凝胶化反应全过程的激光光散射跟踪研究

在苯乙烯（Ｓｔ） 二乙烯苯（ＤＶＢ）自由基共聚的凝胶化反应过程中定时取样，得到凝胶化点前后及至终点的一系列样品，然后用激光光散射技术，包括研究散射光强及其角度依赖性的静态光散射（ＳＬＳ）和研究散射光频移的动态光散射（ＤＬＳ），表征了这系列样品的重均分子量Ｍｗ、均方旋转半径Ｒｇ、第二维利系数Ａ２及流体力学半径Ｒｈ等静、动态参量及这些参量的变化规律，定量地描述了凝胶化反应全过程     

反应型二烷基脲凝胶剂及有机溶剂的室温凝胶化研究

通常制备有机分子凝胶是在高温下溶解凝胶剂,凝胶剂分子在冷却过程中进行自组装并使有机溶剂凝胶化。该方法限制了某些低沸点溶剂的凝胶化。利用甲苯二异氰酸酯与烷基胺的高反应活性,制备了三种不同烷基链长的反应型凝胶剂甲苯–2, 4–二（N, N’ –烷基）脲。这种反应型凝胶剂能以较低的浓度在室温下使某些芳香族和卤代烃溶剂中形成热可逆的有机分子凝胶。不同烷基链长的亲溶剂作用以及溶剂性质对有机分子凝胶的形成有较大影响。场发射扫描电镜表明这种反应型凝胶剂在有机溶剂中自组装形成纤维状三维网络结构。烷基链长度不同,形成的纤维状聚集体的形态也不同。红外光谱（FT-IR）和核磁共振波谱（1H-NMR）研究表明分子间氢键作用是这种凝胶剂自组装的驱动力。通过X射线衍射（XRD）和分子模拟推测了其聚集体的结构形态。     

反应型二烷基脲凝胶剂及有机溶剂的室温凝胶化研究

通常制备有机分子凝胶是在高温下溶解凝胶剂,凝胶剂分子在冷却过程中进行自组装并使有机溶剂凝胶化。该方法限制了某些低沸点溶剂的凝胶化。利用甲苯二异氰酸酯与烷基胺的高反应活性,制备了三种不同烷基链长的反应型凝胶剂甲苯–2, 4–二（N, N’ –烷基）脲。这种反应型凝胶剂能以较低的浓度在室温下使某些芳香族和卤代烃溶剂中形成热可逆的有机分子凝胶。不同烷基链长的亲溶剂作用以及溶剂性质对有机分子凝胶的形成有较大影响。场发射扫描电镜表明这种反应型凝胶剂在有机溶剂中自组装形成纤维状三维网络结构。烷基链长度不同,形成的纤维状聚集体的形态也不同。红外光谱（FT-IR）和核磁共振波谱（1H-NMR）研究表明分子间氢键作用是这种凝胶剂自组装的驱动力。通过X射线衍射（XRD）和分子模拟推测了其聚集体的结构形态。     

高分子凝胶化反应的分形几何分析

据分形理论,基于实验基础上,进行了高分子凝胶化反应的分形几何行为分析,以苯乙烯-二乙烯苯凝胶化反应为例,分别由激光及小角x-光散射测定其反应中大分子重量、尺寸及散射光强角度依赖性,来定量描述化学反应及分析体系的分形行为和测定分数维D值.这种避开各种复杂的凝胶化理论,立足于现代物理技术及新理论,去剖析高分子凝胶化反应的分形几何行为,能够在更本质的深度揭示这类复杂反应的规律.     

SAXS研究凝胶化反应全过程分形行为

The dependence of the scattered intensity on angles was measured by SAXS for a series of samples taken during the span process of the gelation of styrene with divinylbenzene. Based on these data. we obtained the fractal dimensions and their evolution for both sols and gels successfully.     

