Liquid Crystalline Polyacrylates Research Articles

Microscopic Surface Patterns of a Liquid Crystalline Polyacrylate Film

Lamellae-like surface ripples, as shown in the Figure, can be induced on liquid crystalline polyacrylate films. The film surface shows regular height modulations, which are attributed to coupling between local liquid crystal ordering and surface curvature energy. The properties of these films, including their use for the patterning of otherwise homogeneous surfaces, are discussed in this communication.

Frustrated Behavior of a Side-Chain Liquid Crystalline Polyacrylate

Polyacrylate with phenyl benzoate mesogenic side groups was synthesized and fractionated into narrow fractions. Structure and phase behavior of the narrow-molecular-weight samples have been studied by X-ray diffraction. Depending on the degree of polymerization the polymer shows nematic, smectic A d , re-entrant nematic and new phase with two-dimensional (2D) periodicity. Such behaviour is implicit to so-called frustated systems. However, the mesogenic side chains are nonpolar and thus the origin of frustation is different from that in conventional polar liquid crystals. We found that this phenomenon is steric (entropic) in nature and depends on the length of the polymer backbone. The phase transformations of mesogen side chain polyacrylates are discussed in terms of coupling between the smectic ordering of the side groups and the polymer backbone conformations.

Thermotropic side chain polyacrylates with azobenzene mesogenic groups: Synthesis and thermal behaviour

Four side chain liquid crystalline (LC) polyacrylates containing substituted (methyl/long alkyl) azobenzene mesogens attached directly to the polymer backbone were synthesized. The polyacrylates were synthesized by free radical polymerization of the respective monomers, 4-[(4-acryloylexyphenyl)azo]benzoic acid, 4-[(4-acryloyloxy-3-methylphenyl)azo]benzoic acid, 4-[(4-acryloxy-2-methyl]phenyl)azo]benzoic acid and 4-[(4-acryloyloxy-2-pentadecylphenyl)azo[benzoic acid. The monomers were obtained by acryloylation of the azo derivatives prepared by the diazo coupling reaction between p-aminobenzoic acid and the respective phenolic derivatives with varying hydrocarbon substituents. All polymers were soluble in polar solvents. The inherent viscosities of the polymers in DMSO at 28°C were in the range of 0.55-0.62 dL/g. The monomers and their polymers were characterised by elemental analysis, IR, UV-vis, 1 H and 13 C NMR spectroscopies and WAXD. The thermal and phase transition behaviour of the polymers were investigated using DSC and a hot stage polarized light microscope (PLM). The polyacrylates exhibited stir opalescence and low viscosity characteristic of nematic phase on melting. However, the polymer with the long alkyl side chain (C 15 H 31 ) was polymorphic with a smectic phase besides a nematic phase. The methyl substituted polymers showed only nematic phases. The effect of regioisomers on transition temperatures was significant. The carboxylic acid groups of the azophenyl mesogen are found to exist as hydrogen bonded dimers as indicated by IR, NMR and finally confirmed by WAXD. It is proposed that the long alkyl substituent might be involved in the stabilisation of the mesophase through its alignment paralled to the long axis of the molecule and might probably be supporting the formation of a smectic phase by reducing the transition temperature enough to maintain the layered arrangement of hydrogen bonded dimers.

Thermotropic side chain polyacrylates with azobenzene mesogenic groups: Synthesis and thermal behaviour

Four side chain liquid crystalline (LC) polyacrylates containing substituted (methyl/long alkyl) azobenzene mesogens attached directly to the polymer backbone were synthesised. The polyacrylates were synthesised by free radical polymerization of the respective monomers, 4-[(4-acryloyloxyphenyl)azo]benzoic acid, 4-[(4-acryloyloxy-3-methylphenyl)azo]benzoic acid, 4-[(4-acryloyloxy-2-methylphenyl)azo]benzoic acid and 4-[(4-acryloyloxy-2-pentadecylphenyl)azo]benzoic acid. The monomers were obtained by acryloylation of the azo derivative prepared by the diazo coupling reaction between p-aminobenzoic acid and the respective phenolic derivatives with varying hydrocarbon substituents. All polymers were soluble in polar solvents. The inherent viscosities of the polymers in DMSO at 28°C were in the range of 0.55–0.62 dL/g. The monomers and their polymers were characterised by elemental analysis, IR, UV-vis, 1H and 13C NMR spectroscopies and WAXD. The thermal and phase transition behaviour of the polymers were investigated using DSC and a hot stage polarized light microscope (PLM). The polyacrylates exhibited stir opalescence and low viscosity characteristic of nematic phase on melting. However, the polymer with the long alkyl side chain (C15H31) was polymorphic with a smectic phase besides a nematic phase. The methyl substituted polymers showed only nematic phases. The effect of regioisomers on transition temperatures was significant. The carboxylic acid groups of the azophenyl mesogen are found to exist as hydrogen bonded dimers as indicated by IR, NMR and finally confirmed by WAXD. It is proposed that the long alkyl substituent might be involved in the stabilisation of the mesophase through its alignment parallel to the long axis of the molecule and might probably be supporting the formation of a smectic phase by reducing the transition temperature enough to maintain the layered arrangement of hydrogen bonded dimers.

