Emulsion polymerization of methyl methacrylate under pulsed microwave irradiation

Emulsion polymerization of methyl methacrylate (MMA) under pulsed microwave irradiation (PMI) with higher peak pulse power was studied. The effects of various parameters of PMI on the polymerization were analyzed and compared with that under conventional heating (CH) process. The results were summarized, as compared with that under CH, as follows. The amount of initiator used to reach constant conversion reduced by 50% at the same polymerization time; at the same initiator concentration 0.15 and 0.2 wt.%, the polymerization rate increased by 131% and 163%, respectively. The molecular weight of polymer obtained was 1.1-2.0 times larger than that under CH; at the same irradiation energy, the conversion achieved using a lower pulse power was greater than that using a higher pulse power. There seemed to be a factor of the irradiation energy efficiency; in other words, for the monomer conversion, the irradiation energy of low pulse power had a higher efficiency. The conversion achieved using a 3.5 μs pulse width was almost the same as that using a 1.5 μs pulse width. The results indicated that PMI had a significant non-thermal effect on the emulsion polymerization of MMA so as to effectively enhance the polymerization rate. The glass transition temperature (T_g), the polydispersity index (PDI) and the regularity of the polymer obtained using two processes were similar, indicating that the physical properties and microstructure of the polymer were not modified by the use of microwaves.     

Study of a mathematical model of metal ion complexes in solvent sublation

Separation of metal ion complex, [(C(12)H(8)N(2))(3)Fe(2+)], with surfactant sodium dodecylphrate (DLS) complex from aqueous phase was carried out by solvent sublation, which obeys first-order kinetics. On the base of the complete transport mechanisms, the Langmuir adsorption, and the ion complex equilibrium in the aqueous phase, a mathematical model for the [(C(12)H(8)N(2))(3)Fe(2+)]-surfactant ion complex is obtained with the aid of the Mathematic 4.0 program, 4th Runge-Kutta method, and the Matlab programs. The effects of many parameters, such as K(a), K(l), K(ow), d(i), V(o), V(w), and Q(a), on solvent sublation are investigated. Furthermore, the simulation showed that the model is substantiated for experiments on the solvent sublation of the complex.     

Photocurrent generation in multilayer self-assembly films fabricated from water-soluble poly(phenylene vinylene)

A novel, water-soluble, cationic PPV derivative poly[(2,5-bis(3-bromotrimethylammoniopropoxy)-phenylene-1,4-divinylene)-alt-1,4-(2,5-bis(2-(2-hydroxyethoxy)ethoxy))phenylene vinylene] (BH-PPV) has been synthesized by a Heck coupling reaction. Multilayered assemblies of the BH-PPV and the sodium salt of hexa(sulfobutyl)fullerenes (C(60)-HS) were fabricated successfully by an alternate deposition technique. The multilayer structures were studied by UV/Vis spectroscopy, small angle X-ray diffraction, and atomic force microscopy. The photoinduced charge transfer property of the self-assembled multilayer film was also measured by a three-electrode cell technique. A steady and rapid cathodic 5.5 microA cm(-2) photocurrent response was measured as the irradiation of the multilayer film was switched on and off. Importantly, the response of on/off cycling is prompt and reproducible. A possible mechanism for the electron-transfer process is proposed.     

Thermodynamics and kinetics of the hydride-transfer cycles for 1-aryl-1,4-dihydronicotinamide and its 1,2-dihydroisomer

