4,5-环氧环己烷1,2-二甲酸单丁酯单缩水甘油酯/m-PDA的热固化特征

本文叔述了4,5-环氧环己烷1,2-二甲酸单丁酯单缩水甘油酯(DME-47)/间-苯二胺(m-PDA)体系的热固化特征。结果表明,由于DME-47中羧酸缩水甘油酯型环氧基的反应活性远大于脂环环氧基。所以,DME-47/m-PDA体系固化反应明显地分两阶段进行。由TBA恒温固化动力学数据求得体系在100—160℃表观反应活化能E_α=13.9kcal/mol,在160—240℃E_α=16.6kcal/mol,根据实验数据按Arrhenius关系式推算,本体系在室温25℃下可以存放80天左右而不凝胶化,20℃下可存放120天左右。     

样条函数逼近法研究环氧树脂固化动力学

采用样条函数逼近DSC曲线,分别对4,5-环氧环已烷1,2-二甲酸二缩水甘油酯、四氢邻苯二甲酸二缩水甘油酯及双酚A二缩水甘油醚与间苯二胺的固化动力学作了研究.结果表明,样条函数逼近DSC曲线有较高的精度,由模拟函数处理实验数据取得较满意的结果.     

T_(31)环氧树脂固化过程研究——1.动态扭振法确定最佳固化条件

在新设计制造的HLX-1型树脂固化仪上对T_(31)-环氧树脂E51进行了最佳配方和最佳条件的选择。T_(31)含量为20phr的环氧树脂体系,最佳固化温度为333K,固化反应活化能E=52.7KJ/mol。用非平衡态涨落理论也成功地预估了T_(31)-环氧树脂体系的固化行为。     

Investigation of the curing reactions of some multifunctional epoxy resins using differential scanning calorimetry

Curing reaction of three tetrafunctional epoxy resins in the presence of tetraethylene tetramine was examined by differential scanning calorimetry at different heating rates. The kinetic parameters of the curing reaction were determined using various computational methods (Barrett, Borchardt–Daniels and Kissinger). The heating rate shows a great influence on the curing process. The activation energy varied in the range 43–80 kJ/mol, and the order of the curing reaction is observed to be ≈1.0 with slight variations.     

不同温度下环氧树脂代木搪塑模具的固化过程

采用流变学的方法研究了环氧树脂代木搪塑模具在不同温度下的固化过程。 为了找到合适的测试条件,首先研究了应变和振荡频率对环氧树脂代木搪塑模具的测试结果的影响。 环氧树脂代木搪塑模具固化过程中,体系交联程度逐渐变大;在不同的固化阶段,固化程度的变化快慢不同,先缓慢增加,然后迅速增加,最后缓慢增加至平台值;储能模量和损耗模量的变化速度在不同阶段的变化与固化程度的变化相似,根据储能模量和损耗模量的最快增长速率与温度的关系得到体系的活化能约为27.2 kJ/mol;随着固化温度升高,环氧树脂代木搪塑模具固化完全所需的时间减少,同时环氧树脂的施工容留时间也相应地减少。     

THE CURING BEHAVIOR OF DIGLYCIDYL-4, 5-EPOXYCYCLOHEXANE-1,2-DICARBOXYLATE

The curing behavior of diglycidyl-4, 5-epoxycyclohexane-1, 2-dicarboxylate with m-phenylenediamine has been studied by using torsional braid analysis. It is shown that the whole curing processproceeds in two stages, that is, curing reaction at temperatures below 100℃mainly occurs at the ali-phatic epoxy rings, whereas a rapid increase in reaction rate of the remaining cycloaliphatic epoxy ringoccurs only at temperatures above 130℃. Between the temperature range from 100℃to 130℃, the"full reaction" of the aliphatic epoxy rings is approximated, while the reaction rate of the cycloaliphaticepoxy ring begins to increase gradually. The maximum glass transition temperature (T_(g∞)) of the systemdoes not emerge before 220℃. The apparent activation energy is 13 .2 kcal/mole.     

