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- Author or Editor: G. S. Zhang x
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Abstract
The concept of crystallization dynamics method evaluating the miscibility of binary blend system including crystalline component was proposed. Three characteristic rates, nucleation, crystal growth rates (N*, G*) and growth rate of conformation (G c*) were used to evaluate the miscibility of PVDF/at-PMMA and PVDF/iso-PMMA by the simultaneous DSC-FTIR. N*, G* and G c* depended remarkably on both temperature and blend fraction (ϕPMMA) for PVDF/at-PMMA system, which indicated the miscible system. PVDF/iso-PMMA showed small ϕPMMA dependency of N*, G* and G c*, was estimated the immiscible system. The ΔT/T m 0 values, corresponding to Gibbs energy required to attend the constant G* and G c*, evaluated from G* and G c* showed the good linear relationships with different slope. The experimental results suggested that the concentration fluctuation existed in PVDF/iso-PMMA system.
Abstract
Polypropylene homopolymer (PP) and a copolymer (P/E) were processed using the Reicofil® spunbonding line at the Textiles and Nonwovens Development Center of the University of Tennessee, Knoxville. The properties of the filament samples taken before thermal-bonding were determined through a variety of techniques such as differential scanning calorimetry, thermomechanical analysis, thermal deformation analysis and mechanical properties. The two process variables investigated, primary air temperature and throughput had a strong influence on the structure and properties of both the filaments and the bonded nonwovens. As the primary air temperature and throughput decreased, there was a tendency for decrease in filament diameter with a simultaneous increase in their crystallinity, birefringence and thermal stability. The copolymer filaments showed lower crystallinity and orientation for all the corresponding processing conditions.
Abstract
2,2-dinitropropyl acrylate (DNPA), 2,2-dinitrobutyl acrylate (DNBA) and 2,2-dinitrobutyl methacrylate (DNBMA) were synthesized and the kinetics of their free-radical polymerization in the presence of 2,2′-azobisisobutyronitrile (AIBN) were investigated by DSC in the non-isothermal mode. The kinetics of the free-radical polymerization as estimated by the Kissinger and Ozawa methods showed that the reaction is disfavoured by increasing steric hindrance around the acrylyl double bond. The rate constants calculated from the activation parameters showed the structural dependency. The polymerization kinetics revealed that the polymerizability of three monomers decreased due to the presence of substituent methyl groups on the acrylyl double bond and 2,2-dinitrobutyl on ester group. Thus, the polymerization tendency increased in the order DNPA>DNBA>DNBMA.
Abstract
We have conducted thermal and X-ray diffraction experiments on binary mixtures of symmetric stearic-oleic mixed-acid triacylglycerol (TAG) (1,3-distearoyl-2-oleoyl-glycerol: SOS) and asymmetric stearic-oleic mixed-acid TAG (1,2-dioleoyl-3-stearoyl-sn-glycerol: OOS), in which optically active sn-OOS was employed. We found that SOS–OOS mixtures exhibited immiscible monotectic or peritectic mixing behavior. This result was consistent with previous study on binary mixtures of 1,3-dipalmitoyl-2-oleoyl-glycerol (POP) and 1,2-dioleoyl-3-palmitoyl-rac-glycerol (OOP), in which racemic rac-OOP molecules were employed. The differences between the SOS–OOS and POP–OOP mixtures were in the polymorphic behavior of the fractions of POP and SOS. No effect was found from using an optically active (sn-OOS) or racemic mixture (rac-OOP) as an asymmetric oleic–oleic-saturated acid TAG. From the two results, we may conclude that an immiscible phase was formed in the binary mixtures of symmetric saturated-oleic-saturated TAGs and asymmetric oleic–oleic-saturated TAGs, of both racemic and optically active types. This result stands in contrast to mixtures of SOS–OSO (1,3-dioleoyl-2-stearoyl-glycerol), SOS–SSO (1,2-distearoyl-3-oleoyl-rac-glycerol), POP–OPO (1,3-dioleoyl-2-palmitoyl-glycerol), and POP–PPO (1,2-dipalmitoyl-3-oleoyl-rac-glycerol), all of which exhibited molecular-compound-forming behavior with molecular compound crystals at an equal ratio of the binary mixtures. Molecular-level mechanisms to explain this difference are discussed, based on possible roles of glycerol groups acting during the mixing processes of saturated–unsaturated mixed-acid TAGs.
