Effects of the H-bond donor structure on the properties of supramolecular side chain liquid crystalline polymers based on poly(3-carboxypropylmethylsiloxane-co-dimethylsiloxane)s and stilbazoles

Supramolecular side chain liquid crystalline polymers (SCLCPs) based on poly(3-carboxypropylmethylsiloxane-co-dimethylsiloxane) (PSIX, X=100, 76, 60, 41 or 23, denoting the mole percentage of 3-carboxypropylmethylsiloxane unit in the polymer) and stilbazole derivatives have been obtained through intermolecular hydrogen bonding (H-bonding) interactions between the carboxylic acid and the pyridyl moieties. The formation of H-bonding and self-assembly results in the formation of new mesogenic units, in which H-bonds function as molecular connectors. FTIR shows the existence of H-bonding in the complexes. The polymeric complexes behave as single component liquid crystalline polymers and exhibit stable and enantiotropic mesophases. The liquid crystalline properties of the supramolecular SCLCPs were studied using differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction, and were found to exhibit smectic A phases with focal-conic textures. The thermal stability of the SCLCP increases on increasing the carboxylic acid content in the polysiloxane and the concentration of the stilbazole derivative in the complex. However, the thermal stability decreases on increasing the chain length of the stilbazole derivative. The crystal phase was not formed even on cooling to the glass transition temperature of the polymeric complex.     

Effect of electron donor-acceptor interaction on the thermal stability of supramolecular side chain liquid crystalline polymers based on poly(3-carboxypropylmethylsiloxane)

Supramolecular side chain liquid crystalline polymers were prepared from poly(3-carboxypropylmethylsiloxane) (PSI100) and azobenzene-based derivatives through intermolecular hydrogen bonding between the carboxylic acid groups of PSI100 and the imidazole rings in the azobenzene-based derivatives. The presence of H-bonding was confirmed using FTIR spectroscopy. The polymeric complexes behave as liquid crystalline polymers and exhibit nematic mesophases identified on the basis of the observation of Schlieren textures. The mesogenic behaviour of these complexes was studied by polarizing optical microscopy and X-ray diffraction. The thermal behaviour of the complexes was investigated by differential scanning calorimetry. On increasing the spacer length, the transition temperatures initially increase. A further increase in spacer length, however, leads to a decrease in the transition temperatures. The electron donor-acceptor interaction between unlike mesogenic units in supramolecular copolymeric complexes helps to stabilize the mesophase.     

Effect of electron donor-acceptor interaction on the thermal stability of supramolecular side chain liquid crystalline polymers based on poly(3-carboxypropylmethylsiloxane)

Supramolecular side chain liquid crystalline polymers were prepared from poly(3-carboxypropylmethylsiloxane) (PSI100) and azobenzene-based derivatives through intermolecular hydrogen bonding between the carboxylic acid groups of PSI100 and the imidazole rings in the azobenzene-based derivatives. The presence of H-bonding was confirmed using FTIR spectroscopy. The polymeric complexes behave as liquid crystalline polymers and exhibit nematic mesophases identified on the basis of the observation of Schlieren textures. The mesogenic behaviour of these complexes was studied by polarizing optical microscopy and X-ray diffraction. The thermal behaviour of the complexes was investigated by differential scanning calorimetry. On increasing the spacer length, the transition temperatures initially increase. A further increase in spacer length, however, leads to a decrease in the transition temperatures. The electron donor-acceptor interaction between unlike mesogenic units in supramolecular copolymeric complexes helps to stabilize the mesophase.     

Electro-optical properties and nonlinear response of side chain liquid crystalline polymers

Among the NLO processes that have been studied, one of the most visually dramatic is the frequency doubling. In the field of optical information storage this process can provide the conversion of near-infrared laser light from diode lasers into deep blue light. Compared to the more traditional inorganic NLO materials, polymers with polarizable aromatic pendant side groups are increasingly being recognized as the materials of the future. Recently it has been pointed out that the axial ordering spontaneously present in nematic and smectic A polymers can be used to enhance field-induced polar ordering by elongating the orientational distribution function along the electric field direction. Depending on the value of the microscopic order parameters <P>₂ and <P>₄, the performance may be improved by a factor of 1 to 5 by using LCPs instead of ordinary amorphous polymers for SHG.^1-4) Interesting results have been obtained for copolyethers prepared by chemical modification of polyepichlorohydrin with classical 4-cyano-4'-hydroxybiphenyl mesogenic group which possesses NLO properties itself.^5-8) These copolyethers afford the opportunity to fine-tune the polymer properties by varying the concentration of the mesogenic side groups. As the concentration is increased, we move from a purely isotropic polymer to a nematic polymer. Spin-coated films have been activated using the corona poling technique and the order parameters <P>₂ have been determined from optical absorption spectra. The second harmonic coefficients d₃₃ and d₃₁ have been measured and compared with different statistical models. In view of the great practical importance, characterization of the wavelength dispersion has been carried out. It agrees well with the two-level approximation model. The dynamics of optical SHG has been investigated. It has been shown that both the presence of LC character in the material and the temperature at which the films are stored below Tg are important in determining the stability of the SH coefficients. A polyacrylate and a polymethacrylate bearing the same 4-cyanobiphenyl-based side groups have also been studied.^7-8) Of particular interest is the fact that the former is nematic while the latter is purely isotropic at rest, the addition of a methyl group to each structural unit of the polyacrylate backbone creating a higher conformational barrier to mesogen packing. Studies of the temporal and thermal characteristics of the poling process have been performed to: •understand and control the poling process with the intention of maximizing poling induced nonlinearity and stability. •elucidate the influence of the polymer backbone, our data including the use of the same mesogenic unit attached to increasing flexible backbones (e.g. polymethacrylate and polyether). •establish if, in the isotropic cases, noticeable axial order can be induced by the poling field, especially when the system is pulled through nematic/isotropic transition by the electric field.     

