丁二烯气相聚合产物分子量分布和粒径分布模型研究

对非均相催化的丁二烯气相聚合,基于聚合物多层模型,考虑催化剂颗粒间活性位初始浓度和粒径分布对聚合物分子量分布和粒径分布的影响,建立了聚合物分子量分布和粒径分布的数学模型。模拟了反应温度、催化剂颗粒间活性位初始浓度和粒径分布等因素的影响,结果表明。随着温度升高,聚合物颗粒平均粒径变小,粒径分布变窄,聚合物分子量变小,分子量分布变宽;催化剂颗粒间的活性组分负载越均匀,聚合物分子量越大,分子量分布和粒径分布越窄;随着催化剂平均粒径变大,聚合物分子量变小,分子量分布变宽,不存在催化剂颗粒粒径分布和聚合物颗粒粒径分布间的复制现象。模型模拟结果与实验结果吻合较好,可用于预测丁二烯气相聚合产物的分子量、分子量分布和粒径分布。     

A240沥青和C—石油渣油沥青 原料及其缩聚物的分子量和分子量分布

为了从沥青原料调制出适宜于纺丝的“中间相沥青”,测定沥青原料及缩聚沥青的分子量和分子量分布是必不可少的研究工作。 本文在考察了应用凝胶渗透色谱法,VPO法及Li—乙二胺加氢还原法测定沥青原料及缩聚沥青的分子量和分子量分布后,对A240沥青原料和C—石油渣油沥青原料及其不同热缩聚条件下所得的纺丝物料进行了分子量和分子量分布的测定,并初步分析了纺丝物料的可纺性与分子量及分子量分布之间的关系。     

聚丙烯分子量及分子量分布的化学和机械降解的影响

本文研究了化学和机械降解对聚丙烯分子量和分子量分布的影响。原始聚丙烯树脂的分子量,分子量分布与聚合过程中氢调量、催化剂类型有密切的关系。随着氢调量增加,原始树脂的分子量变小、分子量分布变宽。但是,由原始聚丙烯树脂降解的产物在熔体流动指数(MFI)相同的条件下,氢调量多则降解树脂的分子量大、分子量分布宽,从高效催化聚丙烯得到的降解树脂的分子量、分子量分布都明显低于用普通催化剂产生的降解树脂。通过调节聚合过程中的氢调量、催化剂及聚合后的化学降解程度,可以在较大的范围内选择适合于纺制优质聚丙烯纤维的分子量和分子量分布。     

凝胶色谱法在聚丙烯分子量及分子量分布测定中的应用

根据聚丙烯在凝胶色谱柱上的淋洗特点,确定了测定其分子量及分子量分布试验条件;采用示差和黏度双检测凝胶色谱系统,利用普适校正方法,不需要Mark常数K、α值,可直接测定聚丙烯分子量分布并给出分子量分布曲线;采用统计方法计算数均分子量、重均分子量、黏均分子量,可以为课题研究提供一定的依据和指导。     

分子量分布对聚乙烯性能的影响及控制方法

通过分析分子量分布对聚乙烯产品性能的影响,阐述了分子量分布的控制方法,改变工艺流程、催化剂种类和催化剂加入反应器的状态能控制聚乙烯的分子量分布。     

分子量分布对低密度聚乙烯光氧老化特性的影响

采用衰减全反射红外光谱技术（ATR-FTIR）、热重分析法（TG）、凝胶渗透色谱（GPC）、扫描电子显微镜（SEM）和力学试验比较研究了不同分子量分布指数低密度聚乙烯（LDPE）的光氧老化特性,分析了分子量分布对LDPE化学结构、热稳定性、平均分子量、表面微观形貌和力学性能的影响规律。结果表明分子量分布越宽,LDPE不饱和度增长越剧烈,支化作用增长越显著;分子量分布越窄,羰基指数增长越快;分子量分布对于分子结构的断链行为并无影响。分子量分布指数越大,LDPE起始热分解温度和失重5%对应温度下降更快,热稳定性更容易变差,平均分子量下降更多,表面微观形貌老化现象越严重;弯曲强度和冲击强度受影响更显著,指数为6.0的LDPE老化24 d冲击强度就已丧失。分析认为,分子量越大、分布越窄表明分子链越长、短分子链越少,与氧接触而产生自由基的概率也越小,因此聚乙烯分子量分布越宽,材料越容易老化。     

HDPE树脂流变参数与分子量分布的关系研究

测定了4种高密度聚乙烯(HDPE)树脂的分子量及其分布,研究了其毛细管流变行为和动态流变行为,并分析了得到的流变参数和分子量分布的关系。结果表明:仅在较低挤出速度或较高温度条件下,用毛细管流变测得的非牛顿指数才能用作分子量分布的量度;用动态流变测得的剪切变稀指数、流变多分散指数、幂率指数均可在一定程度上反映了HDPE树脂分子量分布的大小,其中幂率指数与分子量分布的相关性最好(相关系数r2=0.994)。     

