Synthesis of novel polypyromellitimides with n‐alkyloxy side chains and their liquid‐crystal aligning property

New well‐defined brush polypyromellitimides with n‐octyloxy and n‐dodecyloxy side chains were prepared by two‐step polycondensations of 3,6‐di(n‐alkyloxy)pyromellitic dianhydrides with various conventional aromatic diamines. Their structures and properties were investigated and compared with those of polyimides without the side chains. The alkyloxylated poly(amic acid)s had inherent viscosities of 0.45–1.09 dL/g. The polyimides showed enhanced solubility in organic solvents and had layered structures in the solid state. As the side‐chain length increased from n‐octyloxy to n‐dodecyloxy, the extent of layered structure formation increased, whereas the glass‐transition temperature and thermal resistance decreased. As for the liquid‐crystal (LC) aligning ability measured with 4‐n‐pentyl‐4′‐cyanobiphenyl on rubbed thin‐film surfaces, all the side‐chain polyimides revealed homogeneous LC alignment parallel to the rubbing direction with distinctively higher pretilt angles than those of the polyimides without the side chains. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3130–3142, 2004     

Phase behavior and elastic properties of a slightly crosslinked liquid crystalline main-chain polymer

A liquid crystalline main-chain polymer was slightly crosslinked by a reaction with, -difunctionalized oligo-siloxanes. Crosslinking does not disturb the liquid crystalline phases, which are identified by x-ray measurements as smecticB and smecticA phases. Measurements of the elastic properties of the crosslinked sample show rubber-like elasticity, even in the liquid crystalline phases. A difference of 7 K was found between cooling and heating for the smecticA/isotropic transition from DSC and mechanical measurements.     

Synthesis and characterization of rigid‐chain liquid–crystalline polymers containing laterally attached side rods

A series of rigid‐chain polymers containing different concentrations of laterally attached side rods was synthesized. These polymers exhibited liquid crystallinity even up to a maximum side rod concentration of 20 mol %. The crystallinity of the polymers, however, decreased with an increase in the side‐rod concentration. These polymers had lower dielectric constants compared with their parent polymers, that is, similar polymers, but without laterally attached side rods. A dielectric constant of 2.6 can be achieved by incorporating 10 mol % of laterally attached side rods, which is 0.5 lower than that of its parent polymer. The reduction of dielectric constant may be attributed to low crystallinity as well as the less dense packing structure of the polymers induced by the incorporation of laterally attached side rods. This series of polymers also had good thermal stability. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1288–1294, 2001     

Thermal properties and fracture toughness of a liquid‐crystalline epoxy resin cured with an aromatic diamine crosslinker having a mesogenic group

A mesogenic‐type curing agent was synthesized to introduce a mesogenic group not only into epoxy resin backbones but also into the crosslink units. In the mesogenic curing agent system, the domain size became larger, and the network arrangement in each domain existed to a greater extent than that in a system cured with the ordinary diamine curing system according to the evidence from polarized optical micrographs and polarized Fourier transform infrared mapping measurements. Moreover, the fracture toughness of the system was considerably improved. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2486–2494, 2006     

Liquid crystalline main chain polymers with a poly(p-phenyleneterephthalate) backbone. 2. Fiber spinning and mechanical properties of polyesters with alkoxy side chains

Fiber spinning and mechanical properties of four rigid polyesters with alkoxy substituents of different length and placement were evaluated. Properties of oriented fibers from the polymer with dodecyloxy substituents on the terephthalate moiety, PTA12HQ, were significantly affected by the crystal modification. At room temperature the following properties (tensile modulus E, tensile strength σ_b, and strain at break ε_b) could be obtained: E = 9.5 GPa, σ_b = 85 MPa and ε_b = 1.1% for phase L_f (the “frozen in layered mesophase”); E = 10.4 GPa, σ_b = 59 MPa and ε_b = 0.6% for modification A; E = 17.3 GPa, σ_b = 158 MPa and ε_b = 1.2% for modification B. Because of the higher amount of main chains per cross sectional area the polymer with hexyloxy side chains, PTA6HQ, showed better properties at a comparable degree of molecular orientation: E = 24 GPa, σ_b = 270 MPa, ε_b = 1.4%. Fibers obtained from the polyester with dodecyloxy substituents on the hydroquinone moiety, PTAHQ12, were too brittle to handle. The polyester with dodecyloxy substituents on both moieties, PTA12HQ12, was spun from the isotropic melt. Because of the obtained low degree of orientation, properties (E = 1 GPa, σ_b = 40 MPa, and ε_b = 6.3%) were governed by interactions between the chains (the main chains are not load-bearing). © 1993 John Wiley & Sons, Inc.     