A novel quantum mechanical/molecular mechanical approach to the free energy calculation for isomerization of glycine in aqueous solution

The free energy change associated with the isomerization reaction of glycine in water solution has been studied by a hybrid quantum mechanical/molecular mechanical (QM/MM) approach combined with the theory of energy representation (QM/MM-ER) recently developed. The solvation free energies for both neutral and zwitterionic form of glycine have been determined by means of the QM/MM-ER simulation. The contributions of the electronic polarization and the fluctuation of the QM solute to the solvation free energy have been investigated. It has been found that the contribution of the density fluctuation of the zwitterionic solute is estimated as -4.2 kcal/mol in the total solvation free energy of -46.1 kcal/mol, while that of the neutral form is computed as -3.0 kcal/mol in the solvation free energy of -15.6 kcal/mol. The resultant free energy change associated with the isomerization of glycine in water has been obtained as -7.8 kcal/mol, in excellent agreement with the experimental data of -7.3 or -7.7 kcal/mol, implying the accuracy of the QM/MM-ER approach. The results have also been compared with those computed by other methodologies such as the polarizable continuum model and the classical molecular simulation. The efficiency and advantage of the QM/MM-ER method has been discussed.     

聚酯型扩链脲改性环氧树脂E-51/DDS体系反应活性研究

提高二氨基二苯砜(DDS)固化环氧树脂体系的反应活性,降低反应温度、提高反应速率,具有重要的研究意义和实用价值.本研究以聚酯(PEGA1000,2000,PNGA1000,2000)、甲苯-2,4-二异氰酸酯(TDI)、二甲胺为原料合成了含有聚酯型柔性间隔基的扩链脲U-PEGA1000,2000,U-PNGA1000,2000,用其改性环氧树脂E-51/DDS体系,采用DSC系统考察了改性体系的固化反应活性.结果表明,改性体系固化反应活性明显提高,固化反应表现活化能降低,固化反应峰顶温度从230℃降至170℃,固化反应的表观活化能由67.74kJ/mol降至47.80kJ/mol.     

Theoretical investigation of the reactivity of copper atoms with OCS: comparison with CS2 and CO2

The reaction mechanism of the Cu atom with OCS and CO2 has been studied by means of density functional method (B3LYP). The overall energetics has been refined at the CCSD(T) level. In the case of the Cu + OCS reaction, the CS insertion route is found much more favorable than the CO insertion one. This later reaction is direct and involves an activation energy of 83.3 kcal/mol and is endothermic by 50.0 kcal/mol at the CCSD(T) level. The insertion into the CS bond proceeds through the eta1s and eta2cs coordination species as intermediates and is found exothermic by about 20 kcal/mol. The highest transition structure along this route is only 11.5 kcal/mol higher in energy than the reactant's ground states. In the case of the Cu + CO2 reaction, the insertion route into the CO bond is also found direct but with a lower endothermicity (30.6 kcal/mol) and smaller activation energy (61.1 kcal/mol) than that into the CO bond of OCS. In all cases, the insertion mechanism proceeds simultaneously with electron transfer from the Cu atom to OCS (or CO2) molecule.     

松香改性酚醛环氧树脂的固化反应动力学研究

以自制的松香改性酚醛环氧树脂（RPAE）为对象,采用差示扫描量热法研究了其与4,4．二氨基二苯砜组成的体系（RPAE／DDS）的固化动力学,利用Kissinger方程计算得到体系的固化热约为109．29J／g,表观活化能为51．56kJ／mol,该体系反应级数为0．85,近似为1级反应,反应速率常数为2．69×10^4／s。采用Ozawa-Flynn-Wall方程分析,得到体系的表观活化能为70。1kJ／mol。     

Curing of mixtures of diane and aliphatic epoxy oligomers with different reactivities

Curing of diane and aliphatic epoxy oligomers and their blends is studied by DSC. The use of the traditional dynamic procedure and preliminary heating of the samples at a constant temperature are shown to be convenient for estimating the degree of conversion, glass-transition temperature, and activation energy of curing. Curing of diane, aliphatic epoxy oligomers, and blends with aliphatic amine is adequately described by the Kamal—Sourour equation, and the apparent activation energy of curing is 61.4–55.7 kJ/mol according to the Flynn—Wall—Ozawa model and 54.7–48.5 kJ/mol according to the Kissinger model. This value slightly changes with variation in the content of epoxy oligomers.     

