Photochemical Sciences Ph.D. Dissertations

Reprocessable and Photoresponsive Silicones for Increased Longevity and Upcycling/Recycling abilities

Date of Award

2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Photochemical Sciences

First Advisor

Joseph Furgal (Committee Chair)

Second Advisor

Hong Lu (Committee Member)

Third Advisor

Alexis Ostrowski (Committee Member)

Fourth Advisor

Lee Nickoson (Other)

Abstract

In 2022, silicon materials had a worldwide market value of 19.94 billion dollars, and it is estimated to steadily increase by 6.1% by 20301. Interest in silicon-based materials has expanded over the years due to their ability to impart high thermal stability, chemical inertness, durability, biocompatibility, and hydrophobicity. Their unique chemical and physical properties are attributed to the Si-O bond strength and the vastly tunable functionalities within attached organic groups, which is a reason they are widely used in the fields of medicine, and high-performance technology applications. These materials, however, require large amounts of energy and release large amounts of CO2 to produce, but then are only very minimally recycled or reprocessed. Thus, it is beneficial and cost effective if silicon materials such as silicones/siloxanes were not simply discarded, but able to be recycled/upcycled or reused multiple times with low energy cycling. Previous work by our lab demonstrated a simply way of recycling siloxane polymers/elastomers by degrading them at room temperature with a F- catalyst. The products of the degradation were cyclic siloxanes (D4, D5, D6) that are commercially used as building blocks to make siloxane polymers. Chapter 1 will give a literature background and analysis to set the stage for recycling and developing reprocessable silicones. Chapter 2 will contain the detail the synthetic and characterization methods used related to the studies of the supramolecular siloxane polymers, and degraded silicones discussed within this work. Chapter 3 will entail mechanistic and solvent studies of the F-catalyzed depolymerization of silicones to cyclic siloxanes and how this information can be used to control the outcome of the reactions. Chapter 4 will focus on Zn2+ and Cr3+ linked reversible supramolecular silicones that are responsive to light and heat to give metal-ligand dynamic bonding systems (adhesives/elastomers) as an alternative method to reprocessing that does not depend on full depolymerization to increase longevity of materials like elastomers, thermosets, etc. Chapter 5 focuses on the use of other supramolecular systems with Cr3+ bound silicones to induce further photoresponsive control over healing and mechanical properties for further alternatives to silicone disposal. Chapter 6 will give a conclusion of the work and give perspective as to the future of the field.

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