The kinetics of oxidation of atactic polystyrene in solution

The oxidation of polystyrene initiated by the photodecomposition of 2,2′-azoisobutyronitrile at λ > 300 nm was studied at 25°C in chlorobenzene solution. The order of the reaction is approximately unity with respect to AIBN concentration and to the light intensity. The effects of concentration and molecular weight on the rate are apparently related to their effects on bulk viscosities of the solutions. The overall kinetics have been interpreted by a general oxidation scheme which incorporates the effect of bulk viscosity on the rate of radical production in the initiation step. Diphenyl alkanes were oxidized under identical conditions and their kinetic parameters are compared with those of the polymer. It would appear that a considerable degree of intramolecular propagation occurs in both systems.     

Bromoindirubins: the synthesis and properties of minor components of Tyrian purple and the composition of the colorant from Nucella lapillus

The identification of 6, 6′-dibromoindirubin as a component of Tyrian purple has been confirmed by a practical synthesis. Two monobromoindirubins, which could be minor components, have also been synthesised. These compounds have been fully characterised by UV/vis, NMR, IR and MS data. However, the use of UV/vis absorption maxima in solution is shown to be an unreliable identification tool, being solvent dependent. MS cannot distinguish 6, 6′-dibromoindirubin from 6, 6′-dibromo-indigotin, the major component; solution NMR is precluded by lack of solubility and the colorant is best characterised by HPLC. The first investigation of the composition of Tyrian purple from Nucella lapillus is reported.     

Synthesis and Characterisation of Sulphonated Poly(arylene sulphone) Terpolymers with Triphenylphosphine Oxide Moieties for Proton Exchange Membrane Fuel Cells

For application in fuel cells, a series of sulphonated poly(phenylene sulphone) terpolymers with triphenylphosphine oxide moieties as constitutional units in the polymer backbone have been prepared. The synthesis of the terpolymers represents a two‐step process including: (i) an aromatic nucleophilic substitution polycondensation of three difluoro monomers with varying ratios, i.e. 3,3′‐disulphonate‐4,4′‐difluorodiphenylsulphone, 4,4′‐difluorodiphenylsulphone and bis(4‐fluorophenyl)phenyl phosphine oxide (BFPPO), with 4,4′‐thiobisbenzenethiol yielding sulphonated poly(phenylene sulphide) terpolymers (sPPSPO) and (ii) their following oxidation with hydrogen peroxide in acidic solution to yield sulphonated poly(phenylene sulphone) terpolymers (sPPSO2PO). The structures and molecular compositions were confirmed by ¹H and ¹³C NMR spectroscopy. The ion exchange capacity (IEC) was adjusted at will choosing the appropriate ratio of sulphonated and unsulphonated monomers. Terpolymers with 1.72 ≤ IEC ≤ 2.32 have been obtained. Sulphonated poly(arylene) ionomers containing only sulphone (–SO₂–) linkages and phosphine oxide (–PO–) units rather than ether or sulphide in the backbone reveal a high thermal and oxidative stability. Membranes were cast either from dimethylformamide (DMF) or from dimethyl sulphoxide (DMSO) solutions. For all terpolymers some general characteristic trends were observed, such as an increase of the proton conductivity with increasing IEC, water uptake and temperature. The series of sPPSO2PO membranes offered high conductivities at high humidification, however, their performance strongly depends on the relative humidity. The mechanical properties of sulphonated poly(phenylene sulphone)s have been considerably improved by means of terpolymerisation with phenylene oxide moieties. Even under high humidification the terpolymers form clear, flexible membranes the stress at break of some membranes exceeds that of Nafion® under the same conditions by 40%.     