Five 1-(p-substituted phenyl)-1,4-dihydronicotinamides (GPNAH-1,4-H(2)) and five 1-(p-substituted phenyl)-1,2-dihydronicotinamides (GPNAH-1,2-H(2)) were synthesized, which were used to mimic NAD(P)H coenzyme and its 1,2-dihydroisomer reductions, respectively. When the 1,4-dihydropyridine (GPNAH-1,4-H(2)) and the 1,2-dihydroisomer (GPNAH-1,2-H(2)) were treated with p-trifluoromethylbenzylidenemalononitrile (S) as a hydride acceptor, both reactions gave the same products: pyridinium derivative (GPNA(+)) and carbanion SH(-) by a hydride one-step transfer. Thermodynamic analysis on the two reactions shows that the hydride transfer from the 1,2-dihydropyridine is much more favorable than the hydride transfer from the corresponding 1,4-dihydroisomer, but the kinetic examination displays that the former reaction is remarkably slower than the latter reaction, which is mainly due to much more negative activation entropy for the former reaction. When the formed pyridinium derivative (GPNA(+)) was treated with SH(-), the major reduced product was the corresponding 1,4-dihydropyridine along with a trace of the 1,2-dihydroisomer. Thermodynamic and kinetic analyses on the hydride transfer from SH(-) to GPNA(+) all suggest that the 4-position on the pyridinium ring in GPNA(+) is much easier to accept the hydride than the 2-position, which indicates that when the 1,4-dihydropyridine is used the hydride donor to react with S, the formed pyridinium derivative GPNA(+) may return to the 1,4-dihydropyridine by a hydride transfer cycle; but when the 1,2-dihydropyridine is used as the hydride donor, the formed pyridinium derivative can not return to the 1,2-dihydropyridine by the hydride reverse transfer from SH(-) to GPNA(+). These results clearly show that the hydride-transfer cycle is favorable for the 1,4-dihydronicotinamides, but unfavorable for the corresponding 1,2-dihydroisomers.     

Neue neutrale und kationische Mono‐Aziridin‐Komplexe des Typs [CpMn(CO)2Az], [CpCr(NO)2Az]+ und [(Ph3P)(CO)4ReAz]+ über CO‐, Hydrid‐ und Chlorid‐Abspaltungsreaktionen

Novel Neutral and Cationic Mono‐Aziridine Complexes of the Type [CpMn(CO)₂Az], [CpCr(NO)₂Az]⁺, and [(Ph₃P)(CO)₄ReAz]⁺ via CO‐, Hydride‐, and Chloride‐Elimination Reactions The monoaziridine complexes 1 — 5 are obtained by three differently induced substitution reactions. The photolytically induced CO substitution reaction of [CpMn(CO)₃] with 2, 2‐dimethylaziridine leads to the neutral N‐coordinate aziridine complex [Cp(CO)₂Mn{$\overline{N(H)CMe₂C}$ H₂}] ( 1 ). The protonation of [(Ph₃P)(CO)₄ReH] with CF₃SO₃H and consecutive treatment with 2, 2‐dimethylaziridine or 2‐ethylaziridine gives the salt‐like aziridine complexes [(Ph₃P)(CO)₄Re{$\overline{N(H)CMe₂C}$ H₂}](CF₃SO₃) ( 2 ) or [(Ph₃P)(CO)₄Re{ H₂}](CF₃SO₃) ( 3 ) by hydride elimination reactions. The like‐wise salt‐like complexes [Cp(NO)₂Cr{$\overline{N(H)CMe₂C}$ H₂}](BF₄) ( 4 ) and [Cp(NO)₂Cr{ H₂}](CF₃SO₃) ( 5 ) are synthesized from [CpCr(NO)₂Cl] by chloride elimination with AgX (X = BF₄, CF₃SO₃) in the presence of 2, 2‐dimethylaziridine or 2‐ethylaziridine, respectively. As a result of X‐ray structure analyses, the metal atoms are trigonal pyramidally ( 1, 4, 5 ) or octahedrally ( 2, 3 , cis‐position) configurated; the intact three‐membered rings coordinate through the distorted tetrahedrally configurated N atoms. All compounds 1‐5 are stable with respect to the directed thermal alkene elimination to give the corresponding nitrene complexes; the IR, ¹H‐ and ¹³C{¹H}‐NMR, and MS spectra are reported and discussed.     