Luminescent Iridium-containing liquid crystalline polymers in the side chain

Luminescent liquid crystalline polymers consisting of Iridium attached to polysiloxanes are prepared. 4-Cyanophenyl 4-(allyloxy) benzoate (M₁) and an Iridium complex (Ir-M₂) grafted to poly(methylhydrogeno)siloxane are used for the preparation of the Iridium-containing liquid crystalline polymers. The chemical structures are characterised by Fourier transform infrared spectroscopy and ¹H NMR. The mesomorphic properties and phase behaviour are investigated by differential scanning calorimetry, thermogravimetric analysis, polarising optical microscopy and X-ray diffraction. The polymers containing <1.2 mol% of the Iridium ions reveal reversible mesomorphic phase transition, wide mesophase temperature ranges and high thermal stability. The introduction of the Iridium ions does not change the liquid crystalline state of polymer systems; on the contrary, the polymers are enabled with the luminescent properties. With the Iridium ion contents ranging between 0.3 and 1.2 mol%, luminescent intensity of polymers gradually increased. The temperature dependence of luminescent intensity was studied in the liquid crystalline phase.     

Liquid crystalline polymers VII. Thermotropic liquid crystalline poly(azomethine-ether)s containing dibenzylidene derivatives in the main chain

A new homologous series of thermotropic liquid crystalline poly(azomethine-ether)s based on dibenzylidene derivatives was synthesized by solution polycondensation of various diformyl-α,ω-diphenoxyalkanes, I-VIII with 2,7-bis-(m-aminobenzylidene)cycloheptanone IX and bis-(m-aminobenzylidene)acetone X. The inherent viscosities of the polymers were in the range 0.23-0.69 dl/g. All the poly(azomethine-ether)s were insoluble in common organic solvents but dissolved completely in concentrated H₂SO₄ and methanesulphonic acid. The mesomorphic properties were studied as a function of the diphenoxyalkane space length. Analysis by differential scanning calorimetry and optical polarized microscopy demonstrated that the poly(azomethine-ether)s from nematic mesophases over wide temperature ranges.     

New side chain liquid crystalline polymers: synthesis and thermal properties of side chain polyacrylates having segmented spacers

In order to acquire high mobility of a mesogenic group, we propose a new type of side chain liquid crystal polymer having segmented spacers, consisting of binary moieties of an oligo(ethylene oxide) segment and analkylene segment. Six kinds of polyacrylates having segmented spacers consisting of different lengths of an oligo(ethylene oxide) and an alkylene, and having 4'-cyanobiphenyl as a mesogenic group have been synthesized, and their thermal properties investigated. Some of these polyacrylates exhibit a mesophase and show an extremely low glass transition temperature compared with LC polyacrylates having ordinary alkylene spacers.     

New side chain liquid crystalline polymers: synthesis and thermal properties of side chain polyacrylates having segmented spacers

In order to acquire high mobility of a mesogenic group, we propose a new type of side chain liquid crystal polymer having segmented spacers, consisting of binary moieties of an oligo(ethylene oxide) segment and analkylene segment. Six kinds of polyacrylates having segmented spacers consisting of different lengths of an oligo(ethylene oxide) and an alkylene, and having 4'-cyanobiphenyl as a mesogenic group have been synthesized, and their thermal properties investigated. Some of these polyacrylates exhibit a mesophase and show an extremely low glass transition temperature compared with LC polyacrylates having ordinary alkylene spacers.     

