蠕虫状链模型下梳状共聚物分子的均方回转半径的理论分析及其在聚羧酸系减水剂分子中的应用

利用蠕虫状链模型对梳状共聚物分子的均方回转半径进行了理论分析,建立了回转半径与主链轮廓长度、主链持久长度、侧链轮廓长度、侧链持久长度、侧链数目以及侧链沿主链的分布情况(均匀分布和梯度分布)之间的定量数学关系.在此基础上,以被称为"第一代聚羧酸系高性能减水剂"(以下简称为MPEG-type PCE)的甲基丙烯酸(MAA)/烯酸甲酯(MAA-MPEG)梳状共聚物分子为研究对象,结合实验数据,对其聚电解质主链的持久长度进行了分析,并考察了主侧链长度、刚柔性、侧链分布、接枝密度等分子结构参数对PCE回转半径的影响,最后对模型的局限性作简要说明.梳状共聚物分子的蠕虫状链模型物理图像简洁,参数意义明确,应用于PCE分子体系时较之前所报道的柔性链模型要更为合理,能够为分析PCE的分子结构与溶液构象和吸附构象之间的关系提供更科学的视角.     

用NMR分析可生物降解的两亲性嵌段共聚物的相对分子质量和组成

凝胶渗透色谱(GPC)法是根据聚合物分子链流体力学体积大小的比较来测定聚合物相对分子质量(以下简称分子量)的,测得的聚合物分子量与聚合物分子链在溶剂中的构象有关[1]。两亲性嵌段共聚物分子链中亲水链段和亲油链段的极性差异很大,几乎在任何溶剂中它们的构象都不相同,因此可     

凝胶色谱—光散射联机法测定高聚物的长链支化度

运用凝胶渗透色谱-光散射联用技术(GPC-LALLS)测定聚合物的长链支化度的基本原理是:在将聚合物分子按其流体力学体积顺序分离的同时,通过光散射仪逐滴测定溶液中聚合物的分子量。经过对谱图上逐点进行扩展效应的改正,通过普适标定线,求出支化分子与线型分子回转半径的比值,以计算试样的支化度及其分布。具体方法如下:     

疏水缔合聚丙烯酰胺在盐水中的自组装行为

使用静态光散射、动态光散射以及原子力显微镜(AFM)研究了疏水缔合聚丙烯酰胺(HAPAM)在盐水溶液中的自组装行为.研究了聚合物分子在不同盐浓度中的表观重均分子量(Mw,a),均方根回转半径(),流体力学半径(),第二维里系数(A2)的变化,并根据/的比值得出聚合物分子的聚集形态.实验结果表明:随着盐浓度的增强,聚合物溶液的分子链由舒展变得卷曲.     

聚乙酸乙烯酯的溶液性质及长链支化度

用粘度法,GPC和LALLS测定了线型及不同转化率的PVAc分级级份的粘度与分子量。提出了以线型和支化聚合物的K,α计算临界分子量的方法。讨论了表征PVAc长链支化的各种参数与分子量和转化率之间的关系以及不同条件下迭代法计算的支化频率λ的差异。实验结果表明,特性粘数和数均分子量乘积所表示的流体力学体积更适合GPC的普适标定概念。     

长棒状T形三组分双亲分子相行为的耗散粒子动力学模拟

采用耗散粒子动力学方法建立了以侧链长度和温度为变量的相图,计算了相关结构参数及每个液晶相对应侧链的有效体积分数,重现了实验上观察到的五边形、六边形柱状相及刚棒在层内位置的有序堆垛层状结构.研究发现,长棒状T形三组分双亲分子相图中的相序列和相结构符合相关报道,并且侧链有效体积分数f L与实验值一致.表明粗粒化模型反映了真实T形分子的主要特性,如分子的拓扑结构、排除体积效应及分相趋势、刚棒液晶基元的长径比和侧链的空间效应.证实了侧链尺寸对主/侧链非线性连接体系的自组装结构及各组成单元的位置分布的重要作用.     

