Synthesis and thermal transitional properties of side-chain liquid crystalline polyacrylates containing para-nitroazobenzene as mesogenic groups

The synthesis and characterization of side-chain liquid crystalline (LC) polyacrylates containing para-nitroazobenzene (Pn) as mesogenic groups were described. Homopolymers with 3 and 4 carbon atoms in the spacers were non-LC polymer; for homopolymers with 6 carbon atoms in the spacer, nematic LC behavior was observed. Copolymers with acrylic acid as one componenet exhibited an S_Ad phase according to the WAXD results which showed the d/l of 1.4–1.54 for the copolymers with 3,4 and 6 carbon atoms in the spacers. Considering the molecular structure as well as the WAXD results of the copolymers, the possible molecular arrangement in the smectic S_Ad phase was proposed, in which the smectic layers were composed of the antiparallel mesogens and the antiparallel arrangement was considered to be enhanced due to the H bond between  COOH and  NO₂. The stress-induced orientational phenomena of Pn in the LC states was also discussed. © 1996 John Wiley & Sons, Inc.     

The influence of lateral substituents on the phase behavior of side-chain liquid crystalline polysiloxanes containing trans-2,5-disubstituted-1,3-dioxane based mesogenic side groups

The synthesis and characterization of the polysiloxanes containingtrans-2,5-disubstituted-1,3-dioxane-based mesogenic side groups were described in this present study. Among three polysiloxanes containing three methylene units in their spacers, one without the lateral substituent exhibited two enantiotropic smectic phases while the other two polymers with a lateral methyl- or methoxy-substituent displayed an enantiotropic nematic phase. For polymers containing a longer spacer length (n 4), those without lateral substituent presented two enantiotropic smectic phases while the others containing a lateral substituent showed only an enantiotropic smectic A phase. The lateral substitution exerted a strong effect on the mesomorphic properties of the synthesized polymers.     

Phase behaviors of comb-like liquid crystalline polysiloxanes containing fluorinated mesogenic units

Several liquid crystalline polysiloxanes (Pa-Pf) bearing fluorinated mesogenic units were synthesized using poly(methylhydrogeno)siloxane, 4′-(4-undec-10-enoyloxy-benzoyloxy)-biphenyl-4-yl 4-fluoro-benzoate and 4′-propionyloxy-biphenyl-4-yl 4-allyloxy-benzoate, and effect of fluorinated mesogenic units on phase behaviors of the fluorinated LC polysiloxanes was studied as well. The samples Pa and Pb showed single nematic mesophase when they were heated and cooled, but Pc, Pd, Pe and Pf exhibited both smectic and nematic phases. The glass transition temperature and smectic A-nematic mesophase transition temperature of polymers increased slightly with increase of fluorinated units in the polymer systems, but mesophase-isotropic phase transition temperature decreased slightly. In XRD curves, the intensity of sharp reflections at low angle increased with increase of fluorinated mesogenic units in the polymers' systems, indicating that the longer spacer and the fluorophobic effect of fluorinated mesogenic units could lead to a significant stabilization and even to modifications of smectic mesophases.     

Thermotropic liquid crystalline polyesters containing naphthalenic mesogenic groups

Summary Recently, the use of naphthalene in liquid crystalline compounds has become more commonplace primarily in the industrial research into LC polymers with wholly aromatic structures. A large number of compositions have appeared in the patent literature, and have been well summarized in several recent articles. Even though a large number of LC naphthalene-containing copolyesters have been prepared and reported, much of this work deals with wholly aromatic systems which include no flexible spacers. In order to investigate the effects that the naphthalene structure has on liquid crystalline behaviour, a series of low molecular weight model compounds and polymers with flexible spacers were synthesized and characterized.     

