2-cyanoprop-2-yl dithiobenzoate mediated reversible addition-fragmentation chain transfer polymerization of acrylonitrile targeting a polymer with a higher molecular weight

The reversible addition-fragmentation chain transfer (RAFT) polymerization of acrylonitrile (AN) mediated by 2-cyanoprop-2-yl dithiobenzoate was first applied to synthesize polyacrylonitrile (PAN) with a high molecular weight up to 32,800 and a polydispersity index as low as 1.29. The key to success was ascribed to the optimization of the experimental conditions to increase the fragmentation reaction efficiency of the intermediate radical. In accordance with the atom transfer radical polymerization of AN, ethylene carbonate was also a better solvent candidate for providing higher controlled/living RAFT polymerization behaviors than dimethylformamide and dimethyl sulfoxide. The various experimental parameters, including the temperature, the molar ratio of dithiobenzoate to the initiator, the molar ratio of the monomer to dithiobenzoate, the monomer concentration, and the addition of the comonomer, were varied to improve the control of the molecular weight and polydispersity index. The molecular weights of PANS were validated by gel permeation chromatography along with a universal calibration procedure and intrinsic viscosity measurements. H-1 NMR analysis confirmed the high chain-end functionality of the resultant polymers.

含分子内氢键的苯硫酚在水相中的Michael加成反应

苯硫酚的巯基是一个较强的亲核基团 [1] ,对 α,β-不饱和双键的 Michael加成反应已有报道 [2～ 4 ] .但是当巯基的邻位存在与其形成氢键的基团时 ,如果按文献条件进行反应 ,或者反应无法进行 [5,6 ] ,或者要使用反应条件苛刻的丁基锂 [6 ] ,或者使用吡啶等毒性较大的反应溶剂 [2～ 9] ,而且产率较低 .本文选择了饱和碳酸氢钠水溶液 /n-四丁基硫酸氢铵的反应条件 ,探讨了该类化合物在此条件下的 Michael加成反应 .以 3个含分子内氢键的苯硫酚 (邻羟基苯硫酚、邻氨基苯硫酚和邻羧基苯硫酚 )为起始物 ,对丙烯酸乙酯和丙烯腈进行了 Michael加成反应 .本方法的特点在于不使用特殊的有机溶剂 ,反应在水相[10～ 12 ] 中进行 ;反应速度快 ,收率高 ,无巯基偶联 [13] 副产物生成 .反应式如 Scheme1所示 .RSH1 a— 1 c+ OONa HCO3,H2 On-Bu4 N HSO4RSOO2 a— 2 cRSH1 a— 1 c+ NC Na HCO3,H2 On-Bu4 N HSO4RSCN3 a— 3 ca. R =OH;b. R =N H2 ;c. R...

Synthesis, molecular structures, and norbornene addition polymerization activity of the neutral nickel catalysts supported by beta-diketiminato [N, N], ketiminato [N, O], and Schiff-Base [N, O] ligands

A series of neutral nickel complexes [Ni(Ph)(PPh3)(N, O)] with Schiff-base ligands (N, O) [N, O = 5-Me-3-tert-Bu-(Ar-N=CH)C6H2O (1, Ar = 2,6-Me2C6H3; 2, Ar = 2,6-i-Pr2C6H3)], [Ni(Ph)(PPh3)(N,O)1, with beta-ketiminato ligands (N, O) [N, O = CH3COCHC=(CH3)N-Ar (3, Ar = 2,6-Me2C6H3; 4, Ar = 2,6-i-Pr2C6H3)] and [Ni(N, N)(PPh3)], and with beta-diketiminato ligands (N, N) [5, N, N = [2,6-i-Pr-2(C6H3)N=C(CH3)](2)CH] have been synthesized and characterized. The molecular structures of complexes 1, 4, and 5 have been confirmed by X-ray single-crystal analyses. Although their ligands have similar structures, complex 4 possesses a structure similar to that of four-coordination nickel with complex 1, while complex 5 reveals a rare three-coordination nickel geometry. These compounds show high catalytic activities of up to 3.16 x 10(7) g PNB mol(-1) Ni h(-1) for the addition polymerization of norbornene in the presence of modified methylaluminoxane (MMAO) as cocatalyst. Catalytic activities, polymer yield, molecular weights, and molecular weight distributions of polyborbornene have been investigated under various reaction conditions.

