Enhanced Nucleation of Monomer Droplets in Miniemulsion Polymerization

细乳液聚合中单体液滴的增强成核

• 批准号: 9628783
• 负责人: Mohamed El-Aasser
• 金额: $ 19.68万
• 依托单位: Lehigh University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1996
• 资助国家: 美国
• 起止时间: 1996-06-15 至 2000-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9628783&HistoricalAwards=false
• 关键词: Enhanced; Nucleation; Monomer; Droplets; Miniemulsion

Abstract - El-Aasser - 9628783 The potential advantages of applying miniemulsion technology to the preparation of latexes through free radical polymerization of vinyl monomers have not been realized, one reason being that only a fraction (circa 20%) of the initial droplets (50 - 500 nm) are nucleated to become polymer particles. This limits the control of the particle size and copolymer composition by requiring diffusion of monomers from the droplets which are not nucleated to the growing polymer particles. This is a particular disadvantage for monomers with low water solubility which do not readily diffuse through the aqueous phase (e.g., macromonomers). Recent developments in the miniemulsion polymerization of styrene have shown that the addition of a small amount of polymer to the miniemulsion droplets enhances their nucleation which can reach 100% under certain conditions, thereby increasing the polymerization rate and resulting particle number. This phenomenon has been attributed to an increased rate of radical entry into these droplets which improves their ability to compete with the existing polymer particles for aqueous phase free radicals. The mechanistic explanation for this phenomenon and the extension of the method to other monomer systems are the focus of this research. A combination of techniques will be applied in this investigation including continuous measurements of the reaction rate via reaction calorimetry and monitoring the evolution of the number of particles through the particle size distribution. The nature of the added polymer will be varied in terms of its molecular weight and the functionality of its end-groups in order to determine whether it is an interfacial phenomenon or a ObulkO phenomenon. Likewise, the composition of the droplet/water interface will be varied and characterized. In addition to the normal water-soluble initiator (i.e., persulfate), oil-soluble initiators will be used to determine the effect of the origin of the free radicals (aqueous vs. droplet phase) on particle nucleation. Other monomer/comonomer systems will also be investigated. And finally, mathematical modeling will be used in conjunction with the above findings to aid in mechanistic understanding of the miniemulsion polymerization process as a function of the variables chosen in these studies.

摘要- El-Aasser - 9628783 应用细乳液技术通过乙烯基单体的自由基聚合制备胶乳的潜在优点尚未实现，一个原因是只有一部分（约20%）的初始液滴（50 - 500 nm）成核成为聚合物颗粒。 这通过要求单体从未成核的液滴扩散到生长的聚合物颗粒而限制了粒度和共聚物组成的控制。 这对于不容易扩散通过水相的低水溶性单体（例如，大分子单体）。 苯乙烯细乳液聚合的最新进展表明，向细乳液液滴中加入少量聚合物可增强其成核作用，在某些条件下可达到100%，从而提高聚合速率和所得颗粒数。 这种现象归因于自由基进入这些液滴的速率增加，这提高了它们与现有聚合物颗粒竞争水相自由基的能力。 对这一现象的机理解释以及将该方法推广到其他单体体系是本研究的重点。 在这项研究中，将应用一种技术的组合，包括通过反应量热法连续测量反应速率，并通过粒度分布监测颗粒数量的演变。 添加的聚合物的性质将根据其分子量和其末端基团的官能度而变化，以确定其是界面现象还是ObulkO现象。 同样地，液滴/水界面的组成将被改变和表征。 除了通常的水溶性引发剂（即，过硫酸盐），油溶性引发剂将用于确定自由基来源（水相相对于液滴相）对颗粒成核的影响。 还将研究其他单体/共聚单体系统。 最后，数学建模将与上述研究结果结合使用，以帮助细乳液聚合过程作为这些研究中选择的变量的函数的机械理解。