Supramolecular hydrogen-bonded liquid–crystalline polymer complexes. Design of side-chain polymers and a host–guest system by noncovalent interaction

Supramolecular liquid–crystalline polymeric complexes based on a backbone that contains vinyl pyridine units and azobenzene or biphenyl derivatives that posses alkyl chains terminated by carboxylic acid have been obtained by the formation of intermolecular hydrogen bonds between the carboxylic acid and the pyridyl moieties. The polymeric complexes behave as side-chain liquid–crystalline polymers and exhibit smectic phases. A new type of H-bonded host-guest liquid–crystalline system is also reported. The liquid–crystalline host copolymers contain both mesogenic acrylate and 4-vinylpyridine units. The guest molecule is an azobenzene that has a carboxylic acid moiety at one of its extremities. The H-bonded polymeric host–guest complexes exhibit nematic phases. Sequential UV and visible light irradiation of the polymeric complex causes reversible photochemically induced phase transitions. The isothermal nematic–isotropic and isotropic–nematic transitions result from the trans-cis and cis-trans photoisomerization of the guest azobenzene in the host–guest system. © 1996 John Wiley & Sons, Inc.     

Liquid crystalline main chain polymers with a poly(p-phenylene-terephthalate) backbone: 7. Thermal expansion of oriented films of the polyester with dodecyloxy side chains

The linear thermal expansion coefficients of oriented films of poly(p-phenylene-2,5-didodecyloxy-terephthalate) in the three structures B, A, and L_f are reported. The results are interpreted in terms of a molecular laminate model in which the rigid main-chain layers are separated by the aliphatic side chains. In a film oriented unidirectionally the rigid mainchain layers provide a negative contribution to the thermal expansion coefficient, while the side chains supply a positive contribution. Therefore, the resulting expansion coefficient α depends on the details of the main- and side-chain packing and low-temperature values between α = +0.3 × 10^?5 K^?1 (A and L_f and α = ?1.2 × 10^?5 K^?1 (B) are found in highly oriented films. Measurements on undrawn films are in accordance with the molecular laminate model. © 1994 John Wiley & Sons, Inc.     

Synthesis and properties of photochromic liquid‐crystalline copolymers containing both spironaphthoxazine and cholesteryl groups

Photochromic liquid‐crystalline copolymers consisting of a photochromic monomeric unit containing both a spironaphthoxazine group and an undecamethylene spacer, and a liquid‐crystalline monomeric unit containing both a cholesteryl group and a decamethylene spacer were prepared to investigate the effect of the thermal properties of the photochromic monomeric unit on the mesomorphic order of the side chain of the related copolymers. The photochromic liquid‐crystalline copolymers containing a photochromic liquid‐crystalline monomeric unit showed only a smectic phase. On the other hand, the photochromic liquid‐crystalline copolymers containing a photochromic non‐liquid‐crystalline monomeric unit showed a chiral nematic phase (cholesteric phase). The photochromic chiral nematic liquid‐crystalline copolymer containing 14 mol % photochromic monomeric unit reflected visible light around 104 °C. To lower the temperature range of reflection of visible light, cholesteryl oleyl carbonate was used as a chiral nematic plasticizer for the photochromic chiral liquid‐crystalline polymer systems. Photo‐induced pitch change of the mixture by means of UV irradiation was investigated and it was concluded that the pitch change observed under UV irradiation was mainly induced by thermal effect in the case of our system. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 887–894, 2000     

Kinetics of orientation of a side-chain liquid–crystal polymer as measured by a high-temperature SQUID-magnetometer

