一种确定氧化数的新方法

氧化数是元素的重要性质,在无机化学中应用广泛。长期以来,确定元素氧化数主要根据桐山良一和鲍林等建立的规则,这些规则对于氧化数概念在化学中的推广普及起了很大的作用,但在遇到结构复杂或未知化合物时有时仍然会出现问题。本文根据IUPAC的氧化数定义提出,氧化数完全取决于成键两原子之间的电子供需关系,元素的最高正氧化数受到其原子价层电子数的限制,而元素的最低负氧化数受到同周期稀有气体元素外层电子数与其价层电子数差值的限制,据此建立了确定元素氧化数的新方法,该方法既不需要考虑分子结构,也不依赖元素氧化数的习惯规定,符合氧化数概念提出的初衷,简便易行,例外情况少,不仅适合大学化学教学,也适合中学化学教学。     

树状高分子的特性粘数与代数的关系

从爱因斯坦的粘度理论出发 ,联系树状高分子的分子结构参数 ,计算了树状高分子的特性粘数 ,得到了树状高分子的特性粘数与代数的内在关系 ,分析了树状高分子特性粘数特异行为的内在原因 ,使得对树状高分子特性粘数的理论预测成为可能     

碳还原数的概念和意义

作者认为,对氧化数的概念稍作调整,即可构成一个新的概念,不仅能定量标示有机物分子的还原态,而且是一个有用的生物能力学参数,姑且称之为碳还原数。一、联还原数的概念根据IUPAC对氧化数的定义,各种碳原子的氧化数如表1。氧化数虽也可用于比较不同有机分子的氧化态,但相加时正负数抵销,致使许多化合物的碳氧化数为0,如葡萄糖和乙酸均为0(图1)。欲扩大它的应用范围,必须设法消除负值。为此,作者建议以价     

利用不饱和度计算桥环化合物的环数

正确算出桥环化合物的环数是正确命名桥环化合物的基础。目前确定环数的方法主要有五种,即规则多面体面数法、断键法、块数法、P.A.Reddy计算法、桥头碳原子数法。笔者受不饱和度概念的启发,建立了一种桥环化合物环数的计算方法。所谓不饱和度(又称氢不足指数、双键等价数)指的是在某一化合物结构中环与双键的总数目(叁键当作两个双键)。若知道有机物的分子式,便可由下式求算其不饱和度(Ω)。     

高师化学系(科)的评估刍议

教育评估是教育管理系统中的一个组成部分,是实施教育目标和质量管理的重要环节,是根据一定的目标(社会对系科的要求),通过系统地收集信息从而对客体作出价值判断的过程。高师化学系科的评估可从以下几方面考虑: 一、师资队伍包括高级职称的教师数;国外学成归国的教师数;获得博士、硕士学位的教师数;具有授予化学硕士、博士学位的教师数;正副教授、讲师和助教的比例;派往国外进修或学术访问的教师数;教师队伍的年龄梯队结构(如35岁以下、35～49岁、50～59岁、60岁以上的人数);教师中化学学科学部委员数,国家级化学学科教材编委会委员数等。     

一种计算桥环化合物环数的简便方法

陈亚元同志在“桥环化合物环数的计算方法”一文中,提出了几种如何计算比较复杂的桥环化合物环数的具体方法,同时还介绍了P.A.Reddy对桥环化合物中环数的计算公式c=b-a+1(c为环数,b为环上的键总数,a为环上的原子总数),从而为计算桥环化合物的环数提供了比较简便的方法。由于桥环化合物与桥头原子并存,而化合物中桥头原子的总数目(包括主桥头原子和次桥头原子)又与环数的多少密切相关,所以,可以用桥环化合物中桥头原子的总数来正确计算桥环化合物的环数。设一种桥环化合物中的桥头原子总数为N,环数为M,根据两个桥头原子可以构成一个双环的原则,推导出计算环数的一般公式:     

惰性电子对效应的热力学探讨

一、前言大量实验表明,ⅢA、ⅣA、ⅤA族元素的族数氧化态的稳定性,在同一族中从上而下减弱,而(族数减2)氧化态的稳定性增加,以致到第六周期时,(族数减2)氧化态的稳定性接近、甚至超过族数氧化态的稳定性。这明显地表现在第六周期元素Tl、Pb、Bi的族数氧化态化合物的强氧化性上。N.V.Sidgwick把这     