Cirality induction in liquid crystalline side-chain polyethers prepared by copolymerization of oxiranes with mesogenic and non mesogenic groups

Copolymers prepared by anionic initiation from racemic or optically active styrene oxide and a racemic oxirane bearing cyanobiphenyl mesogenic group in the side chain are liquid crystalline when the content of the mesogenic monomer exceeds 60 mole %. Copolymers prepared from a mesogenic oxirane with a short spacer and racemic styrene oxide exhibit a nematic phase, while those prepared with optically active styrene oxide exhibit a cholesteric phase, thus indicating a transfer of chirality from the main chain towards the mesophase. Such a transfer of chirality is no more observed in the case of a copolymer prepared from a mesogenic oxirane with a long spacer. Received: 18 October 1996/Revised: 18 November 1996/Accepted: 20 November 1996     

Synthesis and thermal transition of side-chain liquid crystalline polyoxetanes having laterally attached mesogenic group

Side-chain liquid crystalline polymers with laterally attached mesogenic group were synthesized. Polymers having polyoxetane main chain were obtained by cationic polymerization, and with polymethacrylate main chain by radical polymerization. Some of the polymers showed nematic phase, and polyoxetanes having mesogen with electron-withdrawing and electron-donating groups in the molecule showed a little more discrete mesophase.     

Liquid crystalline properties of cholesteric elastomers based on a mesogenic monomer containing menthyl groups

A new chiral mesogenic monomer (M_LC) based on menthyl groups and the corresponding cholesteric elastomers (LCE₁–LCE₃) were prepared. Their chemical structures and purity were characterized by Fourier transform infrared, nuclear magnetic resonance and elemental analyses. The liquid crystalline properties were investigated by differential scanning calorimetry, polarizing optical microscopy, thermogravimetric analysis and X‐ray diffraction. The selective reflection of light for M_LC was characterized with ultraviolet/visible/near infrared. The effect of the content of crosslinking units on the liquid crystalline behaviour of LCE₁–LCE₃ is discussed. The experimental results show that the chiral monomer and the corresponding elastomers containing menthyl groups can show mesomorphism when a flexible linkage chain is inserted between the mesogenic core and the bulky terminal menthyl fragments to reduce the steric effect. M_LC exhibited a chiral smectic C phase, a cholesteric phase and a cubic blue phase. LCE₁–LCE₃ with a low content of crosslinking units showed a cholesteric phase because of the introduction of the nematic crosslinking unit. With increasing content of crosslinking units, the corresponding glass transition temperature increased, while the clearing temperature decreased. Thermogravimetric analysis showed that LCE₁–LCE₃ have good thermal stability. Copyright © 2012 Society of Chemical Industry     

Synthesis of side-chain liquid crystalline polyacrylates,polymethacrylates and polysiloxanes containing 4-cyano-biphenyl 4-alkanyloxybenzyl ether side groups

Summary The synthesis and characterization of side-chain liquid crystalline polyacrylates, polymethacrylates and polysiloxanes containing 4-cyanobiphenyl 4-alkanyloxybenzyl ether side groups are presented. All polymers display respectively a smectic A mesophase. The influence of the polymer backbone flexibility on the phase transition temperatures of the synthesized side-chain liquid crystalline polymers is discussed. The results demonstrate that flexible backbones enhance the decoupling of the motions of the side chain and main chain. Therefore, among three kinds of polymer backbones which contain the same mesogenic side groups, the most flexible one, i.e., polysiloxane, reveals a highest isotropization temperature and a widest temperature range of mesophase.     

Synthesis and phase behavior of chiral side‐chain liquid‐crystalline polysiloxanes containing two mesogenic groups

The synthesis of chiral side‐chain liquid‐crystalline polysiloxanes containing both cholesteryl undecylenate (M_I) and 4‐allyloxy‐benzoyl‐4‐(S‐2‐ethylhexanoyl) p‐benzenediol bisate (M_II) mesogenic side groups was examined. The chemical structures of the obtained monomers and polymers were confirmed with Fourier transform infrared spectroscopy or ¹H‐NMR techniques. The mesomorphic properties and phase behavior of the synthesized monomers and polymers were investigated with polarizing optical microscopy, differential scanning calorimetry, and thermogravimetric analysis (TGA). Copolymers IIP–IVP revealed a smectic‐A phase, and VP and VIP revealed a smectic‐A phase and a cholesteric phase. The experimental results demonstrated that the glass‐transition temperature, the clearing‐point temperature, and the mesomorphic temperature range of IIP–VIP increased with an increase in the concentration of mesogenic M_I units. TGA showed that the temperatures at which 5% mass losses occurred were greater than 300°C for all the polymers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2670–2676, 2002     

