Fully Liquid-Crystalline ABA Triblock Copolymer of Fluorinated Side-Chain Liquid-Crystalline A Block and Main-Chain Liquid-Crystalline B Block: Higher Order Structure in Bulk and Thin Film States

Fully liquid-crystalline (LC) ABA-type triblock copolymers were synthesized by atom transfer radical polymerization; the A block was a fluorinated side-chain LC polymer, PFA-C₈, and the B block was a main-chain LC polyester, BB-5­(3-Me). The volume fraction of the A block (φ_A) was 0.11–0.70, and the B block had a constant molecular weight. Nanometer-scale segregated structures in the bulk and thin film states were investigated by synchrotron X-ray diffraction (XRD) in transmission and grazing-incidence (GI) geometries to examine the effect of competition between the LC orientation and polymer chain dimensions on the morphology. When φ_A is 0.11, matching of the mesogen orientation in the A and B blocks dominates the main-chain orientation, whereas when φ_A exceeds 0.28, matching of the lateral dimensions of the A and B blocks dominates the mesogen orientation, although all the polymers showed lamellar structure before isotropization of BB-5­(3-Me). GI-XRD revealed that the lamellar structure in the thin film with φ_A = 0.70 was completely perpendicular to the Si substrate without surface modification or solvent annealing

Synthesis and Postfunctionalization of Rod–Coil Diblock and Coil–Rod–Coil Triblock Copolymers Composed of Poly(3-hexylthiophene) and Poly(4-(4′‑<i>N</i>,<i>N</i>‑dihexylaminophenylethynyl)styrene) Segments

Poly­(3-hexylthiophene) (P3HT) with a bromobutyl functional group at the ω-chain-end (P3HT-C₄Br) and P3HT with bromobutyl functional groups at the α,ω-chain-ends (BrC₄-P3HT-C₄Br) were synthesized by selecting the appropriate initiators for the Grignard metathesis (GRIM) polymerization. The high end-functionality was confirmed by matrix assisted laser desorption-ionization time-of-flight (MALDI–TOF) mass spectrometry. These polymers were efficiently reacted with the living anionic polymers of 4-(4′-<i>N</i>,<i>N</i>-dihexylaminophenylethynyl)­styrene (DHPS) to yield novel rod–coil diblock and coil–rod–coil triblock copolymers composed of rigid P3HT and flexible poly­(4-(4′-<i>N</i>,<i>N</i>-dihexylaminophenylethynyl)­styrene) (PDHPS) segments. The expected structures of the block copolymers were confirmed by size exclusion chromatography (SEC), proton nuclear magnetic resonance (¹H NMR), and Fourier transform infrared (FT-IR) spectroscopies. Furthermore, the side chain alkynes of the PDHPS segments of both P3HT-<i>b</i>-PDHPS and PDHPS-<i>b</i>-P3HT-<i>b</i>-PDHPS were quantitatively functionalized by a [2 + 2] cycloaddition followed by a cycloreversion with tetracyanoethylene (TCNE), producing the corresponding block copolymers with donor–acceptor moieties in the flexible polystyrene segments. The formation of the new chromophores was confirmed by UV–vis spectroscopy and cyclic voltammetry (CV), which revealed strong intramolecular charge-transfer bands and redox activities ascribed to the formed donor–acceptor moieties. The thermal properties and surface morphology of the block copolymers were also evaluated by differential scanning calorimetry (DSC), atomic force microscopy (AFM) observations, and small-angle and wide-angle X-ray scattering (SAXS and WAXS). This is the first report about the development of P3HT-based block copolymers with tunable optoelectronic properties, which was achieved by the combined synthetic techniques of the GRIM polymerization, living anionic polymerization, and click postfunctionalization

Highly birefringent polymer films from the photo-crosslinking polymerisation of bistolane-based methacrylate monomers

<div><p>The photo-polymerisation of mixtures of mono- and di-methacrylates, containing a bistolane moiety with a central fluorine-substituted benzene ring, resulted in the formation of highly birefringent polymer films (Δ<i>n</i> = 0.40), which were obtained in a nematic liquid crystal (NLC) phase. While the dimethacrylate forms enantiotropic NLCs at <i>T</i> = 110–138°C, smectic phases at <i>T</i> = 50–138°C and crystallises at <i>T</i> = 50°C, whereas the monomethacrylate forms NLCs at a wider temperature range (<i>T</i> = 98–185°C) and crystallises at a lower temperature (<i>T</i> = 98°C). These methacrylates were infinitely miscible and a 20/80 (w/w) mixture of the dimethacrylate/monoacrylate was able to form an NLC phase over a broad temperature range (<i>T</i> = 73–179°C). The mixed NLC phase exhibited a Δ<i>n</i> value of 0.36, even though the Δ<i>n</i> values of the mono- and di-methacrylates were determined as 0.35 and 0.25, respectively, suggesting that the Δ<i>n</i> of the mixture follows an additivity rule. Furthermore, the Δ<i>n</i> of the NLC phase could be increased to 0.40 by photo-polymerisation.</p></div

Thermal Diffusivity of Hexagonal Boron Nitride Composites Based on Cross-Linked Liquid Crystalline Polyimides