Studies on thermotropic liquid crystalline polymers. XIV. Synthesis and properties of liquid crystalline poly(imide-ester)s by the direct polycondensation

A series of semi-aromatic poly(imide-ester)s were prepared by the direct polycondensation of N-(4-carboxyphenyl) trimellitimide or N-(3-carboxyphenyl) trimellitimide with various pyromellitic diimide diols containing methylene spacer = 2–6, respectively. The effect of the amount of LiCl, pyridine, and the kinds of condensation agents on the direct polycondensation were studied. The structures and thermal properties of the synthesized poly(imide-ester)s were examined by FTIR spectrum, wide-angle x-ray diffraction (WAXD), differential scanning calorimetry (DSC), thermal optical polarized microscopic observation, and thermogravimetric analysis (TGA). It is found that P1 series [derived from N-(4-carboxyphenyl) trimellitimide] with even number methylene spacer (n = 4, 6) exhibit smectic mesophase, but P2 series [derived from N-(3-carboxyphenyl) trimellitimide] do not show LC phase. © 1996 John Wiley & Sons, Inc.     

Electrooptical properties of liquid crystalline side chain polymers with laterally attached mesogenic units

The electrooptical properties of side-chain liquid crystalline polymers were investigated for the case that the mesogenic units were attached laterally rather than longitudinally to a flexible chain backbone via flexible spacer units. The experimental finding is that these polymers display unusual electrooptical properties within the isotropic phase in the neighborhood of the transition into the nematic phase. The polymers are characterized by the occurrence of a fast and a slow electrooptical response both of which show a critical divergence of the Kerr constant and the Kerr relaxation time. In addition, they show deviations between the rise and the decay values of the Kerr constants and in certain cases also of the Kerr relaxation times. Finally an overshoot of the induced birefringence following a sudden stepwise increase of the applied electric field has been found for one of these polymers. All these features can be accounted for on the basis of a newly developed theoretical approach that considers the particular dipolar and optical polarization configurations of these polymers.     

Luminescent lanthanide-containing chiral liquid crystalline polymers in the side chain

Luminescent lanthanide-containing chiral liquid crystalline polymers are graft-copolymerised using poly(methylhydrogeno)siloxane (PMHS), crosslinking agent, liquid crystalline monomer and lanthanide complexes. The chemical structures of the monomers are characterised by FTIR, ^1?H NMR and elemental analyses. The mesomorphic properties and phase behaviour are investigated by differential scanning calorimetry, thermogravimetric analysis, polarising optical microscopy and X-ray diffraction. The polymers containing less than 9 mol% of the crosslinking units reveal reversible mesomorphic phase transition, wide mesophase temperature ranges and high thermal stability. With the introduction of lanthanide complex units, the polymers are enabled with the significant luminescent properties. The temperature dependence of fluorescence intensity was studied in the liquid crystalline phase. The IR imaging shows that the lanthanide complex units evenly distribute in polymers.     

Liquid-crystalline side chain polymers by chemical modification of poly(chloroalkylvinylether)s

The synthesis of polyalkylvinylethers with pendant 4-cyano-4'-oxybiphenyl groups gives thermotropic liquid-crystalline polymers. The new method developed here consists of the living cationic polymerization of chloroalkylvinylethers and the subsequent modification of the polymer by the mesogenic groups. The liquid-crystalline polymers have a controlled degree of polymerisation and narrow molecular weight distributions. The influence on the mesomorphic properties of various parameters such as the degree of polymerization, the spacer length and the proportion of the mesogenic side chain content has been investigated. Binary phase diagrams with low molar mass analogues are also reported and the properties of both neat materials and binary mixtures are compared.     

Synthesis, micro structure, and thermal stability of side chain liquid crystalline polysiloxane polymers with an oligo (ethylene oxide) unit in the side chain

A series of new alkene monomers [MS3BDBEn, n=1-3] containing 4-oligo (ethylene oxide) monomethyl ether 4-biphenyl ether carboxyl benzoate as terminal groups were synthesized. These polymers were prepared by grafting these monomers onto the poly (methylhydrosilox-ane) (PMHS) backbone. The transition temperatures, liquid crystalline textures, and thermal stability of the polysiloxane polymers have been determined by thermal data, by optical texture, and by X-ray diffraction patterns. Polymers PS3BDBEn showed smectic or smectic and nematic phases which were not analogous to their precursor nematic monomers. The terminal length of the polymers affects not only the mesophase transition temperatures but also the layer-spacing length (d₁) and the side-chain distance (d₂). The long- and short-range orders can remain to some extent above the isotropization temperature and below the melting point. The polymer PS3BDBE3 decomposed in air 20°C above the isotropization temperature and lost its short range orders as detected by the X-ray diffraction analysis.     

