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Browsing by Subject "polymerization"

Now showing 1 - 3 of 3
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    Data for Combining photocontrolled-cationic and anionic-group transfer polymerizations using a universal mediator: enabling access to two- and three-Mechanism block copolymers
    (2024-08-15) Hosford, Brandon M; Ramos, William; Lamb, Jessica R; jrlamb@umn.edu; Lamb, Jessica R; Lamb Research Group
    An ongoing challenge in polymer chemistry is accessing diverse block copolymers from multiple polymerization mechanisms and monomer classes. One strategy to accomplish this goal without intermediate compatibilization steps is the use of universal mediators. Thiocarbonyl thio (TCT) functional groups are well-known mediators to combine radical with either cationic or anionic polymerization, but a sequential cationic-anionic universal mediator system has never been reported. Herein, we report a TCT universal mediator that can sequentially perform photocontrolled cationic polymerization and thioacyl anionic group transfer polymerization to access poly(ethyl vinyl ether)-block-poly(thiirane) polymers for the first time. Thermal analyses of these block copolymers provide evidence of microphase separation. The success of this system, along with the established compatibility of radical polymerization, enabled us to further chain extend the cationic-anionic diblock using radical polymerization of N-isopropylacrylamide. The resulting terpolymer represents the first example of a triblock made from three different monomer classes incorporated via three different mechanisms without any end-group modification steps. The development of this simple, sequential synthesis using a universal mediator approach opens up new possibilities by providing facile access to diverse block copolymers of vinyl ethers, thiiranes, and acrylamides.
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    Nanoporous and Functionalized Polymer Thermosets by Polymerization-Induced Microphase Separation in Bulk, Dilution, and Suspension
    (2021-10) Peterson, Colin
    The microphase separation of diblock polymers allows for excellent control over the nanostructuring of polymer-based materials. Polymers are also readily functionalized and chemically manipulated to alter their chemical properties. Therefore, block polymers represent an important tool in the preparation of precision nanostructured functional materials. Polymerization-induced microphase separation (PIMS) is a convenient and powerful strategy towards the development of such materials. In PIMS, the diblock polymer is simultaneously grown while one block is crosslinked. This captures a non-equilibrium percolating morphology. In this thesis, the morphology is used as a host for photochromic dyes, diluted with solvent to increase the possible porosity, and prepared in suspension to give uniform mesoporous beads.Chapter 1 is a brief overview of key topics relevant to the entire thesis. Chapter 2 describes the incorporation of photochromic dye molecules into a variety of materials from liquid solvent to rigid polymer. PIMS thermosets were created using a liquid-like polycaprolactone derivative and crosslinked polymethylmethacrylate. The liquid-like domains provide an environment for the dye where fast structural relaxation allows for fast dye decoloration while being encased in a rigid matrix. Chapter 3 shifts focus to porous PIMS derivatives. In particular, the effect on the pore size distribution of diluting the monomer solution with solvent to create an organogel is explored. Chapter 4 presents a new synthetic method to prepare beads from PIMS thermosets by performing the chain-growth and cross-linking steps in aqueous suspension. The size of the particles is tuned independently from the size of the pores. Also, functionality is incorporated into the pore walls using a diblock precursor. Chapter 5 provides general conclusions and possible future directions for research relating to disordered diblock thermoset materials.
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    Understanding Organic Reaction Mechanisms Through Applications of Density-Functional Theory
    (2016-08) Marell, Daniel
    The application of computational chemistry has a wide scope of utility. From large systems such as proteins or metal-organic frameworks down to the understanding of individual bonding patterns between atoms, there are endless opportunities to explore. Further utility is gained when the insights and resources of computational chemists can be applied to systems under investigation by experimental chemists The combined information of computational details with experimental findings can lead to new understanding of the systems being investigated. The ring-opening transesterification polymerization of caprolactone with an aluminum- salen catalyst is a useful reaction for the conversion of caprolactone to polyester. Mechanistic understanding of this reaction was gained through the interrogation of this process with density functional theory. Further, the origins for rate-enhancement through modification of electron-withdrawing groups was explained through the analysis of partial atomic charges. A rate enhancement observed by altering the backbone of the catalyst was also explained through the development of a distortion framework analysis. Rieske oxygenase are a class of protein that executes a variety of chemical reactions such as oxygenations, O- and N-demethylations, oxidations, and C–C bond formations en route to the formation of medically relevant natural products. The continued elucidation of the mechanism, including the characterization of reactive species was persued. Computational work to understand the impact partial atomic charge on the aromatic system (by inclusion of fluorine substituents) had on the rate constant demonstrated a clear correlation between the partial atomic charge on the C(2) position and the rate constant for a variety of substrates. A new reaction, the hexadehydro-Diels–Alder (HDDA) reaction takes a diyne and a diynophile to create a reactive benzyne intermediate. A series of six intramolecular HDDA substrates were found to undergo this transformation at relatively similar rates. Analysis of transition state geometries, investigation of both closed-shell and diradical mechanistic pathways, as well as insight from high-level calculations provide information about the nature of this intramolecular reaction. Extension of the mechanism led to predictive capability in good agreement with a new set of substrates as well.