稀土催化聚丁二烯“氚数均分子量”的研究

本文应用示踪原子氚醇淬灭法,测出用多种稀土催化剂制得的聚丁二烯之“氚数均分子量”,并对稀土催化聚丁二烯氚数均分子量随转化率变化关系进行了讨论。本文还对某些稀土聚丁二烯氚数均分子量与渗透压法测定的数均分子量作了比较,其数值很相近,从而认为氚醇淬灭法有可能作为测定某些稀土聚丁二烯数均分子量的一种方法。     

电动势法测定硫酸铜的离子迁移数

离子迁移数作为物理化学的重要参数,其测定是大学物理化学实验中的基础内容.以基础物理化学实验中离子迁移数的测定为基础,结合电动势的测定等实验,设计建立了一套电动势法测量溶液中铜离子与硫酸根离子迁移数的实验装置,得到的离子迁移数与文献值基本一致.尝试基于大学生在物理化学实验中已掌握的实验技能,综合电化学学科领域的知识,设计探索电动势测量离子迁移数的新方法,有助于提升学生对知识的综合运用能力.     

测试条件对聚酰胺粘数测试结果的影响

分析了测试条件对聚酰胺粘数测试结果产生影响的原因。结果表明,样品实验前的烘干处理对聚酰胺粘数结果影响不大,但是对于长期敞口放置的聚酰胺样品以及做异常调查测试等,建议还是有必要对样品进行烘干处理的;浓硫酸的浓度对结果有明显影响,98%浓硫酸的粘数结果比96%浓硫酸的粘数结果至少偏高10 mL/g,对原料的影响更加显著;样品浓度对粘数的结果有显著的影响,样品浓度太低或太高都会导致粘数结果发生明显地偏差。     

Molecular information on the dissolution of polydisperse polymers: Mixtures of long and short poly(ethylene oxide)

A systematic study of the dissolution of dry, polydisperse poly(ethylene oxide) (PEO) samples, obtained from mixtures of low-molecular-weight and high-molecular-weight PEO, was made. During the dissolution process, the individual release of the low- and high-molecular-weight fractions was monitored. The high-molecular-weight/low-molecular-weight ratio controls the release rate, and the fraction of high-molecular-weight polymers dominates the effect on the overall release rate in mixed PEO tablets. Both fractions are released at the same rate during the main part of the dissolution process; however, during the initial dissolution period a fractionation occurs. The release rate is not a unique function of the average molecular weight of the polymer, but also depends on the polydispersity. By contrast, the average dimension of a polymer coil, as given by the intrinsic viscosity, gives a good prediction of the release rate irrespective of the polydispersity or details of the molecular weight distribution.     

从特性粘数和GPC谱图获得数均分子量方法的误差分析

凝胶渗透色谱法(GPC)广泛用于测量高聚物的分子量及其分布,但即使是根据普适校准原理也需知道溶液体系的K、α值。已经提出了几种改进方法来估算分子量,其中文献[2]提出利用特性粘数和GPC谱图来估算平均分子量。后来有些学者从实验角度对此方法     

Synthesis Characterization and Viscosity Studies of Homopolymer of Methyl Methacrylate and Copolymer of Methyl Methacrylate and Styrene

A homopolymer of methyl methacrylate (MMA) and its copolymer with styrene at different compositions were synthesized and characterized. Viscosity measurements of the synthesized homopolymer and the copolymers in toluene solutions were performed at 313 K. Different equations were used to calculate the intrinsic viscosity, viscometric constants values, and molecular weight of the synthesized polymers. The values of intrinsic viscosity and viscosity average molecular weight obtained by the two methods (single point determination and graphical extrapolation) were compared in order to verify the validity of the single point determination for the polymers. Viscometric properties derived included the specific viscosity (it determines the contribution of the solute to the viscosity of the solution), the reduced viscosity (that provides a measure of the polymer capacity for increasing the solution viscosity), and the intrinsic viscosity.     

Relative molecular weight distributions of cis-polybenzoxazole/polyphosphoric acid rodlike liquid crystalline polymer solutions from dilute solution rheometry

The molecular weight for a dilute solution of cis-polybenzoxazole (PBO) in polyphosphoric acid (PPA) was determined by fitting the rheological data with a semiempirical polydisperse hybrid theory. The hybrid theory models a semiflexible rigid rod as an elastic cylinder. The cylinder has both a rotational relaxation spectrum given by an ideal rigid rod and an internal bending relaxation spectrum spaced in accord with the relaxation time spectra of a flexible coil with fully developed hydrodynamic interactions. The model was fitted to rheological data collected for a 0.05 weight percent solution with intrinsic velocity (one-point determination) of 320 ± 10 cc/g. The model predicts a number-average molecular weight near 12800 ± 400 g/mol with a polydispersity index of 2.5 ± 0.1. By using the Yamakawa-Yoshizaki equation the intrinsic viscosity is calculated for the model molecular weight distribution as 310 cc/g.     

