Date of Submission

5-2026

Document Type

Dissertation

Degree Name

Doctor of Philosophy Engineering and Applied Science, Ph.D.

Department

Engineering and Applied Science Education

Advisor

Hao Sun, Ph.D.

Committee Member

Pier Cirillo, Ph.D.

Committee Member

Chong Qui, Ph.D.

Committee Member

Alireza Senejani, Ph.D.

LC Subject Headings

Ring-opening metathesis polymerization, Petroleum waste—Recycling, Biodegradable plastics, Monomers, Biomedical materials, Plastic scrap--Biodegradation

Abstract

Polymers have become indispensable materials in modern society. The majority of these materials are synthetic, petroleum-based polymers. Their lightweight nature, durability, and low cost have led to a global production of approximately 400.3 million tons annually by 2022. Due to their exceptional durability, these polymers can persist in the environment for hundreds of years, if not longer. Despite the high production volume, polymer recycling remains extremely limited, with over 90% of waste being landfilled or incinerated. This challenge has directed researchers’ interest toward sustainable, degradable polymers derived from renewable feedstocks. Ringopening metathesis polymerization is marked as a powerful method for synthesizing functional polymers; however, polymers synthesized via conventional ROMP lack degradability due to their all-carbon backbones. Recent advances have addressed this limitation by integrating degradable moieties into polymer backbones through alternating copolymerization strategies. My research developed diverse classes of acid-degradable and functionalizable polymers synthesized via alternating ROMP of oxanorbornene- and oxanorbornadiene-based monomers with cyclic enol ethers, including 2,3-dihydrofuran, 3,4-dihydropyran, and cyclic acetal 4,7- dihydro-1,3-dioxepin. The resulting poly(enol ether)s and polyacetals exhibit tunable glass transition temperatures ranging from 11.2 to165 °C, controlled molecular weights, and robust aciddegradability. In addition, post-polymerization modification via aza-Michael and thia-Michael additions enables the introduction of diverse functional groups, allowing for polymers with tunable properties for targeted applications. This versatile approach establishes a synthetic platform for designing sustainable, degradable, and functionalizable polymers with significant potential in addressing plastic waste management and developing biomedical materials. Chemical recycling to monomers, on the other hand, offers a sustainable and environmentally friendly approach to polymer recycling, in which post-consumer polymer waste is depolymerized back into its original monomers, achieving a closed-loop recycling system. However, the scope of monomers suitable for ROMP synthesis of depolymerizable polymers remains limited due to the narrow range of ring strain energies (RSEs = 4.7–5.4 kcal mol-1) required to achieve both polymerization and depolymerization in closed-loop recycling processes. To address these limitations, my work demonstrates the chemical recyclability of polyheptenamers to cycloheptene under standard RCMD conditions. In addition, we present a new class of chemically recyclable polyolefins based on cycloheptene derivatives with RSEs ranging from 3.8 to 7.2 kcal mol-1. This broad RSE range enabled highly efficient depolymerization of polyheptenamers and facilitated the establishment of a structure–polymerizability– depolymerizability relationship, providing insights into the role of RSE in both polymerization and depolymerization. To further enhance and achieve highly efficient closed-loop circular economy system, we developed a functional group transformation strategy based on reversible ketone-to-acetal chemistry. This approach overcomes the low polymerizability of low-strain monomers and the moderate depolymerizability of polymers derived from moderate-strain monomers. The resulting polymers exhibit decomposition temperatures ranging from 226°C to 432.3°C, indicating high thermal stability, and glass transition temperatures ranging from -7°C to 104°C, highlighting their potential applications in plastics and elastomers. Relying on monomers with low ceiling temperatures and small enthalpic driving forces for depolymerization often compromises polymerization efficiency. In light of that we develop a depolymerizable polymer system based on strained bicyclo[3.2.1] monomers that combines a substantial enthalpic driving force with a significant entropic penalty. The large entropic penalty associated with polymerization lowers the ceiling temperature and imparts depolymerizability to the polymer system, while the enthalpic driving force remains sufficient to enable efficient ringopening metathesis polymerization and block copolymer synthesis under dilute conditions. This entropy-driven strategy overcomes the traditional trade-off between polymerization and depolymerization, allowing both processes to proceed efficiently and establishing a new class of chemically recyclable polymers with enhanced sustainability.

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