聚合工艺对核壳型丙烯酸酯乳液性能的影响

采用间歇法、半连续滴加法和预乳化半连续滴加法等种子乳液聚合工艺,制备了核壳型丙烯酸酯乳液,研究了聚合工艺对乳液性能以及漆膜力学性能的影响,并用激光纳米粒度仪和透射电镜(TEM)对乳胶粒子进行了表征。结果表明,当丙烯酸质量分数为4%,核、壳层中甲基丙烯酸甲酯与丙烯酸丁酯的质量比分别为3∶7和7∶3,核壳总单体质量比为1∶1,核层和壳层反应温度分别为70℃和80℃时,采用预乳化半连续滴加法可以合成黏度适中、乳胶粒径小且分布均匀、稳定性好和漆膜力学性能优良的核壳型丙烯酸酯乳液。     

核／壳结构聚合物改性硬质聚氯乙烯的力学性能

采用种子乳液聚合制备了丙烯酸酯核/壳结构聚合物,总转化率超过95%,乳胶粒理论粒径与实测值基本一致,说明聚合体系没有明显的二次成核过程.将其用于硬质聚氯乙烯改性,当加入量为3 phr时,就能产生显著的增韧效果,常温缺口冲击强度达到16.51 kJ/cm2,而拉伸强度基本保持不变.扫描电镜分析冲击断口表明,核/壳聚合物已经很好分散到聚氯乙烯基体中,呈网状结构,为明显的韧性断裂过程.该研究有望应用于工业生产.     

AAS核壳结构共聚物的制备及其改性SAN树脂的性能

随着社会对环保问题的关注,乳液聚合用于脆性聚合物的改性研究越来越受到重视。文中采用种子乳液聚合方法制备了核壳结构聚丙烯酸丁酯/苯乙烯-丙烯腈共聚物(PBA/AS,简称AAS),单体总转化率达99.35%,乳胶粒理论粒径与实测值基本一致,说明该体系没有明显的二次成核过程。当乳胶粒粒径在326 nm、橡胶质量分数为15%时,AAS改性苯乙烯-丙烯腈共聚物的共混体系发生明显的脆-韧转变,而拉伸强度保持较高的值。DMA谱图表明,随橡胶相含量的增大,两相转变峰越来越接近,相容性提高;SEM观察证实了这种力学性能的转变。     

丙烯酸酯乳液在氯乙烯悬浮聚合体系中稳态原位增韧改性

以丙烯酸丁酯(BA)、丙烯酸乙酯(EA)为单体,通过乳液聚合制备了粒径100 nm左右的均相交联共聚乳液(AC),并将其作为氯乙烯悬浮聚合用接枝改性剂,原位接枝共聚和原位共混进行增韧改性,以制备高抗冲复合聚氯乙烯树脂(AC-PVC)。研究了乳化剂种类和EA用量对AC乳液稳定性及乳胶粒粒径的影响,模拟了AC乳液在三氯乙烯悬浮聚合体系中的稳定性,并在20 L高压反应釜中进行了氯乙烯悬浮聚合试验,对不同分散剂用量下所得AC-PVC颗粒形态及力学性能进行了表征。结果表明,反应釜粘釜现象明显改善,粗粒径的AC-PVC比例降低,且AC-PVC的抗冲性能显著提高,最高缺口冲击强度可达普通SG-5型PVC树脂的27倍。     

硅溶胶存在下的聚丙烯酸酯无皂乳液聚合

采用无皂乳液聚合法合成了粒径分布单一的硅溶胶/聚丙烯酸酯复合乳液。讨论了硅溶胶对无皂乳液聚合成核过程、乳胶粒粒径及其分布、乳液稳定性的影响。结果表明,硅溶胶的加入减小了乳胶粒粒径,并且对乳液有稳定作用。通过透射电镜(TEM)对复合乳胶粒结构进行观察,表明乳胶粒具有两相复合结构。结合实验结果,提出了该体系无机有机两相复合机理,即无皂乳液聚合初期的聚丙烯酸酯初始微粒不稳定,易与硅溶胶粒子聚并。     

