Regularities and Peculiarities of Solid Polydialkylsilane Order-Disorder Transitions as Studied by Optical (UV,Raman and IR) Spectroscopy

As a result of systematic studies of numerous polydi-n-alkylsilane order-disorder transitions using a combination of UV, Raman, IR as well as XRD methods some generalizations are made concerning the nature of these processes. A criterion is proposed for a given UV band assignment to a given polymer modification based not only on its λ_max value but also on the band width, contour and temperature behaviour of these parameters. Three types of ordering possible for these polymers were shown not to be necessarily interrelated. Side chain “melting” does not inevitably lead to thermochromism while thermochromic structural transitions can occur within the same phase.     

High‐Temperature Neutron Diffraction,Raman Spectroscopy,and First‐Principles Calculations of Ti3SnC2 and Ti2SnC

Herein, we report—for the first time—on the additive‐free bulk synthesis of Ti₃SnC₂. A detailed experimental study of the structure of the latter together with a secondary phase, Ti₂SnC, is presented through the use of X‐ray diffraction (XRD), and high‐resolution transmission microscopy (HRTEM). A previous sample of Ti₃SnC₂, made using Fe as an additive and Ti₂SnC as a secondary phase, was studied by high‐temperature neutron diffraction (HTND) and XRD. The room‐temperature crystallographic parameters of the two MAX phases in the two samples are quite similar. Based on Rietveld analysis of the HTND data, the average linear thermal expansion coefficients of Ti₃SnC₂ in the a and c directions were found to be 8.5 (2)·10^?6 K^?1 and 8.9 (1)·10^?6 K^?1, respectively. The respective values for the Ti₂SnC phase are 10.1 (3)·10^?6 K^?1 and 10.8 (6)·10^?6 K^?1. Unlike other MAX phases, the atomic displacement parameters of the Sn atoms in Ti₃SnC₂ are comparable to those of the Ti and C atoms. When the predictions of the atomic displacement parameters obtained from density functional theory are compared to the experimental results, good quantitative agreement is found for the Sn atoms. In the case of the Ti and C atoms, the agreement is more qualitative. We also used first principles to calculate the elastic properties of both Ti₂SnC and Ti₃SnC₂ and their Raman active modes. The latter are compared to experiment and the agreement was found to be good.     

Conformation of poly(ethylene oxide) in the solid state,melt and solution measured by Raman scattering

The Raman spectrum of poly(ethylene oxide) (PEO) $\text{M}\text{?}{}_{\mathrm{w}}\text{= 3 × 10}{}^6$ and 6 × 10³ has been measured in bulk as a function of temperature and in aqueous and chloroform solution as a function of solvent concentration. The spectral features are assigned to particular isomeric configurations and the changes on melting are found to be consistent with a helix-coil transition. In both solvents the ordered nature of the polymer is largely lost at a critical concentration, approximately 50% by weight; residual ordering in dilute aqueous solution is lost and the random coil configuration attained only above the melting temperature. The wavenumber change of the 862 cm^?1 mode as a function of water concentration showed formation of a complex involving three water molecules and was consistent with a simple H-bonding model. The differences between the spectra in the two solvents are explained by this H-bonding. The results are in general agreement with n.m.r. work.     

Epoxidation of E-1,4-poly(2-triethylsilyl-1,3-butadiene) and E-1,4-poly-[2,3-bis(trimethylsilyl)-1,3-butadiene] Stereochemical analysis of E-1,4-poly(2,3-epoxy-2-triethylsilyl-1,3-butadiene) and E-1,4-poly-[2,3-bis(trimethylsilyl)-1,3-butadiene] by 13C and 29Si NMR

Summary Reaction of E-1,4-poly(2-triethylsilyl-1,3-butadiene) (I) with m-chloroperbenzoic acid (MCPBA) yields E-1,4-poly(2,3-epoxy-2-triethylsilyl-1,3-butadiene) (II). Similar reaction of E-1,4-poly[2,3-bis(trimethylsilyl)-1,3-butadiene] (III) with MCPBA gives E-1,4-poly[2,3-epoxy-2,3-bis(trimethylsilyl)-1,3-butadiene] (IV). The product polymers have been characterized by ¹H, ¹³C, and ²⁹Si NMR, IR, GPC, TGA and elemental analysis. ¹³C and ²⁹Si NMR permit Stereochemical analysis on the microstructures of II and IV.     

