A. Blumstein

Orientation of Thermotropic Liquid-Crystalline Polyesters in High Magnetic Fields

Abstract Strongly oriented poly-crystalline samples of polyesters containing mesogenic moieties and flexible spacers in the main chain have been produced by slowly cooling the molten samples in magnetic fields of up to 16 Tesla. This simple method appears to be successful for those polymers forming a “true” nematic phase over an extended range of temperatures. Cholesteric polymers are not oriented. Mesogenic polymers (such as SEB-5, SUC-5, and SEB-7) which pass only through a state of partial parallel ordering of chain segments before cystallizing cannot be oriented macroscopically. In these samples crystallization may interfere with the chain alignment in the magnetic field. In contrast to low molecular weight liquid crystals, the isotropic-liquid crystalline transition of the polyesters investigated has a strong thermal hysteresis.

Synthesis and properties of some polyesters with mesogenic groups and flexible spacers in the main chain

Abstract Polymers containing, in the main chain, various mesogenic moieties separated by flexible spacers have been prepared by condensation of the corresponding diphenol or diol with an aliphatic diacid chloride. The polymers have been characterized by X-ray, d.s.c. and polarizing microscopy. The diacids used were sebacic (SEB), succinic (SUC) and 3-methyladipic (MAA). The biphenols were 4-hydroxyl- N -benzylidene-4′-hydroxyaniline(1), 4.4′-biphenol(2), 4,4′-bis (2-hydroxyethoxy)-biphenyl(5) and 3,3′-dimethyl-4,4′-di(2-hydroxyethoxy)-stilbene(7). The polymers SEB-1 and SEB-2 were classified as giving thermotropic lamellar mesophases; SEB-5, SEB-7 and SUC-5 as potentially nematic; MAA-2 and SUC-2 gave crystalline polymers.

Influence of Molecular Weight on Phase Transition Entropies of a Thermotropic Nematic Polyester

Abstract We report the values of isotropisation enthalpies and entropies of some model compounds, oligomers, and polymers of poly(2,2′-methyl-4,4′-oxyazoxybenzene dodecanedioyl), a thermo-tropic nematic polymer with moderately low transition temperatures and regularly alternating rigid-flexible units in the main chain. The values of ΔHIN and ΔIN increase rapidly with increasing molecular weight, to reach a plateau at M n > 3,000 g/mole. Results are interpreted in terms of increasing participation of the flexible aliphatic spacer units in the ordering process of the nematic phase. In the polymer, the entire repeating unit is aligned by the nematic potential.

Reorientation instabilities and viscoelastic measurements in a main chain thermotropic nematic polymer Optical and NMR studies

Abstract The reorientational behaviour of a nematic monodomain, in a static magnetic field, following the rotation of the mean director through an angle α ≈ π/2 to the magnetic field direction, is investigated by optical polarizing microscopy and proton NMR spectroscopy. Optical evidence supporting a reorientation process through a pure bend transient distortion of the director field is reported for poly (4,4′-dioxy-2,2′-dimethylazoxybenzene nonanediyl), a main-chain nematic thermotropic polymer. The time evolution of the distortion and flow patterns are deduced from a detailed analysis of the NMR lineshapes recorded during the reorientational process. The viscosity coefficients γ1, α1, α2, ηc and the ratio K 3/K 1 of the bend to splay Frank elastic constants are determined and discussed in terms of the existing theories.

Cholesteric, Thermotropic Polymers with Mesogenic Moieties and Flexible Spacers in the Main Chain

Abstract The synthesis of a new type of thermotropic soluble cholesteric polymer is described. The polymer contains nematogenic moieties separated by flexible spacers with an asymmetric center in the backbone. The polymer gives spontaneously characteristic Grandjean texturers when heated above its transition temperature between slide and cover slip. Selective reflection of light in the visible (λ ∼ 5000–5600A) occurs for a co-polymer containing ppl-azoxyphenol/dodecanedioic acid and (+)3-methyladipic acid units.

Nematic and Cholesteric Thermotropic Azoxy Polyesters with Moderately Low Transition Temperatures

Abstract The synthesis and properties of a new nematic and twisted nematic polyester system based on 4, 4′ azoxy-2, 2′methylphenyl moiety separated by flexible spacers with an asymmetric center in the backbone is described. The polymers of the system have moderately low transition temperatures and are well soluble in various solvents. The polyesters described flow easily and give characteristic textures of nematic and cholesteric fluids including selective reflections of light. The thermal properties of these polyesters indicate an increase of isotropisation entropy with the increase of average spacer length.

