monomers with an activated tetrakis isocyanide nickel(II) catalyst could form cholesteric LC phases in tetrachloroethane in concentrations between 18 and 30 wt %. Cholesteric LC phases that were formed in solutions of greater than 25 wt % displayed a reversal of the cholesteric helix upon annealing at 50 °C. Diastereomeric PIAA mixtures displayed cholesteric LC behavior only when the PIAAs had the same helix screw sense. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 981–988, 2007     

Side‐chain supramolecular polymers with induced supramolecular chirality through H‐bonding interactions

Side‐chain supramolecular polymers that show columnar mesomorphism have been prepared through H‐bonding interactions between a polyvinylpyridine polymer as H‐acceptor and different H‐donors derived from benzoic acid. These compounds have been designed according to a promesogenic structure, that is, either disk‐like or banana‐like, to promote stacking and therefore the formation of columnar arrangements. IR studies confirmed the formation of H‐bonds and demonstrated that the H‐bond intensity decreases upon increasing temperature. The mesophase organizations were studied by polarized optical microscopy, differential scanning calorimetry, and X‐ray diffraction. Associations containing poly‐3‐methyl‐4‐vinylpyridine showed supramolecular optical activity, as evidenced by circular dichroism studies on thin films. It is proposed that these supramolecular polymers adopt a helical structure that can be biased toward a given handedness by virtue of the configuration of the stereogenic centers in the peripheral tails of the acids. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5528–5541, 2008     

Effect of the tail‐group length and degree of polymerization on the order parameter of side‐chain liquid‐crystalline polymethacrylates containing phenylbenzoate mesogenic groups

The orientation of the side‐chain liquid‐crystalline polymers (LCP) containing phenylbenzoate mesogenic groups in the magnetic field was examined with ²H NMR spectroscopy. The influence of the degree of polymerization as well as the length of the methylene tail group (n = 1–4) have been established. The decrease of the order parameter S of the LCPs with an increased length of the tail group was found. The order parameter S of LCPs does not depend on the degree of polymerization. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2044–2048, 2002     

Interfacial slip at the thermotropic liquid‐crystalline polymer/poly (ethylene naphthalate) interface

The unique rheological properties of a thermotropic liquid‐crystalline polymer (TLCP) were first studied. The thermal and shear history of the TLCP was found to play a critical role in its rheological properties. Crystallites were observed in the TLCP melt even above the melting temperature detected by differential scanning calorimetry. Because interfacial slip had long been suggested as an important reason for viscosity reduction in TLCP/thermoplastic blends, for the first time, interfacial slip at the TLCP/poly(ethylene naphthalate) (PEN) interface was investigated with an energy model. The model quantified the degree of interfacial slip at the TLCP/PEN interface by an energy factor. The calculated energy factors revealed a high degree of interfacial slip at the TLCP/PEN interface. It was proposed that the high rigidity of rodlike TLCP chains and their alignment parallel to the interface prevented mutual entanglements at the TLCP/PEN interface. The lack of mutual entanglements promoted the interfacial slip. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 302–315, 2004     

Liquid‐crystalline thermosets by the curing of dimeric liquid‐crystalline epoxyimine monomers with 2,4‐toluene diisocyanate

We studied the curing processes of several series of dimeric liquid‐crystalline epoxyimine monomers with 2,4‐toluene diisocyanate (TDI) alone or with added catalytic proportions of 4‐(N,N‐dimethylamino)pyridine. We obtained isotropic materials or liquid‐crystalline thermosets with different degrees of order, which depended on the structures of the monomers. To fix ordered networks, we had to do the curing in two steps when TDI was used alone as the curing agent. However, when a tertiary amine was added in catalytic proportions, the ordered networks were fixed in just one step. In this way, we were able to fix both nematic and smectic mesophases. The significance of the polarization of the mesogen for obtaining liquid‐crystalline thermosets was demonstrated. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2521–2530, 2003     

Liquid‐crystalline thermosets from mesogenic dimeric epoxy resins by tertiary amine catalysis

Liquid‐crystalline thermosets (LCTs) were prepared by the curing of difunctional liquid‐crystalline dimeric epoxy monomers with imine moieties in the mesogenic core and central spacers of different lengths. Tertiary amines were used as catalysts in different proportions. The locked mesophases of the LCTs were characterized by polarized optical microscopy and wide‐angle X‐ray scattering and identified as smectic‐C, regardless of their smectic‐A or smectic‐C initial state. The influence of a 7.1‐T magnetic field on the macroscopic orientation of these materials was studied by dynamic mechanical analysis, and the orientation parameter was determined by IR dichroism. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3916–3926, 2002     

Dimeric liquid‐crystalline epoxyimine monomers: Influence of dipolar moments on mesomorphic behavior and the formation of liquid‐crystalline thermosets

We examine some of the structural aspects that influence the mesomorphic behavior of liquid‐crystalline dimeric epoxy resins with imine groups in the mesogens. We synthesized two new series of monomers and compared them with previously synthesized monomers. Compared with previously studied series, the imine group in the new monomers is oriented differently with respect to the ether and ester groups linked to the end of the mesogenic unit. Our results confirmed the importance of polarization of the mesogenic groups and the presence of an ester group in the inner position in the formation of smectic mesophases. By curing with primary and tertiary amines, we demonstrate that these two requirements are necessary if liquid‐crystalline thermosets are to be obtained with different degrees of order. These studies were carried out with differential scanning calorimetry, polarized optical microscopy, and X‐ray diffraction. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1465–1477, 2003     