Relaxation characteristics and intrinsic birefringence and viscosity of polystyrene solutions for a wide range of molecular weights

A comparison is made between measurements on polystyrene solutions and the relaxation characteristics and intrinsic birefringence and viscosity given by the theory for the flexible Gaussian chain of variable number of segments and with internal viscosity and internal hydrodynamic interaction. This is done in order to determine the applicability of the theory to polymers over a wide range of molecular weights, including the low molecular weight range in which there may be conflict with the theoretical assumption of chains having a large number of segments. The longest, terminal relaxation time and the number of chain segments are determined from measurements of the frequency dependence of oscillatory flow birefringence while the intrinsic birefringence and viscosity are determined from steady flow measurements. The range of molecular weights studied is from approximately 900 at 10⁶. It is found that the segment weight is approximately 1000 and the number of segments is in direct proportion to the molecular weight for the range from 1 to 1000 segments. The terminal relaxation time has a molecular weight dependence of the type given by the theory but with better agreement for higher molecular weights. While the measured dependences of the intrinsic viscosity and birefringence are in agreement with theory for molecular weights greater than 5 × 10⁴, they deviate significantly for molecular weights below 1 × 10⁴. The ratio of the intrinsic birefringence to intrinsic viscosity, which in theory is a constant independent of molecular weight, is found to change at the lower molecular weights.     

从特性粘数和GPC图谱获得重均分子量的新方法

本文提出了从未知样品的特性粘数和GPC图谱计算重均分子量的新方法,该方法可用于计算窄分布和宽分布的未知Mark-Houwink 常数的样品的重均分子量。用七个不同分子量和不同分布的实例验证了所提出的方法。结果与已知Mark-Houwink常数用普适校准法得到的结果一致。     

Synthesis and solution properties of star‐shaped poly(tert‐butyl acrylate)

A series of star polymers consisting of poly(tert‐butyl acrylate) arms and an ethyleneglycol dimethacrylate (EGDMA) microgel core were synthesized using anionic polymerization. The effect of various parameters (precursor length, ratio [[EGDMA]/[Initiator], reaction time, and overall concentrations) on the average number of arms was investigated. Molecular weights were determined using GPC coupled with an online viscometer and MALLS. The exponents for the relation between intrinsic viscosity or radius of gyration and molecular weight, respectively, are extremely low, indicating that the dimensions of the star polymers only slightly increase with the number of arms. After a certain number of arms is reached the intrinsic viscosity even decreases with molecular weight. Computer simulations for star polymers were carried out where the radius of gyration was calculated as a function of the number of arms. The results are in good agreement with the experimental data.     

Universal calibration in GPC: A new approach for the calculation of molecular weights

A method has been developed for determining simultaneously the molecular weight of a broad-distribution polymer and the Mark-Houwink coefficients for that polymer type by using only GPC and intrinsic viscosity data. Standardized samples of poly(vinyl chloride), polystyrene, polybutadiene, and an experimental cycloolefin polymer were analyzed by this method. Shear-corrected intrinsic viscosities were used in all cases because of the high molecular weights involved. Molecular weight data for all samples were found to be in good agreement with molecular weight data obtained by membrane osmometry and from other GPC techniques. The proposed technique provides a means for calculating the molecular weight of a single polymer sample through universal calibration of GPC without knowledge of the Mark-Houwink coefficients for that polymer type.     

热处理对照相明胶溶液粘度和分子量分布的影响

本文以四种照相明胶为研究对象,探讨热处理对照相明胶溶液粘度和分子量分布的影响。实验结果表明,随着加热温度上升,照相明胶溶液粘度下降,数均分子量下降。照相明胶溶液粘度和数均分子量密切相关,照相明胶溶液粘度下降发生的内在原因是数均分子量下降。在本实验条件下,惰胶、活性胶的加热温度不超过75℃,PA胶的加热温度不超过60℃。     

褐藻酸钠溶液的超声辐照效应及其对分子量参数的影响

观察了超声辐照过程中褐藻酸钠溶液的pH值、温度、表现特性粘度和表现分子量及其分布的变化,发现在超声辐照过程中,褐藻酸钠的表现平均分子量经历了下降→回升→再下降的过程;当超声辐照停止后,表现特性粘度和表观平均分子量又略有回升,因而推测在这一过程中褐藻酸钠的构象可能发生了变化。