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You searched for +publisher:"Clemson University" +contributor:("Dr. Rhett Smith"). Showing records 1 – 3 of 3 total matches.

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Clemson University

1. Wickramasinghe, Anuradhi Nimesha Kumari. Structural Study of Multifunctional Block Co-polymers in Solutions and Thin Films.

Degree: MS, Chemistry, 2017, Clemson University

This work focuses on the association of a structured multifunctional co-polymer in solutions and thin films as studied using neutron techniques and atomic force microscopy. Tethering multiple blocks into structured architectures is a promising way to tailor block copolymers with well-defined properties. Polymer films are often cast from solutions. Therefore, understanding the association of complex polymers in solutions and the impact of the aggregates into thin films is crucial to design materials with well-defined properties. Ionically-decorated blocks facilitate transport of ions and response to electrical fields. However they also affect the polymer structure. This work is divided into two sections. The first one resolves aggregation of a symmetric van der Waals pentablock polymer in solutions. The second follows film structure as charged groups are introduced. Specifically, we probed the assembly of polymers having an A-B-C-B-A co-polymer architecture, where co-polymer C is polystyrene, B is hydrogenated poly (ethylene-r-propylene) and A is poly (t-butyl styrene). In solutions we studied non-ionic pentablock polymers and in thin films we studied ionic pentablock polymers. In the solution study, the solvent polarity was tuned by controlling the ratio of cyclohexane to propanol. We find that, in contrast to most block copolymers, this pentablock polymer associates into fractal aggregates in cyclohexane which become more self-similar with increasing temperature. Increasing solvent polarity, by addition of propanol, drives the collapse of pentablock chains which leads the formation of more spherical aggregates. The structured architecture of the pentablock polymer enhances entropy resulting in less well-defined shapes that are maintained over a broad temperature range. In thin films, we probed the ionic analog of the above co-polymer where C is a randomly sulfonated polystyrene with sulfonation fractions of 0, 26 and 52 mole %, as the sulfonation level and thermal annealing times are varied using atomic force microscopy, surface tension measurements and neutron reflectivity. Our results show that as cast films form layers with both hydrophobic blocks dominating the solid and air interfaces and the ionizable block segregates to the center. With annealing at 170°C, above Tg of styrene sulfonate, the films coarsen, with surface aggregation dominating the structure, though interfacial regions remain dominated by the hydrophobic segments. Advisors/Committee Members: Dr. Dvora Perahia, Committee Chair, Dr. Stephen Creager, Dr. Rhett Smith.

Subjects/Keywords: block copolymers

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Wickramasinghe, A. N. K. (2017). Structural Study of Multifunctional Block Co-polymers in Solutions and Thin Films. (Masters Thesis). Clemson University. Retrieved from https://tigerprints.clemson.edu/all_theses/2687

Chicago Manual of Style (16th Edition):

Wickramasinghe, Anuradhi Nimesha Kumari. “Structural Study of Multifunctional Block Co-polymers in Solutions and Thin Films.” 2017. Masters Thesis, Clemson University. Accessed November 28, 2020. https://tigerprints.clemson.edu/all_theses/2687.

MLA Handbook (7th Edition):

Wickramasinghe, Anuradhi Nimesha Kumari. “Structural Study of Multifunctional Block Co-polymers in Solutions and Thin Films.” 2017. Web. 28 Nov 2020.

Vancouver:

Wickramasinghe ANK. Structural Study of Multifunctional Block Co-polymers in Solutions and Thin Films. [Internet] [Masters thesis]. Clemson University; 2017. [cited 2020 Nov 28]. Available from: https://tigerprints.clemson.edu/all_theses/2687.

Council of Science Editors:

Wickramasinghe ANK. Structural Study of Multifunctional Block Co-polymers in Solutions and Thin Films. [Masters Thesis]. Clemson University; 2017. Available from: https://tigerprints.clemson.edu/all_theses/2687

2. Amoah, Emmanuel. Conjugate Addition of Grignard Reagents to Dienones and Thioldienoates, and Copper-Mediated Allylic Substitutions.

