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Mesogenic Units (mesogenic + unit)
Selected AbstractsOligo(triacetylene) Derivatives with Pendant Long Alkyl ChainsHELVETICA CHIMICA ACTA, Issue 6 2004Jean-François Nierengarten Substituted (E)-2-(ethynyl)but-2-ene and (E)-hex-3-ene-1,5-diyne derivatives 6 and 10, respectively, were prepared by dicyclohexylcarbodiimide(DCC)-mediated esterification of tris(dodecyloxy)benzoic acid (4) with (E)-2-[(triisopropylsilyl)ethynyl]but-2-ene-1,4-diol (3) and (E)-2,3-bis[(trimethylsilyl)ethynyl]but-2-ene-1,4-diol (8), respectively, followed by deprotection with Bu4NF in wet THF (Schemes,1 and 2). Oligomerization reactions of diyne derivative 10 were attempted by treatment with the Hay catalyst in the presence of mono-alkyne 6 as an end-capping reagent. Under these conditions, only compound 7 resulting from the homocoupling of 6 (Scheme,1), and polymers of 10 were obtained due to the difference in reactivity of the alkyne groups in 6 and 10. In contrast, when phenylacetylene was used as the stopper, the oligomerization of 10 afforded a mixture of end-capped oligomers, from which 11,13 were isolated by column chromatography (Scheme,3). The poly(triacetylenes) (PTA) 16,18 were prepared in a similar manner starting from diol 8 and stearic acid (Schemes,4 and 5). Whereas the end-capped monomers and dimers 11, 12, 16, and 17 with pendant long alkyl chains do not exhibit any liquid-crystalline behavior, the trimeric derivatives 13 and 18 show mesomorphic properties, thus demonstrating that the poly(triacetylene) backbone can behave as a mesogenic unit. [source] Effect of molecular architecture and size of mesogen on phase behavior and photoactive properties of photoactive liquid crystalline hyperbranched polyester epoxies containing benzylidene moietyJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2008V. Srinivasa Rao Abstract A series of photoactive liquid crystalline linear and hyperbranched polyester epoxies were synthesized by polyaddition of photoactive bis benzylidene alkanone diol monomers and terephthalic acid and trimesic acid respectively with good yield. The effect of molecular architecture (linear and hyperbranched), size of mesogenic unit (cyclic and acyclic units) on the physicochemical, thermal, mesogenic, and photoactive properties of hyperbranched polymers were studied and compared. Degree of branching of hyperbranched polymers was found to be in the range of 0.46,0.49. Monomers containing cyclic moieties only exhibited nematic mesophase, while all polymers exhibited typical nematic mesophase. Intermolecular photo cycloaddition reaction was studied by ultraviolet,visible spectra (UV,vis) and NMR spectroscopy and photo viscosity measurement of UV irradiated polymer solutions. Faster photo induced behavior of hyperbranched polymers containing acyclic alkanone moiety, as compared to polymers containing cycloalkanone moieties, was observed. The change in the refractive index was found to be in the range of 0.02,0.024. Substantial variation of refractive index indicates that this polymer could be used for optical recording. All the polymers were also found to be fluorescent in nature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 552,563, 2008 [source] Novel side-chain liquid-crystalline polyimide for film materialsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2003Haojun Fan Abstract A novel side-chain liquid-crystalline polyimide (SLCPI) was prepared via copolycondensation from 3,5-diamino-benzonic-4,-biphenyl ester, 4,4,-diamino- biphenyl ether, and 3,3,,4,4,-oxydiphthalic dianhydride. The energy-minimized structure and liquid crystallinity of SLCPI were investigated by molecular modeling, differential scanning calorimetry (DSC), wide-angle X-ray scattering, and polarized optical microscopy, respectively. The results indicated that this polyimide (PI) with side-chain mesogenic units exhibited a nematic NI phase. Because of the in situ self-reinforcement of side-chain mesogenic units, the improved tensile strength and modulus of PI films reached 270% and 300%, respectively. The coefficient of thermal expansion of films decreased by 40%. DSC and thermogravimetric analyses indicated that the phase-transition temperature of SLCPI was above 240 °C, and the 5% weight-loss temperature was above 520 °C. Moreover, copolycondensation of two diamines with dianhydride and incorporation of pendent mesogenic units diminished the regularity and symmetry of main chains; as a result, SLCPI exhibits good film processability. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 554,559, 2003 [source] Synthesis and characterization of liquid crystalline elastomers bearing fluorinated mesogenic units and crosslinking mesogensPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 12 2009Fan-Bao Meng Abstract Several new side-chain liquid crystalline (LC) polysiloxanes and elastomers (IP - VIP) bearing fluorinated mesogenic units and crosslinking mesogens were synthesized by a one-step hydrosilylation reaction with poly(methylhydrogeno)siloxane, a fluorine-containing LC monomer 4,-undec-10-enoyloxy-biphenyl-4-yl 4-fluoro-benzoate and a crosslinking LC monomer 4,-(4-allyloxy-benzoxy)-biphenyl-4-yl 4-allyloxy-benzoate. The chemical structures and LC properties of the monomers and polymers were characterized by use of various experimental techniques such as FTIR, 1H-NMR, EA, TGA, DSC, POM and XRD. The effect of crosslinking mesogens on mesomorphic properties of the fluorinated LC polymers was studied as well. The obtained polymers and elastomers were soluble in many solvents such as toluene, tetrahydrofuran, chloroform, and so forth. The temperatures at which 5% weight loss occurred (Td) were greater than 250°C for all the polymers, and the weight of residue near 600°C increased slightly with increase of the crosslinking mesogens in the fluorinated polymer systems. The samples IP, IIP, IIIP and IVP showed both smectic A and nematic phases when they were heated and cooled, but VP and VIP exhibited only a nematic mesophase. The glass transition temperature (Tg) of polymers increased slightly with increase of crosslinking mesogens in the polymer systems, but the mesophase,isotropic phase transition temperature (Ti) and smectic A,nematic mesophase transition temperature (TS-N) decreased slightly. It suggests that the temperature range of the mesophase became narrow with the increase of crosslinking mesogens for all the fluorinated polymers and elastomers. In XRD curves, the intensity of sharp reflections at low angle decreased with increase of crosslinking mesogens in the fluorinated polymers systems, indicating that the smectic order derived from fluorinated mesogenic units should be destroyed by introduction of more crosslinking mesogens. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||