Spectral (FT-IR,NMR) Analyses,Molecular Structures,and Chemical Bonding of Two Hexahydroacridine-1,8(2H,5H)-dione Derivatives: A Comparative Quantum Chemical Study

A comparative study on two hexahydroacridine-1,8(2H,5H)-dione deriv-atives namely, 9,10-bis(4-fluorophenyl)-3,3,6,6-tetramethyl-3,4,-6,7,9,10-hexahy-droacridine-1,8(2H,5H)-dione (FTHD) and 10-(4-fluorophenyl)-3,3,6,6-tetramethyl-9-(3,4,5-trimethoxyphenyl)-3,4,6,-7,9,10-hexahyd-roacridine-1,8(2H,5H)-dione (FTMPHD) has been performed. ¹H and ¹³C NMR spectra have been recorded in the CDCl₃ solvent. The equilibrium geometries of FTHD and FTMPHD have been determined and analyzed at DFT level employing B3PW91/6-311++G (d,p) method. The vibrational spectra of both the molecules are calculated and compared with the experimental FT-IR spectra. ¹H and ¹³C NMR spectra have been calculated by using the gauge-independent atomic orbital (GIAO) method. The calculated spectra have been found to be in good agreement with the experimental spectra. The quantum theory of atoms-in-molecule (QTAIM) approach is employed to study various intramolecular interactions within these molecules. The highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) and the molecular electrostatic potential (MESP) surfaces have been constructed and analyzed. Various electronic as well as thermodynamic parameters have been reported.     

2，6-二（2’-芳基-3’-N-乙酰基-1’，3’，4’-噁二唑啉基）吡啶的合成与表征

2,6-吡啶二甲酸经酯化、肼解首先合成2,6-吡啶二酰肼,再跟芳香醛缩合得到酰腙,进而用乙酸酐脱水闭环,合成7个含吡啶环的双噁二唑啉衍生物,其结构用1HNMR、FT-IR、MS进行了验证并对其波谱学特征予以讨论.     

高效液相色谱法测定4,71-双(5-溴-4-已基噻吩-2-基)-2,1,3-苯并噻二唑

采用反相C18柱,流动相四氢呋喃-甲醇-水(体积比70∶12∶18),320 nm作为检测波长.建立了4,7-双(5-溴-4-已基噻吩-2-基)-2,1,3-苯并噻二唑的反相高效液相色谱法检测方法.结果表明,方法精密度RSD为1.13％(n=9),检出限0.003 mg/L,线性范围0.9 ～45 mg/L,线性相关系数为0.997 1.该方法简便、准确、重现性好,为此类苯并噻二唑中间体材料建立了一种有效的检测方法.     

2，6-二（2’-芳基-1’，3’，4’-噁二唑基）吡啶的合成与光谱性质

合成了3个2,6-二(2'-芳基-1',3',4'-(噁)二唑基)吡啶化合物,用1HNMR、FT-IR、MS对其结构进行了表征.研究了它,们的UV-Vis吸收光谱、荧光光谱.紫外.可见吸收光谱表明:目标化合物在278～309 nm出现最大吸收峰;荧光光谱表明:目标化合物在DMF溶液中发射强的紫色荧光,在364～398 nm出现最大发射峰;固体发射强的紫蓝色荧光,在376～414 nm出现最大发射峰.     

