ELECTROCHEMICAL POLYMERIZATION OF ANILINE IN PHOSPHORIC ACID AND THE PROPERTIES OF POLYANILINE

The behavior of the electrochemical polymerization of aniline in a weak acid, phosphoric acid, is very similar to that in strong acids, i.e. its polymerization rate increases quickly with the electrolysis time. The FTIR spectra of polyaniline samples synthesized in phosphoric acid indicate that the counter ion H2PO4^- is present in both the oxidized form and the reduced form of polyaniline. The counter ion plays an important role in adjusting the pH value at the electrode surface of polyaniline during the oxidation and reduction processes. As a result, a pair of redox peaks still appear in cyclic voltammograms of polyaniline in a solution of sodium sulfate of pH 5.5 and in a solution of NaH2PO4 of pH 7.0,respectively, at low potential scan rate; and the color of polyaniline film also changes with applied potential at pH 7.0. Thus,the pH region for the electrochemical activity and the electrochromism of polyaniline is extended to pH 5.5 for a solution of sodium sulfate and to pH 7.0 for a solution of NaH2PO4. The conductivity of polyaniline is 3.3 S cm^-1, depending on the concentration of phosphoric acid used in the stage of polymerization of aniline. The result of elemental analysis of polyaniline is presented here.     

p-硝基氯苯与α氰基乙酸乙酯-α-碳负离子的电子转移反应动力学研究: 非链式的自由基机理

在p-硝基氯苯(1)与α-氰基乙酰乙酯-α-碳负离子(2)的反应过程中, 测得了反应中间体p-硝基氯苯负离子自由基(3)的ESR谱。用ESR场/频联锁技术测定了(3)的ESR吸收强度-时间曲线, 当[1]《[2]时, 其结果与连续一级反应动力学相吻合。测得了从2向1的电子转移和3的分解反应速率常数和活化参数, 反应产物为α-氰基-α-(p-硝基苯基)乙酸乙酯和微量的硝基苯。为该反应提出了非链式的电子转移-负离子自由基分解-自由基偶合机理。     

Detection of a stable nitroxide during chemical depolymerization of heparin

The use of low-molecular-weight heparins (LMWHs) has become common, since compared to unfractionated heparin (UFH), they have a much longer plasma half-life and lower incidence of side effects. LMWHs are derived from the depolymerization of UFH, obtained either chemically, physically or enzymatically. We employed electron spin resonance (ESR) spectroscopy to study the depolymerization of UFH by copper in the presence of hydrogen peroxide. A stable nitroxide radical was detected. This could be generated by the hydroxyl radical attack either to the N-SO⁻₃ group or to free amino groups present in the UFH preparation.     

三苯基硅自由基的电子自旋共振研究

有机硅自由基的电子自旋共振(ESR)的研究一直十分活跃,Bock等已做了大量工作。然而,对于三苯基硅自由基的ESR研究报道却甚少。采用X射线辐照单晶生成的三苯基硅自由基的ESR谱并未获得理想的超精细结构谱,而采用三苯基硅烷与二苯甲酮热反应仅获得Ph_2COSiPh_3自由基的ESR谱。本文报道在氯仿溶液中,用无水三氯化铝与三苯基硅醇或三苯基硅烷在室温下反应,获得三苯基硅烷正离子自由基(Ph_3Si~+)ESR的研究结果,并进行计算机模拟。     

氮氧自由基研究XVII:水溶液中哌啶氮氧自由基的电化学行为和自衰变动力学研究

循环伏安法研究表明,2,2,6,6-四甲基-4-羟基哌啶-1-氧自由基和2,2,6,6-四甲基-4-氧哌啶-1-氧自由基,在水溶液中的单电子氧化电极反应的可逆性随介质酸性,扫描速度和自由基浓度增加而增加,表明电极氧化产物可进一步发生化学反应.     

