Side-chain Liquid Crystalline Polymers Research Articles

Synthesis of Double Side-Chain Liquid Crystalline Block Copolymers Using RAFT Polymerization and the Orientational Cooperative Effect

We report on the synthesis and characterization of a new type of diblock copolymer that is composed of two side-chain liquid crystalline polymers (SCLCP1-block-SCLCP2). The diblock copolymer of poly{6-[4-(4-methoxyphenylazo)phenoxy]hexyl methacrylate}-block-poly{6-[4-(4-cyanophenyl)phenoxy]hexyl methacrylate} (PAzoMA-b-PBiPMA) was successfully synthesized using the reversible addition−fragmentation chain transfer (RAFT) polymerization. Low-polydispersity samples of various compositions can be prepared using either PAzoMA or PBiPMA macromolecular chain transfer agent. We show that the orientational cooperative effect can be effective even in microphase-separated samples due to the interaction of the two mesogens via the interface. Indeed, the photoinduced orientation of azobenzene groups on the PAzoMA block can bring biphenyl groups on the PBiPMA block to orient in the same direction inside their respective lamellar domains. While RAFT can be used to access to double or all-SCLC block copolymers, this study also demonstrates the potential interest of exploring the interplay of the LC order of different SCLCPs within a microphase-separated system.

A Micellar Route to Layer-by-Layer Assembly of Hydrophobic Functional Polymers

We demonstrate a general approach to introduce hydrophobic functional polymers into a multilayer film using the layer-by-layer (LBL) assembly method that normally works for water-soluble polyelectrolytes. To this end, two new amphiphilic diblock copolymers each containing a hydrophobic side-chain liquid crystalline polymer (SCLCP) were synthesized using atom transfer radical polymerization, followed by a modification reaction. They are poly(acrylic acid)-b-poly{6-[4-(4′-cyanophenyl)phenoxy]hexyl methacrylate} (PAA-b-PCMA) and quaternized poly(4-vinyl pyridine-b-poly{6-[4-(4-ethyloxyphenylazo)phenoxy]hexyl methacrylate} (QP4VP-b-PAMA). We show that through the use of their micelles in aqueous solutions, which have a polycation (QP4VP-b-PAMA) or a polyanion (PAA-b-PCMA) corona, the two hydrophobic SCLCPs can be LBL assembled. The characterization results indicate that the LC phases are retained in the film, and that the SCLCPs are subjected to confinement effects inside the nanodomains defined by the core regions of the micelles. This micellar route to LBL assembly of hydrophobic functional polymers is general and offers new possibilities of designing nanostructured materials.

Image storage based on circular-polarization holography in an azobenzene side-chain liquid-crystalline polymer

Image storage was investigated in a liquid-crystalline azobenzene polymer film based on circular-polarization holographic recording. An image was stored in pure polarization holograms using two orthogonal circularly polarized 532 nm beams and was reconstructed with a 633 nm beam. The polarization holograms showed high stability and a high diffraction efficiency of 31.8%. Moreover, the polarization holograms could convert arbitrary probe polarization state into circular polarization, and the diffraction efficiency was dependent on the probe polarization state, which was favorable for controlling the reconstructed images.

A Model for Self-Assembly in Side Chain Liquid Crystalline Block Copolymers

We present a new model based on self-consistent field theory (SCFT) approach and complement it by strong segregation theory (SST) based calculations to characterize the self-assembly behavior in side-chain liquid crystalline block copolymers. Our model considers a micromechanical representation of flexible coil−coil diblock copolymers, with rodlike units grafted to one of the blocks. We present results which elucidate self-assembly arising from the interplay between block copolymer microphase separation and the orientational ordering of the rod segments. We determine the morphological phase diagram for this system by assuming two dimensional variations of composition profiles. Our numerical results are in very good agreement with reported experimental observations. Many of the traditional flexible diblock copolymer microphases are also predicted to occur for side chain liquid crystalline polymers, with smectic ordering accompanying within the microphases. The equilibrium phase morphologies are observed to depend on the molecular weight of the copolymer, the length of the rod units, the relative volume fractions of each block, and the energetic and orientational interactions between different components. Moreover, for the parameters considered in this article, microphase separation was observed to be a requisite for developing orientational ordering between mesogenic units. The results of SST provide a physical explanation for the observations and are in good agreement with that of the SCFT calculations.

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.

