Advanced Calorimetric Techniques in Polymer Engineering

Summary: In polymer synthesis, reaction calorimetry (RC) is an appropriate technique for on-line process monitoring, since polymerization reactions are highly exothermic. Measurements are noninvasive, rapid, and straightforward. Nowadays RC is the technique recognized as the most powerful way to study such process in near-to-the- industrial conditions. Our approach was focused on temperature oscillation calorimetry (TOC). Two different reaction calorimeters were used, i.e. a isoperibolic calorimeter and a Calvet type high sensitivity differential calorimeter, respectively. A special attention was paid to the interpretation of the measured signals in order to obtain reliable calorimetric data. The evolution of heat transfer coefficient UA was followed by performing appropriate Joule effect calibrations, before and after the reaction. A convolution differential method of the measured heat flow by the generated one was used for determining the time constants and deconvoluting the measured heat flow.     

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.     

Enumeration of internal rotation reactions and their reaction graphs

Threefold and twofold internal rotation reactions and their reaction graphs are enumerated using the generalized wreath product method developed by the author in an earlier paper. The correspondence between reaction directed graphs (digraphs) and finite topologies on isomers is established. It is shown that the reaction digraphs can be represented by Borel fields. Atropisomerism in polyphenyl compounds is discussed. Applications to spontaneous generation of optical activity and NMR spectroscopy are considered. Borel fields are enumerated by bumping squares of the upper rows of Young diagrams starting from the Young diagram containing just one row.     

Calorimetry of electrode reaction under linear sweep-current polarization

The mathematical-physical equation concerning the process of calorimetry of electrode reactions was deduced, and the corresponding solutions were obtained respectively for the period of the electrochemical polarization and that of the natural cooling. The calorimetry of the anodic oxidation of ferrocyanide to ferricyanide under linear sweep-current polarization was carried out, the obtained apparent enthalpy change of the electrode reaction agreed well with that obtained by the calorimetry with constant currents. The developed calorimetry with linear sweep-current and the data processing method are applicable for quick determination of apparent enthalpy changes of electrode reactions.     

The estimation of reaction enthalpy for complex molecules using Benson groups</o:p>

Estimation methods developed over years by S. W. Benson and co-workers for calculation the thermodynamic properties of organic compounds in the gas phase are applied to a pharmaceutical real process with all type of non-idealities. The different strategies used to calculate the reaction enthalpy of a chemical process, in the absence of data for complex molecules, using the Benson group additivity method are presented and also compared with the experimental value of reaction enthalpy obtained using reaction calorimetry (Mettler-Toledo, RC1?). We demonstrate that there are some strategies that can be followed to obtain a good estimation of the reaction enthalpy in order to begin the safety assessment of a chemical reaction. This work is part of an industrial project [1] in which the main objective was the risk assessment of chemical real and complex processes using the commonly available tools for the SMEs (with limited resources).     

Model Reactions for Photosynthesis—Photoinduced Charge and Energy Transfer between Covalently Linked Porphyrin and Quinone Units

Photosynthesis is one of the fascinating fields of current interdisciplinary research. It seems miraculous that nature, in the process of evolution, has managed to bring about the process of photosynthesis. The first step involves a charge separation at the reaction centers, which proceeds with 100% quantum yield from the photoexcited singlet state of the bacteriochlorophyll donor, despite the fact that the wasteful deactivation of the electron into the ground state should be highly favored. Biomimetic model compounds (that is, those which resemble the pigments nature has developed) have been constructed from porphyrins and quinones. These model systems have allowed the study of the factors contributing to the highly efficient charge separation. This report focuses on recent developments in the study of electron transfer in porphyrinoquinones. Some of the results of these investigations may not be not fully understood and are often the subject of controversial discussions.     

Analysis in terms of valence-bond structures of environmental effects on the electronic structure of molecules

Environmental effects on the electronic structure of molecules caused by external perturbations are studied by means of an expansion of molecular orbital wave functions into valence-bond (VB ) wave functions. Applications are carried out to the π system of butadiene, hydroxyethylene, acrolein, and carbonyl oxide and also to the full electronic system of water. The external perturbations considered are uniform electric fields, nonuniform electric fields, and reaction fields created by solvents. A different behavior is found between nonpolar and polar species in the presence of solvents. Some consequences on the behavior of molecules under the influence of the different electric fields are discussed.     

New developments and applications in titration calorimetry and reaction calorimetry

Isothermal titration calorimetry (ITC) and reaction calorimetry (RC) have been used to construct the solid-liquid equilibrium line in ternary systems containing the solute to precipitate and an aqueous mixed solvent, and to study polymerization reactions under real process conditions, respectively. Phase diagrams have been established over the whole concentration range for some benzene substituted derivatives, including o-anisaldehyde, 1,3,5-trimethoxybenzene and vanillin, in {water + alcohol}mixtures at different temperatures. Acrylamide polymerization in aqueous solution using potassium permanganate/acid oxalic redox system as initiator was investigated on a homemade calorimeter, which works according to the isoperibolic mode. A Calvet type differential RC was used to illustrate the applicability of temperature oscillation calorimetry (TOC) for the evaluation of the heat transfer coefficient during the course of reaction.     

厚体液膜动力学拆分普萘洛尔外消旋体

以S,S-酒石酸正十二酯和H3BO生成的配合物为手性载体, 通过量热分析结果初步证明该配合物的存在, 采用厚体液膜拆分了普萘洛尔外消旋体. 考察了S,S-酒石酸十二酯浓度和水相pH值对拆分性能的影响, 优化了其拆分操作条件, 同时进行了动力学分析. 得出厚体液膜拆分的一般规律, 即其拆分属于动力学拆分过程, 适当提高手性载体的浓度有利于提高对映单体流量和拆分的立体选择性, 水相pH值对于拆分性能有着重要的影响. 其拆分过程中萃取反应过程为控速步骤, 对映单体的跨膜传递可以用两个串联的准一级不可逆过程进行描述.     

