Kinetics and mechanism of the epoxide-amine polyaddition

The mechanism and kinetics of the epoxide-amine polyaddition reaction have been studied by isothermal and scanning DSC measurements. The initial concentrations of the reactants (epoxides: bisphenol-A-diglycidyl ether (DGEBA) and phenyl glycidyl ether (PGE), amines: N,N′-dibenzylethylenediamine (DBED) and aniline) in our model systems have been strongly varied. The suggested kinetic model describes the reaction behavior of mixtures with any initial epoxide/amine ratios over the whole range of cure by a single parameter set. To find the optimum kinetic parameters, we have solved the set of differential equations numerically by the technique of multivariate non-linear regression (Mult-NLR). Excellent agreement was obtained between calculated and experimental curves.     

Self‐polyaddition of triethylsilyl perfluoroisopropenyl ether

The results on radical self‐polyaddition reactivity of two trialkylsilyl perfluoroisopropenyl ethers, triethysilyl perfluoroisopropenyl ether [CF₂?C(CF₃)OSi(C₂H₅)₃] (FTEE) and dimethylphenylsilyl perfluoroisopropenyl ether [CF₂?C(CF₃)OSi(CH₃)₂C₆H₅] (DMPE), and two perfluoroisopropenyl carboxylates, 2‐butyroxypentafluoropropene [CF₂?C(CF₃)OCOC₃H₇] (BuFPP) and 2‐(methoxyacetoxy)pentafluoropropene [CF₂?C(CF₃)OCOCH₂OCH₃] (MFPP), are described. Radical self‐polyaddition of FTEE afforded a polymer as high as 1.87 × 10⁴ in molecular weight in the presence of radical generators such as benzoyl peroxide and di‐tert‐butyl peroxide. DMPE gave only addition products with initiating radicals. BuFPP and MFPP scarcely yielded even addition products with radical. The mechanism that the self‐polyaddition of FTEE was initiated by the addition of radical onto the perfluoroisopropenyl group followed by a 1,5‐shift to afford a methyl radical that attacked the perfluoroisopropenyl group of another FTEE molecule is proposed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2743–2754, 2003     

Laser-induced fluorescence spectroscopy of NC3S

In a discharged supersonic jet of acetonitrile and carbon disulfide, we have for the first time observed an electronic transition of the NC(3)S radical using laser-induced fluorescence (LIF) spectroscopy. A progression originating from the C-S stretching mode of the upper electronic state appears in the excitation spectrum. Each band of the progression has a polyad structure due to anharmonic resonances with even overtones of bending modes. Rotationally resolved spectra have been observed by high-resolution laser scans, and the electronic transition is assigned to A 2Pii-X 2Pii. For the vibronic origin band, the position and the effective rotational constant of the upper level have been determined to be 21 553.874(1) and 0.046 689(4) cm(-1), respectively. The dispersed fluorescence spectrum from the zero vibrational level of A 2Pi3/2 has also been observed; its vibrational structure is similar to that of the LIF excitation spectrum, showing a prominent C-S stretching progression with polyad structures. The vibrational frequencies of the C-S stretching mode in the ground and excited electronic states are determined to be 550 and 520 cm(-1), respectively. Fluorescence decay profiles have been measured for several vibronic levels of the A state.     

