Interpolymer association between hydrophobically modified poly(sodium acrylate) and poly(N-isopropylacrylamide) in water: The role of hydrophobic interactions and polymer structure

The association between hydrophobically modified poly(sodium acrylate) (HMPA) and poly(N-isopropylacrylamide) (PNIPAM) in aqueous solution was studied using turbidimetry, viscometry and fluorescence measurements. Both the polymeric and the amphiphilic nature of the HMPA influence the association process. The tendency for association, as reflected by the increase in the cloud point and the reduced viscosity of PNIPAM, increases with the length of the alkyl group and the degree of substitution of HMPA. The fluorescence study, using pyrene as a probe, ascertains that the association is of hydrophobic nature and the association process is gradual and less cooperative than the association of PNIPAM with ionic surfactants. When high molar mass HMPA is used, the hydrophobic association between HMPA and PNIPAM leads to the formation of a reversible network with significantly enhanced thickening properties as compared to the thickening ability of the corresponding pure HMPA in aqueous solution.     

Reentrant phase transition and network parameters of hydrophobically modified poly[2-(diethylamino)ethylmethacrylate-co-N-vinyl-2-pyrrolidone/octadecyl acrylate] hydrogels

Hydrophobically modified poly[2-(diethylamino)ethylmethacrylate-co-N-vinyl-2-pyrrolidone/octadecyl acrylate] [P(DEAEMA-NVP/OA)] hydrogels with different OA content were prepared by free-radical crosslinking copolymerization of corresponding monomers in tert-butanol. The swelling equilibrium of the hydrogels was investigated as a function of temperature and hydrophobic comonomer content in pure water. An interesting feature of the swelling behavior of the P(DEAEMA-NVP/OA) hydrogels was the reentrant phase transition where the hydrogels collapse once and reswell as temperature increased. The average molecular mass between crosslinks and polymer-solvent interaction parameter (χ) of the hydrogels were calculated from equilibrium swelling values. The enthalpy (ΔH) and entropy (ΔS) changes appearing in the χ parameter for the hydrogels were determined by using the Flory-Rehner theory. It was observed that the experimental swelling data of the hydrophobic hydrogels at different temperature agreed with the Flory-Rehner theory, that provided that the sensitive dependence of χ parameter on both temperature and polymer concentration is taken into account.     

Studies on foam stability by the actions of hydrophobically modified polyacrylamides

Hydrophobically modified polyacrylamide (HMPAM), as a foam stabilizer, was prepared with a cationic surfomer, acrylamide and acrylic acid by free-radical polymerization in aqueous solution. The actions of HMPAM on foam stability have been investigated with the Waring blender method. The results showed the foam containing HMPAM was stabler than that contained polyacrylamide. Moreover, a linear relationship between the logarithm of the half decay time and polymer concentration was observed, and the slope reflects the polymer ability to stabilize the foam.     

Reactions of P4S10 and pyPS2Cl with N,N′-diphenylurea and N,N′-diphenylthiourea

The reaction of P₄S₁₀ (1) with N,N′-diphenylurea (PhNH)₂CO (2) results in new heterocyclic compounds: the pyridinium salt of 1,3-diphenyl-2-sulfido-2-thioxo-1,3-diaza-2λ⁵-phosphetidine (3) (with a P–N–C–N cycle) and the pyridinium salt of 1,4-diphenyl-2,5-disulfido-2,5-dithioxo-1,4-dithiadiaza-2λ⁵,5λ⁵-diphosphinane (4), containing the (P–S–N)₂ cycle and the cyclic thiophosphates [pyH]₂[P₂S₈] (5), [pyH]₂[P₂S₇] (6) and [pyH]₃[P₃S₉] (7). A similar reaction, but carried out with N,N′-diphenylthiourea (PhNH)₂CS (8), leads to the formation of 4 and 6. pyPS₂Cl (9), used as an alternative starting material, also yields compounds 3, 4, 5, and further [pyH][PS₂Cl₂] (10) and S₈ after reaction with 2. Compound 3 reacts with Pd(CH₃COO)₂, with the formation of the complex [Pd(Ph₂N₂COPS₂)₂] (11). The crystal structures of 3 and 7 were determined by single-crystal X-ray diffraction.     