Mechanistic Studies in Photocatalysis

The fast‐moving fields of photoredox and photocatalysis have recently provided fresh opportunities to expand the potential of synthetic organic chemistry. Advances in light‐mediated processes have mainly been guided so far by empirical findings and the quest for reaction invention. The general perception, however, is that photocatalysis is entering a more mature phase where the combination of experimental and mechanistic studies will play a dominant role in sustaining further innovation. This Review outlines the key mechanistic studies to consider when developing a photochemical process, and the best techniques available for acquiring relevant information. The discussion will use selected case studies to highlight how mechanistic investigations can be instrumental in guiding the invention and development of synthetically useful photocatalytic transformations.     

Thermochemistry of complex salts of transition metal perchlorates with tetrazole ligands

Standard enthalpies of formation of transition metal (cobalt, nickel, and zinc) complex salts with an organic ligand 5-aminotetrazol-2-ylacetohydrazide (ATH-2) were obtained by combustion and solution calorimetry. The enthalpy of combustion of the ligand was determined using combustion calorimetry and the standard enthalpy of formation of the ligand was calculated. For calculations by reaction calorimetry, a thermochemical cycle was developed that allows determination of the standard enthalpy of formation of complex salts. The enthalpies of solution of the ligand and transition metal complex salts in water and in 0.1 M hydrochloric acid were determined. The data obtained allow calculations of the enthalpies of salts formation and the enthalpies of three new complex ions. The enthalpies of position isomerization in different compounds were analyzed.     

Determination of Activation Energies by Using Different Factors Φ in Adiabatic Calorimetry

Traditionally, the kinetic treatment of adiabatic calorimetry data has been based on the results of one or more experiments, but always with the assumption of the kinetic model that the reaction follows to calculate the kinetic parameters. In this paper a method for the determination of the activation energy that uses a set of adiabatic calorimetry data is developed. To check the method, the thermal decompositions of two peroxides were studied.This revised version was published online in November 2005 with corrections to the Cover Date.     

Laser field induced charge transfer: Para-nitroaniline coupled to a quantum mechanical radiation field

Summary We present a preliminary model for describing a solvated intramolecular charge transfer reaction coupled to a quantum mechanical radiation field. Actual calculations of energies and couplings were performed with a recently developed self-consistent reaction field response method. The representation of dressed molecular states is used for calculating state populations for various laser fields. The state populations are sensitive to the properties of the laser field.     

两种量热模式下物质热分解的动力学补偿效应

热分析量热仪主要包括动态、等温、恒温及绝热四种操作模式。很多学者基于动态及等温模式的测试结果,采用Arrhenius速率常数进行动力学计算,进而发现了所谓的“动力学补偿效应”。为了解绝热模式下是否也存在动力学补偿效应,分别采用绝热加速量热法(ARC)及动态差示扫描量热法(DSC)研究了过氧化二异丙苯(DCP)、40%(质量分数,下同)DCP溶液、葡萄糖、45%葡萄糖溶液的热分解特性,在此基础上基于Arrhenius公式计算了对应的表观活化能E和指前因子A,并对计算结果进行了分析。结果表明:绝热模式下,不同质量的同种样品及其溶液的最佳动力学参数,或者同一组数据采用不同的反应级数获得的lnA和E之间均存在明显的线性关系。此外,尽管由动态DSC数据计算获得的E和lnA普遍小于绝热模式的结果,但两种模式下获得的lnA和E之间仍然存在动力学补偿效应。由此可以推断,具有相同或类似反应机理的反应,虽然实验模式不同,但其E和lnA之间存在明显的动力学补偿效应。     

热动力学的滴定量热法研究2: 单底物酶促反应的热动力学

用滴定量热法分别建立了滴定期和停滴反应期单底物酶促反应热动力学的数学模型。根据这两种模型,可由一次实验的滴定量热曲线同时解析出单底物酶促反应的热力学参数(Δ~rH~m)和动力学参数(K~m和k~2)。用滴定量热法研究了一个经典的单底物酶促反应---过氧化氢酶催化分解过氧化氢反应的热动力学,由滴定期和停滴反应期热动力学模型解析出在298.15K和pH=7.0时该反应的米氏常数K~m分别为(5.41±0.24)×10^-^3和(5.43±0.21)×10^-^3mol.L^-^1,酶转换数k~2分别为(3.58±0.33)×10^3和(3.60±0.41)×10^3s^-^1,摩尔反应焓为(-86.75±0.88)kJ.mol^-^1,实验结果验证了上述热动力学模型的正确性。     

Overview of calorimeter chips for various applications

This paper gives an overview of some of the recent developments in the area of chip calorimetry. Using several chip calorimeters developed at Xensor Integration and tested by users, examples of chip calorimetry and its applications will be given. Examples of chip calorimeters developed at various universities are given to widen the overview. The examples will be used to give more insight in the design and fabrication of various chip calorimeters.     

Heteroleptic Copper(I)‐Based Complexes for Photocatalysis: Combinatorial Assembly,Discovery, and Optimization

A library of 50 copper‐based complexes derived from bisphosphines and diamines was prepared and evaluated in three mechanistically distinct photocatalytic reactions. In all cases, a copper‐based catalyst was identified to afford high yields, where new heteroleptic complexes derived from the bisphosphine BINAP displayed high efficiency across all reaction types. Importantly, the evaluation of the library of copper complexes revealed that even when photophysical data is available, it is not always possible to predict which catalyst structure will be efficient or inefficient in a given process, emphasizing the advantages for catalyst structures with high modularity and structural variability.     

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.