Phase Equilibria of a Mixture of Side-Chain Liquid Crystalline Polymer and Low Molecular Mass Liquid Crystal

A side-chain liquid crystalline polymer based on p-methoxyphenyl-p‘-acryloyloxy benzoate was synthesized for utilization in a polymer dispersed liquid crystal. Phase diagram of the blends of side-chain liquid crystalline polymer and low molecular mass liquid crystal (K21) was established by means of light scattering and differential scanning calorimetry. A theoretical phase diagram was established by self-consistently solving the combined free energy densities of Flory−Huggins, Maier−Saupe, and phase field theory of solidification. The theoretical phase diagram was established to compare with the observed phase diagram of the binary mesogenic mixtures, showing the isotropic, isotropic + nematic (L1 + N2), nematic + nematic (N1 + N2), and crystal + nematic (Cr1 + N2) coexistence regions. The morphologies of these coexistence regions were further confirmed by polarized optical microscopy.

β Dielectric relaxation mode in side-chain liquid crystalline polymer film

Abstract In this paper, side-chain liquid crystalline polymer (SLCP) film was studied by dielectric relaxation spectroscopy (DRS). Dielectric properties were measured in the frequency range from 1 kHz to 10 MHz at some fixed temperatures. The experimental data were fit non-Debye type Cole–Cole dielectric relaxation function. A single dielectric relaxation mode was observed in polymer film. It is observed that relaxation characteristics show Arrhenius type behavior. Activation energy value obtained from the relaxation data was found to be 0.1 eV. The relaxation process is interpreted in terms of side-chain dipole group motion (β relaxation).

Preparation and characterization of side-chain liquid crystalline polymers containing chenodeoxycholic acid residue

A series of new side-chain liquid crystalline polymers containing chenodiol residue derived from 24-[4′-hydroxybiphenyl-4-yl-4-(allyloxy)benzoyloxy]-3α,7α-di{n-[4′-(4-ethoxybenzoyloxy)biphenyl-4-yloxy]-n-oxoalkanoyloxy}-5β-cholane was designed and prepared. The chemical structures of the monomer and polymer were confirmed by Fourier transform infrared and 1H NMR spectra. The mesomorphic properties of monomer and polymer were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X-ray diffraction. The side-chain liquid crystalline polymers revealed wide mesophase temperature range and high thermal stability, and they showed nematic liquid crystalline phase. The influence of flexible space group length on thermal properties and specific rotation was examined.

Structure and internal dynamics of a side chain liquid crystalline polymer in various phases by molecular dynamics simulations: A step towards coarse graining

Side chain liquid crystalline polymer with relatively long spacer was modeled on a semiatomistic level and studied in different liquid crystalline phases with the aid of molecular dynamics simulations. Well equilibrated isotropic, polydomain smectic and monodomain smectic phases were studied for their structural and dynamic properties. Particular emphasis was given to the analysis on a coarse-grained level, where backbones, side chains, and mesogens were considered in terms of their equivalent ellipsoids. The authors found that the liquid crystalline phase had a minor influence on the metrics of these objects but affected essentially their translational and orientational order. In the monodomain smectic phase, mesogens, backbones, and side chains are confined spatially. Their diffusion and shape dynamics are frozen along the mesogen director (the one-dimensional solidification) and the reorientation times increase by one to one-and-half orders of magnitude. In this phase, besides obvious orientational order of mesogens and side chains, a stable detectable order of the backbones was also observed. The backbone director is confined in the plane perpendicular to the mesogen director and constantly changes its orientation within this plane. The backbone diffusion in these planes is of the same range as in the polydomain smectic phase at the same temperature. A detailed analysis of the process of field-induced growth of the smectic phase was performed. The study revealed properties of liquid crystalline polymers that may enable their future fully coarse-grained modeling.

Theory of microphase separation on side-chain liquid-crystalline polymers with flexible spacers

We model a melt of monodisperse side-chain liquid-crystalline polymers as a melt of comb copolymers in which the side groups are rod-coil diblock copolymers. We consider both excluded-volume and Maier-Saupe interactions. The first acts among any pair of segments while the latter acts only between rods. Using a free-energy functional calculated from this microscopic model, we study the spinodal stability of the isotropic phase against density and orientational fluctuations. The phase diagram obtained in this way predicts nematic and smectic instabilities as well as the existence of microphases or phases with modulated wave vector but without nematic ordering. Such microphases are the result of the competition between the incompatibility among the blocks and the connectivity constraints imposed by the spacer and the backbone. Also the effects of the polymerization degree and structural conformation of the monomeric units on the phase behavior of the side-chain liquid-crystalline polymers are studied.

