Structure–property relationship of photoactive liquid crystalline polyethers containing benzylidene moiety

Abstract

A series of main chain photoactive liquid crystalline polyethers, containing rigid bisbenzylidene photoactive mesogen and flexible methylene spacers, were synthesized by polycondensation of bisbenzylidene diols and dibromoalkanes. The polyethers were characterized with 1 H NMR, gel permeation chromatography (GPC), differential scanning calorimeter (DSC), thermo gravimetric analyzer (TGA), and polarized light optical microscopy. The individual and combined effects of spacer length and number of methoxy substituents on mesogenic and photoactive properties were investigated. Both first order and second order transition temperatures decreased with increased spacer length and the number of substituents. The combined effect of spacers and substituents drastically reduced the transition temperatures. All monomers and polymers showed mainly the smectic mesophase. In a few cases, nematic droplets along with the smectic phase were observed. The width of the liquid crystalline phase reduced with an increasing number of methoxy substituents on mesogenic unit. Variation of spacer length has a negligible effect on photocycloaddition. However, steric hinderance caused by the substituents decreased the photoactivity as the number of substituents increased. Total energies of crosslinked dimers calculated from modeling studies supported the above findings. Intermolecular photocycloaddition was also confirmed by photoviscosity measurement. The refractive index change was found to be in the range of 0.017-0.031. V V C 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem

Photoactive poly(hydroxyl-amino ether)s based on 4-methyl-cyclohexanone and 4-tert-butylcyclohexanone moieties in the main chain: synthetic methodology and characterization

“…The bis arylidene-cycloalkanone molecules facilitate photochemical reactions of the polymer chains under the influence of UV irradiation [29][30][31][32].…”

Preparation of Main-Chain Thermotropic Polyesters With Two Types of Mesogens Connected Alternatively by Aliphatic Spacers

“…[3,5] Furthermore, the reproducible DSC data of the obtained polymers from the first and second heating (data not shown) suggest that the molecular weights were hardly influenced during the heating processes in our case. According to the literature, [4,30] we assume that the MarkHouwink constants of the polymers only slightly differ with different flexible spacers in the present range. Consequently, the obtained similar intrinsic viscosities indicate that the polyesters have rather close molecular weights.…”

“…[1] For practical applications, TLCPs with high solubility, wide mesogenic zones, low melting transition temperatures, and good thermal stability are generally desirable. Some structural modifications are thus applicable and conditioned by the effect of structural parameters, such as chemical nature of mesogens, [2,3] substituents on mesogens or spacers, [4,5] chemical nature of spacers, [6,7] spacer length, [8][9][10] linking group between the spacer and mesogen, [11] copolymer composition, [12] copolymer sequence, [13,14] and intermolecular hydrogen bonds. [15][16][17] The incorporation of flexible spacers into the main chain [18,19] and the chemical nature of mesogenic units are important to the properties of TLCPs.…”

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A homologous series of main-chain thermotropic polyesters (PBTn, n = 2,4,6) containing biphenyl and triad aromatic ester mesogenic units interconnected by n-methylene spacers in the main chain were prepared from terephthaloyl bis(4-oxybenzoyl chloride) (TOBC) and 4,4 -bis(ω-hydroxyalkyloxy)biphenyls (n-BP, n = 2, 4, 6) by solution polycondensation. The chemical structures of the monomers and PBTn were characterized by spectroscopic techniques and elemental analysis.

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Synthesis, Characterization and Photocrosslinkable Studies of Certain Thermotropic Liquid Crystalline Poly(ester-amides)

“…This photo-active molecule has attracted the attention of macromolecular chemists [3][4][5][6][7]. They were found to be a potential mesogen [8][9][10] and their incorporation in the polymeric backbone has imparted thermotrophic liquid crystalline property to the polymeric materials. Thermotropic liquid crystalline polymers have wide range of applications from ultrahigh strength fibres to nonlinear optical devices [11][12][13].…”