Hexagonal boron nitride (h-BN) composites with the oriented cross-linked liquid crystalline (LC) polyimide have been developed as high thermally conductive materials. Well-dispersed h-BN composite films were obtained, as observed by scanning electron microscopy. The morphology of the composite films was further investigated in detail by the wide-angle X-ray diffraction. The obtained composite films based on the cross-linked LC polyimide showed that the polymer chains vertically aligned in the direction parallel to the films, while those based on the amorphous polyimide showed an isotropic nature. Moreover, the alignment of the cross-linked LC polyimides was maintained, even after increasing the volume fraction of h-BN. This alignment plays an important role in the effective phonon conduction between h-BN and the matrices. Indeed, the thermal diffusivity in the thickness direction of the composite films based on the LC polyimide measured by a temperature wave analysis method was increased to 0.679 mm² s^–1 at a 30 vol % h-BN loading, which was higher than that based on the amorphous polyimide

Halogen Substitution Effects on the Molecular Packing and Thin Film Transistor Performances of Carbazoledioxazine Derivatives

Solution-processable carbazoledioxazine derivatives with different halogen substituents (F, Cl, and Br) were newly synthesized by condensation and subsequent cyclization reactions. The chemical structures were confirmed by ¹H NMR and IR spectroscopies as well as MALDI-TOF mass spectrometry. All three carbazoledioxazines possessed a high thermal stability with decomposition temperatures exceeding 270 °C and exhibited thermal transitions upon heating. The phases were characterized by their wide-angle X-ray diffraction patterns at various temperatures. In addition, the energy levels of the carbazoledioxazines were estimated from the optical absorption spectra and electrochemical redox potentials of the thin films. All three derivatives displayed more or less the same energy levels: highest occupied molecular orbitals (HOMOs) of −5.3 eV and lowest unoccupied molecular orbitals (LUMOs) of −3.5 ∼ −3.6 eV. Despite this fact, the Br derivative showed higher hole mobilities with the maximum mobility of 4.9 × 10^–3 cm² V^–1 s^–1 in the thin film transistors as compared to those of the counter F and Cl derivatives. This was attributed to the bimodal carrier pathways formed through the monoclinic molecular orientation of the Br derivative, revealed by grazing-incidence X-ray diffraction (GIXRD) measurements

Extended Chain Lamella Formation Characteristics of Main-Chain Smectic Liquid Crystalline Copolyesters Comprising Different Length Units

A series of liquid crystal (LC) PB-8/12 copolyesters have been synthesized from 4,4′-biphenol with sebacic acid and tetradecanedioic acid, and their LC structures and morphologies have been examined. The copolyesters formed smectic I (SmI) LCs similarly as to the corresponding PB-8 and PB-12 homopolyesters; however, dissimilarity of the comonomer lengths decreased the smectic layer order while sustaining the hexagonal order in the lateral packing of the chains. The SmI LCs consisted of 100-nm-thick lamellae stacked along the polymer chain direction. The lamella thicknesses are more than two times greater than the thicknesses of the homopolyesters and comparable to or greater than the chain contour lengths, indicating the formation of extended chain lamellae

Self-Assembly of Hierarchical Structures Using Cyclotriphosphazene-Containing Poly(substituted methylene) Block Copolymers

The cyclotriphosphazene-substituted diazoacetate homopolymer (polyPNDA′) (PNDA′ = hexaphenoxy-substituted phosphazene-containing methylene) and a novel poly­(substituted methylene) block copolymer, polyPNDA′-<i>block</i>-poly­(hexyloxycarbonylmethylene) (polyPNDA’-<i>b</i>-polyHDA′), were synthesized, and the self-assembly behavior of these polymers was studied in detail. A hexagonally packed aggregated structure was observed in the self-assembled structure of polyPNDA′, whereas a lamellar structure was observed in the microphase-separated nanoassembly of polyPNDA′-<i>b</i>-polyHDA′. These results indicate that a hierarchical structure composed of highly regular polyPNDA′ nanoaggregates and the long-range microphase-separated polyPNDA′ and polyHDA′ domains had formed

Thermotropic Behavior of Syndiotactic Polymethylenes with ω‑[4‑(<i>trans</i>-4-Pentylcyclohexyl)phenoxy]alkyloxycarbonyl Side Chains

A series of syndiotatic P5CP<i>n</i> polymethylenes was prepared with 4-(trans-4-pentylcyclohexyl)­phenoxy moieties linked to each backbone carbon atom via an alkyloxycarbonyl spacer and with even numbers of alkyl carbons <i>n</i> ranging from 2 to 14, and their thermotropic behaviors were investigated. The P5CP<i>n</i>, except P5CP2, formed smectic phases in which the rod-like polymethylene backbones were arranged in rectangular lattices, and the side-chain mesogens were aggregated into layers parallel to the shorter sides of the rectangular lattices. The packing of the mesogens changed with decreasing temperature from smectic C-like to smectic I-like (SmI-like) for <i>n</i> = 4–8 and from smectic A-like to SmI-like for <i>n</i> = 10–14. In the SmI-like phases, each mesogen along the main-chain axis was connected to every sixth backbone carbon atom, revealing a correlation between the packing of the mesogens and the main-chain conformation of a 3/2 helix. Conversely, P5CP2 formed a smectic phase with the main chains arranged in rows and with the mesogens barely aggregated into layers due to the short spacers