Determination of the rheological behavior of epoxy–amine thermosets by dynamic mechanical analysis: Isothermal methods versus nonisothermal methods

The reticulation process of an epoxy resin using an amine as a cure agent was studied at different temperatures and concentrations of the cure agent with dynamic mechanical thermal analysis. The study was performed under both isothermal and nonisothermal conditions, and a temperature–time–transformation diagram was obtained. The measurements from the two modes gave similar results, although the nonisothermal mode required fewer experiments. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1965–1977, 2003     

TTT Cure Diagram

Curing reactions of the epoxy system consisting of a diglycidyl ether of bisphenol A (BADGE n=0) and m-xylylenediamine (m-XDA) were studied to calculate time-temperature-transformation (TTT) isothermal cure diagram for this system. Gel times were measured as a function of temperature using solubility test. Differential scanning calorimetry (DSC) was used to calculate the vitrification times. DSC data show a one-to-one relationship between T _g and fractional conversion, a independent of cure temperature. As a consequence, T _g can be used as a measure of conversion. The activation energy for the polymerization overall reaction was calculated from the gel times obtained using the solubility test (41.5 kJ mol^-1). This value is similar to the results obtained for other similar epoxy systems. Isoconversion contours were calculated by numerical integration of the best fitting kinetic model. This revised version was published online in July 2006 with corrections to the Cover Date.     

Time-temperature transformation (TTT) cure diagram of an unsaturated polyester resin

The curing of an unsaturated polyester resin was studied by differential scanning calorimetry (DSC), thermal mechanical analysis (TMA), and Fourier-transform infrared spectroscopy (FTIR). The results are presented in the form of a time-temperature-transformation (TTT) diagram. The kinetic analysis was performed by means of the dynamic Ozawa method. This analysis was used to determine the curing times (t) at various conversions (α) and temperatures (T) (isoconversional lines ln t = A + E/RT). The equivalence of the Ozawa method and the isothermal isoconversional adjustment ln t = A + E/RT were demonstrated. The relationship between the glassy transition temperature (T_g) and the conversion α was determined by DSC. It was established that this relationship is one-to-one and independent of mass, initiation system, and curing temperature (T_c). The T_g-α relationship was adjusted using the DiBenedetto equations and heat capacity data. Using the T_g-α relationship and the isoconversional lines, the vitrification curve was determined and it was observed that the vitrification times obtained are consistent with those obtained experimentally when T_c = T_g. Gelation was determined by TMA, the material being considered gelled when it reached sufficient mechanical stability for the TMA measuring probe to become embedded in it. At that moment the conversion reached was determined by DSC. It was seen that the material always gels at constant conversion, regardless of the curing temperature. The gelation line (gel times) were traced from the corresponding isoconversional line. © 1997 John Wiley & Sons, Inc.     

Solidification of molten zinc chloride

Solidification of molten zinc chloride was studied both experimentally and theoretically. By isothermal thermal analysis the time needed for the melt to crystallize at a given temperature ranging between 453 and 553 K was determined and the data obtained were compared with those of a calculated TTT curve. The extremum coordinates (temperature T _N, time t _N) of the curve, critical cooling rate v _CR, interfacial energy σ, and an additional parameter of kinetics barrier for nucleation ɛ were determined as T _N=508 K, t _N=7.29 s, v _CR=11.38 K s⁻¹, σ=0.11956 J m⁻² and ɛ=0.5712. By non-isothermal method the critical cooling rate of glass formation was determined as 1.25 K s⁻¹.     

关于次序统计量广义TTT序的几个结果

研究了次序统计量在广义TTT变换序(TTT变换序)和剩余财富序下的性质. 讨论了寿命分布类NBUT在增凹变换下的封闭性以及NWUT寿命分布在次序统计量下的特征.     

Influence of the curing cycle selection on the thermal degradation of an epoxy-diamine system

Summary Polymers have a great interest for the study and design of new materials. Among these materials are epoxy resins, that have good properties, such as low shrinkage during cure, good adhesion, high water and chemical resistance, etc. They have also fast and easy cure in a broad range of temperatures. TTT diagrams are very helpful to design new epoxy materials as they allow the search for very important final properties, such as thermal stability, conversion or glass transition temperature of a material cured through a selected curing cycle. In this work the dependence of the thermal stability on the selected curing cycle for a DGEBA/1,2 DCH system was studied.     

随机寿命间的TTT序关系的一个非参数检验

本文先建立了一个具有TTT序关系的两个非负随机变量之间距离的概率度量，然后构造了一个非参数检验方法以判断严格的TTT序关系，利用L-统计理论获得了检验统计量的渐近分布，数值模拟的结果也表明该方法的性能是令人满意的．     

基于松香酸酐的环氧树脂体系固化动力学及TTT图绘制

研制了基于松香酸酐固化剂的生物质环氧树脂体系,采用全动态DSC法研究了树脂体系的固化反应动力学,通过半经验的唯象模型拟合得到了固化反应参数,活化能Ea为59.68 kJ/g,指前因子A0为1.28×1015s-1,反应级数n为2.483,由此建立了体系固化温度/时间/固化度间的关系;采用恒温DSC及DMA方法测试玻璃化转变温度,应用DiBenedetto经验方程拟合得到了玻璃化转变温度与固化度间的关系.应用锥板旋转黏度计测试了树脂体系不同温度下的凝胶时间,通过线性回归分析得到了凝胶时间与温度之间的关系.由唯象模型和DiBenedetto方程分别计算得到凝胶时的固化度为0.386,玻璃化转变温度为26.22°C.由上述工作绘制了基于松香酸酐生物质树脂体系的TTT(time-temperature-transition diagram)固化图,可确定树脂体系在不同温度任意时间下的状态.     

四氢噻唑-2-硫酮用于赖氨酸侧链选择性保护反应

用四氢噻唑-2-硫酮(TTT)分解赖氨酸-铜配合物,合成侧链氨基被选择性保护的赖氨酸衍生物N^a-Boc-N^e-Fmoc-L-Lys-OH. 研究结果表明四氢噻唑-2-硫酮分解氨基酸铜配合物比传统试剂(H₂S, EDTA, HCl)速度快, 反应彻底, 且副产物易除去.     

Cure kinetics modeling and thermomechanical properties of cycloaliphatic epoxy‐anhydride thermosets modified with hyperstar polymers

Hyperstar polymers (HSPs) with hyperbranched aromatic polyester core and arms consisting of block copolymers of poly(methyl methacrylate) and poly(hydroxyethyl methacrylate) have been used as polymeric modifiers in cycloaliphatic epoxy‐anhydride formulations catalyzed with tertiary amines, with the purpose of enhancing the impact strength of the resulting materials without compromising other thermal and mechanical properties.> In this work, the effect of these polymeric modifiers on the curing kinetics, processing, thermal‐mechanical properties and thermal stability has been studied using thermal analysis techniques such as DSC, TMA, DMA, and TGA. The morphology of the cured materials has been analyzed with SEM. The curing kinetics has been analyzed by isoconversional procedures and phenomenological kinetic models taking into account the vitrification during curing, and the degradation kinetics has been analyzed by means of isoconversional procedures, summarizing the results in a time‐temperature‐transformation (TTT) diagram. The results show that HSPs participate in the crosslinking process due to the presence of reactive groups, without compromising significantly their thermal‐mechanical properties. The modified materials show a potential toughness enhancement produced by the formation of a nano‐grained morphology. The TTT diagram is shown to be a useful tool for the optimization of the curing schedule in terms of curing completion and safe processing window, as well as for defining storage stability conditions. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1227–1242