Self‐Assembly Behavior and Optical Properties of Poly(3‐thiopheneacetate)/Dialkyldimethylammonium Complexes

Poly(3‐thiopheneacetate)/dialkyldimethylammonium complexes (PTA‐Cn) were prepared by mixing regiorandom poly(3‐thiopheneacetic acid) with dialkyldimethylammonium bromide to study the effect of their self‐assembled structures on the optical properties. The lengths of the alkyl groups in the ammonium salts were varied from decyl (C10) to octadecyl (C18) groups. These complexes showed fully developed layer structures with ordered mesophases. PTA‐C16 and PTA‐C18 with longer alkyl groups showed side‐chain crystalline phases, and PTA‐C10, PTA‐C12, and PTA‐C14 with shorter alkyl groups showed side‐chain crystalline and liquid crystalline phases at room temperature. When PTA‐C18 was heated, a melting transition from side‐chain crystalline to smectic liquid crystalline phase was observed at 41.5 °C. The maximum absorption and emission wavelengths of these complexes increased with increasing alkyl chain length indicating that the π‐conjugated structure of the regiorandom thiophene backbone changes according to the alkyl groups.

     

Self‐Assembly of a Hydrogen‐Bonded Association Chain Liquid Crystalline Polymer (LCP)

A hydrogen‐bonded association chain liquid crystalline polymer (LCP) based on tetraethyleneglycoxy‐bis(2,6‐dimethyl‐4‐benzoic acid) and 4,4′‐(p‐phenylenedi‐1,2‐ethenediyl)bipyridyl in a 1 : 1 stoichiometric ratio was synthesized using melting mixing method. X‐ray scattering from fiber drawn from its nematic phase exhibits preferred orientation, indicating that hydrogen bonding association chain polymer can also be strong enough to withstand the shear or tensile force and could be macroscopically oriented under shear or tensile force. Two complimentary components are likely to form a co‐crystallized structure to form a monoclinic crystal.     

Synthesis and Characterisation of Side‐Chain Liquid Crystalline Poly[1‐({[(4‐cyano‐4′‐biphenyl)oxy]alkyl}oxy)‐2,3‐epoxypropane]

Summary: A new series of side‐chain liquid‐crystal polymers, the poly[1‐({[(4‐cyano‐4′‐biphenyl)oxy]alkyl}oxy)‐2,3‐epoxypropane], has been synthesized in which the spacer length is varied from 2 to 8 methylene units. The synthesis used for the chemical modification of polyepichlorohydrin (PECH) involved the phase transfer catalyzed etherification of the chloromethyl groups with sodium 4‐cyano‐4′‐biphenoxide and lithium n‐(4‐cyano‐4′‐oxybiphenyl)‐alkanoates. All the resulting polymers (except polymers 7 and 8), including that without spacer, characterized by ¹H NMR, and IR, exhibit thermotropic liquid crystalline mesomophism. The thermal behavior of the polymers has been characterized using differential scanning calorimetry (DSC) and polarized light microscopy (POM) equipped with hot‐stage. A more pronounced odd‐even effect in the clearing temperatures is observed on increasing the spacer length in which the odd members display slightly higher values, which were also dependent on the substitution degree of PECH. The flexible PECH chain assists nematic LC formation compared with other more rigid backbone polymers where a smectic phase is often encountered with the same mesogen. A comparison of the thermal properties of the cyanobiphenyl based series reported here. Polyacrylate (PA) and poly(methacrylate)‐based (PMA) SCLCPs containing 4‐cyanobiphenyl as the mesogenic unit are consistent with the general rule that increasing backbone flexibility for a given mesogenic unit and spacer length enhance the clearing temperature. This was not found from the PECH‐based series, which show the lower clearing temperature than the PMA and PA series, even though they have more flexible backbone than PA and PMA series. So the clearing temperature is not solely determined by the flexibility of the backbone.

Schlieren textures of PECHOC2‐B taken at 110 °C (cooling from isotropic phase after annealing 1 h).     