良溶剂中环形高分子单链的结构与动力学性质的模拟研究

本文采用多粒子碰撞动力学与分子动力学耦合的模拟方法研究了环形高分子单链在良溶剂中的静态与动态性质,并与线形分子进行了对比.研究发现,环形高分子链内粒子之间的平均距离小于线形链,即粒子排列得更加紧密;相应的均方回转半径也小于线形链,线形链与环形链的均方回转半径的比值为1.77;同时,环形链扩散的速度也比线形链快,两者比值为1.10.模拟结果揭示了扩散行为是排斥体积作用和流体力学相互作用耦合的结果,在扩散过程中,流体力学相互作用消减了排斥体积作用对扩散行为的贡献.此外,通过对有和没有流体力学相互作用的多粒子碰撞动力学得到的结果作对比,研究了流体力学相互作用对高分子静态和动态行为的影响,结果表明,流体力学相互作用使高分子链在极稀溶液中的扩散速度变快.     

RI-UV双检测器GPC法测定SBS的分子量分布

SBS是一种新型的高分子材料,是苯乙烯-丁二烯的嵌段共聚物,它的聚苯乙烯(PS)段对紫外光有吸收,聚丁二烯(PB)段对紫外光无吸收。采用RI-UV(示差-紫外)双检测器GPC法同时测定此共聚物的分子量分布和组成分布,Runyon等在计算中假定:SBS分子的流体力学体积可看作相应组成的均聚物分子的流体力学体积之和,以及均聚物的校正曲线斜率相同,其SBS分子量的计算式为,     

凝胶色谱与多角激光光散射联用研究聚氧化乙烯的扩展效应和链构象

采用凝胶色谱与多角激光光散射联用的方法,测定了一系列不同分子量的聚乙二醇(PEG)和聚氧化乙烯(PEO)在色谱柱中的扩展效应.扩展因子随PEG/PEO分子量的增加而增大,经扩展效应改正后得到了样品的准确分子量和分子量分布.同时建立了PEO的Z均回转半径Rgz与重均分子量Mw之间的单分散标度关系:Rgz=0.0272 Mw0.56,结果表明,长链PEO在水溶液中由于排除体积效应采取溶胀的无规线团构象.     

乙酰化处理对碱木质素在四氢呋喃中微结构的影响

通过对比碱木质素(AL)和乙酰化碱木质素(ACAL)在四氢呋喃(THF)中溶液行为和物理化学性质的差异, 揭示了乙酰化处理对碱木质素在THF中微结构的影响. 分别采用动态光散射、凝胶渗透色谱(GPC)、透射电子显微镜(TEM)、特性粘度、荧光光谱仪、耗散型石英晶体微天平(QCM-D)和自组装技术等研究了AL和ACAL在聚集形态、聚集机理以及吸附特性等方面的特征. 研究发现, 乙酰化处理会降低碱木质素在THF中的分子间和分子内聚集程度. AL在THF中以单分子和聚集体的形式共同存在, 分子较为蜷曲; ACAL在THF中则更多地是以单分子形式存在而几乎不存在大聚集体, 分子较为伸展, 其流体力学半径要比相同绝对分子量的AL更大.THF中的AL聚集体会在液固界面上发生强烈的吸附, 但ACAL由于与溶剂间的相互作用较强而几乎不会吸附在液固界面上. 由于AL分子在THF中较为蜷曲且吸附能力较强, 因此利用以THF为流动相的GPC直接测量AL的分子量时所得结果并不准确, 为保证GPC的测量结果更加全面可靠, 需要在测量前对碱木质素进行乙酰化处理.     

Conformational Properties of Comb-shaped Polyelectrolytes with Negatively Charged Backbone and Neutral Side Chains Studied by a Generic Coarse-grained Bead-and-Spring Model

A generic coarse-grained bead-and-spring model,mapped onto comb-shaped polycarboxylate-based(PCE)superplasticizers,is developed and studied by Langevin molecular dynamics simulations with implicit solvent and explicit counterions.The agreement on the radius of gyration of the PCEs with experiments shows that our model can be useful in studying the equilibrium sizes of PCEs in solution.The effects of ionic strength,side-chain number,and side-chain length on the conformational behavior of PCEs in solution are explored.Single-chain equilibrium properties,including the radius of gyration,end-to-end distance and persistenee length of the polymer backbone,shape-asphericity parameter,and the mean span dimension,are determined.It is found that with the increase of ionic strength,the equilibrium sizes of the polymers decrease only slightly,and a linear dependenew of the persistence length of backbone on the Debye screening length is found,in good agreement with the theory developed by Dobrynin.Increasing side-chain numbers and/or side-chain lengths increases not only the equilibrium sizes(radius of gyration and mean span)of the polymer as a whole,but also the persistence length of the backbone due to excluded volume interactions.     