Photoreactive main‐chain liquid‐crystalline polyesters: Synthesis,characterization, and photochemistry

Three series of semiflexible and rigid main‐chain polyesters containing photoreactive mesogenic units derived from p‐phenylenediacrylic acid (PDA) and cinnamic acid have been synthesized by high‐temperature polycondensation. The thermal and mesomorphic properties of the polymers have been determined. The photochemical behavior of polymer P‐[1]‐T, which contains a PDA unit, has been studied both in solution and in films. In solution, [2+2] photocycloaddition, E/Z photoisomerization, and photo‐Fries rearrangement can take place. In contrast, the dominant process in spin‐coated films is the [2+2] photocycloaddition reaction, which causes crosslinking of the polymer. In films, the photochemistry and induction of anisotropy are strongly influenced by the aggregation of the PDA phenylester unit. A dichroism of about 0.2 has been induced in films by irradiation with linearly polarized UV light, and thus the capability of these films to induce optical anisotropy and align liquid crystals has been demonstrated. Liquid‐crystalline cells have been made with polarized irradiated films of P‐[1]‐T as aligning layers. A commercial liquid‐crystalline mixture has been used for this study, and a similar liquid‐crystalline order determined by polarized Fourier transform infrared to a commercial cell with rubbed polyimide as an aligning layer has been detected. Because of crosslinking of the irradiated P‐[1]‐T photoaligning layer, the photoinduced anisotropy is stable at high temperatures, and the liquid‐crystalline molecules are insoluble in the irradiated polymer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4907–4921, 2005     

Synthesis and crosslinking of a series of dimeric liquid‐crystalline diglycidylester compounds containing imine groups

We used readily available commercial reagents and well‐known procedures to synthesize a series of aromatic imine mesogenic diglycidylester compounds with dimeric architectures. The compounds obtained were characterized by spectroscopic techniques. Their liquid‐crystalline behavior was examined by differential scanning calorimetry, hot‐stage polarized optical microscopy (POM), and wide‐angle X‐ray scattering (WAXS) and related to the different structures that varied in the length of the central spacer. All the compounds exhibited nematic mesophases with the exception of the dimer with a three‐methylene central spacer that did not reveal liquid‐crystalline character. We investigated the crosslinking of the synthesized compounds and obtained liquid‐crystalline thermosets (LCTs) with several primary aromatic diamines in stoichiometric ratios or a tertiary amine as a catalyst. The curing processes were measured by calorimetry, and the thermal stability of the LCTs was evaluated by thermogravimetry. The ordered character of the LCTs was confirmed by POM and WAXS. Finally, the mechanical characterization of the LCTs obtained was examined by dynamic mechanical thermal analysis. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4344–4356, 2002     

Lightly crosslinked,mesomorphic networks obtained through the reaction of dimeric,liquid‐crystalline epoxy–imine monomers and heptanedioic acid

We reacted various dimeric, liquid‐crystalline epoxy–imine monomers, differing in the length of the central aliphatic spacer or the dipolar moments, with heptanedioic acid. The resulting systems showed a liquid‐crystalline phase in some cases, depending on the dimer and on the reaction conditions. The systems were characterized with respect to their mesomorphic properties and then were submitted to dynamic mechanical thermal analysis in both fixed‐frequency and frequency‐sweep modes in the shear sandwich configuration. The arrangement in the liquid‐crystalline phase seemed to be mainly affected both by the polarization of the mesogen and by the reaction temperature, which favored the liquid‐crystalline arrangement when it was lying in the range of stability of the dimer mesophase. In agreement with other recent literature data, dynamic mechanical thermal analysis results suggested that the presence of the mesogen directly incorporated into the main chain increased the lifetimes of the elastic modes both in the isotropic phase and in the liquid‐crystalline phase with respect to side‐chain liquid‐crystalline elastomers and that the time–temperature superposition principle did not hold through the liquid‐crystalline‐to‐isotropic transition. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44:6270–6286, 2006     

Rhythmic growth of ring‐banded spherulites in blends of liquid crystalline methoxy‐poly(aryl ether ketone) and poly(aryl ether ether ketone)

Rhythmic growth of ring‐banded spherulites in blends of liquid crystalline methoxy‐poly(aryl ether ketone) (M‐PAEK) and poly(aryl ether ether ketone) (PEEK) has been investigated by means of differential scanning calorimetry (DSC), polarized light microscopy (PLM), and scanning electron microscopy (SEM) techniques. The measurements reveal that the formation of the rhythmically grown ring‐banded spherulites in the M‐PAEK/PEEK blends is strongly dependent on the blend composition. In the M‐PAEK‐rich blends, upon cooling, an unusual ring‐banded spherulite is formed, which is ascribed to structural discontinuity caused by a rhythmic radial growth. For the 50:50 M‐PAEK/PEEK blend, ring‐banded spherulites and individual PEEK spherulites coexist in the system. In the blends with PEEK as the predominant component, M‐PAEK is rejected into the boundary of PEEK spherulites. The cooling rate and crystallization temperature have great effect on the phase behavior, especially the ring‐banded spherulite formation in the blends. In addition, the effects of M‐PAEK phase transition rate and phase separation rate on banded spherulite formation is discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3011–3024, 2007