Influence of hydrophobe content and salt concentration on dilute solution behaviour of hydrophobically modified ionic polymers from diallylammonium salts/sulfur dioxide cyclocopolymerization: Light scattering and fluorescence spectroscopy

Novel hydrophobically modified polyelectrolytes were synthesized using the cyclocopolymerization of sulfur dioxide, N,N-diallyl-N-carboethoxymethylammonium chloride and the hydrophobic monomer N,N-diallyl-N-octadecylammonium chloride. Aggregation of these polymers in aqueous solutions was characterized in the dilute regime by static light scattering and fluorescence spectroscopy as a function of hydrophobe content and NaCl concentration. Copolymers were observed to associate at very low concentrations (0.005 wt%). The copolymer is capable of associating at this very low polymer concentration because of the extended length of the hydrophobic monomer (C₁₈) that can reach far enough from the backbone to avoid electrostatic repulsion. Aggregation of the polymers increased with increasing hydrophobe content. Upon addition of salt, the apparent molecular weight of polymer aggregates decreased as a result of neutralization of the charges. At high salt concentrations, the size of the polymer aggregates was observed to increase again as a result of increased polarity of the solvent that resulted in more hydrophobic association.     

Effects of poly(N‐isopropylacrylamide) on the solution properties of hydrophobically modified acrylamide copolymer

The hydrophobic interaction between hydrophobically modified acrylamide copolymer (HMPAM) and poly(N‐isopropylacrylamide) (PNIPAM) in aqueous solutions was investigated. The results show that the solution properties of HMPAM are significantly influenced by the addition of PNIPAM. In dilute regime, the intrinsic viscosity of HMPAM in 0.025 wt % PNIPAM/0.1 M NaCl mixed solution is 17.52 dL g^?1, about 2 times 8.66 dL g^?1, that in 0.1 M NaCl solution, which is due to the attractive interaction between the hydrophobic parts of PNIPAM and HMPAM molecules. In semidilute regime, below the saturation concentration, the addition of PNIPAM can lead to both the apparent viscosity and the modulus of HMPAM solutions increasing, which is attributed to the number of aggregation junctions increasing, responsible for the increase of the contribution of the reversible network to the viscosity increase, the β value. In addition, a thermothickening behavior for the HMPAM/PNIPAM mixed solution is observed with increasing temperature over 15–30 °C, which is consistent with the large increase of the Huggins coefficient of HMPAM in the presence of PNIPAM from 1.95 to 7.59 as temperature increases from 25 to 30 °C. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 709–715, 2005     

Inorganic-Organic Hybrid Materials: Synthesis and X-Ray Structure of N,N′-Dimethylimidazolium Salts [(Me2Im)2][Cd2(SCN)6] and N,N′-Dicyclohexylimidazolium [(Cy2Im)2][Cd2(SCN)6]·C3H6O

Two novel N,N′-dialkylimidazolium thiocyanate-cadmium complexes [(R₂Im)₂][Cd₂(SCN)₆] for R=Me (3), and cyclohexyl (4) have been synthesized and characterized by single-crystal X-ray diffraction. Compound 3 crystallizes in the monoclinic unit cell dimensions of 17.468(3), 7.7273(12), 10.6750(16) Å, 104.833(2)°, and space group C2 with two [(Me₂Im)₂] [Cd₂(SCN)₆] per unit cell. The two cadmium atoms in 3 are octahedrally coordinated in 4N2S and 2N4S coordination environment, and linking into one-dimensional zigzag chains. Compound 4 belongs to the monoclinic space group Cc with unit cell of dimensions 13.3049(12), 17.5550(16), 20.8012(19) Å, 101.494(2)°, and four [(Cy₂Im)₂][Cd₂(SCN)₆]·C₃H₆O per unit cell. The cadmium atoms in 4 are all 3N3S hexa-coordinated with six bridging SCN⁻ ions in an fac configuration and form infinite zigzag polymeric chains. The infinite chains in 3 form an approximate hexagonal array, making triangular channels which are occupied by N,N′-dimethylimidazolium ions, whereas the chains in 4 form layered structure, and the layers are stacked perpendicularly with respect to the orientation of the infinite anionic chains alternatively. N,N′-dicyclohexylimidazolium cations and solvent molecules fill in between layers.     