Synthesis, homopolymerization, and block copolymerization of N‐ethyl‐2‐ethynyl‐pyridinium trifluoromethanesulfonate with styrene and butadiene

A novel acetylenic monomer 2-N-ethyl pyridinium trifluoromethane sulfonate (2EPyEtTf) was synthesized and polymerized. Diblock copolymers of 2EPyEtTf with styrene and with butadiene were prepared. Initiation of the polymerization by living anionic polystyryl - -Li + and polybutadienyl - -Li + (Scheme 1) resulted in polystyrene-block-poly(N-ethyl-2-ethynylpyridinium trifluoromethanesulfonate) (PS 57 PA 8 ), and polybutadiene-block-poly(N-ethyl-2-ethynylpyridinium trifluoromethanesulfonate)(PB 30 PA 8 ). These amphiphilic block molecules contain rigid, conjugated, and strongly hydrophilic polyacetylene chain fragments attached to hydrophobic polystyrene or flexible polybutadiene chain fragments. The structure of these copolymers was studied by FTIR, UV-visible, and NMR spectroscopy. GPC and viscometry were also used to obtain information on the molecular mass and the molecular mass distribution. Thermal behavior was investigated by means of TGA and DSC. Both block copolymers were shown to form stable monolayers at the air-water interface. The positively charged rigid polyacetylene portion of the copolymer is believed to be partially submerged, while the more flexible hydrophobic chains are forced out of the water. Multilayers of PB 30 PA 8 deposited using the Langmuir-Blodgett technique were found to be less uniform than in the case of the previously reported polystyrene-block-poly(2E-PyMeTf)(PS 12 PA 4 ) copolymer (Balogh et al., Macromolecules, 29, 1996). Polycation-polyanion self-assembly deposition was also investigated, using polystyrenesulfonate (PSS) as polyanion. While PS 57 PA 8 /ASS layer-by-layer deposition was not uniform, it was found that PB 30 PA 8 /ASS gave homogenous and stable films on hydrophilic glass substrates.

Diacetylenic Liquid Crystals: A Systematic Investigation of the Homologous Series of 4, 41 - Dialkanoyloxydiphenyldiacetylenes

Abstract The homologous series of 4, 41 -dialkanoyloxydiphenyldiacetylenes with n ranging from zero to ten have been prepared. Optical microscopy, differential scanning calorimetry and X-ray diffraction have been used to study the mesomorphic behavior of these compounds. All homologs with n=1-7 are liquid crystals having nematic phases. In addition to nematic phases, these esters have extensive solid-state polymorphism. The transition enthalpies and entropies have also been calculated.

Inherently flexible thermotropic main chain polymeric liquid crystals

Abstract Phase behavior (isotropic—nematic transition, disorder in the crystal) and order of chains in the mesophase (orientational and conformational) are investigated in the homologous series of polymers and corresponding Siamese twin models. Results from the following experiments are presented: DSC (normal and high pressure), polarizing microscopy, broad line NMR (PMR and DMR), small angle X-ray and neutron scattering, induced magnetic birefringence and melt rheology. Influence of chain length, spacer length and parity, temperature and concentration in nematic solutions on nature and level of order is discussed. Molecular segregation by chain length in the nematic—isotropic biphase is considered in relation to its impact on morphology of the isotropic, nematic and solid phases. This series provides a model system for characterization of inherently flexible main chain PLCs formed by alternating mesogens and spacers. Such PLCs are easily processable materials with potentially high levels of micro and mac...

Cross‐linked Multilayer Polymer‐Clay Nanocomposites and Permeability Properties

Abstract Electrostatically layered aluminosilicate nanocomposites have been prepared by the sequential deposition of poly(allylamine hydrochloride)/poly(acrylic acid)/poly(allylamine hydrochloride)/saponite (PAH/PAA/PAH/saponite)10 on poly(ethylene terephtalate) (PET) film. Exfoliated saponite nanoplatelets were obtained by extensive shaking, sonication, and centrifugation of a water suspension. To minimize permeability and improve the mechanical integrity, cross‐linking of composite films was carried out at different temperatures. The formation of amide linkage induced through heating was observed by Fourier Transform Infrared (FT‐IR) and x‐ray photoelectron spectroscopy (XPS). The cross‐linking of nanocomposites (PAH/PAA/PAH/saponite)10 showed 60% decrease in permeability of oxygen when compared with the pristine PET substrate film. In contrast, water permeability of the nanocomposite membrane was not affected by heating temperature and deposition cycles.