Synthesis,Structure and Properties of Melamine‐Based pTHF‐Urethane Supramolecular Compounds

The properties of melamine based supramolecular compounds have been studied with rheological, thermal, mechanical, dielectric and scattering techniques and compared with similar covalently bonded materials. The complexes are based on a linear pTHF‐diol (M _n = 1 000) connected via a diisocyanate with melamine. The results obtained show that, despite of the material's low molecular weight (< 2 000 g · mol^?1), it has properties typical for high molar mass polymers. The material has a high modulus above the glass transition temperature, and shows behavior similar to a semi‐crystalline material. This is attributed to the presence of the hydrogen bonds, in combination with phase separation giving rise to hard domain formation. In comparison with a covalently bonded and a low molecular weight material of similar composition, the supramolecular compounds have a higher and more temperature dependent viscosity. By exchanging parts of the pTHF with a low molecular weight diol, in our case hexane diol, the mechanical properties at room temperature could be modified to a stiffer but more brittle material.

     

Synthesis and Photoinitiated Polymerization of Nematic Liquid‐Crystalline Diepoxides

Various liquid crystalline bifunctional symmetrically and unsymmetrically substituted diepoxides based on the 4‐(ω‐oxiranyl‐alkoxy)‐benzoic acid 4‐(ω‐oxiranyl‐alkoxy)‐phenyl esters were synthesized. By modification of the length of the flexible alkylene chains, the phase transition temperature from the crystalline into the liquid crystalline state could be adjusted between 40°C and 90°C. The phase transition behavior of the monomers was examined by DSC. These diepoxides are capable to undergo photoinduced polymerization in the presence of a cationic photoinitiator with intramolecular photosensitization in the liquid crystalline phase as well as in the isotropic phase. The photoinduced polymerization was monitored by RTIR. For most monomers the rate constants for polymerization are higher in the liquid crystalline state compared to the isotropic melt. A polymer network with liquid crystalline superstructure is formed if the polymerization of the monomers is carried out in the liquid crystalline phase. No glass‐transition is measurable for the cross‐linked materials, and the gel content is about 96%. Although the polymers are highly cross‐linked, they are not brittle at all.     

Amorphous‐Smectic Glassy Main‐Chain LCPs, 1. Poly(ether esters) Derived from Hydroxybibenzoic Acid and (R,S)‐ and (R)‐2‐Methylpropane‐1,3‐diol

The synthesis and the characterization of main‐chain liquid‐crystalline poly(ether esters), derived from hydroxybibenzoic acid and (R,S)‐ and (R)‐2‐methylpropane‐1,3‐diol, are reported. These polymers show an interesting thermal behavior. They develop mesophases with a slow rate of formation, allowing the easy quenching of the melt into: a) the glassy amorphous state, b) the glassy liquid‐crystalline state, or c) a mixture of both, depending on the thermal treatment. The extent of the transformation and the symmetry of the different phases have been determined by means of calorimetric and X‐ray diffraction methods. Dielectric spectroscopy results provide additional evidence for the detection of distinct glass transitions. The results show that the racemic polymer forms a low‐ordered SmC_alt mesophase, while a more ordered phase is obtained in the case of the enantiomerically pure polymer. The comparison of the properties of the different states evidences the special behavior and properties of the glass transition (T_g) in these polymers. Emphasis is paid to the location of the T_g of the liquid‐crystalline state in comparison to the T_g of the amorphous state. It is found that the glass transition of the SmC_alt glass in R,S‐PBO3 (the poly(ether ester) derived from hydroxybibenzoic acid and (R,S)‐2‐methylpropane‐1,3‐diol) appears at lower temperatures than the glass transition of the amorphous state. However, in R‐PBO3 (the poly(ether ester) derived from hydroxybibenzoic acid and (R)‐2‐methylpropane‐1,3‐diol), where the more ordered phase is present, the glass transition follows the classical tendency of semicrystalline polymers.