Pd2dba3/P(i-BuNCH2CH2)3N: a highly efficient catalyst for the one-pot synthesis of trans-4-N,N-diarylaminostilbenes and N,N-diarylaminostyrenes

A Pd₂dba₃/P(i-BuNCH₂CH₂)₃N catalyzed one-pot synthesis of unsymmetrically substituted trans-4-N,N-diarylaminostilbenes and both symmetrically and unsymmetrically substituted N,N-diarylaminostyrene derivatives is reported. The procedure involves two or more palladium catalyzed sequential coupling reactions (an amination and an inter-molecular Heck reaction) in one-pot using the same catalyst system with two different aryl halides, including aryl chlorides and hetero aryl halides as the coupling partners.     

SO2对钙基CO2吸收剂循环煅烧/碳酸化反应的影响

在循环煅烧/碳酸化反应系统中,研究了SO₂对钙基吸收剂CaCO₃捕集CO₂的影响,获得了SO₂对钙基吸收剂碳酸化特性、煅烧特性以及循环稳定性的影响规律,并结合SEM分析结果,从循环煅烧/碳酸化反应角度,分析了可能存在的原因。结果表明,钙基吸收剂吸收CO₂的能力随着循环反应次数的增加逐渐发生衰减,在SO₂影响下,这种衰减会进一步加剧,且衰减程度随着SO₂浓度的增加而增大,经过十次循环后,碳酸化转化率分别为25.5%(0%SO₂)、16.9%(0.1%SO₂)和5.2%(0.2%SO₂)。造成这种衰减加剧的主要原因是反应产生较厚的硫酸化产物层,硫酸化产物层使颗粒表面孔隙发生堵塞,阻碍了CO₂在吸收剂内部的扩散,降低了碳酸化转化率。     

Alkynylation of N-tosylimines with aryl acetylenes promoted by ZnBr2 and N,N-diisopropylethylamine in acetonitrile

We found a suitable condition for the effective alkynylation of N-tosylimines with aryl acetylenes. The reaction of N-tosylimines and aryl acetylenes in the presence of ZnBr₂ and DIEA (N,N-diisopropylethylamine) in CH₃CN afforded the desired N-tosyl propargylamines in moderate to good yields.     

改性橄榄石对C_7H_8/CO_2催化重整的影响

在固定床反应器中,以甲苯作为生物质气化焦油模型化合物,橄榄石作为甲苯裂解催化剂,结合XRD、SEM、BET、H2-TPR等表征手段,考察了不同重整反应温度、CO_2浓度、橄榄石煅烧温度以及载镍量对甲苯催化重整性能的影响。结果表明,甲苯转化率随着重整反应温度的升高而增加,橄榄石对甲苯具有较高的催化活性,经900℃煅烧后的橄榄石活性最高。相比于橄榄石直接催化裂解甲苯,CO_2的加入能够显著降低催化剂表面的积炭率,当CO_2/C_7H_8物质的量比为4时,橄榄石催化剂表面的积炭率降低至17.0%。橄榄石载镍后,对C_7H_8/CO_2的催化重整性能进一步提高,甲苯转化率最高达到99.4%,但是积炭率也会随之增加。     

Investigation of phase equilibria in the systems K2SO4Sc2(SO4)3, Rb2SO4Sc2(SO4)3 and Cs2SO4Sc2(SO4)3

Phase diagrams of the systems K₂SO₄Sc₂(SO₄)₃, Rb₂SO ₄Sc₂(SO₄)₃ and Cs₂SO₄ Sc₂(SO₄)₃ have been investigated by X-ray diffraction phase analysis and differential thermal analysis techniques. A salient feature of all the systems is the formation of M₃Sc(SO₄)₃, which melt incongruently, and MSc(SO₄)₂, which on heating decompose in the solid state.     

改性SiO2对铁基催化剂H2、CO吸附及加氢性能的影响

采用溶胶凝胶方法通过掺杂修饰剂M（M=Mn、Zn、Zr、Sr）制备出改性SiO₂载体,再用浸渍法将Fe元素负载于该载体上制成系列催化剂。采用X射线衍射（XRD）、氮气物理吸附-脱附、X射线光电子能谱（XPS）等手段表征了催化剂的织构性质、晶相组成和电子性质。利用程序升温手段研究了催化剂的H₂还原吸附性质和CO加氢性能。借助动力学分析方法研究了催化剂与H之间的相互作用。结果表明,少量掺杂的修饰剂对催化剂的Fe物相组成以及表面Fe物种电子状态基本没有影响,但降低了催化剂的比表面积以及活性相分散度,削弱了对H₂的吸附能力,降低催化剂的H₂脱附活化能。Zn、Zr的掺杂抑制了催化剂的还原,而Mn、Sr的掺杂却促进催化剂的还原。Mn、Zn、Zr的掺杂抑制催化剂表面CO的解离吸附,Sr则促进CO的解离吸附,Mn、Zn、Zr、Sr均促进低温区间C-C耦合和加氢反应,其中,Mn、Zr促进加氢的作用更显著。     

