Ep10 Alkenes and pi bonds, block copolymers, dendrimers - UC San Diego - NANO 134 Darren Lipomi

The paragraph introduces the topic of polymerization, specifically anionic and cationic processes. It discusses the grading of exams and hints at grade adjustments, then delves into the chemistry of polymerization, explaining the influence of electron-donating and electron-withdrawing groups on the reactivity of vinyl monomers. The instructor provides an in-depth look at the molecular orbitals of alkenes and the sp2 hybridization of carbon atoms involved in the formation of pi bonds. The role of resonance in vinyl monomers and the stability of radicals and charges on substituted carbon atoms are also highlighted.

This section focuses on the mechanism of cationic polymerization, explaining the need for an electron-rich alkene and the role of substituents in the process. The resonance structures that lead to the formation of a positive charge on the more substituted carbon atom are discussed, along with the initiation of the polymerization by an acid. The paragraph also touches on the concept of formal charge and its calculation, providing insight into the stabilization of the growing polymer chain.

The paragraph explores anionic polymerization, contrasting it with cationic polymerization by emphasizing the need for electron-poor alkenes and electronegative atoms that withdraw electron density. It describes the resonance structures that result in a reactive carbon atom with a formal positive charge, which is essential for the anionic polymerization process. The use of alkyl lithium reagents and the concept of 1-4 conjugate addition are also mentioned, illustrating how the polymer chain grows.

This section highlights the unique characteristics of anionic polymerization, including its non-terminating nature and the ability to perform chain end functionalization with high efficiency. The discussion covers the 'living' nature of anionic polymerization, where chains grow simultaneously and can be intentionally terminated by adding substances like water. The paragraph also explains the limitations of anionic polymerization in terms of its incompatibility with electrophilic groups.

The paragraph discusses the technique of chain end functionalization in anionic polymerization, which allows for the alteration of the polymer chain's end group with high yield. It also introduces the concept of block copolymers, explaining how they can be created using living polymerization methods to achieve a covalent linkage between different polymer chains. The benefits of block copolymers in combining mechanical properties such as elasticity and toughness are also explored.

This section delves into the types of block copolymers, including their formation and the benefits they offer in material science. It explains how block copolymers can be synthesized using anionic polymerization and how they differ from statistical or random copolymers, alternating copolymers, and graft copolymers. The paragraph also touches on the challenges of mixing polymers and the advantages of creating block copolymers to achieve desired material properties.

The paragraph introduces the concept of synthetic polymer structures beyond copolymers, such as dendrimers, which are three-dimensional nanostructures. It explains the synthesis of dendrimers through divergent synthesis, starting from a multifunctional core and adding generations of branched molecules. The unique properties of dendrimers, including their monodispersity and potential applications in drug delivery, are highlighted.

This section focuses on the application of dendrimers in drug delivery and the development of nanoparticle therapeutics. It describes the process of synthesizing dendrimers, emphasizing the importance of protection groups in controlling the growth of the dendrimer structure. The paragraph also discusses the potential for dendrimers to carry and release drug molecules, as well as their use in targeting specific biological environments such as tumors.

The final paragraph teases the upcoming lecture on the thermodynamics of polymer solutions, with a focus on regular solution theory. It acknowledges the groans from students at the mention of thermodynamics but promises to make the topic as engaging as possible. The paragraph also invites any questions from the audience on the topics covered during the session.