Ab-initio molecular geometry and normal coordinate analysis of tetrahydrothiophene molecule.

The molecular geometry of tetrahydrothiophene (THT) was quantum mechanically calculated using the split valence 6-31G** basis set. Electron correlation energy has been computed employing MP2 method. The molecule showed a twist form puckered structure with a twist torsion angle of 13 degrees and has a total energy of -347,877.514 kcal/mol of which a 436.715 kcal/mol electron correlation energy. The envelope form of the molecule showed an inter-plane angle of 22 degrees and has a total energy of -347,874.430 kcal/mol involving -436.558 kcal/mol electron correlation energy. The normal coordinates of the molecule were theoretically analyzed and the fundamental vibrational frequencies were calculated. The IR and laser Raman spectra of THT molecule was measured. All the observed vibrational bands including combination bands and overtones were assigned to normal modes with the aid of the potential energy distribution values obtained from normal coordinate calculations. The molecular force field was determined by refining the initial set of force constants using the least square fit method instead of using the less accurate scaling factor methods. The determined molecular force field has produced simulated frequencies which best match the observed values. The lowest-energy modes of vibration were two molecular out-of-plane deformations, observed at 114 and 166 cm(-1). The barrier of ring twisting estimated from the observed ring out-of-plane vibrational mode at 114 cm(-1) was estimated.     

Free energy profiles for monomer capture in Grubbs- and SHOP-type olefin polymerization catalysts: a constraint ab initio molecular dynamics study

Density functional theory together with Car-Parrinello ab initio molecular dynamics simulation has been used to investigate the free energy profiles (FEP) of monomer capture in Grubbs- and SHOP-type olefin polymerization catalysts. The FEPs along the reaction coordinates at 300 K were determined directly by a point wise thermodynamic integration technique. Comparison between potential energy profile (PEP) and the FEP has been made. The results show that, for both catalysts, the PEP for the monomer ethylene uptake by the metal center is a typical Morse curve without energy barrier. However, a small barrier (1.8 kcal/mol for Grubbs catalyst and 2.4 kcal/mol for SHOP catalyst) exists on the FEP. The pi complexation energy on the FES at 300 K is higher by 10-12 kcal/mol over that on the PES. The differences between FES and PES are due to entropy contribution. Slow growth simulations on the ethylene capture process show that the ethylene attacks the metal center by an asynchronous mode. This indicates that the forming of the pi-bonding between the metal and ethylene is initiated by electrophilic attack of the metal to one of the ethylene carbons.     

Ab initio study of gas phase and water-assisted tautomerization of maleimide and formamide

Maleimide serves as an important starting material in the synthesis of drugs and enzyme inhibitors. In the present paper, knowing the importance of tautomerization in maleimide for its drug action, potential energy surface of maleimide is studied and its tautomerization has been discussed and compared with tautomerization of formamide. Gas phase tautomerization of maleimide requires large amount of energy (23·21 kcal/mol) in comparison to formamide (15·05 kcal/mol) at HF/6-31+G* level. Thus making the proton transfer reaction a difficult process in gas phase. Water molecule lowers the energy barrier of tautomerization thus facilitating the tautomerization of maleimide to 5-hydroxy-pyrrol-2-one. Water assisted tautomerization of maleimide requires 19·60 kcal/mol energy at HF/6-31+G* and 17·63 kcal/mol energy at B3LYP/6-31+G* level, a decrease of 3·61 and 5·96 kcal/mol over gas phase tautomerization. Whereas, tautomerization of formamide requires 14·16 and 12·84 kcal/mol energy, a decrease of 0·89 and 2·01 kcal/mol energy over gas phase tautomerization at HF/6-31+G* and B3LYP/6-31+G* level, respectively. Water-assisted tautomerization in maleimide and formamide showed that difference in energy barrier reduces to 2·83 kcal/mol from 10·41 kcal/mol (in gas phase) at B3LYP level, which resulted that maleimide readily undergoes tautomerization in water molecule.     