CH_2CH(~2A')自由基与臭氧反应机理的理论研究

用量子化学MP2（full）方法,在6－311+ +G~(**)基组水平上研究了CH_2CH (~2A~＇)自由基与臭氧反应的机理,全参数优化了反应过程中反应物、中间体、过 渡态和产物的几何构型,在QCISD（T,full）/6-311+ +G~(**)水平上计算了它们的 能量,并对它们进行了振动分析,以确定中间体和过渡态的真实性,研究结果表明 ：CH_2CH(~2A~＇)自由基与臭氧反应有两条可行的反应通道,分别为：CH_2CH (~2A~＇)+O_3→TS1→M1→TS2→O_2+OCH_2CH→TS4+O_2→O_2(~3∑_g)+CH_2CHO (~2A~＂)和CH_2CH(~2A~＇)+O_3→M2→TS3→O_2(~3∑_g)+CHO(~2A~＂),后一个反 应通道较容易发生,而且反应活化能小（2.97kJ/mol）,说明CH_2CH(~2A~＇)自由 基与臭氧之间的反应活性很强。     

KINETIC ANALYSIS OF CO-CONDENSATION POLYMERIZATION OF AB2 AND AB MONOMERS

This work deals with the kinetics of co-condensation polymerization of AB2 and AB monomers, giving expressions of the two-dimensional molecular weight distribution function and the number/weight average molecular weights of the resulting copolymers. The two-dimensional molecular weight distribution depends on two indices, n and l, which are the respective numbers of AB2 and AB units in a copolymer species. The evolution of the two-dimensional weight and z distributions during the co-condensation polymerization has been evaluated systematically. Finally, the two-dimensional distribution was transformed into a one-dimensional molecular weight distribution with only one variable (the molecular weight of the products instead of the degree of polymerization). The calculated results show that the highly branched copolymer has a very broad molecular weight distribution when the co-condensation polymerization approaches completion.     

NARROW-DISPERSED CROSSLINKED CORE-SHELL POLYMER MICROSPHERES PREPARED BY SURFACE-INITIATED ATOM TRANSFER RADICAL POLYMERIZATION＊

Grafting of polystyrene with narrowly dispersed polymer microspheres through surface-initiated atom transfer radical polymerization (ATRP) was investigated. Polydivinylbenzene (PDVB) microspheres were prepared by dispersion polymerization with poly(N-vinyl pyrrolidone) (PVP) as stabilizer. The surfaces of PDVB microspheres were chloromethylated by chloromethyl methyl ether in the presence of zinc chloride as catalyst to form chloromethylbenzene initiating core sites for subsequent ATRP grafting of styrene using CuCl/bpy as catalytic system. Polystyrene was found to be grafted not only from the particle surfaces but also from within a thin shell layer, resulting in the formation of particles size increased from 2.38-2.58μm, which can further grow to 2.93μm during secondary grafting polymerization of styrene. This demonstrates that grafting polymerization proceeds through a typical ATRP procedure with living nature. All of the prepared microspheres have narrow particle size distribution with coefficient of variation around 10%.     

Preparation of Encapsulated Polymer Adhesion Beads and Adhesion with Porous Fibers

Adhesion beads of 10–130 μm, prepared by suspension polymerization, were encapsulated by melamine–formaldehyde. The capsule-type adhesives prepared consist of core and shell structure where the core region is sticky and viscous and the shell region consists of a hard shell at room temperature. The air permeable pads are made by hot pressing the mixture of capsule-type adhesives and porous materials including charcoal chips and Camellia sinensis fibers, which have a porous structure. The interfacial adhesion between polymer adhesion bead and porous fibers after processing shows a good porous sheet structure, which can penetrate air.     

Preparation of nanocomposite superabsorbents based on hydrotalcite and poly(acrylic-co-acrylamide) by inverse suspension polymerization

Firstly, hydrotalcite (HT) was synthesized by the urea method. Then, sodium methyl allyl sulfonate (SMAS) was used as intercalation agent to prepare intercalated HT (SMAS–HT). Finally, a novel poly(acrylic-co-acrylamide)/HT nanocomposite superabsorbent was prepared by inverse suspension polymerization, using N,N′-methylenebisacrylamide (NMBA) as a cross-linking agent and potassium persulfate (KPS) as an initiator. The morphology of the superabsorbents was characterized by FT-IR, XRD, SEM and TEM. The influences of the amount of SMAS–HT on the water (salt) absorbency were investigated. Results showed that the intercalation was successful and the intercalated SMAS–HT incorporated into the superabsorbent was completely exfoliated. The superabsorbent particles approach a spherical shape and the average size is 200–300 nm. The particle sizes of the superabsorbents decrease with increasing the content of SMAS–HT. In addition, the superabsorbent acquired its highest water (salt) absorbency when the content of SMAS–HT is 3 wt%. The highest absorbencies of the superabsorbent for deionized water and 0.9% NaCl_(aq) were 900 g/g and 140 g/g, respectively.