明胶化学基础讲座 二、凝胶层析法(上)

<正> 在上一讲中,针对明胶分子量多分散性的问题,讨论了统计平均分子量的几种方式:数均分子量(Mn),重均分子量(Mw),Z 均分子量(Mz),粘均分子量(Mn);并对表示分子量分布的累积重量分布曲线(积分重量分布曲线),微分重量分布曲线,以及表征分布特性的多分散系数(Mw/Mn)与多分散指数(M_(0.9)/M_(0.1))作了说明。从本讲开始,我们要着重介绍测定明胶分子量及分子量分布的几种方法。测定高分子物质的分子量及分子量分布是一项很重要的工作。这不仅是因为高分子材料的物理机械性能与加工性能,都和分子量及分子量分布密切相关,而且我们还可以根据由测定所了解到的规律性,做到在工艺     

涂料用聚合树脂的分子量及分子量分布与性能的关系(续)

概述K、α参数未知时的求证方法。并当K、α参数已知时,如何使用其参数用于分子量分布的测定步骤,以及采用待测物与参照物GPC流出曲线定性比较分子量分布的实用技术。讨论了聚合树脂的分子量和分子量分布与性能的关系。     

涂料用聚合树脂的分子量及分子量分布与性能的关系

概述K、α参数未知时的求证方法。并当K、α参数已知时,如何使用其参数用于分子量分布的测定步骤,以及采用待测物与参照物GPC流出曲线定性比较分子量分布的实用技术。讨论了聚合树脂的分子量和分子量分布与性能的关系。     

Effect of molecular weight and molecular weight distribution on the rheological properties of aqueous poly(ethylene oxide) solution

The effect of the molecular weight and the molecular weight distribution on the rheological properties of aqueous poly(ethylene oxide) (PEO) solutions has been investigated with four PEO samples differing in their M_w, M_w/M_n and purity. The main result of this study is that the steady shear viscosity as well as the complex dynamic viscosity of the samples with broad molecular weight distribution greatly differed from the viscosities of the samples having a narrow molecular weight distribution. Furthermore, the samples with broad molecular weight distribution showed a distinct molecular weight dependent non-Newtonian behavior at increasing shear rates and frequencies. This behavior was not observed for the sample with a narrow molecular weight distribution. Both effects are mainly attributed to the influence of the high molecular weight fraction in the PEO samples of broad molecular weight distribution. The often reported degradation of PEO solutions was not observed within the time scale of our experiment.     

离子液体中ATRP法合成聚合物分子量控制

在氯化1-烯丙基-3-甲基咪唑（[AMIM]Cl）离子液体中,采用原子转移自由基聚合（ATRP）技术,以CuBr/乙二胺为催化体系,合成了分子量分布窄的聚甲基丙烯酸甲酯（PMMA）分子。探索了聚合反应条件对PMMA分子量大小及分布的影响。通过GPC对PMMA分子量大小及分布进行测试,结果表明,在[AMIM]Cl离子液体体系中的ATRP反应,反应时间是控制PMMA分子量大小主要因素,而催化体系是控制PMMA分子量分布宽窄的决定性因素。通过优化反应条件可以设计聚合物分子量的大小和分布,可以实现对聚合物分子量的精确控制,使合成的聚合物材料满足在化工医药中的特定应用。     

Eigenschaftskennfunktionen thermisch hergestellter polystyrole unterschiedlichen molekulargewichts und unterschiedlicher molekulargewichtsverteilung

Mechanical properties and melt flow behaviour have been measured on thermal polystyrenes in order to study the effect of different molecular weight and different molecular weight distribution. The mechanical properties (impact strength, tensile strength and flexural strength) were found to depend upon a critical molecular weight M_w = 1.5 × 10⁵, where the polystyrenes reached ultimate strength. An influence of molecular weight distribution only can be observed when the average molecular weight is near the critical molecular weight limit. The broader the distribution, the poorer are mechanical properties. Injection molded specimens with different molecular weight distribution but equal average molecular weight showed different molecular orientation and different anisotropic mechanical properties. On the basis of equal orientation the narrow distributed specimens showed higher mechanical strength in direction of orientation. The broader the distribution, the higher the elastic properties of melt. An optimum of physical properties and ease of fabrication will be obtained with narrow molecular weight distributed polystyrenes with an average molecular weight slightly above the critical molecular weight limit.     

Molecular weight and polydispersity measurements of polystyrene by quasielastic light scattering

The molecular weight and polydispersity of a polydisperse polystyrene sample was measured by quasielastic light scattering. The molecular weight distribution of the polymer was represented by the Schultz distribution. The weight average molecular weight and polydispersity of distribution was adjusted until the quasielastic light scattering spectra calculated for the distribution agreed with the measured spectra. The calculation was repeated using the logarithmic normal distribution for the polymer. The calculated value of the weight average molecular weight is accurate and insensitive to the assumed molecular distribution function. However, the calculated values of the polydispersity are only of fair accuracy. Thus quasielastic light scattering gives values of the weight average molecular weight at least as accurate as elastic light scattering and gives a crude estimate of the polydispersity of the polymer.     