Studies on thermotropic liquid crystalline polymers. XV. Synthesis and properties of liquid crystalline copoly(imide-ester)s

Three series of the thermotropic liquid crystalline copoly(imide-ester)s were prepared by direct polycondensation. The first two series of the copoly(imide-ester)s were synthesized from N-(4-carboxyphenyl) trimellitimide with N,N-di(hydroxypropyl) pyromellitic diimide and various aromatic diols. The third series of copoly(imide-ester)s were prepared by N-(4-carboxyphenyl) trimellitimide with various imide-diols (methylene spacer = 2–6) and phenyl hydroquinone. The structures and thermal properties of the synthesized poly(imide-ester)s were examined by FTIR spectrum, wide-angle x-ray diffraction (WAXD), differential scanning calorimetry (DSC), thermal optical polarized microscope, and thermogravimetric analysis (TGA). The effects of the structures of the aromatic diols on the thermal properties of the resulting copoly(imide-ester)s were investigated. It was found that most of the copoly(imide-ester)s possessed excellent mesophase stabilities and thermostabilities. The mesophase stabilities of poly(imide-ester)s decreased with the increase of the size of lateral group, and the mesophase range increased with the increase of the amount of PhHQ. No significant odd-even effects were observed between the methylene spacer lengths and transition temperatures. © 1996 John Wiley & Sons, Inc.     

Synthesis and characterization of halogen-containing ferroelectric liquid crystals and side chain liquid crystalline polymers

A new series of ferroelectric liquid crystals and side chain liquid crystalline polymers based on halogen-containing chiral centres has been synthesized. Chemical structures were analysed by NMR. Liquid crystal phases were characterized by differential scanning calorimetry, optical polarizing microscopy, and X-ray diffractometry. The behaviour of the liquid crystalline phases was investigated as a function of spacer units and differing terminal asymmetric moieties. It was found that phase transition temperatures decreased with increasing length of the oligooxyethylene spacer unit. Differing terminal asymmetric moieties led to differing mesophase phenomena. Furthermore, a wide temperature range (including room temperature) of a chiral smectic C phase was achieved.     

Synthesis and characterization of halogen-containing ferroelectric liquid crystals and side chain liquid crystalline polymers

A new series of ferroelectric liquid crystals and side chain liquid crystalline polymers based on halogen-containing chiral centres has been synthesized. Chemical structures were analysed by NMR. Liquid crystal phases were characterized by differential scanning calorimetry, optical polarizing microscopy, and X-ray diffractometry. The behaviour of the liquid crystalline phases was investigated as a function of spacer units and differing terminal asymmetric moieties. It was found that phase transition temperatures decreased with increasing length of the oligooxyethylene spacer unit. Differing terminal asymmetric moieties led to differing mesophase phenomena. Furthermore, a wide temperature range (including room temperature) of a chiral smectic C phase was achieved.     

Novel study on the liquid crystalline behavior of poly(methacrylate)s with biphenyl side groups

We report the synthesis and characterization of a series of liquid crystalline polymers substituted with the 4′-methoxybiphenyl-4-yloxy group. The spacer length is varied from 4–8 methylene units. The materials are characterized by polarized light microscopy, differential scanning calorimetry, and X-ray analysis. All homologues show highly ordered phases. Additionally, the butylene polymer shows a broad nematic mesophase. For the first time, the narrow nematic phase of the hexylene homologue could be confirmed experimentally. X-ray analysis of the polymers made exact assignments of the low temperature phases possible, thus giving access to the analysis of the arrangement of the mesogenes within the layers. The pentylene homologue shows a distinct deviation from the behavior of the other polymers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2669–2679, 1998     

Study on the thermotropic liquid crystalline polycarbonates. IV. Synthesis and properties of liquid crystalline poly(imide-carbonate)s

Two series of novel thermotropic liquid crystalline poly(imide-carbonate)s were prepared by melt polycondensation from various arylene or alkylene bis(phenylcarbonate)s by using N,N′-bis(hydroxyethyl)pyromellitimide and N,N′-bis(hydroxypropyl)pyromellitimide as monomers. Thermotropic liquid crystalline properties were characterized by a polarizing microscope with a heating stage and a differential scanning calorimeter (DSC). Nematic melts were found for the synthesized aromatic poly(imide-carbonate)s. In order to investigate whether the pyromellitimide unit could be used as a mesogenic unit for preparing LC polymers, a series of aliphatic poly(imide-carbonate)s was prepared in this study. However, no significant LC textures were found under the observation by polarizing microscope. It was suggested that the aspect ratio of the pyromellitimide unit was too short to form liquid crystalline poly(imide-carbonate)s. In addition, it was interesting that the aliphatic poly(imide-carbonate)s with a longer spacer (n = 3) in the pyromellitimide unit showed better crystallinity. Thermostabilities of all synthesized poly(imide-carbonate)s were measured by thermogravimetric analysis (TGA). © 1994 John Wiley & Sons, Inc.