细乳液聚合制备纳米二氧化硅-丙烯酸酯复合乳液的研究

采用硅溶胶和丙烯酸酯单体通过细乳液聚合制备纳米二氧化硅/丙烯酸酯复合高分子乳液。考察了聚合过程中硅溶胶量对于单体转化率和聚合物粒子粒径的影响,并用GPC、XPS表征所得的复合乳液。实验结果表明:二氧化硅的引入提高了聚合反应速率,增加聚合物的分子量并使分子量分布变窄;在复合乳液粒子中,二氧化硅主要以分散相分布在连续的丙烯酸酯相内部;复合乳液的力学性能明显优于不含二氧化硅的纯丙烯酸酯聚合物乳液。     

乳液聚合条件对纳米Fe3O4/导电聚苯胺介电常数的影响

以十二烷基苯磺酸(DBSA)为乳化剂和掺杂剂,过硫酸铵(APS)为氧化剂,采用乳液聚合的方法合成了导电聚苯胺包覆磁性四氧化三铁的纳米核-壳复合材料。利用3 cm波导式测量线法分别研究了聚合反应中Fe3O4的含量、DBSA和APS与苯胺的相对含量对复合材料介电常数(ε′,ε″)的影响。测量结果表明,Fe3O4的大量加入会提高复合材料的介电损耗ε;″DBSA和APS的加入量会对导电聚苯胺的共轭结构和导电性产生影响,从而改变复合材料的ε′和ε″。     

Morphological characterization of composite latex particles by positron annihilation lifetime spectroscopy

A series of thermoplastic/elastomer composite particles has been prepared by two step emulsion polymerization techniques. The morphology of the obtained composite particles as a function of the system composition has been studied by transmission electron microscopy. Afterwards, a correlation between the structural behavior of the composites and the ortho- positronium lifetime and formation probability was also established. This correlation can be explained in terms of free volume changes associated to phase transitions in the particles. Received: 18 December 2000 / Reviewed and accepted: 4 April 2001     

低温液相化学法在合成单分散纳米微粒中的应用

单分散纳米微粒的获得,为进一步研究某一特定尺寸的纳米微粒的各种性质提供了方便.单分散纳米微粒比多分散纳米微粒具有更显著的性能,更适合于应用.国内外在这方面开展了大量的研究工作,主要报道了低温液相化学法在合成单分散金属纳米颗粒、单分散半导体纳米颗粒、单分散复合氧化物纳米颗粒、单分散聚合物纳米微球、单分散核壳结构复合纳米微粒等方面的应用情况.     

Electrophoretic Build‐Up of Alternately Multilayered Films and Micropatterns Based on Graphene Sheets and Nanoparticles and their Applications in Flexible Supercapacitors

Graphene nanosheets and metal nanoparticles (NPs) have been used as nano‐building‐blocks for assembly into macroscale hybrid structures with promising performance in electrical devices. However, in most graphene and metal NP hybrid structures, the graphene sheets and metal NPs (e.g., AuNPs) do not enable control of the reaction process, orientation of building blocks, and organization at the nanoscale. Here, an electrophoretic layer‐by‐layer assembly for constructing multilayered reduced graphene oxide (RGO)/AuNP films and lateral micropatterns is presented. This assembly method allows easy control of the nano‐architecture of building blocks along the normal direction of the film, including the number and thickness of RGO and AuNP layers, in addition to control of the lateral orientation of the resultant multilayered structures. Conductivity of multilayered RGO/AuNP hybrid nano‐architecture shows great improvement caused by a bridging effect of the AuNPs along the out‐of‐plane direction between the upper and lower RGO layers. The results clearly show the potential of electrophoretic build‐up in the fabrication of graphene‐based alternately multilayered films and patterns. Finally, flexible supercapacitors based on multilayered RGO/AuNP hybrid films are fabricated, and excellent performance, such as high energy and power densities, are achieved.