Synthesis,characterization, and properties of new siloxane grafted copolyimides

Three new siloxane containing grafted copolyimides have been prepared by one‐pot solution imidization technique. The polymers are made by the reaction of 4,4′‐(4,4′‐isopropylidenediphenoxy)bis(phthalic anhydride) (BPADA) with commercially available diamine 4,4′‐oxydianiline (ODA) with variation of silicon containing diamine, namely 3,5‐diaminobenzoate terminated polydimethylsiloxane (DBPDMS), as a comonomer to 10, 20, and 30 wt %. The films of the polymers were prepared by casting the polymer solution in dichloromethane. The polymers have been well‐characterized by GPC, IR, and NMR techniques. Thermal stabilities and decomposition behavior of the copolyimides were studied by DSC and TGA. The water contact angle values of the films indicate hydrophobic nature of the polymers. Thermal, flame retardant, mechanical, and surface properties of these polymers have been compared with the homopolyimide and with polyimides where polysiloxane is incorporated in the main chain. DSC revealed melting of the grafted siloxane chain at sub‐ambient temperature and a glass transition corresponding to the main polymer chain above 200°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Electrochemical reduction of 2,2′-dinitrobiphenyl-X type substances in nonaqueous and aprotic solvents

The oxidation-reduction behaviour of 2,2′-dinitrobiphenyl-X type compounds (X = O, S, NH, CH₂, CO) and of 2,2′-dinitrobiphenyl in non-aqueos acetonitrile and dimethylformamide and their mixtures with water was investigated by polarography and cyclic voltammetry at mercury drop electrodes. In combination with ESR-spectroscopy the reversible formation of a radical anion has been found in the primary one-electron step which is followed by a second one-electron uptake leading to a di-anion. According to the group X, to the water content and to the supporting electrolyte the second reduction step is or is not reversible. The ease of reduction decreases in the following sequence with changing X : CO > NH > S > O> - >CH₂(ie E_{$\text{1}\text{2}$} becomes more negative). According to the composition of the solution further 2 or 6 electrons are consumed at more negative potentials, giving to the 2-hydroxylamine-2′-nitro derivative or to the 2,2′-di-hydroxylamine compound, respectively. In solutions with more than approx 5–10% (by vol.) of water the reduction of the two nitro groups proceeds either in a single 8-electron step or in two 4-electron waves. In 90–94% acetonitrile solutions with alkali metal cation salts as supporting electrolytes a dip appears on the limiting current of the overall 8-electron reduction wave with the dme. The inhibition of the reduction process has been interpreted in terms of formation at the electrode of an insoluble precipitate of tri-ions resulting from the interaction between the di-anion and the alkali metal cations.     

Formation of honeycomb films based on a soluble polyimide synthesized from 2,2′‐bis[4‐(3,4‐dicarboxyphenoxy)phenyl]hexafluoropropane dianhydride and 3,3′‐dimethyl‐4,4′‐diaminodiphenylmethane

A soluble polyimide was synthesized from 2,2′‐bis[4‐(3,4‐dicarboxyphenoxy)phenyl]propane dianhydride (BPADA) and 3,3′‐dimethyl‐4,4′‐diaminodiphenylmethane (DMMDA) by a two‐step method, and it had good solubility both in strong bipolar solvents and in common low‐boiling‐point solvents. The BPADA–DMMDA polyimide was dissolved in chloroform (CHCl₃) and cast onto a glass substrate in a humid atmosphere. The BPADA–DMMDA/CHCl₃ solution easily formed honeycomb films. Some affecting factors, such as the polymer solution concentration, atmospheric humidity, and solvent volatility, were tested. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Nucleophile Substitutionen an Kohlensäurederivaten. XX. Aminolyse des Bis(trichlormethyl)carbonates

Nucleophilic Substitutions at Carbonic Acid Derivatives. XX. Aminolysis of Bis(trichlormethyl)carbonate The rate constants for the two steps of the reaction of bis(trichlormethyl)carbonate with substituted anilines have been determinated by conductivity measurements. The first relatively fast step of the reaction is the nucleophilic attack of the amine to the bis(trichloromethyl)-carbonate leading to trichloromethylurethane through a six or four centers transition state in which the carbon-nitrogen bond is formed parallel with the transfer of the proton. In this reaction a phosgene molecule is also produced, which reacts very fast with amine to form a N,N′-diarylurea. The second, much slower step, is the nucleophilic attack of the amine to the trichloromethylurethane. Through a similar transition state in which the proton transfer has even a higher importance, a N,N′-disubstituted urea and an other molecule of phosgene are formed.     

