Palladium complexes of side‐chain liquid crystal polymers with T‐shaped two‐dimensional mesogenic units

A series of liquid crystal polymers (LCPs) with T‐shaped two‐dimensional mesogenic units were synthesized via solution polycondensation. The LCPs were used as ligand polymers to coordinate with palladium dichloride, by which a series of polymeric palladium complexes were prepared. The liquid crystalline behaviors of the compounds were characterized using differential scanning calorimetry, polarized microscopy and X‐ray diffraction. The entire palladium complexes went to liquid crystal phase when heated to their melting temperature (T _m), and a threaded texture was observed. The melting point of all the complexes changes regularly with the increase of the end alkoxy group length and the flexible spacer unit in the ligand polymer. It is worth noting that some of the complexes without end substituent groups in the ligand polymer were also found to show liquid crystal behaviors, which would be a subject for further investigation. Copyright © 2001 John Wiley & Sons, Ltd.     

SYNTHESIS AND MESOGENIC PROPERTY OF Pd-COORDINATING AZO-TYPE SIDE CHAIN LIQUID CRYSTALLINE POLYSILOXANE

A novel palladium-coordinating Azo-type liquid crystalline polysiloxane (Pd-AZLCP) has been synthesized by chelation reaction of polymeric ligand, Azo-type liquid crystalline polysiloxane(AZLCP), with palladium dichloride and potassium chloride in the presence of tetrahydrofuran (THF) as reaction medium instead of dioxane/water system, which has been used since Cope first reported the synthesis of palladium-azobenzene in 1965 . The mesogenic behaviors examined by DSC, temperature-variable X-ray diffraction and polarizing microscopy indicate that the incorporation of Pd ions into the liquid crystal polymer can play a positive effect on the mesogenic property of the parent polymeric ligand. It is exhibited that the isotropization temperature T_i is increased and the mesophase range ΔT has been widened, too.     

Thermal recordable novel cholesteric liquid crystalline polyacrylates containing various chiral moieties

To investigate the effect of spacer length and linkages between the rigid mesogenic core and the terminal group on the molecular interaction and physical properties of polymers, two series of novel side chain liquid crystalline polyacrylates were synthesized. These were composed of liquid crystalline monomers with six or eleven methylene segments as spacers, and chiral monomers end capped with menthyl or cholesteryl groups. Liquid crystalline phases of the polymers were investigated using differential scanning calorimetry and polarized optical microscopy, and confirmed with X‐ray diffractometry. Color image recording of the synthesized polymer films was achieved using a thermal treatment, and then fixed by quenching. This investigation demonstrates that the introduction of carbonate linking groups between the rigid mesogenic core and terminal group decreases both the lateral molecular interaction and thermal stability of the liquid crystalline polymers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6214–6228, 2008     

STUDY OF CHIRAL SIDE CHAIN LIQUID CRYSTALLINE POLYMERS

Five kinds of side chain liquid crystalline polymers with a chiral component in the pendant group were synthesized and characterized by GPC, polarizing microscopy, DSC, X-ray diffraction ano Dielectric Relaxation Spectroscopy. The liquid crystalline behaviour of the polymers is affected by the length of flexible spacer, which links the mesogenic side chain to the polymer backbone and mesogenic moiety. The characteristic of smectic phase is observed for all the polymers.     

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.     

Phase behavior of liquid crystalline elastomers based on a tri-vinyl mesogenic cross-linker

A series of cross-linked liquid crystalline polymers are prepared by graft copolymerization, and their liquid crystalline properties are characterized by DSC and POM. The results show that low levels of cross-linking do not obviously affect the phase behavior of the network polymers; in contrast, high levels of cross-linking may have more drastic influences, and liquid crystalline phases may lose, and more marked variation in phase transition will occur in materials with more direct coupling through a shorter or stiffer coupling chain between mesogenic side units and polymer backbone. At the same time, the coupling between the polymer chain and sidegroups results in stress-induced orientation in LCEs.     