Effect of P/Si polymeric silsesquioxane and the monomer compound on thermal properties of epoxy nanocomposite

The unique polymeric silsesquioxane/4,4′-diglycidyether bisphenol A (DGEBA) epoxy nanocomposites have been prepared by sol-gel method. The structure of nanocomposites was characterized by attenuated total reflectance (ATR) and solid state ²⁹Si NMR. The characteristic intensity of trisubstituted (T) structure was higher than that of tetrasubstituted (Q) structure from solid state ²⁹Si NMR spectra of 3-isocyanatopropyltriethoxysilane (IPTS) modified epoxy. The activation energies of curing reaction of epoxy system and IPTS modified epoxy system are 28-66 kJ/mol and 57-75 kJ/mol, respectively, by Ozawa’s and Kissinger’s methods. The triethyoxysilane side chain of IPTS modified epoxy might interfere the curing reaction of epoxy/amine and increase the activation energy of curing. The thermal degradation of nanocomposites was investigated by Thermogravimetric analysis (TGA). The char yield of nanocomposites was proportional to the 2-(diphenylphosphino)ethyltriethoxysilane (DPPETES) moiety content at high temperature. A higher char content could inhibit thermal decomposition dramatically and enhance the thermal stability. Moreover, the nanocomposites possess high optical transparency.     

Kinetics and thermodynamics of copper(II) binding to apoazurin

The binding of copper(II) to apoazurin has been probed by isothermal titration calorimetry in cholamine buffer at pH 7.0. The standard enthalpy change was determined to be -10.0 +/- 1.4 kcal/mol. Each calorimetric trace reveals an initial exothermic phase followed by an endothermic phase. The calorimetric data could be fit to a kinetic model involving a bimolecular combination of copper(II) and apoazurin in an exothermic process (k = 2 +/-1 x 103 M-1 s-1, DeltaH degrees = -19 +/- 3 kcal/mol) to form an intermediate that spontaneously converts to Cu(II)-azurin in an endothermic process (k = 0.024 +/- 0.01 s-1, DeltaH degrees = +9 +/- 3 kcal/mol). These data suggest that copper(II) first combines with apoazurin in an irreversible process to form an intermediate that converts to copper(II)-azurin in a process driven by the release of water. The overall standard free energy of copper(II) binding to apoazurin is estimated to be -18.8 kcal/mol.     

非等温法研究TGDDM/DDS体系固化反应动力学

采用DSC对4,4′-四缩水甘油基二氨基二苯基甲烷(TGDDM)和3,3′-二氨基二苯基砜(DDS)体系的固化反应动力学进行了研究.分别通过n级反应法和Malek的最大概然机理函数法确定了固化反应机理函数,求解了固化反应动力学参数,得到了固化反应动力学模型.结果表明,通过Kissinger,Crane方法求解动力学参数所得到的n级反应模型与实验值差别较大;而采用Malek方法判别机理,表明该固化反应按照自催化反应机理进行,实验得到的DSC曲线与模型计算所得到的曲线吻合的较好,所确立的模型在5~20K/min的升温速率下能较好地描述TGDDM/DDS体系的固化反应过程,并为工艺参数的选择和工艺窗口的优化提供了理论依据.     