Control of the J-Aggregation Phenomenon by variation of the N-alkyl-substituents

Cyanine dyes ( 1a–d ) with the 5,5′,6,6′-tetrachloro-1,1′-dialkyl-3,3′-di-(3-carboxypropyl)-benzimidocarbocyanine chromophore differing only in the chain length of their alkyl groups in 1,1′-position have been synthesized, spectroscopically characterized, and compared with 5,5′6,6′-tetrachloro-1,1′-diethyl-3,3′-di-(4-sulfobutyl)-benzimidocarbocyanine( TDBC ). In aqueous solution the dyes form J-aggregates which, depending on the alkyl group chain length, exhibit J-bands differing in spectral positions, bandwidth, and in the number of peaks.     

Electronic absorption spectra and acid—base equilibria of some arylaminoanthraquinones in aqueous medium

The visible absorption spectra of 1,4-di-(4′-methylanilino)anthraquinone (Alizarin Cyanin Green) and its disulphonated derivative (Quinizarin Green); 7,8-dihydroxy-1,4-di-(2′-sulpho-4′-methylanilino)anthraquinone (Alizarin Viridine); 1-hydroxy-4(2′-sulpho-4′-methylanilino)anthraquinone (Alizarin Irisol R) and 1,4-dihydroxy-2-(2′-sulpho-4′-methylanilino)anthraquinone (Alizarin Heliotrope) have been recorded in aqueous solutions at different pH values. The spectral changes are explained in terms of shifts in equilibria between different molecular and ionic species in the solutions. The pKa values have been determined for different acid-base equilibria and discussed in relation to molecular structure. Release of a proton from the NH-group in 1,4-bis(arylamino) derivatives is liable to occur through mesomeric interaction between the imino-nitrogen and C? O group. The mesomeric shift is influenced by the pH of solution as well as the nature of compound.     

Synthesis,characterization and spectroscopic studies of two new schiff-base bithienyl pendant-armed 15-crown-5 molecular probes

Two new ligands provided with a 15-crown-5 as a receptor unit and bithiophen unit as an emissive probe have been synthesized and characterized in order to evaluate the coordination capabilities and their sensor effect. Ligand L1 presents an aromatic crown ether moiety that is directly linked to the imine-2,2′-bithiophene π–conjugated system, and ligand L2 is constituted by an aliphatic crown ether moiety that is linked to the same imine-2,2′-bithiophene system through a methylene unit. Solid metal complexes of Ni(II), Pd(II), Hg(II) and Na(I) have been synthesized using both macrocyclic compounds, and have been studied in solution in the presence of the same metal ions. All solid compounds have been characterized by common analytical and spectroscopic techniques. The sensorial effect has been studied using absorption, emission and MALDI-TOF-MS spectroscopies.     

二苯甲烷双马来酰亚胺的合成工艺研究

以顺丁烯二酸酐和4,4'-二氨基二苯基甲烷(DDM)为原料,采用甲苯为溶剂、共沸蒸馏法,分别用一步法和两步法合成N,N'-4,4'-二苯甲烷双马来酰亚胺(BDM)。通过产物核磁氢谱、红外色谱、示差扫描量热(DSC)及产物收率的计算和双键含量、酸值、凝胶时间、凝胶温度等的测定,对BDM一步法、两步法合成工艺进行了研究并对两种方法中生成的副产物进行了分析。结果表明,一步法比两步法产品产率有很大提高,得到的残渣较少,主要是由DDM与BDM的加成反应生成的低聚物,重新利用价值较小;两步法副产物较多,如高温条件下BMA发生分子间脱水形成的线形低聚物,其可以水解成BMA重新利用。     

Synthesis of (3′,3′-Dimethyloxiranyl)quinones and (Dimethylacetyl)quinones as Potential Cytostatics

1,4-Benzoquinones and 1,4-naphthoquinones carrying 3′,3′-dimethyloxiranyl, dimethylacetyl or oxiranylmethyloxy substituents ( 1, 2 or 3 ) have been synthesized. The methods presented involved epoxidation of a sterically overcrowded double bond as a crucial step for synthesis of (3′,3′-dimethyloxiranyl)quinones 1 . Reaction of aryllithium derivatives with 2-chloro-2-methyl-propanol unexpectedly led to (dimethyl)acetylarenes 11 subsequently oxidized to (dimethylacetyl)-quinones 2 . High cytotoxicity of 1 against KB cells has been revealed contrary to significantly lower activity of 2 and 3 . The structure-activity relationship was discussed in terms of current theory of biologically activated alkylating agents.     

