Interparticle Monomer Transport in Miniemulsion Copolymerization

叙述：提出的研究项目是一项实验和理论尝试的继续，目的是阐明细乳液共聚的基本物理关系。细乳液聚合是在一个由悬浮在较大水相中的油滴组成的多相体系中进行的。油相包含单体和最终聚合物产品，并由表面活性剂(如十二烷基硫酸钠)和助表面活性剂(如十六酮或十六醇)结合在一起。细乳液聚合介于两种众所周知的非均相聚合过程之间：悬浮聚合和乳液聚合。在这两种情况下，都存在两个相，即发生聚合的水溶液相和油相，不同之处在于，在悬浮聚合中，引发剂溶解在油相中，而在乳液聚合中，它溶解在水相中。如果单体液滴非常小(0.1到10微米)，并且水溶和油溶引发剂产生类似的结果，则该过程被认为是微乳液聚合。在细乳液共聚中，液滴的形态可以从共聚物组成在整个粒子的横截面上均匀到核心富含一种聚合物而壳层富含另一种聚合物。这种颗粒形态由聚合部位的共聚单体组成和浓度作为聚合时间的函数以及两种单体的竞聚率和水溶解度决定。本工作旨在研究微乳液液滴间单体迁移的机理、速率及其对粒子形态的影响。这一结果最终可用于预测单体向聚合位置的传输受限的条件(添加剂浓度和液滴大小)，从而开发出一种新的方法来调节最终共聚物的颗粒形态和微结构。PIS已经完成了研究，展示了助表面活性剂在细乳液共聚过程中对粒子生成机理和共聚单体分布的作用和影响。在这个最后阶段，他们计划确定助表面活性剂在单体向不同相的传输过程中的作用和效果。

Narrative: The proposed research project is the continuation of an experimental as well as theoretical attempt to elucidate the fundamental physical relationships in miniemulsion copolymerization. Miniemulsion polymerization is done in a heterogenous system consisting of oily droplets suspended in a larger aqueous phase. The oily phase contains the monomer and final polymer product and is held together by both a surfactant (such as sodium dodecyl sulfate) and a cosurfactant (such as hexadecone or cetyl alcohol). Miniemulsion polymerization falls between two well known heterogeneous polymerization processes: suspension polymerization and emulsion polymerization. In both cases there are two phases present, an aqueous solution phase and an oily phase in which the polymerization occurs, the difference being that in suspension polymerization the initiator is soluble in the oily phase while in emulsion polymerization it is soluble in the aqueous phase. The process is considered miniemulsion polymerizaton if the monomer droplets are very small (0.1 to 10 microns) and both water soluble and oil soluble initiators produce similar results. In miniemulsion copolymerization, the morphology of the droplets can vary from the copolymer composition being uniform throughout the cross section of the particle to the core being rich in one polymer and the shell rich in other. This particle morphology is determined by the comonomer composition and concentration at the site of polymerization as a function of the polymerzation time and the reactivity ratios and water solubilities of the two monomers. This work is aimed at studying the mechanism and the rate of interparticle monomer transport between miniemulsion droplets and its effect on particle morphology. The results could ultimately be used to predict the conditions (additive concentration and droplet size) under which the transport of one monomer or the other to the site of the polymerization becomes limiting and thus develop a novel method for regulating the particle morphology and therefore the microstructure of the final copolymer. The PIs have completed research that showed the role and effect of the cosurfactant on the particle generation mechanism and the comonomer distribution during the miniemulsion copolymerization. During this final phase they plan to determine the role and effect of the cosurfactant on the transport of monomer to the different phases.