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.

Photo‐optical properties and photo‐orientation phenomena in an immiscible blend of cholesteric copolymer with azobenzene‐containing polymer

Novel side chain liquid crystalline polymer blends containing immiscible non‐chiral and cholesteric polymers were prepared. A non‐chiral polymer was used containing azobenzene side groups capable of E–Z photoisomerization. Phase behaviour and miscibility properties of the blends were studied. Thin films of the blends were prepared by spin‐coating; it was shown that just after preparation these films are optically isotropic and homogeneous. Photo‐ and chiro‐optical properties of the films as well as photo‐orientation phenomena induced by the action of polarized light were investigated. It was found that the photo‐optical behavior of these films is rather complicated and considerably different from the properties of both individual components. This difference is associated with the strong influence of blend morphology on the photo‐optical properties.

Synthesis, characterization and photolysis studies on liquid crystalline poly[4-(4′- x-biphenyl)yl-4″-( m-methacryloyloxyalkyloxy) cinnamate]’s

Three series of side chain liquid crystalline polymers containing terminally substituted biphenyl cinnamoyl esters were synthesized and characterized. The para position in the cinnamoyl group was connected with polymer backbone through various even numbers of methylene spacers. The terminal electron acceptor and donor substituted biphenyl groups were linked to cinnamoyl group through ester linkages. Polarizing microscopic and DSC studies confirm the formation of thermotropic mesophase up on heating. All the polymers exhibited nematic/grainy mesophases. The TGA and DSC studies showed that the nature of the terminal substituents have significant effect on mesophase temperatures as well as in thermal stability of these liquid crystalline polymers. UV light promoted photocrosslinking studies reveal that the clear involvement on photocrosslinking efficiency, although they are linked to the olefinic bond of cinnamoyl group through their ester linkage. It is observed that electron-donating group accelerate the photocrosslinking rate, while acceptor group retard the phase of the reaction on the other hand, the unsubstituted polymers show an intermediate rate.

Side-chain cholesteric liquid crystalline polymers containing menthol and cholesterol—synthesis and characterization

A series of new cholesteric side-chain liquid crystalline polymers were prepared containing cholesteric monomer and nonmesogenic chiral monomer. All polymers were synthesized by graft polymerization using polymethylhydrosiloxane as backbone. The mesomorphic properties were investigated by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction measurements, and temperature-changing solidistic optical rotation. The chemical structures of the monomers and polymers obtained were confirmed by Fourier transform infrared and proton nuclear magnetic resonance spectra. M1 showed cholesteric phase during the heating and the cooling cycle. Polymer P1 were chiral smectic A phase, whereas P2–P7 were cholesteric phase. Experimental results demonstrated that nonmesogetic chiral moity offered the possibility of application because of its lower glass-transition temperature, and the glass-transition temperatures and isotropization temperatures reduced, and the ranges of the mesophase temperature changed abruptly at first and then smoothly with increasing the content of chiral agent.

Photochromism of liquid crystalline dendrimer with azobenzene terminal groups in solution

The photochromism of a liquid crystalline dendrimer (LCD) with 36 hexyloxyazobenzene terminal groups in solution was described in this paper. The molar absorption coefficient, quantum yield, photoisomerization, photo back-isomerization, thermal back-isomerization and activation energy of LCD in solution are studied by UV/Vis absorption spectra. The results indicate that the photochromism, photo and thermal back-isomerization of LCD in chloroform (CHCl 3) and tetrahydrofuran (THF) solutions are in accordance with the first order kinetics. The photochromism rate constants of LCD are 10 −1 s −1, it is 10 7 times larger than that of side-chain liquid crystalline polymers (LCP) containing the same azobenzene moieties. These results indicate that the dendritic structure does not significantly affect the photoisomerization activity of the azobenzene unit in its periphery. The k t / k c of LCD is less than that of azobenzene unit shows that the LCD has better photo-reversibility. So the liquid crystalline dendrimer has potential applications.

Nematic and Domain Order Parameters for Partially Oriented Isotropic/Liquid Crystalline Diblock Copolymers: A Dielectric Spectroscopy Study

Dielectric relaxation in a liquid crystalline (LC) side chain polymer and in a series of diblock copolymers with polystyrene is investigated using dielectric spectroscopy. The block copolymer morphology is cylindrical with the LC block forming the continuous matrix. Two processes are found in the nematic state with their relative dielectric relaxation strength strongly dependent on block copolymer composition. The spectra are described using the concept of a local order parameter S and a domain order parameter SD. Application of electric or mechanical fields induce a homeotropic orientation of the nematic domains in the homopolymer without significantly influencing the local order parameter. The block copolymers display a spontaneous orientation even in thick films (d < 300 nm).