Abstract
The free-radical bulk polymerization of 2,2-dinitro-1-butyl-acrylate (DNBA) in the presence of 2,2′-azobisisobutyronitrile (AIBN) as the initiator was investigated by DSC in the non-isothermal mode. Kissinger and Ozawa methods were applied to determine the activation energy (E a) and the reaction order of free-radical polymerization. The results showed that the temperature of exothermic polymerization peaks increased with increasing the heating rate. The reaction order of non-isothermal polymerization of DNBA in the presence of AIBN is approximately 1. The average activation energy (92.91±1.88 kJ mol −1) obtained was smaller slightly than the value of E a=96.82 kJ mol−1 found with the Barrett method.
Abstract
The stability of β-cyclodextrinethyl benzoate6H2O(β-CDC6H5COOC2H56H2O) was investigated by TG and DSC. The mass loss takes place in three stages: the dehydration occurs at 50-120C; the dissociation of β-CDC6H5COOC2H5occurs at 200-260C; the decomposition of β-CD begins at 280C. The kinetics of the dissociation of β-CDC6H5COOC2H5in a dry nitrogen flow was studied by means of thermogravimetry both at constant temperature and linearly increasing temperature. The results show that the dissociation of β-CDC6H5COOC2H5is dominated by a three-dimensional diffusion process (D3). The activation energy E is 116.19 kJ mol-1and the pre-exponential factor A 6.5358109min-1. Cyclodextrin is able to form inclusion complexes with a great variety of guest molecules, and the studies focus on the energy of binding between cyclodextrin and the guest molecule. In this paper, the β-cyclodextrinethyl benzoate inclusion complex was studied by fluorescence spectrophotometry and infrared absorption spectroscopy, and the results show that the stable energy of inclusion complexes of β-CD with weakly polar guest molecules consists mainly of van der Waals interaction.
Abstract
Two peptide ligands conjugated adenine, [9-N-(tritylmercapto acetyl diglycyl aminoethyl) adenine, Tr-MAG2-Ade] and [9-N-(tritylmercapto acetyl triglycyl aminoethyl) adenine, Tr-MAG3-Ade], are synthesized and labeled with 99mTc by directly labeling method. The stability of 99mTc-MAG2-adenine and 99mTc-MAG3-adenine in vitro is measured. The uptake radios of tumor to muscle at 3h post-injection are 5.70 and 4.92, respectively. The biodistribution and scintigraphic imaging studies show that the two complexes have high localization in tumor and high contrasted tumor images can be obtained, which suggest their potential utility as tumor imaging agents. But the high radioactivity of abdomen could prevent the tumor imaging in this area.
Summary
1,7-Dihydroxy-3,8-dimethoxyxanthone (X1) and 1,8-dihydroxy-3,7-dimethoxyxanthone (X2) are two important xanthones of the Tibetan medicinal plant Gentianopsis paludosa (Hook. f.) Ma. They are very similar in structure, the only difference being exchange of OH and OCH3 at the 7 and 8 positions. By calculations based on the geometry of the molecules using the MM+ force field, the different distances between the hydroxyl groups of the two xanthones were obtained (4.64774 Å for X2 and 7.19412 Å for X1), therefore, the two hydroxyl groups of X1 should freely interact with more water molecules than those of X2 in aqueous solution. In other words, X2 is more hydrophobic than X1. Micellar electrokinetic capillary chromatography (MEKC) was therefore chosen for separation of the compounds. The optimum separation conditions were: 20 mm borate + 20 mm SDS (pH 9.8) as running buffer, 17.5 kV applied potential, and detection wavelength 260 nm. The two xanthones were well separated in 9.0 min, with Gaussian peak shapes. The repeatability of the MEKC method (expressed as RSD) for X1 and X2 was 0.9 and 1.1%, respectively, for migration time, and 3.1 and 1.4% for peak area. The limits of detection (S/N = 3) were 0.41 μg mL−1 for X1 and 0.82 μg mL−1 for X2. The recovery of the MEKC method for the two xanthones was also satisfactory.