Kinetic study of epoxy curing in the glass fiber/epoxy interface using dansyl fluorescence

The fluorescence response of the dansyl chromophore has been used to study the kinetic of epoxy curing processes. With this new method, comparison between the curing at the interface of a glass fiber/epoxy and in the epoxy bulk of a composite material was studied. The effect of two glass fiber surface treatments was investigated. Commercial E-glass fibers were surface coated with 3-aminopropyltriethoxysilane (APTES) and 3-aminopropylmethyldiethoxysilane (APDES). Fluorimetry (using fluorescent labels) and FT-NIR (Fourier transformed infrared spectroscopy in the near range) techniques were used to monitor the curing process in these composite materials. From the analysis of the data obtained, different simple kinetic models were discussed and apparent activation energies were obtained. Furthermore, from those techniques the respective results were compared to obtain complementary information. Independently of the sample and the technique used for the kinetic analysis, no variation of the activation energy of the epoxy curing reaction was found, which suggests that there are no changes in the mechanism of the reaction along the process. Fluorescence from dansyl located at the glass fiber/epoxy interface reflected that the kind of reinforcement treatment clearly affects the epoxy curing process exactly in that region. However, when analytical response comes from the whole system the mechanism of the reaction does not seem to change with the silane coating used although is quite different in comparison with the process at the interface.     

Thermally degrading polyethylene studied by means of factor-jump thermogravimetry

Degradation of polyethylene in both linear (NBS 1475) and branched (NBS 1476) form has been studied in the range 410–475°C using factor-jump thermogravimetry. In vacuum, the rate of weight loss was erratic because of bubbling in the sample. The apparent overall activation energy was determined to be 65.4 ± 0.5 kcal/mol (273 ± 2 kJ/mol). There was no distinguishable difference between linear and branched samples. In slowly flowing N₂ at 8 mmHg (1 mmHg = 133 Pa), the overall activation energy was determined to be 64.8 ± 0.3 kcal/mol (271 ± 1 kJ/mol) for linear PE and 64.4 ± 0.2 kcal/mol (269 ± 1 kJ/mol) for a sample of PE with one percent branches. In N₂ at 800 mmHg, the values were 62.6 ± 0.5 kcal/mol for linear PE and 61.2 ± 0.6 kcal/mol for the branched sample, the rate of weight loss being smooth in both cases. Changing the linear flow velocities over the range 1–4 mm/sec at 800 mmHg did not affect the results. From the insertion of typical values in the equation relating the overall activation energy for weight loss from linear polyethylene to the activation energies of the component steps, a degradation mechanism involving scission β to allyl groups, with rapid hydrogen abstraction, slower subsequent β scission, and bimolecular termination, is indicated. The activation energy of β scission for secondary alkyl radicals is estimated to be 33 kcal/mol. The reason for the lower activation energies in N₂ is related to the effects of preformed molecules. The average molecular weights of the volatiles in vacuum and for 8 and 800 mmHg N₂ have been shown to be in the ratios 1 to 1/4 to 1/10, respectively, at these imposed rates of weight loss. The activation energies to use for the initial stage of degradation are 70.6 kcal/mol (295 kJ/mol) in vacuum and 67.8 kcal/mol (284 kJ/mol) at atmospheric pressure.     

TEMPERATURE DEPENDENCE OF PHOTOSENSITIZED ELECTRON TRANSPORT ACROSS LIPID VESICLE WALLS

Abstract— An overall Arrhenius activation energy of 117 plusmn; 19 kJ/mol (28.0 plusmn; 4.5 kcal/mol) has been measured for photosensitized electron transport across phospholipid vesicle walls in the temperature range 18–38°C. A dynamic model for the overall process is proposed which accounts for the parabolic growth curves of the kinetically probed species, heptyl viologen radical. The temperature dependence of the initial quantum yield derived from these curves, and of fluorescence quenching behavior of the ruthenium tris-bipyridyl photosensitizer, is used to estimate an activation energy of 67 plusmn; 21 kJ/mol(16 plusmn; 5 kcal/mol) for the electron transport step itself. The activation energy for the co-transport of charge compensating ions is estimated to contribute no more than 4.6 kJ/mol to this energy.