Geraniol Based Side Chain Liquid Crystalline Polymer: Synthesis and Characterization

Side chain liquid crystalline (SCLC) polysiloxane polymer with a geraniol mesogenic group and polymethylene spacers were prepared, and their properties were compared with those of an equivalent SCLC polymer, SCLCP's, with phenyl benzoate mesogenic group. The phase behavior was studied by differential scanning calorimetry (DSC) and optical polarizing microscopy (OPM). The DSC curve showed a clear melting temperature and isotropization at 72 and 148°C, respectively, with a glass transition at 25°C. The observation of a fan‐shaped texture confirms the presence Smectic A phase under an optical polarized microscope.     

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.     

Side chain polysiloxanes with fluorinated mesogenic groups. The role of the fluorine content on the properties of the smectic A state

A series of liquid crystalline polymers has been synthesized in which fluorinated or semi-fluorinated mesogenic moieties are used as side groups linked to a polysiloxane backbone. Clear-cut differences in the structure of the smectic A phase are evidenced between fluorinated polymers and their classical non-fluorinated homologues. In a comparative analysis, we discuss the relevance of the steric hindrance of perfluorinated sequences and of the microsegregation of the backbone in response to these modifications as related to the fluorine content in the side group and to the proportion of mesogenic groups.     

SYNTHESIS AND CHARACTERIZATION OF PALLADIUM COORDINATING IMINE SIDE CHAIN LIQUID CRYSTALLINE POLYSILOXANES

New thermotropic chloro-bridged dinuclear palladium coordinating imine side chain liquid crystalline polysiloxanes have been synthesized. Their mesomorphic properties have been investigated by DSC, X-ray diffraction and polarizing microscopy. The polymeric complexes show nematicdiscotic (Nd) mesophase. It is found that the temperature range of liquid crystalline state of chloro- bridged polymeric complexes is much wider than that of acetato- bridged ones and imine side chain polysiloxane. This indicates that the disc-like chloro-bridged palladium complexing units play a role as mesogen in mesophase.     

Synthesis and mesomorphic properties of fishbonelike,liquid crystalline polysilsesquioxanes: 4. Pd-coordinating,fishbone-like imine-based liquid crystalline polysilsesquioxane

A new type of Pd-coordinating, imine-based, fishbone-like liquid crystalline polysilsesquioxanes (Pd-FBI) including μ-acetato-bridged Pd-FBI [Pd(μ-oAc)-FBI] and μ-chloro-bridged Pd-FBI [Pd(μ-Cl)-FBI] has been synthesized first by a hydrosilylation reaction to form fishbone-like, imine-based liquid crystalline polysilsesquioxane (H-FBI and MH-FBI respectively,) and then by an ortho-palladation reaction with palladium acetates to obtain Pd(μ-oAc)-FBI. The latter was further subjected to ligand substitution reaction with NaCl to form Pd(μ-Cl)-FBI. Their mesomorphic properties investigated by differential scanning calorimetry (DSC) and optical polarization microscopy (OPM). show that the Pd-FBI is a thermotropic liquid crystalline polymer and its clearing temperatures and mesophase range are much higher than those of the corresponding comb-like imine liquid crystalline polysiloxanes (IMLCP) by about 100 °C. In this paper the influence of the palladium content on mesogenic behavior is discussed.     

Synthesis and properties of two new series of isomeric liquid crystalline polyesters with conjugated double bonds

Two homologous series of flexible main chain liquid crystalline polyesters with isomeric mesogenic groups containing conjugated double bonds, were synthesized and studied by differential scanning calorimetry and optical microscopy. One series (S1) has the p-phenylene-diacryloyloxydibenzoyl moiety as a mesogenic unit. The other (S2) has the terephtaloyl dioxydicinnamoyl moiety as a mesogenic unit. The reactivity of the conjugated double bonds of the p-phenylenediacryloxy unit, at the temperature of mesophase formation, impedes the stability of liquid crystalline mesophases of polymers of series (S1). Two low molecular weight analogues of polymers were also prepared and their properties compared with those of polymers of similar structure. The two model compounds form stable smectic mesophases over a wide range of temperatures, which shows the high mesomorphogenic ability of both mesogenic units.     

