Crystalline Monomer (crystalline + monomer)

Distribution by Scientific Domains

Selected Abstracts

Effect of the different rigidity of the chiral crosslinker on phase behaviors of side-chain chiral liquid crystalline elastomers

Bao-Yan Zhang
Abstract In the present work, the phase behaviors of two series of side-chain liquid crystalline elastomers (PI and PII series) derived from the same nematic liquid crystalline monomer and the different rigidity of chiral bisolefinic crosslinking units have been compared and studied extensively, and the effect of the different rigidity of crosslinker on the phase behavior of elastomers has been discussed. The chemical structure of the monomers and polymers obtained were confirmed by FTIR and 1H NMR spectroscopy. The phase behaviors were investigated by differential scanning calorimetry, polarizing optical microscopy measurement, thermogravimetric analyses, and X-ray diffraction measurement. The two series of elastomers showed smectic or cholesteric phases. When the amount of different crosslinking units was less than 15 mol %, both of the elastomers displayed elasticity, reversible phase transition with wide mesophase temperature ranges, and high thermal stability. It is shown that the isotropization temperature values of PII series are higher than those of PI series, and the glass transition temperature values of PII series varied smoothly and that of PI series changed smoothly first and then abruptly with increasing the contents of crosslinkers with different rigidity. In addition, PI series showed an interesting change in LC texture near clearing point, but PII series did not. 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

A computational NQR study on the hydrogen-bonded lattice of cytosine-5-acetic acid

Mahmoud Mirzaei
Abstract A computational study at the level of density functional theory (DFT) employing 6-311++G** standard basis set was carried out to evaluate nuclear quadrupole resonance (NQR) spectroscopy parameters in cytosine-5-acetic acid (C5AA). Since the electric field gradient (EFG) tensors are very sensitive to the electrostatic environment at the sites of quadruple nuclei, the most possible interacting molecules with the target one were considered in a five-molecule model system of C5AA using X-ray coordinates transforming. The hydrogen atoms positions were optimized and two model systems of original and H-optimized C5AA were considered in NQR calculations. The calculated EFG tensors at the sites of 17O, 14N, and 2H nuclei were converted to their experimentally measurable parameters, quadrupole coupling constants and asymmetry parameters. The evaluated NQR parameters reveal that the nuclei in original and H-optimized systems contribute to different hydrogen bonding (HB) interaction. The comparison of calculated parameters between optimized isolated gas-phase and crystalline monomer also shows the relationship between the structural deformation and NQR parameters in C5AA. The basis set superposition error (BSSE) calculations yielded no significant errors for employed basis set in the evaluation of NQR parameters. All the calculations were performed by Gaussian 98 package of program. 2007 Wiley Periodicals, Inc. J Comput Chem 2008 [source]

Synthesis and characterization of urethane vinyl ether crystalline monomers

Zhaohua Zeng
Abstract UV powder coatings combine the advantages of both conventional thermoset powder coatings and liquid UV-curing coatings. In this paper, a series of crystalline monomers based on urethane vinyl ether have been synthesized by reaction of hexamethylene diisocyanate (HDI) with hydroxybutyl vinyl ether (HBVE) or together with a saturated alcohol such as 1-octanol, 2-butoxy ethanol and 2-ethoxy ethanol. The crystallinity of the monomers was characterized by DSC, WAXD and polarizing microscopy. It was found that the melting point of the monomer can be expediently adjusted to an adequately low level by changing the type and/or the amount of the saturated alcohol added during the synthesis procedure. Thus, when 20,40 mol% of HBVE was replaced by a saturated alcohol, the melting point decreased to around 75,90 C, which is suitable for UV-curing powder coating formulations. Copyright 2006 Society of Chemical Industry [source]