The Competition Kinetics of Unbranched Chain Processes of Free-Radical Addition to Double Bonds of Molecules with the Formation of 1:1 Adducts

Abstract

Based on a kinetic model involving competing parallel reactions for free-radical addition to the double bond of a molecule with the formation of 1:1 adduct and participation of three radical types in the chain propagation, versions of the rate equation with 1 - 3 measurable parameters are derived. These versions make it possible to describe the nonmonotonic (with maximum) dependence of the formation rate of an addition product on concentration of the unsaturated compound. The unbranched chain process occurs in binary liquid systems comprising saturated and unsaturated components at comparable concentrations. Application of the competition kinetics of free-radical addition to oxidation of some hydrocarbons is discussed when the reaction that competes with chain propagation reactions involving the alkylperoxy radical RO₂ gives the cyclic alkylhydrotetraoxy radical [R(_?H)O₄H] as a less reactive radical inhibiting the chain process of formation of the main products of oxidation.     

Effect of roasting on the radical scavenging activity of cocoa beans

The free-radical scavenging activity of cocoa samples subjected to different roasting treatments has been determined. The samples (raw, pre-roasted and roasted) were separated into four molecular weight fractions per sample (>30, 30–10, 10–5, and <5 kDa). The free-radical scavenging activity was determined with the DPPH^• (1,1-dipheny-2-picrylhydrazyl), and ABTS^•+ [2,2’-azinobis (3-ethylbenzothiazoline-6-sulfonic acid)] free-radical scavenging assays for all samples. Both tests were compared in terms of sensitivity and measurement precision, at different reaction times. Comparing the results from each test, the free-radical scavenging activity trends were similar for each fraction but with notable differences in the sensitivity of the assays. Analysis of the concentration of reducing substances, such as water soluble phenolics, melanoidins, carbohydrates, etc, in these fractions by the photometric Folin–Ciocalteu assay, showed a similar pattern to the free-radical scavenging activity trend. Moreover, this comparison showed that there were significantly (P < 0.05) more reducing substances and free-radical scavenging activity in the 10–5 kDa roasted cocoa bean fraction.     

Novel aromatic macrocyclic oligomers: intermediates for the preparation of high-performance polymers

Recent studies aimed at the development of macrocyclic oligomers as the intermediates for the preparation of high-performance polymers are reviewed. Efficient methods for the preparation of a range of cyclic oligomers, such as aryl ether ketones, aryl ether phthalazines, aryl ether isoquinolines, aryl ether phthalazinones, and arylene sulfides, have been developed. Cyclization was achieved via a nucleophilic aromatic substitution reaction under high-dilution conditions. The cyclic aryl ether oligomers undergo a facile ring-opening polymerization to form high molecular weight polymer. Cyclic oligomers containing an aromatic sulfide linkage also undergo a facile free-radical ring-opening polymerization to form high molecular weight polymers which can be amorphous or crystalline. Due to their low molecular weights, these cyclic oligomers have very low melt viscosities which makes them attractive intermediates for a variety of applications for which the conventionally prepared high molecular weight polymers would not be suitable.     

Preparation and characterization of mesostructured polymer-functionalized sol–gel-derived thin films

The present study attempts to incorporate methacrylate-based polymers into ordered lamellar organic/inorganic nanocomposite films composed of alternating SiO₂/polymer layers. The films are prepared by dip-coating from a solution containing the monomers and silica precursors, thus leading to composite lamellar mesostructured materials through evaporation-induced self-assembly (EISA). A polymerizable coupling agent is added to covalently link the polymers to the silica matrix. The final polymer/SiO₂ hybrid material is obtained by a separate free-radical polymerization step, initiated by UV exposure or thermal treatment. Using trimethoxy(7-octen-1-yl)silane as a coupling agent, a procedure was established that preserved the mesostructure and maintained the swelling properties of the polymers, while acrylate-based coupling agents lead to a significant distortion of the film mesostructure. Structure and composition of the films were studied by X-ray diffraction, NMR and IR.     

Free-radical synthesis of narrow polydispersed 2-hydroxyethyl methacrylate-based tetrapolymers for dilute aqueous base developable negative photoresists

Novel (meth)acrylate tetrapolymers based on 2-hydroxyethyl methacrylate (HEMA) were synthesized via free-radical polymerization in refluxing xylene under monomer-starved conditions for use in negative photoresist formulations. 2,2′-Azobis(2-methylbutyronitrile) was used as initiator and 2-mercaptoethanol as chain transfer agent. Optimized resist formulations were obtained with a relatively narrow polydispersed (D=1.86) low molecular weight copolymer (M_n=1677) of 2-hydroxyethyl methacrylate (HEMA), isobornyl methacrylate (IBMA), cyclohexyl methacrylate (CHMA) and acrylic acid (AA), in a 40/30/23/7 weight ratio. A novel high-resolution single layer negative tone photoresist suitable for 193 nm and e-beam lithography that meets basic performance requirements (aqueous-base development, enhanced etch resistance, sub-0.2 μm resolution) was developed from the aforementioned (meth)acrylate tetrapolymer, the poly(2-hydroxyethyl methacrylate-co-cyclohexyl methacrylate-co-isobornyl methacrylate-co-acrylic acid) (PHECIMA) and a sulfonium salt photo acid generator. The key-components for the negative image formation (photoacid induced crosslinking) are the hydroxyl groups of the HEMA moieties. The swelling-free negative resist material was developed in diluted aqueous base [tetramethyl ammonium hydroxide, (TMAH) 0.26×10⁻²N] and presented enhanced etch resistance without the use of etch resistance promoters. 0.20-0.14 μm lines were obtained upon 193 nm and/or e-beam lithography.     