Kinetic and molecular weight control for methyl methacrylate semibatch polymerization. II. Open control

The gel effect will bring a violent increase of conversion for methyl methacrylate (MMA) polymerization in a short time. It will be very dangerous for the reactor, as it causes an increase of molecular weight and broadens the molecular weight distribution. To unify the kinetics, molecular weight, and its distribution, on the basis of the mathematical models for semibatch polymerization of MMA, three controlled objectives that are the heat load distribution index, the change in molecular weight, and molecular weight distribution index are presented. Three materials (monomer, solvent, and chain transfer agent) and their flow rate and feeding mode are analyzed for the open control of kinetics, molecular weight, and its distribution. The optimum flow rate and mode are obtained. The heat load distribution index and molecular weight distribution index are even less than 2.0 and 2.2, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4399–4405, 2006     

High speed molecular weight distribution

It is now possible to do molecular weight distribution of polymeric material almost as fast as you can put them in solution. μSYRAGEL® has opened a new era in the determination of molecular weight distribution of polymers. With operational efficiencies of 800 plates/min., one can obtain a molecular weight distribution in 15 mins. Combining three of the newest advances in liquid chromatography—solvent delivery, septumless injection, and μSYRAGEL—now makes it possible to use molecular weight distribution as a quality control tool in polymerization and fabrication. The reproducibility of the molecular weight distribution is now good enough that overlays can be done from the raw data. The chromatograms can be used right off the recorder. The reproducibility of the weight average and number average molecular weight is 2–3 percent.     

An investigation of the effects of the molecular weight distribution on the sensitivity of positive electron resists

The molecular weight distribution of two grades of poly(methyl methacrylate) was determined, and the solubility of that polymer in methyl ethyl ketone–2-propanol mixtures was studied. The effects of the molecular weight distribution of the polymer and the strength of the developing solvent on electron resist sensitivity were studied experimentally and compared with a computer model of the electron exposure process. The molecular weight and the molecular weight distribution were found to have a significant effect on the sensitivity of poly(methyl methacrylate) as an electron resist. Increased sensitivity is predicted for higher molecular weight and narrower molecular weight distribution.     

Dynamic rheological properties of polyisobutylene

The viscoelastic properties of polyisobutylene melts were investigated as functions of temperature, molecular weight, and molecular weight distribution. The effect of molecular weight distribution was studied through the use of blends of narrow distribution polymers. The Ninomiya and Ferry theory was used successfully to predict the viscosity of the blends. It was observed that the temperature coefficient for flow was independent of molecular weight distribution and of molecular weight. It was shown, at least in the case of polyisobutylene melts, that the temperature dependence of elasticity is less for polymers with greater polydispersity.     

Effects of molecular weight distribution on the spinodal temperature of polymer mixtures

The effects of molecular weight distribution on the phase stability of polymer mixtures were explored theoretically and experimentally. Based on the lattice‐fluid theory and volume‐fluctuation thermodynamics, the spinodal conditions for a lattice‐fluid mixture of two polymers with molecular weight distribution were derived. The results indicated that the phase stability of a polymer mixture decreases by increasing the molecular weight distribution of polymers in the blend. To confirm the theoretical results with experiments, the changes in the spinodal temperatures of poly(ethyl methacrylate)/polystyrene (PEMA/PS) blends and tetramethyl polycarbonate/polystyrene (TMPC/PS) blends were examined when each component has a different molecular weight distribution. When the weight‐average molecular weight of each component is the same, a blend composed of polymers having broad molecular weight distribution always exhibited lower phase separation than that composed of polymers having narrow molecular weight distribution at the same blend composition. Copyright © 2004 Society of Chemical Industry     

Iodine-initiated,solid-state copolymerization of tetraoxane with 1,3-dioxolane in the presence of methylal. V. Studies on molecular weight distribution of copolymer

The iodine-initiated, solid-state copolymerization of the tetraoxane–1,3–dioxolane-methylal system has been studied by measuring the molecular weight distribution of the copolymer. The molecular weight distribution of the copolymer is found to be strongly dependent on the addition method of the 1,3-dioxolane–methylal solution to tetraoxane. The copolymer obtained by the one-addition copolymerization has a molecular weight distribution curve that shows a very broad distribution, with a discernible shoulder; and the copolymer obtained by the continuous-addition copolymerization has a very sharp curve. Particle size of the copolymer also influences the molecular weight distribution. For the one-addition copolymerization, the larger the particle size of the copolymer, the broader the molecular weight distribution. For the continuous-addition copolymerization, however, the molecular weight distribution is nearly constant regardless of particle size. The dependence of the molecular weight distribution on the polymerization time and the concentrations of iodine, 1,3-dioxolane, and methylal is discussed in detail. These results suggest that this copolymerization system is characterized by a reaction that proceeds from the surface to the center of the tetraoxane crystals.