UC Santa Barbara

A grand challenge in polymer chemistry is the development of methods for constructing functional macromolecules with control over the molecular weight, composition, stereoregularity and chain-end fidelity. In particular, living anionic polymerization is a powerful technique to prepare well-defined high molecular weight macromolecules with extremely narrow dispersities and controlled stereochemistries on industrial scales. However, state-of-the art anionic polymerization techniques greatly sensitive to many functional substituents, limiting their chain-end functionalization strategies and subsequent incorporation into advanced materials. In Chapter 2 and Appendix A, the development of new synthetic methods to prepare end-functional, tacticity-controlled polymers are described. In particular, versatile and scalable synthetic strategy to obtain stereocontrolled poly(methyl metacrylate) with diverse chain-ends through living anionic polymerization with precise termination reactions and post-polymerization modifications is presented. The utility of such polymers was demonstrated through their use as nanoparticle ligands, allowing for a new self-assembly platform via stereocomplexation. The synthetic availability of these functional stereocontrolled building blocks presents new opportunities to create designer materials for both industrial applications and fundamental interests. In Chapter 3 and Appendix B of this thesis, a new approach for synthetizing heterotelechelic polydimethylsiloxane (PDMS) through the anionic ring opening of hexamethylcylclotrisiloxane, initiated with a bifunctional H-(SiOMe2)4-OH oligomer is discussed. Careful control of the reaction conditions followed by termination with various silyl chlorides yields PDMS with both Si-H moieties and a wide range of chain ends (eg: alkyl chlorides, methacrylates and norbornenes) with high fidelities. Further end-functionalization by hydrosilylation with terminal olefins (alcohols, epoxides and esters) opens a diverse plethora of asymmetric PDMS materials for use in advanced silicone-based systems. The utility of end functional PDMS materials from living anionic polymerizations is presented in Chapter 4 and Appendix C. In particular, well-defined PDMS-based “block random” structures were developed by the controlled radiclal copolymerization of novel silicone-methacrylate monomers from bromine-terminated PDMS macroinitiators. The physical properties and phase behavior vary dramatically depending on the composition of the random methacrylate block ranging from disordered viscous liquids to glassy solids with well-ordered lamellar structures. This technique presents an exciting platform to prepare PDMS-based block copolymers with tunable segregations strengths for applications in silicone-organic blend-compatibilization. Finally, Appendix D and Appendix E are supplementary provided to describe state-of-the-art strategies to compatibilize silicone-based polymer blends and novel comb nanoparticle radiotracers derived from heterotelechelic poly(ethylene glycol) building blocks.