Synthesis and Characterization of a Novel Liquid Crystalline Polymer Showing a Nematic Columnar to Nematic Discotic Phase Transition

A novel liquid crystalline polyacrylate, exhibiting a nematic columnar and a nematic discotic phase, the latter not found in any polymer previously, has been synthesized using a polymer analogous r...

Side-chain liquid crystalline polyacrylates containing 3,4-disubstituted pyrrole moiety

Polymerization of liquid crystalline bifunctional monomer N-{{ω-{4-[4-(11-acryloyloxy)undecanoxybenzoyl]biphenyleneoxy} alkyl}}-3,4-dimethylpyrrole gave a side-chain liquid crystalline polyacrylate containing 3,4-dimethylpyrrole group. Liquid crystallinity was determined by DSC and optical polarizing microscope measurements. The monomers having pentylene, hexylene, and decylene as the alkylene spacer group between the mesogenic unit and the 3,4-dimethylpyrrole group exhibited smectic and nematic phases on the heating and cooling stages. The radically polymerized polyacrylate derivatives containing the 3,4-dimethylpyrrole group showed nematic phases on the heating and cooling stages. These polymers are the first example of side-chain liquid crystalline polymers containing 3,4-dimethylpyrrole as functional group for further reaction. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1214–1221, 2000

The glass transition relaxation in a side-chain liquid crystalline polymer studied by modulated temperature differential scanning calorimetry

A side-chain liquid crystalline polyacrylate was investigated by modulated temperature differential scanning calorimetry (MTDSC) in the temperature region of the glass to liquid-crystal transformation. The technique provides the possibility of analysing the temperature dependence of the complex heat capacity, and of its real and imaginary components. This allows determination of the kinetic parameters associated with the glass transition, as well as the index of fragility of the substance. The obtained results show very good agreement with those recently obtained on the same sample by thermally stimulated depolarisation currents.

Synthesis and characterization of liquid crystalline polyacrylates and non-liquid crystalline polypyrroles from bifunctional monomers

Two kinds of polymerizations of liquid-crystalline N-{{W-{4-[4-(11-acryloyloxy)undecanoxybenzoyl]biphenyleneoxy}alkyl}}pyrrole gave a side-chain liquid-crystalline polyacrylate containing pyrrole group and a non-liquid crystalline polypyrrole containing acrylate group. Liquid crystallinity was determined by DSC and optical polarizing microscope measurements. The monomers having hexyl or decyl group as the alkyl group exhibited an undefined smectic, smectic B, and smectic A phases on the heating stage. The radically polymerized polyacrylate derivatives containing the pyrrole group showed smectic A, smectic C, and undefined smectic phases on the cooling stage. On the other hand, soluble N-substituted polypyrrole derivatives containing the terminal acrylate group which were prepared by chemical oxidative polymerization by ferric chloride catalyst did not show liquid crystallinity. Structure analysis of the polypyrroles performed by 1H and 13C-NMR and FT-IR spectroscopies demonstrated that the polymerization occurred at the pyrrole ring. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3877–3887, 1999

Synthesis and characterization of liquid crystalline polyacrylates and non‐liquid crystalline polypyrroles from bifunctional monomers

Synthesis and characterization of liquid crystalline polyacrylates and non‐liquid crystalline polypyrroles from bifunctional monomers

Synthesis and properties of photochromic liquid-crystalline polyacrylates containing a spirooxazine group

The novel photochromic liquid-crystalline polyacrylates containing a spirooxazine group were synthesized. The photochromic polymer containing (4-pentamethyleneoxy)biphenylene moiety at the 5-position of spironaphthoxazine showed nematic phase from 122.9 to 133.8°C. The photochromic polymer containing undecamethylene instead of pentamethylene showed smectic phase from 93.1 to 169.7°C. On the other hand, the photochromic polymer containing both undecamethylene as a spacer and spironaphthoxazine-bound biphenylene moiety at 9'-position did not show any liquid crystallinity. All spirooxazine-containing liquid-crystalline polymers showed photochromism in the solid state at room temperature. Because the shape of the absorption spectra of the photochromic quenched liquid-crystalline polymer films was almost the same as those of the photochromic amorphous polymer films, the photochromic properties did not depend on the mesophase in the polymers examined.