Monte Carlo方法研究苯乙烯/二乙烯苯凝胶化反应

在前文基础上,对苯乙烯-二乙烯苯凝胶化反应进行更进一步的Monte Carlo模拟。由于引入了标识符,用三维模型很好地获得了定量表征凝胶化反应的参数：转化率,交联点,分子链数目,重均分子量Mw及数均分子量Mn等的变化规律,得到了与实验基本一致的结果。     

自由基引发的凝胶化反应的Monte Carlo模拟

基于自由基凝胶化反应的基本原理,在一个具有周期性边界条件的二维网络上,利用动态ＭｏｎｔｅＣａｒｌｏ 方法模拟了聚合物凝胶的自由基凝胶化反应,得到了凝胶的具体结构,研究了总单体浓度（ 单体浓度和交联剂浓度之和） 对凝胶的分形结构和孔径分布的影响．模拟中首次考虑了聚合后单体的运动对凝胶结构的影响．结果表明：考虑聚合后单体的运动,可使所得凝胶网络的分形维数和凝胶化所需的最低浓度均显著小于动力学凝胶化模型和ＤＬＡ 模型的相应值．用移动气泡法得到了凝胶网络的孔径分布,发现凝胶网络中大孔所占百分率明显多于随机纤维网络模型．     

利用后凝胶化反应制备低吸附性反相填料

在硅胶基质的反相填料 (如 C18、C8、C4 等 )上 ,蛋白质的变性 ,碱性分子峰展宽、拖尾甚至完全吸附等常被归因为硅羟基产生的次级效应 (Secondary Effect) [1～ 3] .我们认为 ,除填料的孔径效应外 [4 ] ,杂质离子与残余硅羟基的协同效应是导致此类问题的直接原因 ,如金属离子直接作用于溶质以及金属离子和硅羟基的远程作用力导致的溶质变性等 .为解决这一问题 ,可采用高反应性的新硅烷化试剂 ,以尽可能将硅羟基完全屏蔽 [5] ,或以封端试剂消除残余的硅羟基 .但是 ,用硅烷化试剂封端 (End-capping)在多数情况下并不能完全覆盖表面硅羟基 ,…     

St-DVB微凝胶星型两性接枝共聚物的单分子膜性质研究

用自由基引发苯乙烯-二乙烯基苯(St-DVB)共聚合成了带有大量乙烯基的活性微凝胶,再将此活性胶核与甲基丙烯酸(MMA)共聚制得微凝胶星型两性聚合物,并成功地制备了LB膜,此微凝胶星型两性聚合物LB膜与-般典型LB膜的区别在于它的疏水部分不是长脂链,而是分子量比较大的苯乙烯-二乙烯基苯微凝胶;此疏水的微凝胶核与亲水的聚甲基丙烯酸链在气-液界面上形成类似"浮萍"结构的单分子膜,因而在诸多方面表现出特异性质。     

连续型季铵化反应的热动力学研究

应用热动力学法研究了Ｎ，Ｎ，Ｎ＇，Ｎ＇－四甲基－１，３－丙二胺与溴代正丁烷之间的连续季铵化反应，测定了２５．０、３５．０及４５．０℃和ＤＭＳＯ溶剂中该反应的速度常数，计算得到了其活化能及活化自由能，并讨论了温度和溶剂对反应动力学的影响。这些结果对认识季铵盐型离子聚合物的形成机理及反应条件的选择是十分重要的。     

An Experimental Study on the Free‐Radical Copolymerization Kinetics with Crosslinking of Styrene and Divinylbenzene in Supercritical Carbon Dioxide

A study on the effect of process conditions and composition of the reacting mixture on the kinetics and particle properties in the copolymerization of styrene and divinylbenzene in supercritical carbon dioxide is presented. Polystyrene‐block‐polydimethylsiloxane and Krytox 257 FSL (Dupont) were used as stabilizers, and their performance compared. A 38 mL, high‐pressure view cell, equipped with one frontal and two lateral sapphire windows, was used as the reacting vessel. The polymer product was characterized for total monomer conversion, gel content, molecular weight averages of the sol fraction and particle size distribution. Acceptable polymerization rates and partially‐agglomerated spherical particles were produced under the conditions tested.

