芳基乙炔聚合物热分解动力学研究

利用ＴＧ－ＤＴＧ方法研究了聚（ｐ－ＤＥＢ）在氮气和空气气氛中的热分解过程和动力学。实验发现,在氮气中其热分解反应为一步反应,热分解速率较低,热分解４温度随升温速率β的增加而线性增加,在７３０℃下残碳率高达８７％;而在空气中其热分解反应则由多步组成,热分解速率较快,热分解温度低,升温速率对热分解温度影响不大,在６００℃下聚合物已完全分解。在氦气和空气中聚合物的热分解反应均为一级速率对热分解温度不大,     

PEEK复合材料的降解动力学

石墨、碳纤维和聚四氟乙烯(PTFE)填充的聚醚醚酮(PEEK)具有自润滑作用,是高性能的复合材料。采用热失重分析仪研究了聚醚醚酮及其复合材料的热降解行为,用Kissinger方法和Ozawa方法计算了复合材料的反应活化能(Ea)。与PEEK相比较,自润滑PEEK复合材料具有更高的降解反应活化能和更低的反应速率常数(K)。     

聚氨酯弹性体的热分解动力学研究

聚氨酯弹性体的热分解动力学研究;聚醚型聚氨酯;聚酯型聚氨酯;热分解;动力学;模型拟合法     

Application of Continuous Kinetics to Polymer Degradation

Abstract

Degradation of polydisperse polymers is studied in the framework of continuous kinetics which is directly based on continuous distribution functions which depend on the molecular weight and the time. A firstorder formalism is presumed. A Schulz-Flory distribution (with time-dependent parameters) is assumed to be valid during the entire time of degradation. Thus, an essential simplification of the solution procedure of the continuous rate equation is achieved. As a proof of accuracy, the approximation solution and the exact solution are compared for the case of “random scission.” Furthermore, the developed method is shown to be suitable for describing the experimental data of dextran degradation caused by acid hydrolysis, by ultrasonic irradiation, and by enzymatic attack. The model parameters fitted to the experimental data allow the evaluation of the scission probability as a function of the molecular weight and of the location of the bond to be broken within the molecule.     

硼酚醛树脂热分解动力学及其耐热性

用热重法研究了固化硼酚醛树脂的热分解动力学。并用红外光谱法跟踪硼酚醛树脂的固化过程；结果表明，热分解过程为一级反应，由于硼酯键代替了醚键和次甲基键使得热氧化裂解速率常数随硼含量的增加而减小。     

聚甲基丙烯酸甲酯热氧化降解的化学动力学研究

使用质谱、热分析手段研究了PMMA热解反应.结果表明,在氮气中,PMMA-CH=CH2有两个失重阶段,分别对应于主链末端双键引发的断链和主链无规则断链反应,转折点的失重率约为26%.其中,第一阶段的失重速率受扩散过程控制,平均表观活化能E为158.5 kJ/mol, lnA为27.69;第二失重阶段为1.5级化学反应,平均表观活化能E为214.79 kJ/mol, lnA为40.46.在空气中, PMMA也有两个失重阶段,反应机理为1级化学反应,转折点处的失重率约为70%.其中在第一失重阶段平均表观活化能E为130.32 kJ/mol, lnA为24.81,在此阶段中, 过氧化基团的分解反应对PMMA的失重速率有重要影响; 在空气中第二失重阶段平均表观活化能E为 78.25 kJ/mol, lnA为13.97.     

比阿陪南双环母核的合成

从水杨酰胺出发,通过环合、酰化、Reformatsky反应、取代和Dieckmann环化反应,合成了碳青霉烯类抗生素比阿陪南的关键中间体--比阿陪南双环母核{(4R,5R,6S)-6-[(R)-1-叔丁基二甲基硅氧乙基]-3-二苯基磷酰氧基4-甲基-7-氧代-1-氮杂双环-[3.2.0]庚-2-烯-2-羧酸烯丙酯},总收率43.1%,其结构经1H NMR确证.     

Aspects of Degradation Kinetics of Azithromycin in Aqueous Solution

The chemical stability of azithromycin (AZM) in aqueous solution has been investigated utilizing a stability-indicating LC assay with ultraviolet detection. The degradation kinetics were studied as functions of pH (4–7.2), buffer composition (phosphate, acetate, and citrate), buffer concentration, ionic strength, drug concentration and temperature. The observed rate obtained by measuring the remaining intact AZM was shown to follow pseudo-first-order kinetics. The maximum stability of AZM occured at an approximate pH 6.3 in 0.05 M potassium phosphate. The observed degradation rate increased with ionic strength, buffer concentration and obeyed the Arrhenius equation over the temperature range investigated (70–100 °C). The apparent energy of activation (E _a) for AZM in solution was found to be 96.8 kJ mol^?1 and by application of the Arrhenius equation the stability at 25 °C (k ₂₅) and 40 °C (k ₄₀) had been predicted. Moreover, the degradation rate of AZM was independent on its initial concentration. Trace metal ions are unlikely to be involved in the degradation of AZM in aqueous solution. The major degradation product of AZM in aqueous solution was isolated and identified by LC–MS–MS and ¹H and ¹³C NMR spectra.     

