Liquid‐crystalline thermosets from liquid‐crystalline epoxy resins containing bisazomethinebiphenylene mesogens in the central core: Copolymerization with a nonmesomorphic epoxy resin

A new series of liquid‐crystalline epoxy resins was synthesized, and their mesomorphic behavior was investigated with differential scanning calorimetry, polarized optical microscopy, and wide‐angle X‐ray scattering. These glycidylic compounds had central aromatic imine mesogens derived from benzidine and aliphatic spacers of up to 10 methylene units that linked the mesogens to the glycidylic groups. Crosslinking these monomers with primary aromatic diamines led to nematic networks, some of which contained crystal inclusions. However, through curing with tertiary amines as catalytic agents or through copolymerization with different proportions of the nonmesomorphic epoxy monomer and primary amines as crosslinking agents, smectic C organized thermosets were prepared when the spacers had at least four methylene carbons. When they had fewer than four, the networks were nematic. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3631–3643, 2004     

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     

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     

Anisotropic thermosets from liquid‐crystalline azomethynic epoxy resins and primary aromatic diamines

Novel epoxy‐terminated monomers based on imine groups were synthesized and their mesogenic properties studied. Aliphatic spacers of different lengths were introduced between the rigid unit and the glycidylic group, and their liquid‐crystalline behavior was examined. They were reacted with primary aromatic diamines inside a magnetic field so that the formation of anisotropic networks could be investigated. The influence of curing conditions and the structure of monomers and amines on the formation of liquid‐crystal thermosets were investigated. Thermosets with locked nematic textures were obtained in all cases. The influence of a 7.1 T magnetic field on the macroscopic orientation of these materials was studied, and mechanical properties of the resulting networks were evaluated by dynamic mechanical analysis. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1–12, 2003     

New liquid‐crystalline thermosets from liquid‐crystalline bisazomethynic epoxy resins with naphthylene disruptors in the central core

We synthesized novel epoxy‐terminated monomers on the basis of imine groups with spacers of different lengths between mesogens and reactive groups and examined their mesogenic properties. Their reaction with primary aromatic diamines and tertiary amines was carried out to investigate the formation of liquid‐crystalline thermosets. We explored how the curing conditions and the structures of the monomers and amines affected the formation of ordered networks. The special symmetry of a 1,5‐disubstituted naphthalene unit in the central core led to nematic mesophases in the pure liquid‐crystalline epoxy resins, and thermosets with locked nematic textures were obtained in all cases, regardless of the length of the spacer. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1536–1544, 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     

Synthesis and crosslinking of biphenyl and naphthalene liquid‐crystalline polyethers with pendant full‐saturated and vinyl‐terminated aliphatic chains

Two series of vinyl‐terminated, side‐chain liquid‐crystalline polyethers containing 4,4′‐biphenyl and 2,6‐naphthalene moieties as mesogenic cores with several contents of vinyl crosslinkable groups were synthesized by chemically modifying poly(epichlorohydrin) with mixtures of saturated and vinyl‐terminated mesogenic acids. In most cases the degree of modification was over 90%. The polymers were characterized by chlorine analysis, IR and ¹H and ¹³C NMR spectroscopies, viscometry, size exclusion chromatography/multi‐angle laser light scattering, and thermogravimetric analysis. The liquid‐crystal behavior of all the synthesized 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, which generally led to liquid‐crystal elastomers. The mesophase organization was maintained on the crosslinked materials, as confirmed by POM and X‐ray diffraction. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3384–3399, 2003     

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     

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     

Fracture toughness and fracture mechanism of liquid‐crystalline epoxy resins with different polydomain structures

Liquid‐crystalline (LC) epoxy resins were cured at different temperatures to obtain polydomain LC phase–cured resins. The cured resins had polydomain structures with a nematic LC phase and their domain diameters differed depending on the curing temperatures. The relationship between the domain diameter and fracture toughness of the diglycidyl ether of terephthalylidene‐bis‐(4‐amino‐3‐methylphenol) (DGETAM)/m‐phenylenediamine (m‐PDA) systems with the nematic phase and the previously reported smectic LC phase structures was investigated. It was clarified that the highly ordered LC structure (smectic phase) in each domain could improve the fracture toughness. In addition, the changes in the network orientation of the DGETAM/m‐PDA systems were evaluated by a mapping of the microscopic infrared dichroism in the fracture process and their toughening mechanism was suggested. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Synthesis and characterization of liquid‐crystalline epoxy and its blend with conventional epoxy

Terephthaloyl chloride was reacted with 4‐hydroxy benzoic acid to get terephthaloylbis(4‐oxybenzoic) acid, which was characterized and further reacted with epoxy resin [diglycidyl ether of bisphenol A (DGEBA)] to get a liquid‐crystalline epoxy resin (LCEP). This LCEP was characterized by Fourier transform infrared spectrometry, ¹H and ¹³C NMR spectroscopy, differential scanning calorimetry (DSC), and polarized optical microscopy (POM). LCEP was then blended in various compositions with DGEBA and cured with a room temperature curing hardener. The cured blends were characterized by DSC and dynamic mechanical analysis (DMA) for their thermal and viscoelastic properties. The cured blends exhibited higher storage moduli and lower glass‐transition temperatures (tan δ_max, from DMA) as compared with that of the pure DGEBA network. The formation of a smectic liquid‐crystalline phase was observed by POM during the curing of LCEP and DGEBA/LCEP blends. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3375–3383, 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     