     

Autoacceleration and Cyclization Effects on Styrene/Divinylbenzene Copolymerization

Copolymerizations of styrene with divinylbenzene (DVB) are carried out at low monomer concentrations in order to evaluate the incidence of cyclization reactions. The pendant double bond concentration in the synthesized polymers is measured using Fourier transform infrared spectroscopy. Reactions are carried out at monomer concentrations of 6% and 2% (v/v), DVB concentration in the range 15–80 wt% and temperatures in the range 60–90 °C. A previously developed model is used to interpret the results and analyze the cyclization effects. The predictions of the model accounting for cyclization reactions present a better agreement to the experimental data in comparison to predictions without cyclizations. Autoacceleration effects are observed for cases with higher DVB concentrations, in which the formation of highly entangled structures may have occurred. The model provides an estimate of 0.05 for the crosslink parameter (C _P) and 130 s^?1 for the rate constant of cyclization for the smallest sequence (three units) at 90 °C.

     

甲基丙烯酸甲酯和二乙烯苯对苯乙烯共聚合的影响

以甲基丙烯酸甲酯(MMA)、苯乙烯(St)和二乙烯苯(DVB)三元共聚体系为研究对象,采用气相色谱法研究了体系中MMA和DVB浓度对聚苯乙烯型树脂交联的影响。结果表明:MMA加速St和DVB的聚合速率,其中对St的加速作用又明显大于对DVB的。随MMA含量的增加,聚苯乙烯型树脂交联不均匀的情况得以明显改善,而增加体系中DVB的含量,DVB与St、MMA反应速率的差异变大,树脂交联不均匀的情况变严重。     

Kinetic Modeling of the Suspension Copolymerization of Styrene/Divinylbenzene with Gel Formation

Summary : Experimental and theoretical studies concerning the suspension copolymerization of styrene with divinylbenzene are reported. Experiments were carried out in a batch stirred reactor, at 1.2 dm³ scale, and extended beyond gelation in order to synthesize insoluble material. Looking for real time information concerning the building process of such materials, these polymerizations were In-line monitored using a FTIR-ATR immersion probe. Polymer samples collected before and after gelation were Off-line characterized using a SEC/RI/MALLS system allowing the measurement of monomer conversion, average molecular weights, MWD and also the z-average radius of gyration. The weight fraction of insoluble material (gel) was measured for samples with different reaction times. The experimental program has included the study of the influence of key polymerization parameters on the dynamics of gelation and some properties of the resulting networks, namely the initial mole fraction of crosslinker and the initial proportions between monomers and inert diluent. Variable n-heptane/toluene mixtures were used within this purpose. These experimental observations were complemented with theoretical studies using a general kinetic approach allowing the prediction of MWD and z-average radius of gyration before and also after gelation. Comparison of the experimental measurements with these predictions is being exploited to develop modeling tools useful for the design of operating conditions allowing the improvement of the performance of the final products.     

苯乙烯—二乙烯基苯共聚超微球在溶液中的扩散行为

用光子相关光谱测定了苯乙烯-二乙烯基苯(St-DVB)共聚超微粒在良溶剂(甲苯)与θ溶剂(环己烷)中不同温度下的分子扩散系数,与流体力学方程结合给出了该微粒在无限稀时的等效流体力学半径。微粒分子扩散与温度的关系符合Arrhenius方程。不同温度的测试结果表明,St-DVB共聚超微粒的微交联网络结构使其分子形态不易改变。在θ溶剂中,T<θ时,微粒发生聚集,表现出大分子的协同扩散;T>θ时,在较高浓度,扩散系数偏离与浓度的线性关系。流体力学作用和热运动决定了微粒分子的扩散行为。     

Kinetics of Free Radical Copolymerization. V. Copolymerization of Ethyl Acrylate with Styrene. Composition of Copolymers

The composition of copolymers formed at 50°C in ethyl acrylate/ styrene/azo-bis-isobutyronitrile/benzene systems of different composition was investigated. The experimental composition data (based on the elementary analysis of copolymers) were evaluated by the η-ζ transformation method. Finite monomer conversions were taken into account. The classical composition equation was found to describe the system under investigation. The reactivity ratios are p ₁ = 0.152 ± 0.006; p ₂ = 0.787 ± 0.023. The free radical copolymerization of ethyl acrylate and styrene has been investigated in benzene solution at 50°C. Our results on the initiation kinetics were disclosed in our recent publication [1]. Now we are reporting on our studies concerning the composition of ethyl acrylate/styrene copolymers.