The Kinetics of Plasma-Induced Degradation of Organic Pollutants in Sewage Water

The processes of treatment of actual surface water and model solutions in a low-temperature dielectric-barrier discharge (DBD) plasma were studied. The general evaluation of the efficiency of the plasma treatment procedure for sewage purification was made, and a conclusion on the reasonability of its use in combination with conventional treatment methods was drawn. Schemes of conversion processes for organic compounds upon DBD treatment of surface water were proposed, and the effective rate constants of corresponding reactions were estimated (for phenol, k = 0.46 × 10^–5 s^–1). It was found that the reaction of oxidation of pollutants in solutions modeling surface runoff occurs in the diffusion region.     

Kinetics of the Oxidative Degradation of rac-Serine by Aqueous Alkaline Permanganate

Summary.  The kinetics of the oxidation of rac-serine by permanganate in aqueous alkaline medium was studied spectrophotometrically. The reaction showed first order kinetics in permanganate ion concentration and an order less than unity in rac-serine and alkali concentration. Increasing ionic strength and decreasing dielectric constant of the medium increase the rate. The oxidation reaction proceeds via an alkali-permanganate species which forms a complex with rac-serine. The latter decomposes slowly, followed by a fast reaction between a free radical of rac-serine and another molecule of permanganate to give the products. There is a good agreement between the observed and the calculated rate constants under different experimental conditions. Investigations at different temperatures allowed the determination of the activation parameters with respect to the slow step of the proposed mechanism. Received October 15, 1999. Accepted (revised) December 15, 1999     

Kinetics of the Thermo-Oxidative Degradation of Nylon 66 by Oxyluminescence Methods

The chemiluminescence from stabilized nylon 66 fibers during oxidation above T_g has been studied to determine the activation energies of the initiation, propagation and termination reactions. When oxygen is admitted to a nylon 66 sample heated in an inert atmosphere, a pulse of chemiluminescence is observed corresponding to a nonstationary alkyl peroxy radical concentration in the polymer. The analysis of the decay to the steady state can provide kinetic data for peroxy radical reactions in the induction period of the oxidation and the effect of stabilizers on these reactions.     

牡丹花色苷的热稳定性和降解动力学

研究了pH值和温度对牡丹花色苷热稳定性的影响。动力学数据分析表明,牡丹花色苷的热降解符合一级反应动力学模型。在70～90℃条件下,当pH值为2.6、3.0、3.6、4.0和4.6时,牡丹花色苷的半衰期分别为27.0～7.9、32.1～8.5、27.9～8.9、35.9～9.4和27.3～10.7h。提高温度,花色苷降解反应速率增大;降解反应速率常数与温度的关系附合Arrhenius公式,反应活化能为48.4～69.4kJ/mol。牡丹花色苷单体的降解速率依次为矢车菊-3-O-二葡萄糖苷芍药-3-O-葡萄糖苷矢车菊-3,5-O-二葡萄糖苷芍药-3,5-O-二葡萄糖苷。牡丹花色苷降解生成褐色物质,褐变指数随加热时间的延长、加热温度的升高、pH值的增大而增大。     

电生物还原降解二氯酚的动力学特性及功能菌解析

采用电辅助微生物(电生物)体系对二氯酚(2,4-DCP)进行了还原降解研究, 应用聚合酶链式反应-单链构象多肽技术(PCR-SSCP)对微生物群落结构进行解析, 并通过16S rRNA基因克隆及测序构建了系统进化树. 结果表明, 电生物体系对二氯酚的降解符合零级反应动力学特征, 体系中主要以肠球菌(Enterococcus)、 假单胞菌(Pseudomonas)和拟杆菌(Bacteroidales)为优势菌群, 这些菌群在电子传递中起着主要作用. 电生物体系中存在着电极与细胞色素c和脱氢酶的辅酶(NAD)及污染物间的逆向电子传递途径, 可实现电极-微生物-污染物多相界间的长程电子传递.     