     

Crystalline Polymorphism of Alkyl Chains in Supramolecular Complexes of Polyethyleneimine with Octadecanoic Acid

The supramolecular complexes of branched polyethyleneimine and octadecanoic acid (PEI(OA)_x) were prepared via interfacial reaction and homogeneous solution complexation. The binding mode and the crystalline polymorphism of alkyl chains in PEI(OA)_x were investigated by FTIR spectroscopy and WAXS. There are three kinds of OA exist in the complexes, the first one is bound by primary amines through proton transferring, the second one associated with PEI through hydrogen‐bonding, and the third one free OA. The crystal structure of alkyl chains in PEI(OA)_x is different from that of complexes of linear poly(4‐vinylpyridine) and pentadecylphenol reported by G. ten Brinke group.^[1] Hexagonal and orthorhombic and triclinic packing of alkyl chains may occur in PEI(OA)_x with 0.32 ⪇ x ⪇ 4.16 and the hexagonal packing still occurs at high content of OA. The ordered packing of alkyl chains is determined by the binding mode of OA in PEI(OA)_x as well as the specimen‐preparing process.     

An H‐Bonded Main‐Chain Liquid‐Crystalline Polymer Obtained by In Situ Photochemical Conversion from an H‐Bonded LC Dimer

An H‐bonded main‐chain liquid‐crystalline (LC) polymer was obtained by in situ photochemical conversion from an H‐bonded LC dimer. A bifunctional compound, 1 , having a cinnamoyl group at one end and a carboxylic acid group at the other, was synthesized as the H‐bonded LC dimer. UV irradiation of 1 in the LC phase in the presence of a sensitizer resulted in its conversion to a photodimer, with a carboxylic acid at both ends, through photocycloaddition of the cinnamoyl moiety. The LC phase was maintained during irradiation, because that of the photodimer was more thermally stable than that of 1 . FT‐IR analysis revealed that the carboxylic acids of the photodimer dominantly formed hydrogen bonds in the LC phase, which suggests that the photodimers assembled into an H‐bonded main‐chain LC polymer.

     

Thermotropic Phase Behavior of a Liquid‐Crystalline Poly(ether ester) Derived from Hydroxydibenzoic Acid, 2‐Methyl‐1,3‐propanediol and R‐1,3‐Butanediol

The thermotropic phase behavior of a liquid‐crystalline poly(ether ester) derived from 4′‐hydroxybiphenyl‐4‐carboxylic acid and two different spacer diols (2‐methyl‐1,3‐propanediol and R‐1,3‐butanediol) has been analyzed by differential scanning calorimetry, real time synchrotron X‐ray diffraction and solid‐state ¹³C NMR. It has been found that the polymer develops a smectic mesophase that presents order inside the layers. This mesophase has a slow rate of formation, in such a way that it is possible to obtain either an amorphous glass or a liquid‐crystalline glass. These two phases exhibit different and independent glass transition temperatures: 95 °C for the amorphous one and 85 °C for the mesophase. The diffractogram of this mesophase shows two clear diffractions in the wide‐angle region and a long spacing (of low intensity) in the small‐angle region. All those features are characteristic of a mesophase of intermediate order, presumably of the type SmI, in contrast to the low‐ordered SmC_alt mesophase reported for the racemic polymer. Thus, the chirality of the spacer, which provides structural regularity, makes easier the packing of the chains, so that a more ordered mesophase is obtained. In addition, both the solid‐state ¹³C NMR line shapes and the value of are practically the same for the quenched and the annealed samples, indicating that the “ordered” phase obtained by annealing is not a three‐dimensional crystal, thus confirming its assignment as mesophase, with a considerable degree of conformational disorder.

