The Use of Light-Mediated Hydrogen Atom Transfer to Modify Poly(styrene), Poly(methylmethacrylate), and Squalane
Open Access
- Author:
- Knappenberger, Daniel
- Graduate Program:
- Chemistry
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- August 08, 2023
- Committee Members:
- Elizabeth A Elacqua, Thesis Advisor/Co-Advisor
Benjamin James Lear, Committee Member
Philip Bevilacqua, Program Head/Chair
Robert John Hickey, III, Thesis Advisor/Co-Advisor
Eric Nacsa, Committee Member - Keywords:
- Hydrogen atom transfer
polymer degradation
polymer oxidation
polymer functionalization
polystyrene
polymethylmethacrylate
squalane
polypropylene
tetrabutylammonium decatungstate
ferric chloride
FeCl3
TBADT - Abstract:
- Polyolefins are an important and ubiquitous class of commodity polymers in modern society. They possess remarkable stability and chemical resistance, making them highly desirable materials. These materials are often used as single-use plastics despite their biodegradability. Methods of recycling, such as mechanical recycling, post-polymerization modification (PPM), and depolymerization, can incentivize plastic waste collection by upcycling or adding value to the waste material. However, the lack of reactivity of polyolefins requires harsh conditions for PPM or depolymerization. Recent advances in C–H functionalization of both small molecules and polymers have allowed access to highly reactive intermediates under mild conditions, such as C-centered radicals at room temperature without the use of peroxides and heat. Unfortunately, functionalization above just a few mol% is accompanied by degradation of the polymer chain due to the highly reactive intermediates present. Therefore, new methods of PPM must be developed so that functionalization is preferred over polymer degradation. Alternatively, the degradation observed during PPM could be used to encourage polymer deconstruction. In this thesis, three photocatalysts are investigated as potential catalysts to degrade polyolefins. The catalysts were chosen because of their reported ability to enable hydrogen atom transfer (HAT). Benzophenone (BP), tetrabutylammonium decatungstate (TBADT), and FeCl3 are investigated with specific attention to squalane as a small molecule analog of poly(propylene) (PP). Spectroscopic analysis — 1H NMR spectroscopy, 13C APT NMR spectroscopy, IR spectroscopy, and APCI mass spectrometry — supports addition of BP to squalane to form an α-alkylbenzhydrol, while TBADT and FeCl3 facilitated oxidation of squalane to alcohols and ketones. The results with BP support its tendency to form unintended C–C bonds with reactive intermediates, while the results with TBADT and FeCl3 are consistent with their use as oxidation catalysts for hydrocarbons (i.e., cyclohexane). These results may be used to show that BP could be attached to PP and that TBADT and FeCl3 may be used to oxidize PP.