Novel side‐chain liquid‐crystalline polyimide for film materials

A novel side‐chain liquid‐crystalline polyimide (SLCPI) was prepared via copolycondensation from 3,5‐diamino‐benzonic‐4′‐biphenyl ester, 4,4′‐diamino‐ biphenyl ether, and 3,3′,4,4′‐oxydiphthalic dianhydride. The energy‐minimized structure and liquid crystallinity of SLCPI were investigated by molecular modeling, differential scanning calorimetry (DSC), wide‐angle X‐ray scattering, and polarized optical microscopy, respectively. The results indicated that this polyimide (PI) with side‐chain mesogenic units exhibited a nematic NI phase. Because of the in situ self‐reinforcement of side‐chain mesogenic units, the improved tensile strength and modulus of PI films reached 270% and 300%, respectively. The coefficient of thermal expansion of films decreased by 40%. DSC and thermogravimetric analyses indicated that the phase‐transition temperature of SLCPI was above 240 °C, and the 5% weight‐loss temperature was above 520 °C. Moreover, copolycondensation of two diamines with dianhydride and incorporation of pendent mesogenic units diminished the regularity and symmetry of main chains; as a result, SLCPI exhibits good film processability. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 554–559, 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     

Vinyl‐terminated side‐chain liquid‐crystalline polyethers containing mesogenic benzylideneaniline moieties

The synthesis of two vinyl‐terminated side‐chain liquid‐crystalline polyethers containing benzylideneaniline moieties as mesogenic cores was approached in two different ways: by chemically modifying poly(epichlorohydrin) with suitable mesogenic acids or by polymerizing analogous glycidyl ester or glycidyl ether derivatives. In all the conditions tested, the first approach led to materials in which the imine group was hydrolyzed. The second approach led to the desired polymers PG2a and PG2b , but only from the glycidyl ether derivatives and when the initiator was the system that combined polyiminophosphazene base t‐Bu‐P₄ and 3,5‐di‐t‐butylphenol. These polymers were chemically characterized by IR and ¹H and ¹³C NMR spectroscopies. The estimated degrees of polymerization ranged from 30 to 36. The liquid crystalline behavior of the synthesized polymers was studied by differential scanning calorimetry, polarized optical microscopy (POM) and X‐ray diffraction. Both polymers behave like liquid crystals and exhibited a single mesophase, which was recognized as a smectic C mesophase, probably with a bilayer arrangement, i.e., a smectic C₂ mesophase. The crosslinking of both polymers was performed with dicumyl peroxide as initiator, which led to liquid crystalline thermosets. POM and X‐ray diffraction confirmed that the mesophase organization mantained on the crosslinked materials. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1877–1889, 2006     

Synthesis and characterization of new segmented polyurethanes with side‐chain,liquid‐crystalline chain extenders

Liquid‐crystalline, segmented polyurethanes with methoxy–biphenyl mesogens pendant on the chain extender were synthesized by the conventional prepolymer technique and esterification reaction. Two, side‐chain, liquid‐crystalline (SCLC) polyurethanes with mesogens having spacers of six and eight methylene units were prepared. The structures of the mesogenic units and SCLC polyurethanes were confirmed by Fourier transform infrared spectroscopy and ¹H NMR. Polymer properties were also examined by solubility tests, water uptakes, and inherent viscosity measurements. Differential scanning calorimetry studies indicated that the transition temperature of the isotropic to the liquid‐crystalline phase decreased with increasing spacer length. Wide‐angle X‐ray diffraction (WAXD) studies revealed the existence of liquid‐crystalline phases for both SCLC polyurethanes. Polarized optical microscopic investigations further confirmed the thermotropic liquid‐crystalline behaviors and nematic mesophases of both samples. Thermogravimetric analysis displayed better thermal stabilities for both SCLC polymers and indicated that the presence of mesogenic side chains may increase the thermal stability of segmented polyurethanes. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 290–302, 2004     

Synthesis of a novel hybrid liquid‐crystalline rod–coil diblock copolymer

A series of novel rod–coil diblock copolymers on the basis of mesogen‐jacketed liquid‐crystalline polymer were successfully prepared by atom transfer radical polymerization from the flexible polydimethylsiloxane (PDMS) macroinitiator. The hybrid diblock copolymers, poly{2,5‐bis[(4‐methoxyphenyl)oxycarbonyl]styrene}‐block‐polydimethylsiloxane, had number‐average molecular weights (M_n's) ranging from 9500 to 30,900 and relatively narrow polydispersities (≤1.34). The polymerization proceeded with first‐order kinetics. Data from differential scanning calorimetry validated the microphase separation of the diblock copolymers. All block copolymers exhibited thermotropic liquid‐crystalline behavior except for the one with M_n being 9500. Four liquid‐crystalline diblock copolymers with PDMS weight fractions of more than 18% had two distinctive glass‐transition temperatures. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1799–1806, 2003     

Development of the morphology and crystalline state due to hybridization of reinforced toughened nylon containing a liquid‐crystalline polymer

A hybrid composite consisting of rubber‐toughened nylon‐6,6, short glass fibers, and a thermotropic liquid‐crystalline polymers (LCP) was investigated by the LCP content being varied. The thermal behavior, morphology, and crystallization behavior due to hybridization were studied by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and wide‐angle X‐ray scattering (WAXS). DSC results indicated that the crystallinity of the glass‐fiber‐reinforced toughened nylon‐6,6 was reduced by LCP addition, particularly 5–10 wt % LCP. DMA data showed that the miscibility between the blended components was maximum at the 5 wt % LCP composition, and the miscibility decreased with increasing LCP content. SEM photomicrographs revealed information consistent with the thermal behavior on miscibility. It was also observed that the 10 wt % LCP composition showed predominantly an amorphous character with FTIR and WAXS. WAXS results indicated that LCP hybridization increased the interplanar spacing of the hydrogen‐bonded sheets of the nylon crystals rather than the spacing between the hydrogen‐bonded chains. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 549–559, 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     

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