Synthesis and phase behaviour of liquid-crystalline side group polyesters

Several series of liquid-crystalline side group polymers with a polyester backbone structure have been synthesized using mesogenic diethylmalonate and 1,3-propanediol derivatives. The structures of the polymer backbone and the mesogenic units have been varied systematically. As shown by differential scanning calorimetry, polarizing microscopy and X-ray diffraction, the side group polyesters exhibit nematic and/or smectic mesophases. Polyesters synthesized from mesogenic diethylmalonate derivatives can tolerate long non-mesogenic segments in the polymer main chain without losing their liquid crystal properties. X-ray studies suggest that some of the smectic polymers exhibit interdigitated bilayer S_A phases.     

Liquid crystalline side chain polymer with a poly (Geraniol-co-MMA) backbone and phenylbenzoate mesogenic group: synthesis and characterization

A new side chain liquid crystalline polymers have been synthesized and characterized in which [geraniol-co-MMA] polymer are used as a backbone linked via polymethylene spacer to phenyl benzoate mesogenic group. The polymer exhibits enantiotropic liquid crystallinity with nematic phase and does not exhibit side chain crystallization .A clear difference between the nature of the mesophase is evidenced between [Geraniol-co-MMA] main chain and methacrylate polymers .The LC polymer exhibit glass transition at 40 °C. In a comparative analysis, we discuss the relevance of polymer backbone in the synthesis of side chain liquid crystalline polymers.     

Supramolecular side chain liquid crystalline polymers assembled via hydrogen bonding between carboxylic acid-containing polysiloxane and azobenzene derivatives

Supramolecular side chain liquid crystalline polymers were prepared from poly(3-carboxypropylmethylsiloxane) (PSI100) and azobenzene derivatives through intermolecular hydrogen bonding (H-bonding) between the carboxylic acid groups in the PSI100 and the imidazole rings in the azobenzene derivatives. The existence of H-bonding has been confirmed using FTIR spectroscopy. The polymeric complexes behave as liquid crystalline (LC) polymers and exhibit stable mesophases. The LC behaviour of these H-bonded polymeric complexes was investigated by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction. The complexes exhibit nematic LC phases identified on the basis of Schlieren optical textures. On increasing spacer length or the concentration of the H-bonded mesogenic unit in the complex, the clearing temperature and the temperature range of the LC phase of the polymeric complex increase. The terminal group plays a critical role in determining the LC properties of the polymeric complexes. A terminal methoxy group is more efficient than a nitro group in increasing the clearing temperature. The electron donor-acceptor interactions between the H-bonded mesogenic units containing methoxy and nitro terminal groups in supramolecular 'copolymeric' complexes lead to an increase in the clearing temperature and a wider temperature range for the LC phase.     

Supramolecular side chain liquid crystalline polymers assembled via hydrogen bonding between carboxylic acid-containing polysiloxane and azobenzene derivatives

Supramolecular side chain liquid crystalline polymers were prepared from poly(3-carboxypropylmethylsiloxane) (PSI100) and azobenzene derivatives through intermolecular hydrogen bonding (H-bonding) between the carboxylic acid groups in the PSI100 and the imidazole rings in the azobenzene derivatives. The existence of H-bonding has been confirmed using FTIR spectroscopy. The polymeric complexes behave as liquid crystalline (LC) polymers and exhibit stable mesophases. The LC behaviour of these H-bonded polymeric complexes was investigated by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction. The complexes exhibit nematic LC phases identified on the basis of Schlieren optical textures. On increasing spacer length or the concentration of the H-bonded mesogenic unit in the complex, the clearing temperature and the temperature range of the LC phase of the polymeric complex increase. The terminal group plays a critical role in determining the LC properties of the polymeric complexes. A terminal methoxy group is more efficient than a nitro group in increasing the clearing temperature. The electron donor-acceptor interactions between the H-bonded mesogenic units containing methoxy and nitro terminal groups in supramolecular 'copolymeric' complexes lead to an increase in the clearing temperature and a wider temperature range for the LC phase.     

