Controlled Radical Polymerization: Towards Industrially Relevant Conditions
reaction engineering , polymer chemistry
Reversible deactivation radical polymerization (RDRP), also known as controlled radical polymerization (CRP), has been a significant area of polymer research for more than 20 years, allowing the facile synthesis of complex macromolecules previously unattainable by conventional free radical polymerization (FRP). However, industrial adoption of RDRP has been minimal largely due to the significant economic barrier to commercialization, with complex synthesis of the mediating agents required and the necessary post polymerization processing to recover the mediating agent. In an effort to overcome this obstacle to industrial adoption, the mediating agent concentration can be significantly reduced, such as the copper level in activator regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP), or the mediating agent can be incorporated into the polymer as in nitroxide-mediated polymerization (NMP), where no post polymerization processing is required other than removal of residual monomer. This thesis presents a study of these two chemistries towards industrially relevant conditions. To build upon recent developments of continuous ARGET ATRP, a systematic batch study is conducted to pursue decreased copper levels in the generation of short chain acrylic and methacrylic polymers of interest to the coatings industry. The limitations to reducing copper levels are understood with the development of a kinetic model, with the improved understanding of the ARGET ATRP system suggesting that a reduction in copper loading must be accompanied by an increase in reducing agent loading in order to maintain an appreciable polymerization rate. Alternatively, NMP does not require a reduction in mediating nitroxide level as it reversibly terminates the polymer chain end, and may present a smaller barrier to commercialization. Indeed, certain nitroxides are currently produced at pilot scale. However, limited research has been conducted into continuous operation which is commonly used in industry to improve productivity. A batch NMP study at elevated temperatures demonstrates the effectiveness of a novel alkoxyamine to mediate the polymerization of styrene and butyl acrylate under industrially relevant conditions. A kinetic study is developed to understand the novel system, and the polymerization is implemented in a continuous stirred-tank reactor (CSTR), the first demonstration of NMP in an existing industrial process.