Efficient upcycling of low-functionality polymers using trifluoromethyl aryl diazirine chemistry
| dc.contributor.author | Bi, Liting | |
| dc.contributor.supervisor | Wulff, Jeremy Earle | |
| dc.date.accessioned | 2023-08-14T21:46:37Z | |
| dc.date.available | 2023-08-14T21:46:37Z | |
| dc.date.copyright | 2023 | en_US |
| dc.date.issued | 2023-08-14 | |
| dc.degree.department | Department of Chemistry | en_US |
| dc.degree.level | Doctor of Philosophy Ph.D. | en_US |
| dc.description.abstract | Crosslinking technologies are widely employed in our daily life: from silicone bakeware to epoxy adhesives and rubber tires. Traditionally, however, each type of commodity polymer substrate requires the use of a specific crosslinking method. Many desirable polymers—especially low-functionality polyolefins—cannot be crosslinked using these existing methods. To address this limitation, our group developed a family of bis-aryl-diazirine reagents that function through C−H, O–H or N–H insertions, and that can thereby act as universal crosslinkers for aliphatic polymers. Despite their increasing popularity as crosslinkers in a variety of fields (e.g. photopatterning, bioadhesives), little attention has been given to the synthesis of highly efficient reagents with reduced or eliminated side-products. In Chapter 2, structure–function relationships of mono-aryl-diazirines were studied, highlighting the fundamental role played by electronic properties in the thermal and photo-activation of the molecules, as well as their insertion efficiency. Building upon this study, Chapter 3 introduces a new generation of ether-linked trifluoromethyl bis-diazirine crosslinker, which is more than 10 times as effective as previous generations. The new reagent can also be activated using lower temperatures and longer wavelengths than earlier bis-diazirines—permitting the use of visible light for photopatterning. The efficacy of the electron-rich tether has been demonstrated at both the molecular and polymer level, showcasing the ability of the new linker to covalently adhere to low-surface energy materials and strengthen ultra-high molecular weight polyethylene fabrics. The covalent inter-chain crosslinks in thermoset materials make them difficult to reprocess and recycle. To address this issue, Chapter 4 introduces chemically cleavable groups (e.g. carbonates, oxalates, silyl ethers) into the bis-diazirine crosslinker, allowing for further reprocessing of commodity polymers after the initial crosslinking step. This new class of crosslinkers exhibits rapid reactions during both the crosslinking and decrosslinking steps across a wide range of substrates, including small-molecule models and low-functionality polymers (e.g. LDPE, aPP/LDPE, PEG, PDMS). By employing specific chemical uncoupling methods, these materials can be efficiently converted from thermoset to thermoplastic, presenting a new strategy for circularization of the polymer economy. Chapter 5 describes the synthesis of mono-aryl-diazirine reagents along with their successful use for the non-destructive surface modification of polydimethylsiloxane (PDMS) substrates by both thermal and ultraviolet activation. Bovine serum albumin (BSA) and immunoglobulin G (IgG) are immobilized as a model protein and antibody, respectively, and sensitive quantification of their amounts along with their stability on the surface is achieved by radiolabeling with iodine-125. Through both thermal and ultraviolet activation, two types of trifluoromethyl aryl diazirine reagents with electrophilic motifs were able to enhance the amount and stability of BSA and IgG immobilization on the surface. These techniques show great promise for multi-material modifications, patterning of biomolecules on surfaces and various other important biological and medical device applications. Author’s Note: In the context of this thesis, the term "low-functionality polymers" refers to materials like polyethylene and polypropylene that lack conventional organic functional groups such as alcohols, alkenes, aromatic rings, or halogens. Materials lacking these groups are intrinsically more challenging to crosslink, because one cannot make use of traditional organic reactions (e.g. alkylation, acylation, hydrosilylation, thiol-ene reactions, etc.) to form new covalent bonds. | en_US |
| dc.description.scholarlevel | Graduate | en_US |
| dc.identifier.uri | http://hdl.handle.net/1828/15258 | |
| dc.language | English | eng |
| dc.language.iso | en | en_US |
| dc.rights | Available to the World Wide Web | en_US |
| dc.title | Efficient upcycling of low-functionality polymers using trifluoromethyl aryl diazirine chemistry | en_US |
| dc.type | Thesis | en_US |