Self‐polyaddition of hydroxyalkyl vinyl ethers

With tetrahydrofuran as a solvent and pyridium p‐toluenesulfonate as a catalyst, the hydroxyalkyl vinyl ethers 2‐hydroxyethyl vinyl ether (2E), 4‐hydroxybutyl vinyl ether (4B), and 6‐hydroxyhexyl vinyl ether (6H) underwent step‐growth self‐polyaddition, generating polymers with an acetal main‐chain structure. The molecular weight of the resulting polymers increased gradually during the initial polymerization period at room temperature. However, decomposition occurred after about 22–24 h, and the presence of a large amount of catalyst accelerated the latter process. The three monomers exhibited different polymerization capabilities. In contrast to the smooth polymerization of 6H, cyclization side reactions usually took place during the polymerizations of 4B and 2E, which resulted in low polymer yields and low molecular weights because of the formation of unreactive small cyclic acetals. In the self‐polyaddition of 4B, this side reaction was greatly restricted at high concentrations of the monomer. Higher temperatures (60–70 °C) remarkably accelerated the self‐polyaddition process to produce polymers with high molecular weights. However, the polymerizations at high temperatures had to be terminated within about 2 h to avoid the severe decomposition of the polymers. Copolymers were also obtained via the copolyaddition of any two of the monomers. The easiness of the incorporation of the monomers into the copolymers was in the sequence 6H > 4B > 2E. Poly(6H), poly(4B), poly(2E), and the copolymers possessed different hydrophilicities and were stable in basic, neutral, and even weak acidic media but exhibited degradation in the presence of a strong acid. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3751–3760, 2000     

Laser induced fluorescence spectroscopy of NC3O

Laser induced fluorescence spectra of the NC(3)O radical in a supersonic jet have been observed. The radical was produced in a pulsed electric discharge of HC(3)N and O(2) diluted to 0.3% with Ar. A total of 17 vibronic bands with a radiative lifetime of approximately 30 ns have been observed in a region from 27 000 to 27 500 cm(-1). The observed vibronic bands are classified as (2)Pi(12)-(2)Pi(12), (2)Pi(32)-(2)Pi(32), and (2)Sigma-(2)Sigma types. The upper states of the (2)Sigma-(2)Sigma bands have large spin-rotation constants, which should be denoted as Sigma((+)) and Sigma((-)). From high-level ab initio calculations and rotational analyses, the observed transition was assigned to the B (2)Pi-X (2)A(") transition. Dispersed fluorescence spectra from the upper (2)Sigma and (2)Pi vibronic levels have also been observed, yielding fundamental vibrational frequencies for the nu(1), nu(2), nu(3), and nu(7) modes of the ground state.     

EGCG在Tween80胶束体系中的性质(英文)

通过离子萃取技术,从黄山绿茶中提取高纯度儿茶素没食子酸酯(EGCG).在Tween 80/EGCG/H2O体系中,随着EGCG浓度增加,Tween 80临界胶束浓度和胶束动力学半径增大;随着Tween 80浓度增加,EGCG和Tween 80扩散系数减小,而EGCG的紫外-可见吸收光强度和荧光强度增加.对EGCG在Tween 80胶束中的定位也进行了讨论.     

Radical polyaddition of bis(α-trifluoromethyl-β-difluorovinyl) terephthalate with 1,4-dioxane

To develop a radical polyaddition reaction of 2-benzoyloxypentafluoropropene [CF₂C(CF₃)-OCOC₆H₅] (BPFP) with tetrahydrofuran (THF), the reactions of bis(α-trifluoromethyl-β-difluorovinyl) terephthalate [CF₂C(CF₃)OCOC₆H₄COOC(CF₃)CF₂] (BFP) with THF and of BPFP with 1,4-dioxane were investigated as model reactions to form 1 : 1 and 1:2 addition products of BFP with THF. This evidenced that THF is monofunctional, and dioxane is bifunctional since the 1:1 and 2:1 addition products of BPFP with dioxane were formed. The polyaddition reaction of BFP with dioxane turned out to produce a white powdery substance which was found to possess a mole ratio of BFP units to dioxane units in the polymers of 1:1. The highest molecular weight obtained was M _n = 9.9 × 10³.     