两亲性杂侧链聚合物刷的合成及其乳化功能

报道了一种随机高密度接枝亲水、疏水聚合物侧链的刷形两亲性聚合物.首先,结合可逆加成-断裂链转移(RAFT)聚合和后修饰方法,得到含叠氮侧基的聚甲基丙烯酸缩水甘油酯(PGMA-N3)作为主链;再分别合成端炔基聚苯乙烯(PS)和端炔基聚环氧乙烷(PEO),然后通过铜催化的叠氮-炔环加成反应,将疏水性PS和亲水性PEO同时高效的接到PGMA主链上,制得两亲性杂侧链的聚合物刷.由凝胶渗透色谱(SEC)分析得知,在主链叠氮基团与两侧链总炔基的摩尔投料比为1∶1的条件下,PS和PEO的接枝效率很高,都大于90%.通过调节主链长度和2种侧链的投料比,获得不同组成的聚合物刷.通过等质量的甲苯/水混合体系,考察两亲性聚合物刷的乳化能力,发现主链聚合度为100,PS∶PEO比例为70∶30的聚合物刷表现出最佳的乳化性能.     

Hydrodynamic Radius Characterization of a Vinyl-Type Polynorbornene by Size-Exclusion Chromatography with a Static and Dynamic Laser Light Scattering Detector

Both absolute molecular weight and molecular sizes (radius of gyration and hydrodynamic radius) of a vinyl-type polynorbornene eluting from size-exclusion chromatography columns were determined by combined with a static and dynamic laser light scattering detector. The hydrodynamic radius of polymer fraction eluting from size-exclusion chromatography columns was obtained from dynamic laser light scattering measurements at only a single angle of 90° by introducing a correction factor. According to the scaling relationship between molecular sizes and molecular weight and the ratio between radius of gyration and hydrodynamic radius, the vinyl-type polynorbornene took a random coil conformation in 1,2,4-trichlorobenzene at 150 °C.     

Simulation of GPC‐Distribution Coefficients of Linear and Star‐Shaped Molecules in Spherical Pores

Simulations of the distribution coefficients of linear and star‐shaped polymers in spherical pores were performed in order to predict the GPC‐elution behavior of star‐shaped polymers relative to that of linear polymers. Self avoiding walks were generated on a tetrahedral lattice to simulate good solvent conditions. It was found that neither the molecular weight nor the mean squared radius of gyration of the polymer serves as a universal factor to determine the distribution coefficient. However, the calculated distribution coefficients correlate well with the calculated hydrodynamic radii even for different topologies. For molecules at same elution volume the ratios of molecular weights of star and linear polymer agree well with exact calculations for Gaussian chains. These ratios are nearly independent of pore geometry (spherical or cylindrical).     

Reaction of a low‐molecular‐weight free radical with a flexible polymer chain: Kinetic studies on the OH + poly(N‐vinylpyrrolidone) model