SO2对NO催化氧化过程的影响V.NiO/γ-Al2O3上SO2的作用机理

采用程序升温脱附(TPD)及漫反射原位红外光谱(DRIFT)技术分析比较了SO2存 在前后，NO—02反应气体在NiO／γ—Al2O3催化剂上所形成吸附物种的变化情况， 发现SO2能促使硝酸盐物种在低温分解并释放出NO2，而且耐热稳定的硝酸盐物种也 比单纯NO-02吸附时多．室温时催化剂表面上的SO2以弱吸附物种为主，特征红外吸 收峰位于1324cm^-1附近，温度升高后表面硫酸盐物种数量增多．关联SO2气氛中 NO2的生成规律后得出，类似于铅室反应中间体的多分子吸附物种[NO2(SO3)x]是产 生N02的活性物种，由SO2在载体或催化剂表面弱碱位吸附后吸引气相NO所产生，解 离O^-起到稳定活性物种和补充弱碱位的作用．同时该物种也是毒性物质SO4^2-的 前驱体，当KO氧化反应发生后催化剂的失活也开始了．     

Aerobic alcohol oxidation using a PdCl2/N,N-dimethylacetamide catalyst system under mild conditions

A new and simple PdCl₂/DMA catalytic system for the alcohol oxidation has been developed using molecular oxygen as the sole oxidant under mild conditions. The catalytic system could be reused for three runs without significant loss of catalytic activity. A variety of active and non-active alcohols were oxidized to their corresponding carbonyl compounds in good to excellent yields. Gas-uptake kinetics for the catalytic system was also investigated. The ca. 1:1 molar ratio of O₂ uptake to product yield is observed, suggesting the in situ formation of H₂O₂.     

Comments on a modified tutwiler method for the determination of H2S and SO2 in gases

A modified form of the Tutwiler analysis which was proposed a few years ago and has to some extent, been used as a method for controlling the Claus sulphur recovery process, has been examined as to its exactitude for this purpose, viz. for, determining both H₂S and SO₂ in gas mixtures.It has been found suitable for the determination of H₂S alone, and also (with a small modification) of SO₂ alone, but not for both compounds if they occur together.These disadvantages are not possessed by an alternative method of analysis, recently published.     

Efficient synthesis of N,N′-dialkyl-N″-dialkylaminocarbothioyl thioureas from cyclic secondary amines, CS2, and N,N′-dialkyl carbodiimides in water

A mild, convenient, and practical one-pot procedure for direct synthesis of N,N′-dialkyl-N″-dialkylaminocarbothioyl thioureas is described via three-component reaction of cyclic secondary amines, CS₂, and N,N′-dialkyl carbodiimides in water at room temperature.     

Influence of chemical non-steady-state on SO2 conversion in fluidized catalyst bed

The effect of the influence of catalyst non-steady-state on SO₂ conversion ion a fluidized catalyst bed has been studied depending on the ratio of relaxation time for the catalytic reaction step to the characteristic time of particles diffusion.

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SnCl2 mediated efficient N,N-dialkylation of azides to tertiary-amine via potential stannaimine intermediate

A base free one-pot conversion of azides to N,N-dialkylamine is described. A two-step reaction pathway has been postulated invoking the intermediacy of stannaimine. This new carbon-nitrogen bond formation strategy adds to the repertoire of tin(II) chemistry.     

Di-μ-hydroxy-bis(N,N,N′,N′-tetramethylenediamine)-copper(II) chloride [Cu(OH)·TMEDA]2Cl2: an efficient, practical catalyst for benzylation and allylation of amides

An efficient protocol for the benzylation or allylation of amides using the corresponding benzyl or allyl chlorides as electrophiles under basic conditions with commercially available 5 mol % of [Cu(OH)TMEDA]₂Cl₂ as catalyst was developed. Under these conditions, unprotected amino acids were benzylated without any racemization.