The carboxylic acid 4‐hydroxybenzoic acid, bonded directly with (R)‐2‐octanol, is the core molecule of chiral liquid crystal (R)‐MHPOBC. This acid was substituted either by 6‐hydroxynicotinic or by 4‐hydroxyphenylacetic acid. Such a structural variation induced a remarkable influence on the liquid crystal properties of (R)‐MHPOBC. The series of compounds 1˜4 containing 6‐hydroxynicotinic acid moiety tend to exhibit a chiral smectic C (SmC*) phase, while the series of compounds 5˜8 containing 4‐hydroxyphenylacetic acid moiety tend to possess a chiral nematic (N*) phase.
This research is to develop transparent and UV‐shielding Epoxy/SR‐494/APTMS/ZnO nanocomposite materials with high heat resistant and anti‐static properties. Firstly, the APTMS (3‐(acryloxypropyl)trimethoxysilane) performs the silanol intermediates by hydrolysis in pH 4∼5 acid solution. The inorganic anti‐static fillers of powder ZnO can be successfully coupled and crosslinked to Epoxy/SR‐494 organic matrixes with these silanols of APTMS coupling agents. The remained active ‐OH functional groups of the APTMS/ZnO complexes can network bonding with epoxy prepolymers. Therefore, the Epoxy/APTMS/ZnO complexes with good anti‐static composites will be successfully prepared. Finally, in order to improve the thermal resistant and mechanical properties, the polyfunctionalized SR‐494 (pentaery‐thritol tetracrylate) acrylate monomers and the Epoxy/APTMS/ZnO composites are chain polymerized to form an excellent cross‐linking structure of organic/inorganic nanocomposites.
The chemical bonding formation and the best weight contents of reaction components are identified by FT‐IR spectra. The thermal resistance, transparence, surface electric resistance, and hardness of these nanocomposites are measured by TGA, DSC, UV‐Visible, surface resistant meter, and pencil hardness tester respectively. Experimental results show that these nanocomposites have 90% transmittance and the best Td value is 389.3 °C which is 109.0 °C and 78.6 °C higher than those of pure epoxy resin and pure SR‐494 acrylate resin respectively. The glass transition temperature is not detected below 200 °C. The surface electric resistances of Epoxy/SR‐494/APTMS/ZnO hybrid thin films are decreased from 3.14 × 1013 to 5.13 × 107 Ω/cm2. The hardness of these nanocomposites is as high as 8H, and those hybrid films have high UV‐shielding properties. The morphology structures of the hybrid thin films are estimated by SEM. The results show that the optical thin films are evenly distributed with inorganic colloidal particles and the average particle size of these nanocomposites is 45∼80 nm, while the powder ZnO (particle size: 2∼5 μm) was used as inorganic filler.
Three series of compounds 1-21 were prepared by using 2-, 3-, and 4-pyridinemethanol as terminal group of calamitic liquid crystals. These compounds have some similarities in their phase behavior. They all exhibit SmA phase. A tilt smectic phase, SmC, will be formed when their flexible alkoxy chain is longer than hexoxy group. The profound difference between them is that the compounds 15-17 possess a short temperature range of N phase. The compounds 3 and 6 have the widest SmA phase, up to 94°C, and SmC phase, up to 46°C, respectively. . fore, three series of compounds 1-21 were derived from 2-, 3-, and 4-pyridinemethanol and their mesogenic properties were studied. The synthesis and structures of these compounds are shown in Fig. 1.
RESULTS AND DISCUSSIONThree series of compounds 1~21 were prepared by the esterification of seven analogous aromatic carboxylic acids and 2-pyridinemethanol, 3-pyridinemethanol, or 4-pyridinemethanol. Their structures were identified by IR, 1 H-NMR, 13 C-NMR, and MS. The spillting pattern and chemical shift of H-atom positioned ortho to hetero N-atom of pyridyl ring will give enough evidence to differentiate these three pyridyl ring system. The liquid crystal phases and phase transition temperatures of 1~21 were determined by DSC measurement and texture observation. These data
Two new chiral alcohols, 2(S)‐[2(R)‐methylhexyloxy]propanol (5) and 2(S)‐[2(S)‐methylhexyloxy]propanol (6), were prepared from the corresponding propionic acid ethyl ester 1 and 2 in the presence of sodium borohydride. They were used as the chiral moiety for the synthesis of two diastereomeric liquid crystals 7 and 8. Both of them exhibit the phase sequence I‐SmA‐SmC*‐SmX‐Cr. The mesogenic properties of the (S,S)‐diastereomer 8 are more unique in comparison with those of the (S,R)‐diastereomer 7. It possesses not only lower SmA and SmC* phase transition temperature, 103 °C vs. 112 °C for SmA phase and 31 °C vs. 65 °C for SmC* phase, but wider SmA and SmC* phase range, 40 °C vs. 31 °C for SmA phase and 72 °C vs. 47 °C for SmC* phase. The diastereomer 8 also has a larger Ps value than that of 7, 24 vs. 15 nC cm−2 measured at Tc ‐ T = 10 °C. The difference in these mesogenic properties is discussed by comparing their conformation difference at the molecular part of benzoate.
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