Non-isothermal kinetics of dehydration of equilibrium swollen poly(acrylic acid) hydrogel</o:p>

Summary Kinetics of dehydration of equilibrium swollen poly(acrylic acid) hydrogel was investigated using methods of non-isothermal thermal analysis. Methods of Kissinger, Coats-Redfern, Van Krevelen and Horowitz-Metzger were applied for determination the kinetics parameters: activation energy (E), pre-exponent (lnA) as well as the kinetics model ƒ(69) for the process of hydrogel dehydration under different heating rates. An existence of good agreement between determined values of kinetic parameters (Eand A), which were obtained applying different methods under the same heating rate. Functional relationship between changes of kinetic parameters of dehydration and changes of heating rate was established. An existence of compensation effect is accepted and explanation of compensation effect appearance during the hydrogel dehydration is suggested.     

The Role of γ -Aminopropyltriethoxysilane (γ -APS) on Thermal Stability of TEOS-PDMS Ormosils

The degradation process of TEOS-PDMS Ormosils containing different amounts of γ -APS has been studied by means of DTA, TG, FTIR and ²⁹Si-NMR measurements. It has been found that the amount of γ -APS improved the thermal properties of Ormosil materials. The increase in γ -APS content causes the increment on the decomposition temperatures and activation energies of the studied Ormosils. These results have been attributed to the favourable effect of γ -APS in the copolymerisation reaction between TEOS and PDMS molecules. ²⁹Si-NMR analyses have shown that the incorporation of γ -APS increases the concentration of D(Q) units in the Ormosil structure, i.e., increases the number of TEOS molecules bonded to PDMS ones. Initial decomposition temperature (IDT), temperature of maximum weight loss rate (T_max), integral procedure decomposition temperature (IPDT) and activation energy values (E) were calculated from different equations which described the degradation of these materials. Addition of 10 wt% γ -APS produced an increase of 63^∘C in the IDT and of 115 and 110^∘C, respectively, for T_max and IPDT (up to 478 and 610^∘C) compared to the free γ -APS Ormosil. Activation energy values also rise up to 69.4 kJ⋅ mol⁻¹ by introducing 10 wt% of γ -APS.     

Chemical thermodynamics

The curing of composition containing epoxy bond is complicated chemical and technological process where under temperature and pressure conditions a change of its structure occurs. The structure changes are possible to know by thermal methods as DSC, DTA, etc. and also by measurement of dielectrical response under the low frequency electrical field.     

配合物Zn(Phe)(NO3)2·H2O(s)的低温热容和标准摩尔生成焓

利用精密自动绝热热量计直接测定了配合物Zn(Phe)(NO3)2·H2O(s) (Phe:苯丙氨酸)在78-370 K温区的摩尔热容. 通过热容曲线的解析得到该配合物的起始脱水温度为, T0=(324.27±0.37) K. 将该温区的摩尔热容实验值用最小二乘法拟合得到摩尔热容(Cp, m)对温度(T)的多项式方程, 并且在此基础上计算出了它的舒平热容值和各种热力学函数值. 依据Hess定律, 通过设计热化学循环, 选择体积为100 mL浓度为2 mol·L-1 的盐酸作为量热溶剂, 利用等温环境溶解-反应热量计分别测定混合物{ZnSO4·7H2O(s)+2NaNO3(s)+L-Phe(s)}和{Zn(Phe)(NO3)2·H2O(s)+Na2SO4(s)}的溶解焓为, ⊿dH0m,1 =(69.42±0.05) kJ·mol-1, ⊿dH0 m,2 =(48.14±0.04) kJ·mol-1, 进而计算出该配合物的标准摩尔生成焓为, ⊿fH0m =-(1363.10±3.52) kJ·mol-1. 另外, 利用紫外-可见(UV-Vis)光谱和折光指数(refractiveindex)的测量结果检验了所设计的热化学循环的可靠性.     

白术挥发油中苍术酮氧化反应的动力学

白术挥发油;苍术酮;动力学方程;活化能;反应机理     

Excess enthalpies for mixtures of cyclohexanone with isomeric propanols and butanols at 298.15 K

Excess enthalpies (H ^E ) for mixtures of cyclohexanone with propan-1-ol. propan-2-ol, butan-1-ol, butan-2-ol and 2-methyl propan-1-ol at 298.15 K have been measured over the entire composition range. All mixed endothermically with the maximum values ofH ^E occurring at equimole fraction. Comments about the molecular interactions contributing to the excess enthalpies of a cyclic ketone + an alcohol are made on the basis of these results.     

Mechanistic aspects of the Wolff-Kishner reaction. V. The cation effect on the reaction of benzophenone hydrazone in butyl carbitol and decyl alcohol

The rate of the Wolff-Kishner reaction of benzophenone hydrazone in butyl carbitol increases as the cation of the alkoxide base is varied in the order K>Na>Li>Mg. The replacement of butyl carbitol by 1-decanol also accelerates the reaction, and an additional increase is caused by the presence of crown ether. On the basis of changes in the activation parameters, it is concluded that the reactivity of the hydrazone anion increases as the contact ion pair becomes more fully solvated and dissociated.     

Methylmethacrylate complexes of sterically hindered aluminum aryloxides: activation of methacrylic esters

The interaction of AlR₂(BHT)(OEt₂) and AlMe(BHT)₂ with methylmethacrylate (MMA) leads to the formation of the Lewis acid-base complexes AlR₂(BHT)(MMA) [R = Me (1), Et (2)] and AlMe-(BHT)₂(MMA) (3), respectively. The molecular structure of 1 has been determined by X-ray crystallography. The decrease in the C=O and C=C stretching frequencies in the IR spectrum, and downfield shift in the ¹³C NMR spectrum of the - and γ-carbons of the MMA, when compared to free MMA, is presented with respect to the activator ability of sterically crowded aryloxide compounds of aluminum to aluminum-porphyrin catalyzed (Inoue) polymerization of MMA.