Synthesis of polyamides by the polyaddition of bissuccinimides with diamines

Polyamides which contain succinamide units, ? NHCO? (CH₂)₂? CONH? were prepared by the ring-opening polyaddition of bissuccinimides with diamines at 200°C. in bulk. Nylon 24 and nylon 64 were prepared by the reaction of N,N′-ethylenedisuccinimide with ethylenediamine and of N,N′-hexamethylenedisuccinimide with hexamethylenediamine, respectively. It was suggested that the transamidation reaction by aminolysis influenced the detailed structures of the polymers prepared from N,N′-ethylenedisuccinimide and hexamethylenediamine and from N,N′-hexamethylenedisuccinimide and ethylenediamine. The detailed structures of the polymers are discussed on the basis of their melting points and x-ray diagrams. It is concluded that the polymers contain a crystalline portion of \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--}[{\rm NH \hbox{--} (CH}_2 {\rm)}_{\rm 2} {\rm \hbox{--} NHCO \hbox{--}}({\rm CH}_2)_2 {\rm \hbox{--} CONH \hbox{--}}({\rm CH}_2)_6 {\rm \hbox{--} NHCO \hbox{--}}({\rm CH}_2)_2 {\rm \hbox{--} CO\rlap{---}]} $\end{document} sequences.     

Analysis of 3'-azido-3'-deoxythymidine levels in tissues and milk by isocratic high-performance liquid chromatography

A sensitive high-performance liquid chromatographic (HPLC) assay was established to analyze levels of the antiretroviral agent 3'-azido-3'-deoxythymidine (AZT, zidovudine) in serum, milk and tissue extracts. After methanol precipitation, serum samples could be injected directly into the HPLC apparatus, whereas tissue extracts required further clarification. Recovery of AZT was virtually complete. Isocratic elution with a mobile phase consisting of 6% acetonitrile and 0.1 M ammonium acetate, pH adjusted to 4.5 with glacial acetic acid, resulted in good resolution of AZT and its metabolites; retention times for AZT and the internal standard, p-nitrophenol, were 20 and 37 min, respectively. Using this method, we have demonstrated that AZT crosses both the blood-brain and placental barriers and is excreted into milk at high levels.     

Tunable charge-transport properties of I(h)-C80 endohedral metallofullerenes: investigation of La2@C80, Sc3N@C80, and Sc3C2@C80

Fullerene crystals or films have drawn much interest because they are good candidates for use in the construction of electronic devices. The results of theoretical calculations revealed that the conductivity properties of I(h)-C(80) endohedral metallofullerenes (EMFs) vary depending on the encapsulated metal species. We experimentally investigated the solid-state structures and charge-carrier mobilities of I(h)-C(80) EMFs La(2)@C(80), Sc(3)N@C(80), and Sc(3)C(2)@C(80). The thin film of Sc(3)C(2)@C(80) exhibits a high electron mobility μ = 0.13 cm(2) V(-1) s(-1) under normal temperature and atmospheric pressure, as determined using flash-photolysis time-resolved microwave conductivity measurements. This electron mobility is 2 orders of magnitude higher than the mobility of La(2)@C(80) or Sc(3)N@C(80).     

Novel polyaddition catalyzed by transition metals. II. Synthesis of polysulfones using polyaddition of arenedisulfonyl chlorides to diethynyl compounds catalyzed by cuprous chloride

CuCl-catalyzed polyaddition of arenedisulfonyl chloride to diethynyl compound was performed to produce polysulfones consisting of sulfonyl groups between arenylene and chlorovinylene groups. The polyaddition proceeded via both trans and cis addition, whose proportion was affected by the polarity of the reaction medium, the presence of triethylamine · HCl salt, and the nature of the monomer. © 1993 John Wiley & Sons, Inc.     

Effect of simultaneous polyaddition reaction on the curing of epoxides

Epoxy-amine curing reactions were theoretically studied using expectation theory taking into account the different reactivities of (1) the primary and secondary amine hydrogens and (2) the secondary hydroxyl group generated when an amine reacts with an epoxy group. The curing compositions and the fractional conversions at the gel point were computed. Generally the hydroxyl groups react slower than the amines and user these conditions, the reactivity of the OH group has a significant effect only when there is an intial excess of epoxide over the amine. The hydroxyl activity effectively increases the functionality of the epoxides and gelation can occur where it may not be expected.     