Dibenzyl trithiocarbonate mediated reversible addition-fragmentation chain transfer polymerization of acrylonitrile

Reversible addition-fragmentation chain transfer polymerization has been successfully applied to polymerize acrylonitrile with dibenzyl trithiocarbonate as the chain-transfer agent. The key to success is ascribed to the improvement of the interchange frequency between dormant and active species through the reduction of the activation energy for the fragmentation of the intermediate. The influence of several experimental parameters, such as the molar ratio of the chain-transfer agent to the initiator [azobis(isobutyronitrile)], the molar ratio of the monomer to the chain-transfer agent, and the monomer concentration, on the polymerization kinetics and the molecular weight as well as the polydispersity has been investigated in detail. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and H-1 NMR analyses have confirmed the chain-end functionality of the resultant polymer.

Effects of SBS addition and temperature on 3D siliceous mesostructured cellular foam

Siliceous mesostructured cellular foam with three-dimensional (3D) wormhole structure (MSU-type) is prepared by using triblock copolymer (poly(styrene-b-butadiene-b- styrene), SBS) with both hydrophobic head and tail group as template in strong acid condition via microemulsion method. The effects of SBS addition and temperature on the morphology and physicochemical properties, such as pore diameters, surface areas and pore volumes of the materials have been investigated by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscope (FE-SEM) and nitrogen adsorption-desorption analysis. The results show that the pore volumes, pore sizes and specific surface areas depend strongly on the SBS amount and forming micelles temperature. Moreover, the materials obtained with high wall thickness exhibit a relatively good thermal stability.

Gas Phase Addition of Rare-earth Fullerenes with Benzene

Gas phase adduct of endohedral rare-earth fullerenes Nd@C-S2 with the ion system of benzene-[Nd@C-S2-C6H6](+) was observed for the first time by ion-molecular reaction under chemical ionization condition. The possible reaction passageway and molecular structures of this gas phase adduct were discussed and a parallel "reversed umbrella" pi-pi interaction complex of the [C6H6](+) ion reacting with the neutral rare-earth fullerenes Nd@C-S2 was considered to be much reasonable. The experimental result indicated that endohedral rare-earth fullerenes has relatively active reactivity and aromatic properties similar towards benzene molecular ion in gas phase.

Permanent Genetic Resources added to Molecular Ecology Resources Database 1 May 2009-31 July 2009

This article documents the addition of 512 microsatellite marker loci and nine pairs of Single Nucleotide Polymorphism (SNP) sequencing primers to the Molecular Ecology Resources Database. Loci were developed for the following species: Alcippe morrisonia morrisonia, Bashania fangiana, Bashania fargesii, Chaetodon vagabundus, Colletes floralis, Coluber constrictor flaviventris, Coptotermes gestroi, Crotophaga major, Cyprinella lutrensis, Danaus plexippus, Fagus grandifolia, Falco tinnunculus, Fletcherimyia fletcheri, Hydrilla verticillata, Laterallus jamaicensis coturniculus, Leavenworthia alabamica, Marmosops incanus, Miichthys miiuy, Nasua nasua, Noturus exilis, Odontesthes bonariensis, Quadrula fragosa, Pinctada maxima, Pseudaletia separata, Pseudoperonospora cubensis, Podocarpus elatus, Portunus trituberculatus, Rhagoletis cerasi, Rhinella schneideri, Sarracenia alata, Skeletonema marinoi, Sminthurus viridis, Syngnathus abaster, Uroteuthis (Photololigo) chinensis, Verticillium dahliae, Wasmannia auropunctata, and Zygochlamys patagonica. These loci were cross-tested on the following species: Chaetodon baronessa, Falco columbarius, Falco eleonorae, Falco naumanni, Falco peregrinus, Falco subbuteo, Didelphis aurita, Gracilinanus microtarsus, Marmosops paulensis, Monodelphis Americana, Odontesthes hatcheri, Podocarpus grayi, Podocarpus lawrencei, Podocarpus smithii, Portunus pelagicus, Syngnathus acus, Syngnathus typhle,Uroteuthis (Photololigo) edulis, Uroteuthis (Photololigo) duvauceli and Verticillium albo-atrum. This article also documents the addition of nine sequencing primer pairs and sixteen allele specific primers or probes for Oncorhynchus mykiss and Oncorhynchus tshawytscha; these primers and assays were cross-tested in both species.

