Two‐stage copolycondensation of preformed oligomers with bisphenols by tosyl chloride/dimethylformamide/pyridine from distributions of resulting oligomers determined by a combination of gel permeation chromatography and NMR

A two‐stage co‐oligomerization of the oligomers initially formed from an equimolar mixture of isophthalic acid (IPA) and terephthalic acid (TPA) and 2,2‐bis(4‐hydroxyphenyl)propane (BPA, 50 mol %) with bisphenols (BPs, 20 mol %) was carried out using a tosyl chloride/dimethylformamide/pyridine condensing agent. The distributions of the resulting oligomers (n_x‐mers), which were quenched with methanol, were determined by a combination of gel permeation chromatography (GPC) and NMR. These distributions (presented by molar percentage) were conveniently calculated with the equation n_x (mol %) = n_x (% mol by GPC) × n₀ (mol % by NMR)/n₀ (% mol by GPC), where n_x (% mol) = n_x (wt % by GPC)/its molecular weight. The results showed the distributions of the preformed IPA/TPA‐BPA oligomers to be in fairly good accord with those obtained directly from GPC and to be supported by the NMR results. The calculation was applied to the co‐oligomers prepared up to a reaction of 0.7, at which there was an increase in the number of higher oligomers indivisible by GPC and the distributions could no longer be determined by molar percentage. The calculated distributions are discussed in relation to the results of copolycondensation. The sequence distributions in the resulting co‐oligomers, which were also examined by NMR, are compared with those in the copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 44–51, 2004     

(Nd_(1-x)Er_x)_2Co_(15.5)V_(1.5)的结构转变与磁性

利用电弧熔炼制备了 (Nd1 xErx) 2 Co1 5 5V1 5(x=0— 1 0 )化合物样品 .通过x射线衍射分析和磁性测量研究了Er替代Nd2 Co1 5 5V1 5中的Nd时对化合物结构和磁性的影响 .研究结果表明 ,低Er含量 (x <0 4 ) ,化合物为Th2 Zn1 7型结构 ;高Er含量时 (x >0 5 ) ,化合物转变为Th2 Ni1 7结构 ;Er含量为x =0 4和 0 5时 ,两种结构共存 .两种结构的晶胞参数a ,c和晶胞体积V随着Er含量的增加都呈现递减的趋势 .随着Er含量的增加 ,(Nd1 xErx) 2 Co1 5 5V1 5化合物的居里温度和饱和磁化强度都单调下降 .(Nd1 xErx) 2 Co1 5 5V1 5化合物的室温各向异性由低Er含量时的易锥型转变为高Er含量时的易轴型 .x =0— 0 5的化合物在温度升高时发生自旋重取向转变 ,自旋重取向温度Tsr随Er含量的增加而减小     

Synthesis of 2-Acyl-2H-1,2,3-diazaphospholes and Their Diels-Alder Reaction with Cyclopentadiene

2H-1,2,3-Diazaphospholes 3a-3h were prepared from various ketone acylhydrazones and phosphorus trichloride in the presence of triethylamine. Compounds 3 underwent feasible hetero-Diels-Alder reactions with cyclopentadiene to afford the respective anellated [1,2,3]diazaphospholes 4a--4d as well as 4a‘--4d‘ in moderate yields. The endo rule in the reaction was observed under kinetic control conditions.     

Synthesis of 5,6-Dihydro-OSW-1 and Its Antitumor Activities

5,6-Dihydro-OSW-1 (1) was synthesized following our previous procedure for the total synthesis of OSW-1. This compound demonstrated slightly stronger potency than that of OSW-1 against the growth of cancer cells.     

Regioselective Synthesis of Multi-substituted Phenylselenomethyl Isoxazolines

A mild, regioselective 1, 3-dipolar cycloaddition protocol for the preparation ofphenylselenomethyl isoxazolines through substituted allyl phenyl selenides and nitrile oxides wasreported.     

Synthesis of New 13-O-Acylavermectin Bl Aglycones

Six new 13-O-acylavermectin Bl aglycones(3-8) were synthesized from avermectin B1 aglycone and their bioactivities were evaluated against Spodoptera exigua, Spodoptera eridania, Tetranychus urticae and Aphis fabae.     

The First Intramolecular Charge Transfer Transition Based on 2-Ureido-4[1H]-pyrimidinone Binding Module

The first intramolecular charge transfer transition based on 2-ureido-4[1H]-pyrimidinone binding module was reported.     

Solid Phase Synthesis of 2-Substituted 1,3-Oxazin-6-ones Using Resin-bound Cyclic Malonic Acid Ester

A facile solid phase synthesis of 2-substituted 1,3-oxazin-6-ones using polymer-supported Meldrum‘s acid has been reported. Reaction of the resin-bound cyclic malonic acid ester with triethyl orthoformate and subsequent double substitution with amide, afforded the corresponding polymer-supported acylaminomethylene cyclic malonic acid ester, which upon thermal treatment led to 1, 3-oxazin-6-ones in good yields and with high purity.     

Stability Conditions of the MMAP [ K ]/ G [ K ]/1/ LCFS Preemptive Repeat Queue

In this paper, we study the stability conditions of the MMAP[K]/G[K]/1/LCFS preemptive repeat queue. We introduce an embedded Markov chain of matrix M/G/1 type with a tree structure and identify conditions for the Markov chain to be ergodic. First, we present three conventional methods for the stability problem of the queueing system of interest. These methods are either computationally demanding or do not provide accurate information for system stability. Then we introduce a novel approach that develops two linear programs whose solutions provide sufficient conditions for stability or instability of the queueing system. The new approach is numerically efficient. The advantages and disadvantages of the methods introduced in this paper are analyzed both theoretically and numerically.