     

Photo‐Tunable Supramolecular Ultrathin Surfaces for Simultaneous Homeotropic Anchoring and Superfast Switching of Liquid Crystals

Photo‐tunable supramolecular ultrathin surfaces functionalized with a soft ultraviolet (UV) treatment of star‐shaped reactive amphiphiles are fabricated to simultaneously afford homeotropic anchoring of liquid crystals (LCs) and improve the LC switching performance. Photochemically functionalized ultrathin surfaces are generated by cross‐linking star‐shaped amphiphilic monomers in the self‐assembled monolayers with retention of cluster structure under electric field. Since these star‐shaped amphiphiles can construct the close‐packed self‐organized molecular layer with an alkyl brush at the interface between indium tin oxide and LCs through intermolecular hydrogen bonding, they might make elegant alignment surfaces for the homeotropic anchoring of LCs to provide a new type of vertical alignment layer. It is experimentally revealed that supramolecular ultrathin layers with vertical nanopillars form hydrophobic surface, and afford a stable and uniform homeotropic alignment of LCs even in high‐temperature environment. Furthermore, a soft UV irradiation on the self‐assembled ultrathin surfaces under electric field yields superfast responsive cross‐linked ultrathin surfaces with low power consumption compared to conventional polyimide layer. Notably, this controlled methodology offers advantages of simplicity, low‐cost, and scalability in the fabrication of functional alignment surfaces without the need of complex manufacturing steps.     

Phase Behaviour of New Side‐Chain Liquid Crystalline Polyoxetanes

Summary: The synthesis and thermal behaviour of two new polyoxetanes with side chains having a dimer structure mesogen‐spacer‐mesogen and a long terminal alkyl group are reported. The two polymers differ in the chemical structure of the central spacer. The polyoxetanes have been obtained by cationic ring‐opening polymerisation of an appropriately substituted oxetane ring. Both polyoxetanes studied exhibit liquid crystalline properties showing a similar sequence of phases. DSC and synchrotron experiments indicate that a highly ordered phase with a probable orthorhombic packing is observed at low temperature. On heating, this phase melts into a mesophase with hexagonal order within the smectic layers, which, on further heating, is transformed into a disordered smectic mesophase.

Synchrotron X‐ray diffraction patterns of one of the poyoxetanes in a heating experiment.     

Facile Synthesis and Solid‐State Properties of Liquid‐Crystalline Polypeptides Bearing Biphenyl Mesogens and Alkyl Tails

A series of liquid‐crystalline 4‐alkyloxybiphenyl‐poly(γ‐propyl‐l ‐glutamate) conjugates (PPLG_n‐g‐BPC_m, n = 10, 54, 110, and 274, m = 4, 6, and 12) with end‐on biphenyl mesogens and variable alkyl tails is synthesized via a facile copper‐mediated alkyne–azide [2+3] 1,3‐dipolar cycloaddition. ¹H NMR and FTIR analyses reveal a quantitative conjugation efficiency for each sample. Variable‐temperature FTIR results indicate an irreversible α‐helical to β‐sheet transition of the PPLG₁₀‐g‐BPC₆ in the solid state, whereas PPLG_n‐g‐BPC_m samples with a longer main‐chain length (n ≥ 54) only adopt an α‐helical conformation in the temperature range between 25 and 200 °C. DSC, polarized optical microscopy (POM), and wide‐angle X‐ray scattering (WAXS) results collectively reveal that the PPLG_n‐g‐BPC_m samples undergo a reversible crystalline to liquid‐crystalline phase transition depending on the main‐/side‐chain lengths. The PPLG_n‐g‐BPC_m (n ≥ 54, m ≤ 6) samples form highly stable smectic (SmC or SmE) phases with a calculated tilt angle of 73–90°.

     

Hydrogen‐Bonding‐Directed Template Synthesis of Novel Stereo‐Regular Organo‐Bridged Ladder‐Like Polymethylsiloxane

A novel stereo‐regular organo‐bridged ladder‐like polymethylsiloxane ( LPMS ) was synthesized by a stepwise coupling polymerization on the basis of an amido H‐bonding‐assisted self‐assembling template. The monomer N,N′‐bis{4‐[3‐(diethoxymethylsilyl)propoxy]‐phenyl}terephthalamide ( M ), prepared by hydrosilylation reaction at high temperature, was hydrolyzed in a dilute solution at a low temperature to form a ladder‐like supramolecular intermediate through amido H‐bonding interactions, which was further condensed to form the polymer LPMS . A combination of techniques including ¹H NMR, ²⁹Si NMR, and FT‐IR spectroscopies X‐ray diffraction (XRD), and differential scanning calorimetry (DSC) were used to characterize the titled polymer LPMS , and the results indicate that the polymer possesses an ordered ladder‐like structure.

