UC Irvine

This thesis presents two projects focused on the use of polymers to fabricate next-generation sustainable materials and direct the assembly of nanoparticles into ordered architectures. Chapter 1 introduces a brief history of polymer plastic materials, current methods of creating sustainable materials as poly(olefin) replacements, and introduces poly(silyl ether) as a chemically recyclable alternative to traditional poly(olefin) plastics. This chapter also introduces amphiphilic block copolymers as building blocks in the directed assemblies of nanoparticles.Petroleum-derived poly(olefin) plastics produce millions of tons of waste every year, with most waste accumulating in landfills and the natural environment at their end of life. This linear polymer economy encourages and demands new plastic materials to constantly be made to replace those that have been landfilled, ultimately leading to more plastic waste accumulation. Chapter 2 of this thesis presents the synthesis of linear poly(silyl ether) through step-growth and ring-opening metathesis polymerization methods to yield a chemically recyclable material similar to poly(ethylene). A variety of silane monomers and aliphatic diols of varying lengths were synthesized and polymerized, with ring-opening metathesis polymerization yielding polymers with the highest molecular weights.Chapter 3 motivates a different use of organic polymers in materials: the use of amphiphilic block copolymers to direct the assembly of nanoparticles. Nanoparticle organization is a major goal of bottom-up assembly, as these materials can offer emergent properties useful in applications such as sensing and electronics. We report the assembly of CdSe/CdS core/shell quantum dots into highly ordered spherical lattice structures with tunable inter-quantum dot spacing using solvent-induced assembly of poly(styrene)-block-poly(acrylic acid). We prove a spontaneous ligand exchange mechanism between quantum dot ligands and poly(acrylic acid) to result in the precise interparticle spacing observed through electron microscopy and 3D cryo-tomography reconstruction. Small-angle X-ray scattering proves spontaneous ligand exchange occurs over a range of polymer molecular weights, affording tunable interparticle spacings through polymer molecular weight.Finally, Chapter 4 presents the polymer-directed assembly of metallic gold nanoparticles. Using the same poly(styrene)-block-poly(acrylic acid) and solvent-induced self-assembly conditions as in Chapter 3, gold nanoparticles were observed to assemble into hollow, spherical architectures within the polymer colloid. This is hypothesized to be caused by pi-pi interactions between the poly(styrene) ligand on the surface of the gold nanoparticles and the poly(styrene) block of the copolymer forming pseudo-amphiphilic ligands on the gold nanoparticle surface. Transmission electron microscopy and electron tomography indicate a high level of organization in this architecture. Small-angle X-ray scattering proves a precise interparticle spacing between gold nanoparticles that increases with polymer ligand size.This thesis summarizes advancements towards sustainable polymer materials as well as generalizable methods for polymer-directed nanoparticle organization. Step-growth and ring-opening metathesis polymerization methods between different silane and aliphatic co-monomers afforded linear poly(silyl ether), which offers promise towards a circular polymer economy as a chemically recyclable alternative to non-degradable poly(ethylene). Using non-specific chemical interactions between nanoparticle ligands and organic, amphiphilic block copolymers, high levels of nanoparticle organization with tunable interparticle spacing was achieved across multiple types of nanoparticles. This method offers promise as a generalizable, “bottom-up” method to achieving nanoparticle organization.