A superconducting quantum interference device (SQUID) magnetometer suitable for measurements of the magnetic susceptibility up to 600 K has been used to follow the kinetics of realignment in the nematic phase of a side-chain liquid–crystal polymer. Experiments are performed using monodomain and polydomain samples. Results obtained in monodomain samples are in quantitative agreement with the prediction of the continuum theory up to an angle of approximately 60°. Experiments conducted at higher starting angles give clear indication of backflow effects. Data obtained from experiments on polydomain samples have been compared with model calculations using the data on the monodomain samples. This comparison leads to the conclusion that in this case backflow effects play an important role, too. All results show that SQUID magnetometry allows monitoring of the kinetics of realignment with highest precision. © 1992 John Wiley & Sons, Inc.     

Epoxidation of bacterial polyesters with unsaturated side chains. II. Rate of epoxidation and polymer properties

Poly(3-hydroxyoctanoate-co-3-hydroxy-10-undecenoate)s (PHOUs) with controlled amounts of unsaturated repeating units were epoxidized to various extents with m-chloroperbenzoic acid (MCPBA) in homogeneous solution. The epoxidation reaction was second order, with an initial rate constant of 1.1 × 10⁻³Lmol^−1.s⁻¹ at 20°C, regardless of the unsaturated unit content in PHOU. No substantial change in either molecular weight or molecular weight distribution occurred as a result of epoxidation, but the melt transition temperature and enthalpy of melting both decreased as the unsaturated groups were increasingly converted into epoxide groups. In contrast, the glass transition temperature (T_g) increased by approximately 0.25°C for each 1 mol % of epoxidation, irrespective of the composition of the PHOU. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2381–2387, 1998     

Synthesis and properties of segmented main‐chain liquid‐crystalline polyurethanes with a high aspect ratio mesogenic diol as a chain extender

Main‐chain liquid‐crystalline polyurethanes were synthesized based on a high aspect ratio mesogenic diol (4‐{[4‐(6‐hydroxyhexyloxy)‐phenylimino]‐methyl}‐benzoic acid 4‐{[4‐(6‐hydroxyhexyloxy)‐phenylimino]‐methyl}‐phenyl ester) as a chain extender; polycaprolactone (PCL) diol soft segments of different number‐average molecular weights (530, 1250, or 2000); and different diisocyanates, including 1,4‐hexamethylene diisocyanate (HMDI), 4,4′‐methylene bis(cyclohexyl isocyanate) (H₁₂MDI), and 4,4′‐methylene bis(phenyl isocyanate) (MDI). The structure of the polymers was confirmed with Fourier transform infrared spectroscopy, and differential scanning calorimetry and polarizing microscopy measurements were carried out to examine the liquid‐crystalline and thermal properties of the polyurethanes, respectively. The mesogenic diol was partially replaced with 20–50 mol % PCL. A 20 mol % mesogen content was sufficient to impart a liquid crystalline property to all the polymers. The partial replacement of the mesogenic diol with PCL of various molecular weights, as well as the various diisocyanates, influenced the phase transitions and the occurrence of mesophase textures. Characteristic liquid‐crystalline textures were observed when a sufficient content of the mesogenic diol was present. Depending on the flexible spacer length and the mesogenic content, grained and threadlike textures were obtained for the HMDI and H₁₂MDI series polymers, whereas the polyurethanes prepared from MDI showed only grained textures for all the compositions. The polymers formed brittle films and could not be subjected to tensile tests. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1527–1538, 2002     

Synthesis and properties of polyimide–clay hybrid

A polyimide hybrid with montmorillonite clay mineral has been synthesized from a dimethylacetamide (DMAC) solution of poly(amic acid) and a DMAC dispersion of montmorillonite intercalated with an ammonium salt of dodecylamine. Montmorillonite consists of stacked silicate sheets about 2000 Å in length, 10 Å in thickness. In this hybrid, montmorillonite is dispersed homogeneously into the polyimide matrix and oriented parallel to the film surface. Thanks to this special structure, this hybrid showed excellent gas barrier properties. Only 2 wt % addition of montmorillonite brought permeability coefficients of various gases to values less than half of those of ordinary polyimide. Furthermore, this hybrid had low thermal expansion coefficient. © 1993 John Wiley & Sons, Inc.     