Addition reactions of nitrones on the reconstructed C(100)-2 x 1 surfaces

In this paper, the reactions of nitrone, N-methyl nitrone, N-phenyl nitrone and their hydroxylamine tautomers (vinyl-hydroxylamine, N-methyl-vinyl-hydroxylamine and N-phenyl-vinyl-hydroxylamine) on the reconstructed C(100)-2 x 1 surface have been investigated using hybrid density functional theory (B3LYP), Moller-Plesset second-order perturbation (MP2) and multi-configuration complete-active-space self-consistent-field (CASSCF) methods. The calculations showed that all the nitrones can react with the surface "dimer" via facile 1.3-dipolar cycloaddition with small activation barriers (less than 12.0 kJ/mol at B3LYP/6-31g(d) level). The [2+2] cycloaddition of hydroxylamine tautomers on the C(100) surface follows a diradical mechanism. Hydroxylamine tautomers first form diradical intermediates with the reconstructed C(I 00)-2 x I surface by overcoming a large activation barrier of 50-60 kJ/mol (B3LYP), then generate [2+2] cycloaddition products via diradical transition states with negligible activation barriers. The surface reactions result in hydroxyl or amino-terminated diamond surfaces, which offers new opportunity for further modifications. (C) 2007 Elsevier B.V. All rights reserved.

Addition reaction of nitrones on the reconstructed Si(100)-2 x 1 surface

The reaction of nitrone, N-methyl nitrone, and their hydroxylamine tautomers (vinyl-hydroxylamine and N-methyl vinyl-hydroxylamine) on the reconstructed Si(100)-2 x 1 surface has been investigated by means of hybrid density functional theory (B3LYP) and Moller-Plesset second-order perturbation (MP2) methods. The calculations predicted that both of the nitrones should react with the surface dimer via facile concerted 1,3-dipolar cycloaddition leading to 5-member-ring compounds. The reaction of hydroxylamine tautomers on the Si(100) surface follows pi-complex (intermediate) mechanism. For the reaction of N-methyl vinyl-hydroxylamine, the pi-complex intermediate undergoes [2+2] cycloaddition leading to a 4-member-ring compound. But in the reaction of vinyl-hydroxylamine, the intermediate undergoes H-migration reaction ("ene" reaction) resulting in the oxime-terminated Si surface. All the surface reactions result in the hydroxyl-terminated silicon surfaces, which are very useful for the further modification of the semiconductor.

Theoretical study on the mechanism for the addition reaction of SiH3 with propylene and acetic acid

To explore the reactivities of alkene (-CH=CH2) and carboxy (-COOH) group with H-Si under UV irradiation, the addition mechanism for the reactions of SiH3 radical with propylene and acetic acid was studied by using the B3LYP/6-311++ G(d,p) method. Based on the surface energy profiles, the dominant reaction pathways can be established; i.e., SiH3 adds to the terminal carbon atom of the alkene (-CH=CH2) to form an anti-Markovnikov addition product, or adds to the oxygen atom of the carboxy group (-COOH) to form silyl acetate (CH3-COOSiH3). Because the barrier in the reaction of the carboxy group (39.9 kJ/ mol) is much larger than that of alkene (11.97 kJ/mol), we conclude that the reaction of bifunctional molecules (e.g., omega-alkenoic acid) with H-Si under irradiation condition is highly selective; i.e., the alkene group (-CH= CH2) reacts with SiH3 substantially faster than the carboxyl group (-COOH), which agrees well with the experimental results. This provides the possibility of preparing carboxy-terminated monolayers on silicon surface from omega-alkenoic acids via direct photochemical reaction.

Removal of NO by microwave discharge with the addition of CH4

Removal of NO by a continuous microwave discharge at atmospheric pressure with the addition of CH4 is reported. The conversion of NO to N-2 is approximately 80%, and the energy efficiency is up to 0.55 g-NO/kWh. The effects of CH4 addition and three discharge modes on NO conversion and energy efficiency are investigated. The dependence of NO conversion on experimental time is also observed.