Isotropic-to-nematic transition in liquid-crystalline heteropolymers: II. Side-chainliquid-crystalline polymers

We apply a density functional approach for arbitrary branched liquid-crystalline (LC)heteropolymers consisting of elongated rigid rods coupled through elastic joints developedin a companion paper (Wessels and Mulder 2006 J. Phys. Condens. Matter. 18 9335) to amodel for side-chain liquid-crystalline polymers. In this model mesogenic units are coupledthrough finite-length spacers to a linear backbone polymer. The stereochemical constraintsimposed at the connection between spacer and backbone are explicitly modelled. Using abifurcation analysis, analytical results are obtained for the spinodal density of the I–Ntransition and the variation of the degree of ordering over the various molecular parts atthe instability as a function of the model parameters. We also determine the location of thecrossover between oblate and prolate backbone conformations in the nematic phase.

Thermal, morphological, and mechanical characteristics of polypropylene/polybutylene terephthalate blends with a liquid crystalline polymer or ionomer

AbstractThermotropic side‐chain liquid crystalline polymer (SLCP) and corresponding side‐chain liquid crystalline ionomer (SLCI) containing sulfonate acid were used in the blends of polypropylene (PP) and polybutylene terephthalate (PBT) by melt‐mixing respectively, and thermal behavior, morphological, and mechanical properties of two series of blends were investigated by differential scanning calorimetry, Fourier transforms infrared spectroscopy (FTIR), scanning electron microscopy, and tensile measurement. Compared with the immiscible phase behavior of PP/PBT/SLCP blends, SLCI containing sulfonate acid groups act as a physical compatibilizer along the interface and compatibilize PP/PBT blends. FTIR analyses identify specific intermolecular interaction between sulfonate acid groups and PBT, and then result in stronger interfacial adhesion between these phases and much finer dispersion of minor PBT phase in PP matrix. The mechanical property of the blend containing 4.0 wt % SLCI was better than that of the other blends. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4712–4719, 2006

Side-Chain Liquid Crystalline Polymers with [α-terpineol-co-MMA] Main Chain: Synthesis and Characterization of Polymers with Phenyl Benzoate Mesogenic Group

Side chain liquid crystalline (SCLC) [α-terpineol-co-MMA] polymers with a phenyl benzoate mesogenic group with polymethylene spacers have been synthesized and characterized in which the spacer length is taken 9 methylene units. The thermal behavior and liquid crystallinity of the polymer has been characterized using Differential Scanning Calorimetry (DSC) and Polarized Optical Microscopy (POM) techniques . The DSC curve of the LCpolymer shows glass transition at 52 °C followed by nematic phase which undergoes isotropization at 120 °C without undergoing side chain crystallization. Under optical polarized microscope the appearance of characteristic schlieren texture confirms the presence of nematic phase .

Phase Biaxiality in Nematic Liquid Crystalline Side-Chain Polymers of Various Chemical Constitutions

In a previous deuterium NMR study conducted on a liquid crystalline (LC) polymer with laterally attached book-shaped molecules as the mesogenic moiety, we have revealed a biaxial nematic phase below the conventional uniaxial nematic phase (Phys. Rev. Lett. 2004, 92, 125501). To elucidate details of its formation, we here report on deuterium NMR experiments that have been conducted on different types of LC side-chain polymers as well as on mixtures with low-molar-mass mesogens. Different parameters that affect the formation of a biaxial nematic phase, such as the geometry of the attachment, the spacer length between the polymer backbone and the mesogenic unit, as well as the polymer dynamics, were investigated. Surprisingly, also polymers with terminally attached mesogens (end-on polymers) are capable of forming biaxial nematic phases if the flexible spacer is short and thus retains a coupling between the polymer backbone and the LC phase. Furthermore, the most important parameter for the formation of a biaxial nematic phase is the dynamics of the polymer backbone, as the addition of a small percentage of low molar mass LC to the biaxial nematic polymer from the original study served to shift both the glass transition and the appearance of detectable biaxiality in a very similar fashion. Plotting different parameters for the investigated systems as a function of T/Tg also reveals the crucial role of the dynamics of the polymer backbone and hence the glass transition.