Blends of side-chain liquid crystalline polymers: towards self-assembled interpenetrating networks

The possibility of using various types of non-covalent cross-linking, to promote the structure of interpenetrating networks in blends based on side-chain liquid crystalline polymers, was investigated. The polymers used included: (1) random copolymers of liquid crystalline polyacrylates containing benzoic acid units for hydrogen-bond cross-linking through the formation of intermolecular dimers; (2) liquid crystalline polyacrylate-ionomers bearing sodium salt groups for cross-linking through ionic aggregates; and (3) a styrene–butadiene–styrene triblock copolymer having a network structure with polystyrene microdomains as cross-links. The preparation method consists of making a dilute solution of two polymers, then evaporating the solvent and drying the mixture. No evidence of network interpenetrating was observed. The results suggest, however, that blends composed of two components having a network structure, for both H-bond/ionic-aggregate and H-bond/triblock-copolymer combinations, have a greater miscibility, compared with blends containing only one component capable of forming a network structure through non-covalent cross-linking. The improved miscibility is characterized by reduced domain sizes and, for blends of two liquid crystalline polymers, changes in the phase transition behavior.

Mesomorphic and dielectric properties of a side-chain liquid crystalline polyacrylate and copper(II) crosslinked derivatives

A side-chain liquid crystalline polyacrylate containing a salicylaldimine group has been synthesized and complexed with copper(II) ions to generate metallomesogenic crosslinking of polymeric chains. The mesomorphic properties of the parent and complexed polymers have been studied by optical microscopy, DSC and X-ray diffraction. In addition, these materials have been investigated in depth by dielectric spectroscopy. Dielectric measurements of the parent polymer reveal the presence of two sub-glass relaxations (β and γ). The α relaxation associated with the T g is masked by a conductive process, but at higher temperatures a δ relaxation is observed. These relaxation processes have been characterized and their activation energies evaluated. The influence of the mesogenic order and metal crosslinking on some relaxation processes has also been determined.

Dielectric relaxation behaviour of the side group liquid-crystalline polyacrylates having a segmented spacer

The dielectric relaxation behaviour and the alignment property of two kinds of liquid-crystalline (LC) polyacrylates, P-3EO-C6 and P-3EO-C11, having a segmented spacer, which consisted of binary components of an oligo(ethylene oxide) segment and an alkylene segment, was investigated to clarify the effect of the spacer structure on these properties. For P-3EO-C6 showing a glassy behaviour, δ-relaxation was observed in the lower temperature region compared with the case of an ordinary liquid-crystalline polymer with mesogenic side groups (SGLCP). The relaxation behaviour of the samples of both P-3EO-C6 and P-3EO-C11 indicated characteristically low values of ΔG‡. The microphase separation was supposed in the case of P-3EO-C11 to have a long alkylene segment. For the alignment behaviour of P-3EO-C6, the fully aligned sample could be achieved by applying an electric field. From these results, the advantage of the segmented spacer as an accelerator of the motion of a mesogenic group has been discussed in this paper.

The mesophase structure of block copolymers with liquid crystalline and semicrystalline blocks

The mesophase structure of block copolymers containing liquid crystalline polyacrylate and semicrystalline poly(tetrahydrofuran) or poly(cyclohexene oxide) blocks was investigated by X-ray diffraction of powder samples. All the block copolymers were microphase separated, and the number and the nature of the mesophases (smectic E, B and A) were governed by the structure of the liquid crystalline block. We determined the lattice parameters of the mesophases and calculated the electron density profiles ρ( z) along the smectic layer normal.

Preliminary communication Liquid crystalline polyacrylates using hyperbranched poly(p-chloromethylstyrene) as initiator

Two kinds of acrylate monomers, i.e. 4-methoxyphenyl 4-{[2-(1-oxo-2-propenyloxy)ethyl]oxy}benzoate (I) and 4-methoxyphenyl 4-{[6-(1-oxo-2-propenyloxy)hexyl]oxy}benzoate (II) were polymerized using hyperbranched poly(p-chloromethylstyrene) (PCMS) as an initiator by atom transfer radical polymerization (ATRP). The resulting dendritic graft copolymers were characterized by means of gel permeation chromatography, differential scanning calorimetry, and polarization microscopy. The mesophase behaviour of these dendritic copolymers essentially depends on the chemical nature of the polyacrylates.