Nucleophile Substitution in der 1,3,5-Triazinreihe. IX. Kinetik und Mechanismus der Reaktion von Cyanurchlorid mit 4′-substituierten 4-Aminoazobenzenen

Nucleophilic Substitutions in 1,3,5-Triazines. VII. The Kinetic and ¦ Mechanism of Cyanuric Chloride with 4′-Substituted 4-Aminoazobenzens The kinetic and mechanism of cyanuric chloride reaction with 4′-substituted 4-aminoazobenzens in dioxan-water was studied by conductometry. An addition-elimination mechanism with a monomolecular elimination of chlorine ion at low water concentrations or a nucleophilic attack of 4-aminoazobenzens at high water concentration as low step has been supported by experimental data.     

Sulfonated co-poly(ether imide)s with alkyne groups: Fabrication of crosslinked membranes and studies on PEM properties including MFC performance

A new diamine monomer having alkyne side-groups (DADAF) has been successfully synthesized, and it was used to prepare a series of sulfonated co-polyimides (DFN-XX) when reacted with 1,4,5,8-naphthalenetetracarboxylic dianhydride along with different mole% of 4,4′-diaminostilbene-2,2′-disulfonic acid. The membrane was made from the copolymers by solution casting route, and one of the copolymers DFN-70 was used to prepare crosslinked membranes by adding a different amount of 1,6-hexanediazide during solution casting step. The morphological transformation from non-crosslinked S-coPI to crosslinked S-coPI was observed by employing transmission electron microscopy, atomic force microscopy, and small-angle X-ray scattering analyses. Compared to the non-crosslinked DFN-XX membranes, crosslinked DFN-70 copolymer membranes showed low water uptake and improved mechanical and peroxide radical stability. Also, crosslinked DFN-70 copolymer membranes showed significantly higher proton conductivities (0.004-0.06 S cm⁻¹) compared to those of DFN-70 (0.003-0.05 S cm⁻¹) particularly, at 80°C when the relative humidity increased from 40% to 98%. Furthermore, crosslinked DFN-70 copolymer membranes exhibited significantly enhanced performance in a microbial fuel cell (MFC) as compared to those of non-crosslinked DFN-70 membrane.     

RNA Aminoacylation Mediated by Sequential Action of Two Ribozymes and a Nonactivated Amino Acid

In the transition from the RNA world to the modern DNA/protein world, RNA‐catalyzed aminoacylation might have been a key step towards early translation. A number of ribozymes capable of aminoacylating their own 3′ termini have been developed by in vitro selection. However, all of those catalysts require a previously activated amino acid—typically an aminoacyl‐AMP—as substrate. Here we present two ribozymes connected by intermolecular base pairing and carrying out the two steps of aminoacylation: ribozyme 1 loads nonactivated phenylalanine onto its phosphorylated 5′ terminus, thereby forming a high‐energy mixed anhydride. Thereafter, a complex of ribozymes 1 and 2 is formed by intermolecular base pairing, and the “activated” phenylalanine is transferred from the 5′ terminus of ribozyme 1 to the 3′ terminus of ribozyme 2. This kind of simple RNA aminoacylase complex was engineered from previously selected ribozymes possessing the two required activities. RNA aminoacylation with a nonactivated amino acid as described here is advantageous to RNA world scenarios because initial amino acid activation by an additional reagent (in most cases, ATP) and an additional ribozyme would not be necessary.     

Preparation,thermal characterization and tribological evaluation of some polyquinazolinediones and polyquinazolones

The preparation of a series of pre-polymers by solution polycondensation of 4,4′-diaminodiphenyl-3,3′-dicarboxylic acid (BDC) and di-isocyanates, and the melt polycondensation of BDC and diacetyl derivatives of aromatic diamines is described. These pre-polymers have been characterized and cyclized to yield polyquinazolinediones and polyquinazolones whose structures and thermal stabilities have been investigated. The physical characteristics of films made from these materials were determined after cyclization, and friction and wear characteristics of composite films containing polytetrafluoroethylene, lead oxide and graphite were evaluated in a journal bearing bush configuration. The relationship between wear behaviour and polymer structure, thermal stability and physical properties is discussed.     

