Department of Chemistry , The University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599 , United States.
Department of Applied Physical Sciences , The University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599 , United States.
J Am Chem Soc. 2019 Aug 14;141(32):12815-12823. doi: 10.1021/jacs.9b05799. Epub 2019 Aug 2.
Polyolefins represent a high-volume class of polymers prized for their attractive thermomechanical properties, but the lack of chemical functionality on polyolefins makes them inadequate for many high-performance engineering applications. We report a metal-free postpolymerization modification approach to impart functionality onto branched polyolefins without the deleterious chain-coupling or chain-scission side reactions inherent to previous methods. The identification of conditions for thermally initiated polyolefin C-H functionalization combined with the development of new reagents enabled the addition of xanthates, trithiocarbonates, and dithiocarbamates to a variety of commercially available branched polyolefins. Systematic experimental and kinetic studies led to a mechanistic hypothesis that facilitated the rational design of reagents and reaction conditions for the thermally initiated C-H xanthylation of isotactic polypropylene (PP) within a twin-screw extruder. A structure-property study showed that the functionalized PP adheres to polar surfaces twice as strongly as commercial PP while demonstrating similar tensile properties. The fundamental understanding of the elementary steps in amidyl radical-mediated polyolefin functionalization provided herein reveals key structure-reactivity relationships for the design of improved reagents, while the demonstration of chemoselective and scalable PP functionalization to realize a material with improved adhesion properties indicates the translational potential of this method.
聚烯烃是一类具有高体积分数的聚合物，因其具有吸引人的热机械性能而备受推崇，但聚烯烃缺乏化学官能团，这使得它们不能满足许多高性能工程应用的要求。我们报告了一种无金属的后聚合修饰方法，可在不产生以前方法固有的链偶联或链断裂副反应的情况下，赋予支化聚烯烃功能性。确定了热引发聚烯烃 C-H 官能化的条件，并开发了新的试剂，使黄原酸盐、三硫代碳酸盐和二硫代氨基甲酸盐能够添加到各种市售的支化聚烯烃中。系统的实验和动力学研究提出了一个机械假设，有助于合理设计试剂和反应条件，以便在双螺杆挤出机内热引发等规聚丙烯（PP）的 C-H 黄原酸化反应。结构-性能研究表明，功能化的 PP 与商用 PP 相比，对极性表面的附着力强两倍，同时表现出相似的拉伸性能。本文对酰胺基自由基介导的聚烯烃官能化的基本步骤的深入了解，为设计改进的试剂提供了关键的结构-反应性关系，而对具有改善的粘附性能的 PP 进行化学选择性和规模化官能化的演示表明了该方法的转化潜力。