氯化天然橡胶的等速升温热降解动力学

天然胶乳;氯化天然橡胶的等速升温热降解动力学     

Stress Degradation Studies of Anagliptin,Development of Validated Stability Indicating Method,Degradation Kinetics Study,Identification and Isolation of Degradation Products

A gradient-specific stability indicating HPLC method was developed and validated for the determination of the antidiabetic agent anagliptin in laboratory mixtures. Reversed-phase chromatography was performed using a Shimadzu LC-20 AD pump (binary), Shimadzu PDA M-20A diode array detector, and Waters Symmetry C-18 column (150?×?4.6 mm, 3.5 µm) maintained at a column oven temperature of 40 °C with UV detection at 247 nm. A gradient program was run at flow rate of 1 mL min^?1. Mobile phase A consisted of a mixture of acetate buffer(10 mm) pH 5/methanol/acetonitrile in the ratio of 90:5:5. Mobile phase B consisted of a mixture of acetate buffer (10 mm) pH 5/methanol/acetonitrile in the ratio of 50:25:25. The method was validated according International Conference of Harmonization (ICH) guidelines. Linearity was observed in the concentration range of 10–120 µg/mL with regression coefficient r²(0.999). The LOD was found to be 7.8 µg/mL and LOQ was found to be 22.68 µg/mL. Anagliptin was subjected to stresses such as acidic, alkali, oxidation, photolysis, and thermal conditions. The proposed method was validated as per ICH guidelines and was found to be accurate, precise, and specific. The drug showed significant degradation in alkaline and oxidative conditions. Alkaline and oxidative degradation followed first-order kinetics. Degradation rate constant and half-lives were determined. Degradation products in alkaline and oxidative conditions were identified by LC–MS. One major degradation product was isolated from each condition by preparative HPLC. These degradation products were characterized by ¹H NMR, ¹³C NMR, DEPT, D₂O exchange, MS/MS, HRMS, and IR techniques. From the spectral data the alkaline degradation product was characterized as 1-{2-[1-(2-methylpyrazolo[1,5-a]pyrimidine-6-carboxamido)-methyl-propan-2-yl-amino]acetyl}pyrrolidine-2-carboxamide. The oxidative degradation product was characterized as N-[2-({2-[(2S)-2-cyanopyrrolidin-1-yl]-2-oxoethyl}amino)-2-methylpropyl]-2-methylpyrazolo-[1,5-a]pyrimidine-N-oxido-6-carboxamide.     

Kinetics of Carotenoids Degradation during the Storage of Encapsulated Carrot Waste Extracts

The encapsulates of carrot waste oil extract improved the antioxidant properties of durum wheat pasta. The aim of this research was to study the kinetics of carotenoids degradation in the freeze-dried (FDE) and spray-dried (SDE) encapsulates of carrot waste extract during storage at four different temperatures (+4, +21.3, +30, +37 °C) up to 413 days by HPLC. Carotenoids levels decreased as a function of time and temperature, following zero-order kinetics. At 4 °C carotenes were stable for at least 413 days, but their half-lives decreased with increasing temperatures: 8–12 months at 21 °C; 3–4 months at 30 °C; and 1.5–2 months at 37 °C. The freeze-drying technique was more effective against carotenes degradation. An initial lag-time with no or very limited carotenes degradation was observed: from one week at 37 °C up to 3 months (SDE) or more (FDE) at 21 °C. The activation energies (Ea) varied between 66.6 and 79.5 kJ/mol, and Ea values tended to be higher in FDE than in SDE.     

丙烯酸化环状磷腈/环氧丙烯酸酯光固化体系热降解动力学研究

以TGA为手段, 进行了丙烯酸化环状磷腈/环氧丙烯酸酯光固化体系热降解动力学的研究, 同时与加入粉末状环状磷腈混合体系进行了对照. 采用Kissinger, Flynn-Wall-Ozawa和Friedman三种方法计算了固化膜降解反应活化能, 证明了磷腈结构的引入, 使得体系在高温阶段的活化能有所提高, 表明降解变得困难, 热稳定性得到提高. 而反应型丙烯酸化环状磷腈相对粉末状环状磷腈混合体系具有更高的降解活化能.     

钛电极苯酚降解反应动力学的Monte Carlo模拟

应用Monte Carlo方法,结合化学反应随机过程理论,模拟钛电极上苯酚电催化氧化反应机理,研究苯酚降解时间、初始浓度、电极的催化性能及反应中间产物对降解过程的影响.结果表明:苯酚浓度随时间变化逐渐降低并渐趋稳定,苯酚初始浓度较高时降解速率快,具有较高催化性能的电极对降解第1步反应的影响较大,可有效减少中间产物停留时间,但控制第1步反应则对降解过程尤其是第2步反应的产物有明显影响,而控制第2步反应对降解过程影响很小.