自由基聚合反应动力学的数学建模——多自由基数学模型

对自由基聚合过程进行数学建模多采用动力学机理模型。但在文献中的动力学数学建模多是利用了单自由基假设 :即假设每个自由基都位于不同的聚合物活性链上。当存在向聚合物的链转移和大分子反应等基元反应时 ,所得的数学模型是不封闭的 ,需经过近似处理后才能进行求解。研究表明 :若将聚合物活性链和非活性链等同对待 ,应用多自由基反应机理 ,根据矩法推导所得数学模型是封闭的 ,可直接求解。以包含有向聚合物链转移反应的自由基均聚反应机理为例 ,根据矩法分别建立了单自由基和多自由基数学模型 ,所得单自由基模型清楚表明了模型存在的不封闭性 ;而多自由基模型可以直接求解计算。模型中考察了数均和重均链长、数均和重均支化度等微观质量参数。对多自由基模型应用单自由基假设 ,并进一步假设仅仅有向非活性链聚合物的链转移后 ,能直接还原到单自由基数学模型     

新型对二苯醌衍生物的合成与晶体结构

主要报道了三苯基硼引发的2-烷基取代苯酚双锂盐的自由基偶联反应,生成了硼取代的对二苯醌化合物。有机硼化合物被认为参加自由基反应,以有机硼化合物作为自由基引发剂,并应用于芳烃化合物。我们发现当三苯基硼与2-烷基取代苯酚的双锂盐反应时,促进2-烷基取代苯酚的自由基偶联,生成了一种新型的对二苯醌衍生物,是一种收率较高的对二苯醌衍生物新型制备方法。产物的结构经元素分析、红外光谱和X-射线单晶衍射确定。     

The antioxidant and free-radical scavenging activities of extract and fractions from corn silk (Zea mays L.) and related flavone glycosides

This study was designed to evaluate both the antioxidant and free-radical scavenging activities of extract and fractions from corn silk. N-butanol fraction (BF) demonstrated the highest total phenolic content (164.1 ± 9.7 μg GAE/g DCS) and total flavonoids content (69.4 ± 5.1 μg RE/g DCS), accompanied with the highest antioxidant activity compared to other fractions through all antioxidant assays. Two flavone glycosides showing potent antioxidant activity were isolated from BF and identified, by comparing spectral data (UV, FAB-MS and NMR) with literature values, to be isoorientin-2″-O-α-l-rhamnoside and 3′-methoxymaysin. The two isolated flavone glycosides, particularly isoorientin-2″-O-α-l-rhamnoside, demonstrated significant total antioxidant activity, DPPH radical scavenging activity, reducing power and iron-chelating capacity, with EC₅₀ values of 14.24 ± 1.49, 22.69 ± 2.33, 6.58 ± 1.07 and 30.25 ± 3.05 μg/ml, respectively. Results obtained indicated that corn silk extracts can be used potentially as a ready accessible and valuable bioactive source of natural antioxidants.     

Single-ion conductors for lithium batteries via silica surface modification

Single-ion conductors (SICs) have been prepared by free-radical polymerization of sulfonic acid-containing monomer on high-purity silica surface that was first tailored with unsaturated functionality using a silanation reaction. It was found that steric effects limited polyelectrolyte surface loading even when large amount of silane molecules were grafted by forming a cross-linked structure. The results indicate that large surface area is an important factor to achieve high-surface loading of ionic moieties. Composite electrolytes were prepared by dispersing these SICs in aprotic solvents. The effects of filler content and solvent on ionic conductivity were investigated.     

流变仪旋转叶片法在自由基聚合反应中的应用研究Ⅰ:丙烯酰胺自由基聚合反应的空闲时间测试方法

使用装备自制的四叶片旋转叶片的应力控制流变仪研究过硫酸铵(APS)和四甲基乙二胺(TEMED)氧化还原体系作为引发体系引发丙烯酰胺(AM)自由基聚合过程的模量变曲线,交联剂为N,N’-亚甲基双丙烯酰胺(MBAM)。通过与传统的平行板夹具比较说明了旋转叶片法测试丙烯酰胺聚合是准确、方便的。从丙烯酰胺聚合过程的模量曲线和温度曲线可以得到体系聚合的空闲时间(idle time)。