Phase and orientational ordering of low molecular weight rod molecules in a quenched liquid crystalline polymer matrix with mobile side chains

We study the phase diagram and orientational ordering of guest liquid crystalline (LC) rods immersed in a quenched host made of a liquid crystalline polymer (LCP) matrix with mobile side chains. The LCP matrix lies below the glass transition of the polymer backbone. The side chains are mobile and can align to the guest rod molecules in a plane normal to the local LCP chain contour. A field theoretic formulation for this system is proposed and the effects of the LCP matrix on LC ordering are determined numerically. We obtain simple analytical equations for the nematic/isotropic phase diagram boundaries. Our calculation show a nematic-nematic (N/N) first order transition from a guest stabilized to a guest-host stabilized region and the possibility of a reentrant transition from a guest stabilized nematic region to a host only stabilized regime separated by an isotropic phase. A detailed study of thermodynamic variables and interactions on orientational ordering and phases is carried out and the relevance of our predictions to experiments and computer simulations is presented.     

Blends of a thermotropic liquid‐crystalline polymer and a poly(butylene terephthalate)/organoclay nanocomposite

Blends were synthesized via the melt blending of a thermotropic liquid‐crystalline polymer (TLCP) and a poly(butylene terephthalate) (PBT) hybrid containing 2 wt % organoclay. A TLCP was also synthesized with side groups based on a nematic liquid‐crystalline phase. The blends of TLCPs with PBT hybrids were melt‐spun with different concentrations of the liquid‐crystalline polymer and different draw ratios (DRs) to produce monofilaments. Regardless of the TLCP concentration in the hybrids, transmission electron microscopy photographs proved that the clay layers of the organoclay were intercalated and partially exfoliated in the PBT matrix. At DR = 1, the maximum enhancement in the ultimate tensile strength was observed for blends containing 8% TLCP, and the tensile strength decreased with further increases in the TLCP concentration. The initial modulus monotonically increased with increasing TLCP concentration. When DR increased from 1 to 44, the increased stretching caused the tensile property to decrease significantly, debonding to occur, and voids to form. These trends with increasing DR were observed in all the systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3667–3676, 2004     

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     

Supramolecular main-chain liquid crystalline polymers and networks with competitive hydrogen bonding: a study of flexible bis-acids and a mixture of rigid and flexible polypyridyls

A series of novel liquid crystalline supramolecular networks formed through hydrogen bonds have been synthesised. These networks are based on flexible bi-benzoic acid and two types of pyridyl species – a small rigid bipyridyl capable of forming liquid crystalline phases and polyfunctional non-mesogenic pyridyl species that can compete for available hydrogen bond donor molecules. It was found that the networks display monotropic nematic character at high concentrations of disrupting net points – up to 50% for tetrapyridyls, 40% for tripyridyls and 35% for bipyridyls. Weak smectic phases were observed in all systems in loadings up to 10% of each disrupting unit. It is believed that the reversibility of the hydrogen bond allows for the formation of the ordered mesophases in the presence of the non-liquid crystalline groups.     

Anisotropic mechanical properties of thermoplastic elastomers in situ reinforced with thermotropic liquid‐crystalline polymer fibers revealed by biaxial deformations

The anisotropic mechanical properties of the thermoplastic elastomer (TPE) in situ reinforced with thermotropic liquid‐crystalline polymer (TLCP) fibers were investigated by uniaxial, strip‐biaxial, and equibiaxial tensile measurements. The in situ composite sheets were prepared from an immiscible blend of a TLCP, Rodrun LC3000, and a TPE, styrene‐(ethylene butylene)‐styrene (SEBS) triblock copolymer, by a melt extrusion process. The uniaxial orientation of the TLCP fibers in the TPE matrix generated during processing yielded a significant mechanical anisotropy in the composites. The biaxial tensile measurements clearly demonstrated the anisotropic mechanical properties of the composites: The modulus in the direction parallel to the machine direction (MD) was considerably higher than that in the transverse direction (TD), even at large deformations; in equibiaxial stretching, the yield strain in the MD was smaller than that in the TD; the composite containing 10 wt % of TLCP exhibited the highest mechanical anisotropy among the composites, with 0–30 wt % TLCP. The latter result was in accord with the SEM observation that the composite with 10 wt % of TLCP possessed the best fibrillar morphology and the highest degree of uniaxial orientation of the TLCP fibers. The yield strains in uni‐ and biaxial elongation for the composite containing 10 wt % of TLCP were almost the same as those for the neat styrene‐ethylene butylene‐styrene. The TLCP phase with good fibrillation did not appreciably alter the original yielding characteristics of the elastomer matrix. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 135–144, 2005     

