Graduation Term

Summer 2026

Degree Name

Master of Science (MS)

Department

Department of Chemistry

Committee Chair

Susil Baral

Committee Member

Jun-Hyun Kim

Committee Member

Puja Goyal

Abstract

Synthetic polymers are essential materials in modern society, finding use in plastics, rubbers, adhesives, coatings, biomimetic systems, and medical devices. Among the various classes of synthetic polymers, this research focuses on linear and molecular brush polymers. Linear polymers represent the simplest architecture, whereas molecular brush polymers consist of a densely grafted backbone with polymer side chains. The physical, mechanical, and polymerization behavior of these polymers depend upon the architecture. In this study, molecular brush polymers synthesized from norbornene-based macromonomers via ring-opening metathesis polymerization (ROMP) are investigated with respect to their polymer architecture, polymerization behavior, and single-chain mechanical properties. Ensemble polymerization provides insights into polymerization kinetics, but this study cannot probe the heterogeneous properties of individual polymer chains. Magnetic tweezers (MT) force microscopy overcomes this limitation and is used to manipulate single synthetic polymers. In this approach, surface-grafted synthetic polymers are grown by ROMP with one end attached to the glass surface and the other end tethered to a magnetic particle. Forces in the piconewton (pN) range are sufficient to stretch flexible polymers without breaking covalent bonds. By varying the applied force and measuring the resulting extension, force–extension curves are obtained. Force-extension measurements are used to extract single-chain mechanics and rigidity from polymer models.

During this research, Norbornene (NB)-based macromonomers, poly(ethylene oxide) (PEO), poly(lactide) (PLA), and polystyrene (PS) were synthesized and characterized by 1H NMR spectroscopy. This work investigated the synthesis, polymerization kinetics, and single-chain mechanical properties of norbornene-based molecular brush polymers. The ROMP of norbornene-based PEO and PLA macromonomers using the second-generation Grubbs catalyst (G2) was studied to demonstrate its activity. The monomer olefin peak at 6.20 ppm completely disappeared, indicating that the norbornene macromonomer was consumed. Ensemble polymerization kinetic analysis of NB and NB-PEO was performed to characterize their polymerization behavior. The kinetic study shows that the linear norbornene monomer polymerized faster than the NB-PEO macromonomer

For a single-molecule study of NB-PEO, a magnetic tweezers experiment was established by preparing NB silane-functionalized glass coverslips and G2-functionalized magnetic particles, and by fabricating flow cells to grow surface-grafted molecular-brush polymers. The force-extension curve obtained from this study is used to determine the elasticity and mechanical properties of individual polymer chains. To conclude this thesis, this work studies the ensemble polymerization kinetics and the single-chain mechanical behavior of norbornene-based molecular brush polymers.

Access Type

Thesis-Open Access

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Available for download on Monday, April 12, 2027

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