²⁹Si NMR spectrum of the polymer LPMS .     

Synthesis and Properties of Side‐Chain Liquid Crystalline Polypeptides Bearing Various Alkyl Spacers and Oligo‐Ethylene‐Glycol Tails

A series of polypeptides bearing various alkyl (i.e., propyl, hexyl, or octyl) spacers, biphenyl mesogens, and oligo‐ethylene‐glycol (OEG) tails (i.e., PPLG₂₆‐BPOEG _m, PHLG₃₄‐BPOEG_m, and POLG₃₂‐BPOEG_m [m = 3 or 7]) has been synthesized via 1,3‐dipolar cycloaddition reactions with quantitative grafting densities. Fourier transform infrared results reveal that the polypeptides adopted an α‐helical conformation in the solid‐state. Differential scanning calorimetry (DSC) analysis reveals that the glass transition temperatures (T_gs) of the polypeptides with OEG₃ tails decrease with the increasing length of the alkyl spacers. For the samples containing alkyl spacers of the same length, T_g significantly decreases with the increasing lengths of the OEG tails. Polarized optical microscope (POM) results reveal that all polypeptides exhibit strong birefringence at room temperature. Polypeptides with long alkyl spacers (i.e., hexyl or octyl) or OEG₇ tails show isotropic transitions, while PPLG₂₆‐BPOEG₃ show no clear point temperature before thermal decomposition. DSC, POM, and wide‐angle X‐ray scattering results collectively reveal that polypeptides with long alkyl spacers (i.e., hexyl or octyl) and OEG₃ tails undergo a reversible smectic E phase to isotropic phase transition, while polypeptides with OEG₇ tails undergo a reversible liquid crystalline phase to isotropic phase transition. The transition temperatures increase with the increasing length of alkyl spacers.

     

Anthraquinone‐Imide‐Based Dimers: Synthesis,Piezochromism, Liquid Crystalline and Near‐Infrared Electrochromic Properties

A series of anthraquinone‐imide‐based dimers, C5*‐AQI‐Si2, C5*‐AQI‐Si3, C5*‐AQI‐Si4, and C5*‐AQI‐Si8, have been prepared by the hydrosilylation of N‐(hex‐5‐enyl)‐6‐(4′‐((S)‐2‐methylbutoxy)phenyl)anthraquinone‐2,3‐dicarboxylic imide and hydride‐terminated siloxanes with different lengths. Their liquid crystalline behaviors, and piezochromic and near‐infrared electrochromic properties have been characterized by DSC, wide‐angle X‐ray diffraction, cyclic voltammetry, and UV–vis–NIR spectroscopy. Although anthraquinone imide is not liquid crystalline by itself, all the dimers formed a smectic A mesophase. Under moderate pressure, the color of the dimers changed from light yellow to deep red. Upon reduction to a radical anionic state, the dimers exhibited an intense NIR absorption at 844 nm. These anthraquinone‐imide‐based dimers are probably the first multifunctional molecules with combined liquid crystalline, mechanochromic, and NIR electrochromic properties.

     

Unsaturated Polyamides from Bio‐Based Z‐octadec‐9‐enedioic Acid

A series of polyamides based on Z‐octadec‐9‐enedioic acid, a bio‐based unsaturated monomer, and aliphatic‐, cycloaliphatic‐, or benzylic diamines were synthesized and characterized by ¹H and ¹³C NMR analysis, size exclusion chromatography (SEC), DSC, and dynamic‐mechanical analysis (DMA). The high reaction temperature (250 °C) did not lead to the degradation of diacid unit double bonds and unsaturated polyamides were obtained. The aliphatic unsaturated polyamides are semi‐crystalline polymers of high molar mass, relatively flexible at room temperature. The cycloaliphatic unsaturated polyamides are semi‐crystalline or amorphous, present higher melting and glass transition temperatures and are much more rigid. The aliphatic and aliphatic–aromatic unsaturated polyamides present lower T_g and T_m as compared to their parent saturated polymers.