This work addresses the issue of kinetics of diffusion‐controlled reactions of small radicals with macromolecules in solution. Attack of pulse‐generated hydroxyl radicals on poly(N‐vinylpyrrolidone)—PVP—chains of various molecular weight in water was used as the model reaction. Pulse radiolysis with spectrophotometric detection was applied to determine the rate constants by competition kinetics. The rate constant depends both on polymer concentration and on its molecular weight. In dilute solutions, a distinct dependence of the rate constant on the molecular weight is observed. In the studied range of molecular weight, the values of reaction radius, calculated using Smoluchowski equation on the basis of experimental kinetic data, are very close to the radius of gyration of polymer coils. We believe that radius of gyration, as an easily determined parameter, could possibly serve for predicting rate constants of diffusion‐controlled reactions of polymers with low‐molecular‐weight compounds in dilute solutions. With increasing polymer concentration and thus increasing spatial overlap of polymer coils the dependence of the rate constant on the molecular weight fades away, and the rate constant values increase with increasing concentration toward the value determined for low‐molecular‐weight model of PVP. Most steep increase approximately coincides with the hydrodynamic critical concentration of a given PVP sample, reflecting the change in reaction geometry from individual coils to a continuous matrix of interpenetrating chains. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 474–481, 2011     

Improved expression of the mean-square radius of gyration, 2. Poly(1,1-disubstituted ethylene)s

The mean-square radius of gyration of poly(1,1-disubstituted ethylene)s is calculated according to a method already developed for poly(methyl methacrylate), poly(α-methylstyrene) and polyitaconate. During the derivation both the effect of side groups and the masses of skeletal atoms were taken into account. A hypothetical polymer chain was introduced, in which the mass of the substituents on every C^α was considered to be concentrated in their center of mass, and the virtual side bond vector runs from C^α to this center. The mean-square radius of gyration of poly(1,1-disubstituted ethylene)s consists of two parts, one of which is the mean-square radius of gyration of the hypothetical molecule described before and the other is related to the geometrical characteristics of the side groups. Numerical calculations indicated that the dependence of the mean-square radius of gyration of poly(1,1-disubstituted ethylene)s on the molecular weight is analogous to that of vinyl polymers, 〈S²〉 = aM^b, where a and b are constants characteristic of the polymer.     

Comblike poly(ethylene oxide)/hydrophobic C6 branched chitosan surfactant polymers as anti-infection surface modifying agents

A series of structurally well-defined poly(ethylene oxide)/hydrophobic C₆ branched chitosan surfactant polymers that undergo surface induced self assembly on hydrophobic biomaterial surfaces were synthesized and characterized. The surfactant polymers consist of low molecular weight (M_w) chitosan backbone with hydrophilic poly(ethylene oxide) (PEO) and hydrophobic hexyl pendant groups. Chitosan was depolymerized by nitrous acid deaminative cleavage. Hexanal and aldehyde-terminated PEO chains were simultaneously attached to low M_w chitosan hydrochloride via reductive amination. The surfactant polymers were prepared with various ratios of the two side chains. The molecular composition of the surfactant polymers was determined by FT-IR and ¹H NMR. Surface active properties at the air–water interface were determined by Langmuir film balance measurements. The surfactant polymers with PEO/hexyl ratios of 1:3.0 and 1:14.4 were used as surface modifying agents to investigate their anti-infection properties. E. coli adhesion on Silastic^® surface was decreased significantly by the surfactant polymer with PEO/hexyl 1:3.0. Surface growth of adherent E. coli was effectively suppressed by both tested surfactant polymers.     

Analysis of the influence of interdetector volume on local calibration in size exclusion chromatography with dual multiangle-light-scattering/concentration detection

A comparison of the s- and w-detections of molecular weight, a necessary condition for precise determination of interdetector volume in size exclusion chromatography of polymers with the dual light scattering--concentration detection, is examined. From the theoretical analysis for a polymer with the log-normal molecular weight distribution it follows that the error in determination of the local calibration, i.e., of a logarithmic dependence of molecular weight on elution volume obtained by the s-detection, from the known dependence of radius of gyration on elution volume and of molecular weight on the radius of gyration, remains linear and is slightly shifted with respect to that obtained by the w-detection (dual detection giving the weight-average molecular weight) towards higher molecular weights, the difference being below the experimental error. It also follows that the error in the slope of local calibration found by the w-detection is given by the ratio of the error in interdetector volume and the variance of the elution curve. This is demonstrated on several polymer samples with symmetric elution curves of polymer samples differing in polydispersity indices. The range of this rule depends on the broadness and symmetry of elution curves. The precision of the interdetector volume determination depends therefore strongly on the Mw/Mn ratio of the sample.