Synthesis and characterization of side-chain liquid crystalline polysiloxanes

The synthesis and characterization are described for a series of side-chain liquid crystal polysiloxanes using polyhydrosilylation reaction between a poly(hydrogen methyl-co-dimethylsiloxanes),-(OSiHMe)_x,-(OSiMe2)_y-, where x/y was 13/87, 30/70, 55/45, 73/27 and 98/2, and [4-(allyloxy)benzoyll biphenyl mesogenic group. The side-chain liquid crystal polysiloxanes were characterized by¹H NMR,¹³C NMR, IR, gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and optical polarizing microscopy. The dimethylsiloxane segment factors governing thermal transition temperatures and activation energy (E_a) of the nematic-to-isotropic phase transition are discussed.     

Liquid crystalline polymers containing mesogenic units based on half-disc and rod-like moieties

Part 1: V. Percec and J. Heck: J. Polym. Sci. Polym. Lett., submitted     

Liquid crystalline copolymers of monomer-pairs containing mesogenic units which exhibit constitutional isomerism

Summary The synthesis and characterization of side-chain liquid crystalline copolymers obtained from a monomer pair containing a mesogenic unit which exhibits constitutional isomerism are presented. The particular example described refers to copolymethacrylates obtained from 4-hydroxy-4-methoxy--methylstilbene and 4-methoxy-4-hydroxy--methylstilbene containing six and eleven methylenic units in the spacer. The polymer containing six methylenic units presents a nematic mesophase, while the polymer containing eleven methylenic units presents a smectic A or C mesophase. None of these polymers exhibited side-chain crystallization.     

Liquid crystalline polymers containing mesogenic units based on half-disc and rod-like moieties

Summary Oligo(methylacrylate)s with ester end-group are transesterified by allyl alcohol in the presence of lipozyme as catalyst. The transesterification is regioselective: only end-group is modified. The structure of the modified oligomers is studied by ¹³C NMR spectroscopy.     

Liquid crystalline polymers containing mesogenic units based on half-disc and rod-like moieties

Summary The synthesis and characterization of the hemiphasmidic monomers 4-{3,4,5-tri-[S(-)-2-methylbutan-1-yloxy] benzoate}-4'-(10-undecenoate)biphenyl (13), 4-[3,4,5-tri-(n-pentan-1-yloxy) benzoate]-4'-(10-undecenoate)biphenyl (14), 4-[3,4,5-tri-(n-dodecan-1-yloxy) benzoate]-4'-(10-undecenoate)biphenyl (15), 4-[3,4,5-tri-(n-dodecan-1-yloxy) benzoate]-4'-(10-undecen-1-yloxy)biphenyl (16) and of the polymethylsiloxanes derived from them (i.e. 17, 18, 19, and 20) are described. Monomers 13 to 16 are only crystalline. Polymer 17 is crystalline, 18 displays an unidentified mesophase, while 19, and 20 exhibit enantiotropic, most probably hexagonal columnar phasmidic mesophases.     

Phase transition and the packing structure of the side mesogenic groups of liquid crystalline side-chain copolymers

Summary Copolymers consisting of cholesteryl 11-methacryloyloxy-undecanoate (ChMO-10) and t-buthyl methacrylate (t-BMA) were studied by DSC method and by small angle X-ray scattering method (SAXS). Although homopolymer (pChMO-10) has two different packing structures which are a single-layer packing structure and a two-layer packing one, copolymers (co-pChMO-10-t-BMA) have only the single layer packing one in their mesophase. Furthermore, transition entropy at a clearing point of co-pChMO-10-t-BMA (80/20) is larger than that of pChMO-10. Adequate distance of the mesogenic groups in the direction of a short axis of the mesogenic groups, produced by introduction of non-mesogenic units, seems to stabilize the single-layer packing structure.     