Effect of the composition on the structure and ferroelectric properties of side chain liquid crystalline copolyacrylates

The structure and physical properties of two side chain liquid crystalline polyacrylates are discussed, one bearing biphenyl core and chiral carbon atom in the flexible spacer, and the other a phenyl benzoate core. The biphenyl version displays two smectic phases of S*F and S*F types and no ferroelectric switching. The phenyl benzoate variant displays a single SC phase. The copolymerisation of the two monomers led to polymeric materials exhibiting a S*c polymorphism and composition dependent structural features. Only the copolymer of equimolar composition displayed a strong piezoelectric response in the S*F phase and ferroelectric behaviour in the lower temperature S*c modification.

Influence of spacer structure on the molecular dynamics of side-chain liquid-crystalline polyacrylates as studied by dielectric relaxation spectroscopy

The dynamic behaviour of side-chain polyacrylates, whose polymer backbones were connected to a mesogenic core composed of cyanophenyl benzoate or cyanobiphenylyl benzoate via an alkylene (C11) chain or that containing a siloxane bond as a flexible spacer chain, have been studied by dielectric relaxation spectroscopy (102–106 Hz) at different temperatures in the smectic phase. Analyses using the Fuoss–Kirkwood function, WLF equation and activation parameters on the obtained dielectric loss revealed that the siloxane-spacer apparently enhanced the mobility of a mesogenic group owing to a decrease of Tg, and that the introduction of as small a mesogen as possible might be one of the most important factors in responding rapidly to changes of an external field.

A new synthetic approach to side-chain liquid crystalline polyacrylates containing siloxane spacers and their thermal behaviours

The syntheses of novel side-chain liquid crystalline polyacrylates (LCPAs) containing siloxane spacers were carried out according to a convenient route by preparing alcohol compounds having a mesogenic group linked with a siloxane bond as key intermediates of the monomers. A relatively large mesogenic group was necessary to exhibit a mesophase in this system. The introduction of a siloxane spacer lowered the temperature range of mesophase of LCPAs resulting from the decrease of T, as compared with the corresponding LCPAs containing an alkylene spacer. It was also revealed that the chemical structure of spacer component played an important role for the assembly structure in the mesophase. g

Temperature Dependence of the Surface Behaviour of a Side-Chain Liquid Crystalline Polymer Probed by Contact Angle Measurements

In this study the temperature dependence of the surface properties of a side-chain liquid crystalline polyacrylate is investigated through contact angle measurements. In particular, the effect of the glass transition (Tv=46.7°C) on the surface tension of the liquid crystalline polymer is analysed. The total surface tension as well as its dispersive and polar components are determined as a function of temperature, between 24°C and 73°C, from contact angle values of water, diiodomethane and glycerol. For water and diiodomethane the proximity of the glass transition temperature induces an abrupt change in the temperature dependence of the contact angle; the same is not observed for glycerol. The calculations were performed using the most common techniques: the Neumann equation of state for interfacial tensions, the Owens-Wendt approach (also known as the geometric mean approach) and Lifshitz-van der Waals donor-acceptor approach (also known as the acid-base approach). The results obtained for the total surface tension of the polymer surface were compared and discussed. The temperature dependence of the surface tension exibits the behaviour characteristic of a second-order transition: the surface tension is continuous in the vicinity of the glass transition temperature but its first derivative is discontinuous. Furthermore, the decomposition of the surface tension into its components shows that the polar component, γp s, has a small contribution throughout the entire temperature range, while the dispersive component, γd s, largely predominates. The temperature dependence of both components γd s and γp s is clearly different in the two phases (glassy and liquid crystalline), despite the fact that the total surface tension does not present any appreciable discontinuity across the glass transition.

High-pressure mesomorphic behavior of a chiral polyacrylate by x-ray diffraction in situ

The high-pressure mesomorphic behavior of a chiral liquid crystalline polyacrylate has been studied by x-ray diffraction in situ. The results show the existence of monolayer smectic-A and bilayer smectic-C mesophases that coexist in the thermally untreated sample over a well-defined range of temperatures, from ambient pressure up to 133 MPa. Hydrostatic pressures of the order of 100--220 MPa are found to affect strongly the polymorphic behavior of the sample. The smectic-A mesophase, which at ambient pressure coexists with an interdigitated smectic-C structure, is stabilized over a temperature range which increases with pressure, whereas the formation of the smectic-C phase is inhibited above 220 MPa. The pressure increment is found to introduce static positional disorder, and to reduce the long-range positional order in the smectic structure strongly. A transition sequence from the isotropic melt through the smectic-A phase to a new crystalline structure is found by cooling isobarically down to room temperature. The proposed pressure-temperature phase diagram suggests the occurrence of peculiar disorder-order-disorder transitions as pressure is reduced isothermally.