Packing manner of graft copolymers with rigid‐rod main chains and amorphous‐crystalline diblock copolymers as side chains

We have investigated the morphology and packing manner of graft copolymers consisting of rigid‐rod‐like poly(γ‐benzyl L ‐glutamate) (PBLG) main chains and grafted diblock copolymers of amorphous poly(propylene glycol) (PPG) and crystalline poly(ethylene glycol) (PEG). The results of differential scanning calorimetry and wide‐angle X‐ray scattering measurements for graft copolymers with higher side‐chain volume fractions suggest that the rodlike main chains and crystallized PEG chains exist in segregated domains. Small‐angle X‐ray scattering profiles for these samples show diffraction intensity maxima accompanied by higher order peaks, the positions of which suggest the formation of an ordered layered structure. From these observations, the graft copolymers are estimated to form repeated layered structure consisting of segregated PBLG, PPG, and PEG layers. A proposed model for molecular packing of the graft copolymers is consistent with the experimental observation that the repeating distance for the layered structure decreases with an increase in the volume fraction of side chains. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1904–1912, 2002     

Synthesis and characterization of fully aromatic thermotropic liquid‐crystalline copolyesters containing m‐hydroxybenzoic acid units

A series of fully aromatic copolyesters based on p‐acetoxybenzoic acid (p‐ABA), hydroquinone diacetate (HQDA), terephthalic acid (TPA), and m‐acetoxybenzoic acid (m‐ABA) were prepared by a modified melt‐polycondensation reaction. The copolyesters were characterized by DSC, thermogravimetric analysis, ¹H NMR, polarized optical microscopy, X‐ray diffraction, and intrinsic viscosity measurements. The copolyesters exhibited nematic liquid‐crystalline phases in a broad temperature range of about 150 °C, when the content of linear (p‐ABA, HQDA, and TPA) units was over 67 mol %. DSC analysis of the anisotropic copolyesters revealed broad endotherms associated with the nematic phases, and the melting or flow temperatures were found to be in the processable region. The flow temperatures and crystal‐to‐nematic and nematic‐to‐isotropic transitions depend on the type of linear monomer units, and these transitions increased as the content of the p‐ABA units increased, as compared to the HQDA/TPA units. When the content of the p‐ABA units increased, as compared to other linear units (HQDA and TPA), the intrinsic viscosity and degree of crystallinity of the copolyesters also increased, implying a higher reactivity for p‐ABA in the p‐ABA/HQDA/TPA/m‐ABA polymer system. The aromatic region in the ¹H NMR spectra of the copolyesters containing equal molar compositions of p‐ABA, HQDA, and TPA units were sensitive to the sequence distribution of aromatic rings. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3263–3277, 2001     

Cellulose-based fibers from liquid–crystalline solutions. II. Processing and morphology of acetate/butyrate esters

Fibers were spun from isotropic and anisotropic dimethylacetamide solutions of cellulose esters. Take-up speeds of the dry jet/wet spinning process varied. Water served as the coagulant. The mechanical properties of the fibers increased as spinning progressed from the isotropic to the anisotropic state of the solution. A trade-off in solubility and fiber properties was noted as the butyryl acetyl ratio decreased. Whereas high butyryl content enhances both overall solubility and the formation of liquid–crystalline solutions at lower concentration, it results in lower fiber modulus and strength. Morphology of the fibers depended on the coagulation rate which was influenced by the concentration of the sppinning solution. The level of orientation and crystallinity of the fibers increased somewhat when they were spun from liquid-crystalline solutions. © 1993 John Wiley & Sons, Inc.