Advances in Living/Controlled Polymerization in Waterborne Systems: New Opportunities in Designing Latexes with Tailored Microstructure and Properties

摘要

Historically, finely tuned control of the molecular weight distribution in free radical polymerizations has posed a significant challenge. Because of the stochastic nature of the polymer chain growth chemistry, distributions are typically broad with both very short and long chains being produced. Furthermore, once chains have terminated, they are not readily available for additional reactions to make for example, block copolymers or to functionalize the chain ends. The uncontrolled presence of very short or long chains can have deleterious effects on coating properties, and yet it is usually not simple or economical to eliminate them from the polymerization process.rnLiving/controlled radical polymerization (L/CRP) provides a relatively straightforward means to prepare polymers with narrow molecular weight distributions (largely eliminating the presence of very short and long chains), specialized architectures such as di- or tri-block copolymers, and functionalized polymers. The concept is simple and yet elegant. A mediating species such as a nitroxide or transition metal complex is added to the polymerization mixture, where it acts to reversibly terminate propagating polymeric radicals to yield "dormant" chains. These dormant chains undergo repeated growth and reversible termination cycles during the process, producing a "living" polymer with narrow molecular weight distribution that can be subsequently reacted if desired. While L/CRP was originally perceived as a somewhat esoteric, complex and expensive process, increased understanding of the polymerization chemistry coupled with recent developments, particularly in waterborne systems, have created a myriad of opportunities for commercial exploitation of L/CRP chemistry in the coatings area. This presentation will highlight the major features and most recent advances of L/CRP in waterborne systems.