Ep7 free radical and controlled radical polymerization UCSD NANO 134 Darren Lipomi

The script begins with an introduction to the topic of controlled radical polymerization, contrasting it with uncontrolled radical polymerization. It highlights the rapid growth and technological applications of the field over the past two decades. The lecturer also mentions an upcoming lunch event for networking and discussing nanoengineering and chemical engineering. The summary of the previous class on kinetics of polymerization is provided, with an explanation of the steady state connection kinetics and how it relates to calculating molecular weight and chain length.

This paragraph delves into the kinetic chain length, which is the average number of monomers added to a growing polymer chain during its lifetime. The relationship between the propagation rate, chain termination rate, and the kinetic chain length is discussed. The thermodynamic implications of polymerization are also explored, including the importance of enthalpy and entropy in determining the favorability of the reaction. The讲师 emphasizes the exothermic nature of bond formation in polymerization and the unfavorable entropy change due to the confinement of monomers in a chain.

The script discusses various methods of carrying out polymerization reactions, such as bulk, solution, suspension, and emulsion processes. Each method has its advantages and disadvantages, including efficiency, environmental impact, and susceptibility to auto-acceleration and explosion. The lecturer also touches on the importance of heat dissipation in controlling reaction rates and the potential for reaction with solvents in solution polymerization.

This paragraph outlines the characteristics of free radical polymerization, including the immediate formation of high molecular weight polymers, the reactivity of only the growing chain ends, and the steady decrease in monomer concentration throughout the reaction. The讲师 also explains how long reaction times can increase the yield of polymer without affecting the molecular weight, and the impact of temperature on reaction rates and molecular weight.

The讲师 uses analogies to describe the growth of polymer chains, comparing free radical polymerization to popcorn popping and controlled radical polymerization to grass growing. The emphasis is on the simultaneous and controlled growth of polymer chains in controlled radical polymerization, as opposed to the random and explosive nature of free radical polymerization.

The script explains the key to controlled radical polymerization, which involves deactivating the growing chain end with a capping group that can periodically come off, allowing monomers to react and the chain to grow. The讲师 introduces the concept of a living reaction, where the polymer chain remains active and can continue to grow with the addition of more monomers. The advantages of this method, such as the ability to create multi-functional and block co-polymers, are also discussed.

This paragraph focuses on the equilibrium between the dormant and active states in controlled radical polymerization. The讲师 describes the role of activation and deactivation rate constants and how the system maintains a predominance of dormant chains. The process of a dormant chain becoming active upon the addition of monomers and then returning to a dormant state with extended length is detailed.

The script discusses the importance of capping groups in controlled radical polymerization, which are stable radicals that can reversibly terminate a growing chain end without initiating new reactions. The讲师 introduces the concept of a stable free radical, exemplified by the nitroxide group, which is stable enough to cap the chain end but not reactive enough to start new radical reactions.

The final paragraph introduces nitroxide-mediated polymerization, highlighting the use of Tempo, a specific nitroxide, to control the polymerization process. The讲师 explains how Tempo can be used in the reaction vessel, either pre-formed on a monomer or added separately, to cap growing chain ends and allow for controlled addition of monomers. The stability of the Tempo group and its potential modifications for specific end-group functionalities in the polymer are also discussed.