Liquid crystalline epoxy resin cured by mesogenic hardening compounds

Summary A new type of liquid crystalline epoxy resin functionalized with mesogenic hardening agent was obtained by reacting stoichiometrically 4,4-bis (2,3-epoxypropoxy)-3,35,5-tetramethyl biphenyl (EPTB) (diepoxide monomer) with 4,4-bis (-carboxy decanoxy) azoxybenzene (CDA10) (mesogenic hardening monomer) at 145°C for 10 min, using tri-n-butylamine as a catalyst. Mesomorphic phase transition behavior for EPTB-CDA10 prepolymer obtained was studied as function of curing time at 140°C by use of DSC and polarized microscopy. When the curing time is shorter than a gelling time (60 min), EPTB-CDA10 showed a liquid crystalline state reminiscent of smectic phase, while that reminiscent of nematic phase, when the curing time is longer than the gelling time. This work indicates that the new type of epoxy resin cured by mesogenic hardening compound can have a liquid crystal state.     

Synthesis and characterization of optically active liquid crystalline polyacrylates containing mesogenic phenylbenzoate groups

A series of novel side chain liquid crystalline polyacrylates with pendant chiral groups were synthesized. It was found that monomers with electron releasing -OC₄H₉ terminal groups seem beneficial for the formation of liquid crystalline phases. Copolymerization of the monomers was carried out and the physical properties of the copolymers were investigated. All synthesized polymers revealed liquid crystalline phases and appeared highly thermally stable with decomposition temperatures (T_d) at 10% weight loss greater than 384 °C and about 50% weight loss occurred beyond 442 °C under nitrogen atmosphere. Two miscible chiral compounds were also synthesized and used as chiral dopants to induce cholesteric liquid crystalline phases of polymers. Liquid crystalline phases of the polymers were investigated using DSC and XRD, and confirmed with POM technique. The optical properties of the induced cholesteric liquid crystalline polymers were investigated using UV-vis spectrometer. The appearance and the color variation of the polymer films before and after UV irradiation were also investigated. Typical helical morphology of the cholesteric liquid crystalline film was analyzed by SEM technique.     

Liquid crystalline polyesters with two-dimensional mesogenic units

Summary A series of thermotropic, liquid crystalline (LC) polyesters was prepared in which the mesogenic group contained an unusually large, polarizable pendant group in an attempt to increase intermolecular interactions so as to impart a more isotropic character to the mechanical properties of the solid polymer. The series included repeating units containing main chain, polymethylene flexible spacers of increasing lengths. All of the polymers formed stable nematic LC phases and had relatively low melting temperatures, but recrystallization from the melt was very slow in each case. Dedicated to Prof. Dragutin Fleš on the occasion of his 70th birthday     

Liquid crystalline behavior of polymeric glycols terminated with aromatic diester and diacid mesogenic groups

A series of bis(benzylterephthaloyl-p-oxybenzoyl)esters (mesogen I) and bis(p-carboxybenzoyl-p-oxybenzoyl)esters (mesogen II) of several different polymeric glycols was prepared, and their thermotropic liquid crystalline behavior was studied by differential scanning calorimetry and by visual observation on the hot stage of a polarizing microscope. The polymeric glycols used were poly(ethylene oxide) (A), poly(tetramethylene oxide) (B), polybutadiene (C), and the hydrogenated polybutadiene (D) glycols, with molecular weights between 650 and 6000. With one exception, the benzyl ester derivations were not thermotropic, but the corresponding carboxylic acid derivatives were, and the related model compound, the bis(p-carboxybenzoyl-p-oxybenzoyl)ester of 1,12-dodecanediol, was also found to be liquid crystalline. The nature of the mesophases formed by the diacids derived from the macroglycol derivatives could not be clearly identified by their optical textures. Several of the diacid derivatives formed elastomeric films, even though they were still of low molecular weight, presumably because of chain extension by dimerization and association of the terminal mesogenic groups.     

Synthesis of side-chain liquid crystalline polyoxetanes containing 4-dodecanyloxyphenyltrans-4-alkylcyclohexanoate side groups

Summary The synthesis and characterization of side-chain liquid crystalline polyoxetanes containing 4-dodecanyloxyphenyl trans-4-alkylcyclohexanoate side groups are presented. All the obtained monomers exhibit smectic B mesomorphism, while all the obtained polymers present smectic A, smectic B and smectic G mesophases. A longer terminal alkyl group is leading to the formation of a more stable mesophase.