     

A Liquid‐Crystalline Co‐Polysiloxane with Asymmetric Bent Side Chains

A co‐polysiloxane has been prepared with an asymmetric bent side group based on a liquid‐crystalline monomer showing a B₂ (SmCP) phase. In order to dilute the side chain mesogens along the polymer backbone, octyl side chains were also incorporated. X‐ray studies confirmed that the resulting co‐polysiloxane exhibits a liquid‐crystalline layered phase, the siloxane polymer chains being microphase segregated from the incompatible side chain mesogens. The mesophase of polymer exhibits a homeotropic structure that can be successfully aligned by unidirectional shear. This phase does not exhibit polar switching under an applied electric field unlike the bent‐core monomer used as the side chains of this polymer. This can be caused by the homeotropic alignment of the polymer samples.

     

Investigation of the Interpolymer Complex between Hydroxypropyl Cellulose and Maleic Acid‐Styrene Copolymer, 1

Summary: The hydrogen bonding‐interpolymer association of hydroxypropyl cellulose (HPC) with maleic acid‐styrene (MAc‐S) copolymer has been investigated in dilute aqueous solution by viscometry, turbidimetry and potentiometry. At a mixing ratio between MAc‐S and HPC of 10:90, the solution exhibits a phase separation upon heating, while for other mixing ratio no phase separation could be detected. The stability of the interpolymer complex (IPC) increases as the temperature rises. The stoichiometry of the IPC, in mole units, was estimated as being MAc‐S:HPC = 5:2. The thermodynamic functions (enthalpy and entropy) of the complexation process have been determined.

Dependence of IPC concentration in H₂O/MAc‐S/HPC system on the mole fraction of MAc‐S in polymer mixture at different temperatures.     

Formation of Macrocycles in the Synthesis of Poly(N‐(2‐ethylhexyl)carbazol‐3,6‐diyl)

A series of polymerizations of 3,6‐dibromo‐9‐(2‐ethylhexyl)carbazole was carried out in different monomer concentrations using standard Yamamoto reaction conditions. It was found that the molecular weight of the resulting poly(N‐(2‐ethylhexyl)carbazol‐3,6‐diyl) strongly depends on the monomer concentration in the reaction mixture. Matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) measurements confirmed the formation of low‐molar‐mass cyclic oligomers of the 3,6‐disubstituted carbazole. In this paper we describe, for the first time, the formation of large amounts of a cyclic tetramer and of higher macrocycles in the synthesis of poly(N‐alkyl‐3,6‐carbazoles) by the Yamamoto method. This seems to be a limiting factor in the synthesis of high molecular weight poly(N‐alkyl‐3,6‐carbazole)s. The optical, thermal, and electrochemical properties of poly(N‐(2‐ethylhexyl)carbazol‐3,6‐diyl) have been investigated. Poly(N‐(2‐ethylhexyl)carbazol‐3,6‐diyl) is thermally stable, with 5% weight loss at 460 °C in nitrogen. The polymer exhibits a weak blue fluorescence with a maximum at 425 nm. Poly(N‐(2‐ethylhexyl)carbazol‐3,6‐diyl) is electrochemically stable, its highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels are ?5.0 and ?1.6 eV, respectively.

     

Functional Photochromic Methylhydrosiloxane‐Based Side‐Chain Liquid‐Crystalline Polymers

A new azobenzene‐group‐containing monomer and several respective functional side‐chain polymers grafted on a methylhydrosiloxane backbone (with two different degrees of poly­merization; with and without the addition of a photoreactive benzophenone derivative) are designed, synthesized, and characterized. The resulting materials clearly show self‐assembly behavior and possess a nematic liquid‐crystal phase over a broad temperature range, which extends below 0 °C. The optical properties of these new photo­chromic liquid‐crystalline materials are determined from the absorbance spectra of oriented samples and by photo­induced birefringence studies. The results indicate a considerable dichroism of the side‐chain liquid‐crystalline polymers (SCLCPs), and hence demonstrate their potential applicability for optical storage.