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School of Chemistry and Biochemistry
School of Chemistry and Biochemistry
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ItemThiocarbonyl Platform for Degradable Radical Polymers(Georgia Institute of Technology, 2022-07-25) Smith, Ronald AubreyThis thesis focuses on the development of a new thionolactone monomer class for radical ring-opening polymerizations (rROP). Typical monomers used in rROP have been marred with inactivity towards more activated vinyl monomers such as acrylates, acrylamides, and styrene. The thiocarbonyl platform discussed in this thesis uses the radicophilic nature of the thiocarbonyl to overcome these reactivity disparities. Project 1 focuses on the development of a first-generation thionolactone monomer which shows compatibility with more activated monomers (acrylates and acrylamides). Project 2 delves into a second-generation monomer which is also compatible with styrene in addition to acrylates and acrylamides. Project 2 further discusses applications for the blocky incorporation of this monomer in the form of degradable junctions. Project 3 focuses on derivatives of the second-generation monomer to tune rates of incorporation allowing for detailed block or gradient polymer microstructures. Project 4 explores thiophene derivatives of the first-generation monomer which facilitate homopolymerization and autopolymerization of these monomers.
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ItemHomopolymer and block polymer materials derived from highly reactive thionolactone monomers(Georgia Institute of Technology, 2022-05-03) Tennyson, Simone LenaThionolactones are a recently discovered sub-class of radical ring-opening monomers that are notable for their ability to impart labile thioester units into polymer backbones when used as a comonomer. The simple scaffold allows for structural changes to further tune the monomer’s reactivity in order to change rates of copolymerization with different monomer families and can even lead to systems capable of homopolymerization. Thionolactones also demonstrate high degrees of control with reversible addition-fragmentation chain-transfer (RAFT) polymerizations, and rapid reactivity with acrylates. In this thesis, the introduction of the furan heterocycle into a 7-membered thionolactone monomer scaffold is described, and the resulting homopolymerization behavior is studied (Chapter 2). Additionally, a thermally responsive amphiphilic diblock polymer of N,N-dimethylacrylamide and N-isopropylacrylamide with a cleavable thioester junction is prepared using a new 6-membered thionolactone derivative with ultra-fast copolymerization behavior (Chapter 3).
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ItemMild modification of cellulose nanocrystals to compatibilize the polymer and CNC interface(Georgia Institute of Technology, 2022-05-03) Bullard, Krista K.The use of cellulose nanocrystals (CNCs) in material science as nontoxic, inexpensive, and biorenewable reinforcing agents is a rapidly growing field. These rigid, needle-shaped nanomaterials have promising mechanical properties that can improve polymer composites if properly dispersed.1-3 Due to the hydrophilic nature of the CNC surface chemistry, they are prone to agglomeration through intermolecular hydrogen bonding, therefore preventing the even dispersion needed for reinforcement in commonplace hydrophobic polymeric matrices. The long-term goal of this project is to modify the CNC surface chemistry with the addition of cyclodextrin to impart supramolecular interactions which will physically bind polymers to the surface without forming a chemical bond. Cyclodextrins are inexpensive, cyclic oligomers of amylose that take on the shape of a conical cylinder and readily form host-guest complexes with small molecules and thread along the backbone of polymers.4-7 The first step of the project was to efficiently attach cyclodextrin motifs to the surface the CNCs which required the invention a new synthetic modification route. Then a cleavable linker system was devised and synthesized for attachment of cyclodextrins to the CNC surface that allowed for subsequent removal with an external stimulus. Finally, polymers were threaded on the particles, and the cleavable linker system was used to study the rotaxanes that were cleaved from the CNC.
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ItemSynthesis, reactivity and polymerization of bridged bicyclic twisted amides(Georgia Institute of Technology, 2021-12-08) Xu, MizhiAmides are generally robust and hydrolytically resistant due to the nN-to-π*C=O conjugation. Twisted amides represent an unusual subclass of amides containing distorted, non-planar amide bonds as a consequence of geometric, steric or electronic effects. The most common approach to twisting the amide bond involves geometric constraint in the bridged bicyclic amide structure. Due to the disrupted amide resonance, twisted amides feature distinct reactivities compared to normal amides, including enhanced N-nucleophilicity, carbonyl-electrophilicity and “amino-ketone” reactivity. Despite the unusual structure and unique reactivity of twisted amides, their potential as monomers in polymerization has rarely been explored. In this dissertation, the polymerization of a [3.3.1] bicyclic twisted amide system is described through the halide-rebound (Chapter 2) and ring-opening metathesis strategies (Chapter 4). In addition, the remote substituent effects on modulating the geometry and reactivity of this twisted amide framework are investigated via computational and kinetic studies (Chapter 3). Finally, a new halide-abstraction strategy is disclosed in the synthesis of a highly strained [3.2.1] bicyclic twisted amide (Chapter 5).
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ItemThe design and application of functional enyne reagents in metathesis polymerization(Georgia Institute of Technology, 2021-04-19) Zhang, TianqiRing-opening metathesis polymerization (ROMP) using Grubbs-type initiators has become a widespread polymerization technique due to its remarkable functional group tolerance and reliability. This has enabled the synthesis of well-defined materials with applications. However, efficient methods for chain-end modification of ROMP and recycling metal initiators remain significant challenges. The research reported in this thesis explored the design and application of functional enyne reagents to overcome these challenges in ROMP. The key to all of these methods is a terminal alkyne that rapidly reacts with the ruthenium alkylidene and serves as a directing group to promote otherwise inefficient transfer reactions intramolecularly. Using this general relay strategy, different enyne molecules can be designed to give direct polymer-polymer coupling or to generate functional initiators, enabling the functionalization of both ends of the metathesis-derived polymer chain. The enyne derivatives are also capable of recycling the ruthenium catalyst in pulsed-addition ring-opening metathesis polymerization (PA-ROMP) to produce multiple functional chains from single ruthenium initiator with low dispersities. In addition, the terminating type enyne derivatives can be designed as a branching agent, which can be used to synthesize well defined branched ROMP polymers in a convergent synthetic pathway. Overall, the utilities of ROMP for macromolecular construction are widely expanded through these functional enyne reagents and could find broad applications in the design of functional materials.
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ItemSynthesis of Degradable Monomers for Ring-Opening Metathesis Polymerization(Georgia Institute of Technology, 2020-05) Crolais, Alex E.Ring opening metathesis polymerization (ROMP) is a type of olefin metathesis chain-growth polymerization that has shown great versatility in the field of polymer chemistry. Although it allows polymerization of monomers containing a variety of functional groups, how effective it is in polymerizing degradable monomers is largely unknown. In this report, we demonstrate a novel synthetic pathway to synthesize an acetal-containing degradable monomer that is compatible with ROMP and the Grubbs 3 (G3) catalyst. Polymers made from this monomer were characterized by GPC analysis and underwent degradation studies. Acetals generally undergo hydrolysis in mildly acid conditions and even in biologically relevant pH ranges, so this new monomer will have potential applications in drug delivery systems. The monomer also has the capacity to have its functional groups modified, changing its functionality which will be further studied.