Femtosecond Intramolecular Double Proton Transfer in Solution

A review is given of our recent femtosecond fluorescence upconversion studies of photoexcited [2,2′-bipyridyl]-3,3′-diol (BP(OH)₂), and a few derivative compounds thereof. For BP(OH)₂ in liquid solution, concerted and consecutive intramolecular double proton transfers are found to occur concurrently. The concerted (one-step) process takes place in less than 100 fs. The consecutive two-step process (with a first step in less than 100 fs and a second step of a few picoseconds) is solvent and excitation wavelength dependent. From the results we infer that the excited-state double proton transfer in BP(OH)₂ is promoted by low-frequency vibrational stretching and bending modes. Proton transfer dynamics was also studied for BP(OH)₂ in sol-gel glasses. Residual amounts of methanol and water in the pores of the sol-gel glass are found to still solvate the probe molecule and to affect the proton transfer dynamics. Finally, some results of fluorescence upconversion experiments for 6-Me-BPOH (6-methyl-[2,2′-bipyridyl]-3′-ol) and BP(OH)₂-6-COOMe (methyl-3,3′-dihydroxy-[2,2′-bipyridyl]-6-carboxylate) are presented for comparison. It appears that the latter compound in the excited state exhibits a single proton transfer only.     

Preparation of a polyimide nanofiltration membrane for lubricant solvent recovery

Polyimide (PI) membrane has been proven to be an efficient approach for solvent recovery. However, the inherent fragility of the PI membrane limits the range of separation conditions and process economics. In this study, copolyimides were synthesized from 3,3′,4,4′‐benzophenone–tetracarboxylic dianhydride (BTDA) and 4,4′‐biamino‐3,3′‐dimethyldiphenyl–methane (DMMDA) by chemical imidization in a two‐step procedure. Then, a PI nanofiltration (NF) membrane was prepared through a phase‐inversion process for solvent recovery from lube oil filtrates. The results indicated that the immersion of the PI (BTDA–DMMDA) NF membrane in a 1,6‐diaminohexane/ethanol crosslinking agent solution carried on the chemical crosslinking modification, which could effectively improve the solvent resistance of the NF membrane. Moreover, the addition of inorganic salt in the polymer solution further enhanced the solvent resistance and pressure resistance of the membrane, which was favorable for the solvent recovery. The lubricant rejection was above 93%, and the solvent flux was about 30 L m^?2 h^?1 with the NF membrane prepared in optimum conditions, and this membrane showed great potential for future development in the application of solvent recovery from lube oil filtrates. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40338.     

合成丁烷四羧酸过程中间产物的初步分析

以钨作催化剂,由双氧水氧化四氢苯酐合成丁烷四羧酸,采用气相色谱法、液相色谱法、红外光谱法、溴价法、高碘酸氧化法等检测手段,结合反应液中双氧水含量和酸值的测定结果,对丁烷四羧酸合成过程中间产物进行了初步分析。证实四氢邻苯二甲酸氧化成丁烷四羧酸不是一步完成,而是经过中间过程;中间产物经过进一步氧化,能高收率地得到丁烷四羧酸产品。     

Preparation and properties of novel processable polyimides derived from N,N‐bis(isocyanatoalkyl)‐1,2,4,5‐benzenetetracarboxylic‐1,2:4,5‐diimides

Two diisocyanate monomers containing methylene groups and built‐in imide structure have been prepared from the parent diacids via the Curtius–Weinstock rearrangement. Polyimides have been synthesized by solution polymerization of these isocyanates with pyromellitic dianhydride (PMDA), 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA), and hexafluoroisopropylidene‐2,2‐bis(phthalic‐anhydride) (6FDA). All monomers and polymers were characterized by conventional methods, and the physical properties of the polymers, including solution viscosity, solubility, thermal stability and thermal behaviour, were studied. © 2000 Society of Chemical Industry