Anisotropic Network Formation by Photopolymerization of Liquid Crystal Monomers in a Low Magnetic Field

Abstract

Liquid crystalline mixtures of mono-and dimethacrylates were photopolymerized after macroscopic orientation of the monomers under a relatively weak magnetic field or via interaction with a unidirectionally rubbed polyimide substrate. Polymerization kinetics was followed by a thermoanalysis technique, and the transmitted light intensity was measured in real time. The macroscopic order parameter of one of the component comonomers (bearing a cyano group) incorporated into the polymer network prepared under different conditions was evaluated using IR dichroism. The results obtained for the cross-linked polymer network produced under the low strength magnetic field are compared with those for the polymer film produced by surface orientation. Experimental SectionAll monomers were synthesized by the method of Portugal et al.19 All products were purified by column chromatography and recrystallized from 2-propanol. 1,1-Dimethoxy-l-phenylacetophenone (Irgacure 651, Ciba Geigy) was recrystallized from

Structure of polymer networks in liquid crystals studied by 13C NMR

“…Experimental technique lines of the aromatic cores of molecules 1 and 2 are The 13 C NMR measurements were performed in a separated. The lines overlap if both cores have identical magnetic ® eld of 11´7 T at a frequency of 125 M Hz using chemical surround ings ( left hand phenyl rings in a Bruker M SL 500 spectrometer.…”

“…Althoug h temperature shifts due to elastic director deformations the polymerized samples are now in a gel-lik e state, the are absent, althoug h the latter have been observed for ligh t scattering characteristics are similar to those of the liquid crystals which are con® ned to spheres in mixtures nematic phase. For the 13 C NMR measurements, the with high polymer concentration s or glasses [ 28 ]. W ith tube axis, which coincides with the alignmen t axis of increasing temperature, and above the transition point, the network, lies perpendicular to the applied magnetic the negative shifts of the nematic lines decrease slowly.…”

“…The range of concentration s varied In this paper we report on 13 C NMR studies of a liquid crystal with an embedded low-concentration polymer from 5 to 20 mol % monomer with 1 wt % photoinitiator dissolve d in the liquid crystal 2; the samples were network. The NMR technique is widely used to investigate molecular order in bulk systems [ 24 ± 26 ].…”

“…The NMR technique is widely used to investigate molecular order in bulk systems [ 24 ± 26 ]. The 13 C homogenized in the isotropic phase. For every concentration the solution s were characterized by NMR investi-NMR technique needs no special preparat ion of the materials and allows a high resolution of microscopic gation s before polymerization .…”

Preparation of liquid-crystal thermosets:In situ photopolymerization of oriented liquid-crystal diacrylates

“…This kind of optically anisotropic LCN can be used as an optical compensation film for a liquid-crystal display (LCD) to resolve its narrow-viewing-angle problem. [1][2][3][4] Recently, Broer and coworkers, [5][6][7][8][9][10][11][12][13][14] Hikmet and coworkers, [15][16][17][18][19][20] and Hoyle et al 21 demonstrated that macroscopically oriented LCNs can be obtained by in situ photopolymerization of difunctional liquid-crystal monomers (LCMs) in contact with unidirectionally rubbed thin-film substrates. During polymerization, the ordering of the mesogen was fixed, yielding a uniaxially crosslinked network.…”