2-(4-甲氧基苯基)-4,6-双(三氯甲基)-S-三嗪光引发剂的合成及其光聚合动力学性能研究

以对甲氧基苯甲腈和三氯乙腈为原料合成了光引发剂2-(4-甲氧基苯基)-4,6-双(三氯甲基)-S-三嗪(MBTT),通过傅里叶红外光谱仪、核磁共振仪和紫外吸收光谱对所合成的产物结构进行了表征.并利用实时红外(RT-IR)对该引发剂进行了光聚合反应动力学研究,考察了单体、引发剂浓度和光强对引发速率及单体转化率的影响.结果表明,MBTT是一种高效的紫外光引发剂,在引发剂用量为0.1%时光聚合的单体转化率就能达到90%;随着光强的增大,单体的双键转化率和最大反应速率都增大,诱导期缩短;双丙烯酸酯类单体的双键转化率比三丙烯酸酯类单体的双键转化率要高.     

Comparison of tris(dimethylphenylsilyl)methyllithium and tris(trimethylsilyl)methyllithium reactions with carbon disulfide: a new route for the synthesis of some 1,1-bis(benzylthio)- and bis(allylthio)-2,2-bis(dimethylphenylsilyl)ethenes

A series of bis(benzylthio)- and bis(allylthio)-2,2-bis(dimethylphenylsilyl) ethenes has been obtained by the reaction of (PhMe₂Si)₃CLi and CS₂ with benzyl and allyl bromides. A plausible mechanism for the formation of these compounds has been proposed. The reactivity of (PhMe₂Si)₃CLi toward CS₂ has been compared with that of (Me₃Si)₃CLi. The reaction of (PhMe₂Si)₃CLi with CS₂ and 2-methyloxirane gave a cyclic thiocarbonate.     

Clustering Analysis,Structure Fingerprint Analysis,and Quantum Chemical Calculations of Compounds from Essential Oils of Sunflower (Helianthus annuus L.) Receptacles

Sunflower (Helianthus annuus L.) is an appropriate crop for current new patterns of green agriculture, so it is important to change sunflower receptacles from waste to useful resource. However, there is limited knowledge on the functions of compounds from the essential oils of sunflower receptacles. In this study, a new method was created for chemical space network analysis and classification of small samples, and applied to 104 compounds. Here, t-SNE (t-Distributed Stochastic Neighbor Embedding) dimensions were used to reduce coordinates as node locations and edge connections of chemical space networks, respectively, and molecules were grouped according to whether the edges were connected and the proximity of the node coordinates. Through detailed analysis of the structural characteristics and fingerprints of each classified group, our classification method attained good accuracy. Targets were then identified using reverse docking methods, and the active centers of the same types of compounds were determined by quantum chemical calculation. The results indicated that these compounds can be divided into nine groups, according to their mean within-group similarity (MWGS) values. The three families with the most members, i.e., the d-limonene group (18), α-pinene group (10), and γ-maaliene group (nine members) determined the protein targets, using PharmMapper. Structure fingerprint analysis was employed to predict the binding mode of the ligands of four families of the protein targets. Thence, quantum chemical calculations were applied to the active group of the representative compounds of the four families. This study provides further scientific information to support the use of sunflower receptacles.     

Enhancing electrochromic and kinetic properties of poly(2,3-bis(4-tert-butylphenyl)-5,8-di(1H-pyrrol-2-yl) quinoxaline) by copolymerization

Electrochemical copolymerization was utilized to combine several properties into a single material in order to obtain a highly stable polymer with a low band gap to meet the requirements for color variation. In that sense, two new donor acceptor type electrochromic copolymers of 2,3-bis(4-tert-butylphenyl)-5,8-di(1H-pyrrol-2-yl) quinoxaline (TBPPQ) with bis(3,4-ethylenedioxythiophene) (BiEDOT) and with 4,7-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-2-dodecyl-2H-benzo [1,2,3] triazole (BEBT) were synthesized by electrochemical polymerization. Polymers revealed multicolor electrochromic properties with distinct accessible states and low operation potentials. Electrochromic and kinetic properties of polymers were investigated using cyclic voltammetry (CV) and in situ UV-vis-NIR spectroscopy.     