Cholesterol-based dimesogenic bidentate ligands and their Cu(II) and Pd(II) metallomesogens

The synthesis and evaluation of the liquid crystalline properties of non-conventional liquid crystals, consisting of two non-identical mesogenic segments interconnected via a paraffinic chain spacer, are of considerable current interest. In particular, chiral dimesogens possessing a cholesteryl ester unit as the chiral entity joined to other aromatic mesogens through a polymethylene spacer have shown unique and interesting thermal behaviour. In continuation of our investigations on this topic, here we present the synthesis and characterization of the first examples of cholesterol-based unsymmetrical dimesogenic bidentate ligands and their Cu(II) and Pd(II) metal-organic systems (metallomesogens). Our studies reveal that the dimesogenic bidentate ligands exhibit multiple mesophases, whereas their metal complexes stabilize only the mesophase.     

Cholesterol-based dimesogenic bidentate ligands and their Cu(II) and Pd(II) metallomesogens

The synthesis and evaluation of the liquid crystalline properties of non-conventional liquid crystals, consisting of two non-identical mesogenic segments interconnected via a paraffinic chain spacer, are of considerable current interest. In particular, chiral dimesogens possessing a cholesteryl ester unit as the chiral entity joined to other aromatic mesogens through a polymethylene spacer have shown unique and interesting thermal behaviour. In continuation of our investigations on this topic, here we present the synthesis and characterization of the first examples of cholesterol-based unsymmetrical dimesogenic bidentate ligands and their Cu(II) and Pd(II) metal-organic systems (metallomesogens). Our studies reveal that the dimesogenic bidentate ligands exhibit multiple mesophases, whereas their metal complexes stabilize only the mesophase.     

Thermotropic main chain liquid crystalline polyesters containing ferrocene and phosphate units: synthesis and characterization

A new series of liquid crystalline main chain copolyesters were prepared, having ferrocene in the mesogenic segment and a methyl phosphate group along with a methylene spacer. The even numbered methylene groups were varied from two to ten. Liquid crystalline behaviour was investigated on a hot stage optical polarized microscope. Thermal properties of the polymers were analysed by TGA and DSC, revealing that the polymers yield high char products, probably caused by the formation of phosphorus and iron oxides. The glass transition (T_g) temperatures of the polymers were found to be fairly low, the result of the incorporation of bulky phosphorus and ferrocene moieties in the chain. The phase behaviour was analysed and correlated with the structure of the polymers. The liquid crystalline textures of the polymers became more transparent with increasing spacer length. Energy minimized structures for the polymer repeating units reveal that both the ferrocene and phosphorus moieties produce more molecular entanglement, thus reducing the T_g and T_m of the polymers.     

Laterally attached liquid crystalline polymers as stationary phases in reversed-phase high-performance liquid chromatography. II. Optimization of the molecular parameter of the polymer

Stationary phases obtained by coating side-chain liquid crystalline polymers (LCPs) with the mesogenic rod like units laterally attached to a polysiloxane backbone via a flexible spacer have been already reported. These phases show excellent planarity and shape recognition for polynuclear aromatic hydrocarbon (PAH) solutes in reversed-phase liquid chromatography. Optimization of these stationary phases in terms of molecular parameters of the polymer is here described. Fifteen stationary phases have been prepared varying different parameters such as the spacer length, the aliphatic tail length, and the proportion of laterally attached mesogenic units along the polymer chain. The results show that the combination of a long spacer and long terminal chains, which generates a smectic phase in the polymer bulk, leads to the best chromatographic performances towards planarity and shape recognition for PAH solutes.