Synthesis and properties of optically active polyurea by interfacial polyaddition

Optically active polyureas were prepared from optically active diisocyanate (L -lysinediisocyanatemethylester) and optically inactive linear diamine [H₂N(CH₂)_nNH₂, n = 2,3,4,5,6, and 9]. Polymerization was carried out by the interfacial polyaddition technique using the benzene–water system and by solution polyaddition. The values of optical rotation of obtained polyureas were dependent on the methylene number of diamines. Asymmetric selective polyaddition of L -lysinediisocyanatemethylester for racemic 1,2-diaminopropane was unsuccessful.     

Salt effect on polyaddition of bifunctional cyclic carbonate and diamine

The effect of various additives was examined for polyaddition of bifunctional cyclic carbonate and diamine giving poly(hydroxyurethane). Lithium chloride and lithium fluoride especially proved to be effective for the acceleration that resulted in giving polymers with higher molecular weights without coloration. The IR spectroscopic analysis of the mixtures of the additives and the carbonate monomer suggested that the acceleration with the lithium salts depends on the activation of the carbonyl group to enhance its electrophilicity. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6282–6286, 2005     

Pyramidalization of Gd3N inside a C80 cage. The synthesis and structure of Gd3N@C80

The X-ray crystal structure of Gd(3)N@C(80).Ni(II)(OEP).1.5(benzene) shows that the Gd(3)N unit within the I(h) C(80) cage is pyramidal, whereas Sc(3)N@C(80), Sc(3)N@C(78), Sc(3)N@C(68), Lu(3)N@C(80) and Sc(2)ErN@C(80) have planar M(3)N units.     

On the radiation-induced polyaddition of bisperfluoroisopropenyl terephthalate with 1,4-dioxane

Radical polyaddition of bis(α-trifluoromethyl-β,β-difluorovinyl)terephthalate [CF₂C(CF₃)OCOC₆H₄COOC(CF₃)CF₂] (BFP) with 1,4-dioxane (DOX) afforded higher molecular weight polymers under γ-rays radiation from a source when compared to those yielded by benzoyl peroxide initiation. More detailed study on the radiation-induced polyaddition of BFP with DOX and optimization of the reaction conditions were carried out. It was necessary to irradiate with doses of 2000, 1500, and 750 kGy, to obtain quantitative conversion of BFP at the feed molar ratios DOX/BFP of 8.0, 16, and 32, respectively. Step-growth polymerization mechanism was suggested by the measurements of molecular weights of the polymers obtained with several irradiation doses. It was concluded that the molecular weight of the polymer could be controlled by the feed molar ratio of DOX/BFP and irradiation doses. The steep increase of molecular weight was observed at the feed molar ratio of DOX/BFP of 8.0 with the irradiation doses above 2000 kGy and the polymer with the weight-average molecular weight of 2.36×10⁴ was obtained with the dose of 3000 kGy. The reaction between polymers might take place after the quantitative conversion of BFP. Radiation-induced radical polyaddition mechanism of BFP with DOX was proposed.     

Synthesis of polyamides by the polyaddition of bisimidazoline with dicarboxylic acids

N,N′-Dipropionylethylenediamine was synthesized by the ring-opening addition reaction of 2-ethyl-2-imidazoline with propionic acid at 220°C. By applying this reaction to polymerization, polyamides were synthesized by the ring-opening polyaddition reaction at 220°C. of 1,4-bis(imidazoline-2-yl)butane with adipic acid, succinic acid, sebacic acid, and terephthalic acid. The reaction product of 1,4-bis(imidazoline-2-yl)butane with adipic acid, which was proposed to be nylon 26, was compared with an authentic sample of nylon 26 and shown to possess a very similar infrared spectrum and melting point.