3,5-二(2’-芳基-3’-N-乙酰基-1,’3,’4’-噁二唑啉基)吡啶的合成与表征

3,5-吡啶二甲酸经酯化、肼解,合成3,5-吡啶二酰肼,再跟芳香醛缩合得到酰腙,进而用乙酸酐脱水闭环,合成8个含吡啶环的双噁二唑啉衍生物,其结构用1H NMR、FT-IR、MS进行了验证,并对其波谱学特征予以讨论。     

Preparation and physicochemical study of jute and glass composites of epoxy resin of (2E, 6E)-bis(4-hydroxybenzylidene)cyclohexanone

Polymer Bulletin - Jute and glass composites of epoxy resin of (2E, 6E)-bis(4-hydroxybenzylidene)cyclohexanone (EBHBC) were prepared by compressing molding technique using three different hardeners...     

Synthesis of 2(E),6(E)-bis(chloromethylidene)-4-thiomorpholinamine-1-oxide and its hydrazones

An efficient method for preparation of earlier unknown S-oxide of 2(E),6(E)-bis(chloromethylidene)-4-thiomorpholinamine by oxidation of 2(E),6(E)-bis(chloromethylidene)-4-thiomorpholinamine hydrochloride with hydrogen peroxide in H₂O or EtOH/H₂O followed by the reaction mixture neutralization with Na₂CO₃ has been described. Interaction of the S-oxide with acetaldehyde, butanal, benzaldehyde, 4-methoxybenzaldehyde and 4-pyridinecarboxaldehyde in EtOH, C₆H₆, in the mixture of acetonitrile and ethanol or ethanol and benzene affords the unknown hydrazones, N-organylmethylidene-2(E),6(E)-bis(chloromethylidene)-4-thiomorpholinamine-1-oxides.     

Determination of Concentrations of Solutes in Gaseous,Liquid, and Supercritical Co2 by Means of UV Raman Spectroscopy

We measured compositions of high-pressure CO₂ solutions in vapor, liquid, and supercritical phases by means of UV-Raman spectra. Our goal was to investigate whether excimer-based Raman could quantitatively determine compositions of such solutions under high-pressure conditions. Some potential problems include (a) species that can absorb much, or all, of the UV-laser light, (b) fluorescence that might overwhelm the Raman signal, and (c) density gradients that would bend the laser beam. We studied two binary systems that were chosen to avoid such problems and that yielded quantitative composition analyses. These were (a) two-phase mixtures of CO₂ and n-pentane and (b) solutions of 1,1,1,2,3,4,4,5,5,5-decafluoropentane in CO₂. We suggest some changes that could increase the usefulness of the method for future applications.     

Synthesis,structure and catalase mimics of novel homoleptic manganese(II) complexes of 1,3-bis(2′-pyridylimino)isoindoline,Mn(4R-ind)2 (R = H,Me)

The preparation of two homoleptic manganese(II) complexes [Mn(4′R-ind)₂] [ind is the anion of 1,3-bis(2-pyridylimino)isoindoline, R = H (1), Me (2)] is described. Both complexes have been structurally characterized by UV–Vis and IR spectroscopies. Crystallographic characterization of the [Mn(ind)₂] (1) complex has shown that the overall geometry around the six-coordinate manganese(II) ion is described as a slightly distorted octahedron in an N₆ donor set. These complexes represent functional model systems for manganese catalases.     

Synthesis and properties of polyimides from 1,3-bis(4-piperidino-l,S-naphthalic anhydride)propane

Summary A novel dianhydride containing nathphalene units was prepared by Ullmann reaction of 4-bromo-1,8-nathphalic anhydride with trimethylenedipiperidine and polymerized with various aromatic diamines in one-pot polycondensation at high temperature in m-cresol. All the polyimides are soluble in organic solvents and form transparent yellow thin films by solution casting. Their inherent viscosities were ranged in 0.17 - 0.68 dL /g (in m-cresol at 25□). The glass transition temperatures were from 202.7□ to 263.6□ by DSC. These polymers did not show appreciable decomposition up to 380□ in N₂ by TGA and can emit strong green fluorescence in solution and in solid state. They may be potential light emitting and solar energy conversion materials. Received: 26 September 2002/Revised version: 6 January 2003/ Accepted: 10 January 2003 Correspondence to Deyue Yan