Ep8 ATRP and RAFT - UC San Diego - NANO 134 Darren Lipomi

The script begins with a discussion on uncontrolled radical polymerizations, which are common in the production of commodity and engineering polymers like polyolefins. It highlights the ubiquity of these polymers in everyday objects and acknowledges the lack of control over molecular mass distribution as acceptable in many applications. However, the script shifts focus to controlled radical polymerization techniques, necessary for modern applications such as semiconductor manufacturing, antifouling surfaces, and drug delivery systems where precise molecular weight distribution and surface functionalization are crucial. The lecture introduces the concept of equilibrium between a dormant state and an active state in controlled radical polymerization, allowing for a linear increase in molecular mass with the extent of polymerization.

The script delves into three primary methods of controlled radical polymerization: nitroxyl-mediated radical polymerization, atom transfer radical polymerization (ATRP), and reversible addition-fragmentation chain transfer (RAFT) polymerization. It emphasizes the limitations of nitroxyl-mediated methods in terms of functional group tolerance and the versatility of ATRP and RAFT, which are more prevalent in scientific literature and industrial applications. The explanation includes the basic mechanisms of ATRP, involving a copper catalyst and a halogenated compound, and its broader applicability due to its tolerance to various functional groups.

This section explores the practical applications of ATRP, including the creation of polymer brushes, star polymers, and block copolymers. It discusses the process of initiating polymerization from a surface or monomer with multiple adjacent initiator groups, leading to densely packed polymer chains. The script also explains the formation of star polymers with a multi-pronged initiator and the synthesis of block copolymers, which combine the desirable properties of different monomers. The versatility of ATRP in creating gradient copolymers is also mentioned, catering to specific research needs.

The script introduces RAFT polymerization, a technique suitable for use in emulsions and water, with a focus on its unique mechanism involving a dithioester RAFT agent. It outlines the process of initiation, propagation, and the reversible transfer of radicals between the polymer chain and the RAFT agent, leading to controlled polymerization. The explanation includes the formation of the polymer with controlled end groups, which can be tailored for specific applications, such as attaching to nanoparticles or surfaces.

This part of the script provides a detailed look at the RAFT polymerization mechanism, from initiation to termination, emphasizing the equilibrium between active and dormant states. It discusses the formation of polymers with specific end groups, either from the initiator or the RAFT agent, and the implications for the final product. The lecture also touches on the distribution of products, the presence of dead chains, and the overall efficiency of the process, acknowledging the presence of impurities but focusing on the primary product.

The script examines the relationship between the number-average molecular weight and polydispersity index in controlled radical polymerization, as a function of the extent of reaction. It contrasts this with the behavior seen in uncontrolled polymerization, highlighting the linear growth in molecular weight and the reduced polydispersity in controlled processes. The explanation includes the reasons for the initial higher polydispersity and its decrease as the reaction progresses.

Towards the end of the script, the focus shifts to exam preparation, emphasizing the importance of understanding key concepts such as reactivity, solution thermodynamics, and the formation of microstructures in polymers. The lecturer provides a list of topics that will not be covered in the exam, such as the reactivity part of the chemistry, and instead, the focus will be on the properties of polymers. The script also mentions the availability of office hours for additional review and clarification.

The script concludes with a review of essential concepts for the exam, such as the difference between configuration and conformation in polymers, the distinction between glass transition and melting temperatures, and the Carothers equation. It also covers the kinetics of step-growth and chain-growth polymerization, the concept of stoichiometric imbalance, and the importance of understanding various linkages in polymer chemistry, such as ester and carbonate bonds.

In the final paragraph, the script wraps up with a brief acknowledgment of the importance of understanding the various types of polymerization and their applications. It emphasizes the significance of controlled radical polymerization in modern material science and hints at the potential for further exploration of these topics in future classes.