Loss and recovery in hydrophobicity of silicone rubber exposed to corona discharge

This paper describes the loss and recovery in the hydrophobicity of unfilled high temperature vulcanized silicone rubber (HTV-SR) resulting from corona discharge. In this study, HTV-SR specimens were exposed to corona stress generated by a parallel needle-plane electrode system, and physicochemical analyses on the surface layer of SR before and after corona discharge treatment were carried out by using Fourier transform infra-red (FTIR) spectroscopy, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). It is demonstrated that hydrophilic OH groups that are by-products of ageing can be formed instead of hydrophobic CH₃ groups on the surface of aged SR and the corona discharge plays an important role on the temporary loss of hydrophobicity. After a substantial period of ‘rest’, the hydrophobic recovery of SR results from the diffusion of low-molecular weight (LMW) silicone fluid from the bulk onto the aged layer.     

牛血清白蛋白与有机小分子偶氮磺Ⅲ、溴偶氮磺Ⅲ相互作用的研究

本文研究了在不同酸度下．偶氮磺、溴偶氮磺Ⅲ与牛血清白蛋白的作用情况，用光度法求出了不同条件下偶氮磺Ⅲ、溴偶氮磺Ⅲ与牛血清白蛋白的结合个数，并用三种不同的方法相互对照．证明偶氮磺Ⅲ、溴偶氮磺Ⅲ在牛血清白蛋白上有两类不同接合部位。利用Forster非幅射转移理论确定了有机小分子在牛血清白蛋白上的结合位置并对反应机理作了初步讨论。     

二[1,2-二硫代(3,5-二硫杂-4-硫酮)戊烯]铜和锌络合物的四丁基胺盐的晶体结构

1,2-二硫代烯基(1)和1,2-二硫代苯基(Ⅱ)类型的金属络合物的研究,已有很多报道。但Ⅰ和Ⅱ与Zn的络合物的晶体结构至今未见报道。Gray等人发现在[N(C_4H_8)_4]_2[M′(MNT)_2]络合物的X射线粉末图中,Co,Pt,Ni络合物的衍射花样完全相同,但Zn络合物的确有明显的不同。Billig等人在[N(C_2H_5)_4]_2[M″(MNT)_2](M″=Cu,Ni,Zn)络合物的X射线粉末花样中也观察到同样的现象。他们认为Zn络合物为四面体的构型,但未测定其结构。近来,Lindqvist又推出一种1,2-二硫代(3,5-二硫杂-7-硫酮)戊烯基(Ⅲ)新的配位体。为了解Cu,Zn与Ⅲ形成络合物的特征,本文测定了标题络合物的晶体结构。     

富氧条件下乙炔选择催化还原NOx

Acetylene as a reducing agent of metal exchanged HY catalysts, for selective catalytic reduction of NO in the reaction system of 0.16% NO, 0 （C2H2-SCR） was investigated over a series 08% C2H2, and 9.95% O2 （volume percent） in He. 75% of NO conversion to N2 with hydrocarbon efficiency about 1.5 was achieved over a Ce-HY catalyst around 300 ℃. The NO removal level was comparable with that of selective catalytic reduction of NOx by C3H6 reported in literatures, although only one third of the reducing agent in carbon moles was used in the C2H2-SCR of NO. The protons in zeolite were crucial to the C2H2-SCR of NO, and the performance of HY in the reaction was significantly promoted by cerium incorporation into the zeolite. NO2 was proposed to be the intermediate of NO reduction to N2, and the oxidation of NO to NO2 was rate-determining step of the C2H2-SCR of NO over Ce-HY. The suggestion was well supported by the results of the NO oxidation with O2, and the C2H2 consumption under the conditions in the presence or absence of NO.     

New Stephaoxocane Alkaloids from Stephania longa

Three new stephaoxocane‐type alkaloids, stephalonganines A–C ( 1 – 3 ), together with the known eletefine ( 4 ), were isolated from the whole plant of Stephania longa. Their structures were fully characterized spectroscopically, and the absolute configurations of the new alkaloids were assigned by comparison of their circular‐dichroism (CD) data with those of 1,2‐dihydrostephaoxocanine ( 5 ), in combination with 2D‐NMR experiments.