Degree: PhD, Chemistry, 2017, Clemson University

Alkyl Grignard reagents (Et, nBu, iPr, cyclohexyl), with the exception of tBuMgCl, undergo exclusive or exceptionally highly regioselective 1,4-addition reactions to acyclic ,–,-unsaturated ketones, while aryl and heteroaryl Grignard reagents give mixed results ranging from exclusive 1,4-addition (1-naphthyl, 2-N-methylpyrrolyl) to regioselective 1,2-addition (2-furyl, 2:1). All alkyl, aryl, and heteroaryl Grignard reagents examined gave exclusive 1,4-addition reactions with ,–,-unsaturated thiol esters, with the exception of tBuMgCl which gave an 80:20 mixture of 1,4-:1,6-addition products. The high chemo- and regioselectivity observed for these reactions is attributed to a radical or radical-like pathway for the alkyl Grignard reagents and possibly a carbanion pathway for aryl Grignard reagents. The ,-dienyl thiol esters provide for a one-pot tandem 1,4-addition-nucleophilic acyl substitution reaction sequence to afford 3-substituted 4-enone moieties. Allylic opening of functionalized vinyloxiranes has been investigated with Grignard reagents and both catalytic and stoichiometric amounts of copper (I) salts. Specifically, α,β-epoxy-γ,δ-enones were found to undergo allylic opening of the epoxide ring in the presence of either CuCN or CuBr·SMe2 in THF or CH2Cl2 from -55 °C to -78 °C to give δ-substituted-β,γ-unsaturated-α-hydroxyketones in 3 hours. While reactions were conducted with stoichiometric amounts of CuCN, sub-stoichiometric (20 mol%) and catalytic ( 5-10 mol%) amounts of CuBr·SMe2 could be used to effect clean transfer of alkyl Grignard reagents to the substrates. Interestingly, it required two equivalents of the allyl and aryl Grignard reagents with stoichiometric CuBr·SMe2 to effect complete transfer in 3 hours. The CuCN-mediated reaction gave at best 70:30 mixture of the E/Z stereoisomers of the δ-substituted-β,γ-unsaturated-α-hydroxyketones. However, with the use of CuBr·SMe2 only the E-isomer was observed. A tentative model was proposed to rationalize the marked differences in the stereoselection associated with these copper salts. Allowing the reaction to warm to room temperature resulted in the oxidation of the α-hydroxy alcohol to the corresponding δ-substituted-β,γ-unsaturated dione. In the absence of any copper salts, 1,2-addition product arising from nucleophilic attack on the carbonyl carbon was obtained. Alkylmagnesium cuprates and zincates reacted with ethyl 6-bromo-α, β, γ, δ-dienoates to give exclusively the SN2 product while their lithium versions gave mixed results favoring the SN2′ product. When the substrate was changed to ethyl 6-chloro-α, β, γ, δ-dienoates, cuprates and zincates of lithium gave only the SN2′ products while their magnesium versions gave mixed results favoring the SN2′ product. These results suggest that both the leaving group ability of the halide, and the magnesium vs lithium as counter ion in the cuprate or the zincate influenced the regioselectivity of the ethyl… Advisors/Committee Members: Dr. R. Karl Dieter, Advisor and Department Chair, Dr. Daniel C. Whitehead, Dr. William Pennington, Dr. Rhett Smith.

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Amoah, E. (2017). Conjugate Addition of Grignard Reagents to Dienones and Thioldienoates, and Copper-Mediated Allylic Substitutions. (Doctoral Dissertation). Clemson University. Retrieved from https://tigerprints.clemson.edu/all_dissertations/1873

Chicago Manual of Style (16th Edition):

Amoah, Emmanuel. “Conjugate Addition of Grignard Reagents to Dienones and Thioldienoates, and Copper-Mediated Allylic Substitutions.” 2017. Doctoral Dissertation, Clemson University. Accessed November 28, 2020. https://tigerprints.clemson.edu/all_dissertations/1873.

MLA Handbook (7th Edition):

Amoah, Emmanuel. “Conjugate Addition of Grignard Reagents to Dienones and Thioldienoates, and Copper-Mediated Allylic Substitutions.” 2017. Web. 28 Nov 2020.

Vancouver:

Amoah E. Conjugate Addition of Grignard Reagents to Dienones and Thioldienoates, and Copper-Mediated Allylic Substitutions. [Internet] [Doctoral dissertation]. Clemson University; 2017. [cited 2020 Nov 28]. Available from: https://tigerprints.clemson.edu/all_dissertations/1873.

Council of Science Editors:

Amoah E. Conjugate Addition of Grignard Reagents to Dienones and Thioldienoates, and Copper-Mediated Allylic Substitutions. [Doctoral Dissertation]. Clemson University; 2017. Available from: https://tigerprints.clemson.edu/all_dissertations/1873

3. Cain, Lindsey Whitfield. Understanding How Synthetic Organic Chemistry Graduate Students Navigate Scifinder.

Degree: PhD, Chemistry, 2015, Clemson University

Students pursuing a Ph.D. degree are expected to contribute research to their field, for which the success depends, in part, on their ability to find, interpret, and use scholarly information from the primary literature. However, studies from the information sciences show that graduate students from a variety of fields, including the sciences, frequently struggle to comprehensively search their respective dissertation topics because of insufficient prior content knowledge and lack of guidance from their disciplinary community. This body of literature is consistent with the results of my previous research of chemistry graduate students’ laboratory decision-making processes. Specifically, that study showed their search and evaluation of the scientific literature to find a research protocol was critical to the success or failure of the students’ research. For these reasons, I chose to investigate how synthetic organic chemistry graduate students perform literature searches, using SciFinder, to find protocols for preparing previously unreported compounds. For my study, I used situated cognition and communities of practice (CoP) as my theoretical frameworks in conjunction with an ethnomethodological research design. Five organic chemistry graduate students were interviewed to understand their strategies and sense-making procedures for searching the literature, specifically focusing on how they decide to: 1). input a topic or structural representation, 2). evaluate the search results, and 3). use specific procedures for deciding which of the protocols to carry out in the laboratory. The findings from my study indicated that the graduate students’ information-seeking behaviors and sense-making procedures were directly influenced by their domain-specific content knowledge and their exposure to the organic CoP. Specifically, the second-year and third-year graduate students heavily depended on the database because their domain-specific content knowledge was not operational at this stage in their training. Comparatively, the sixth-year graduate students could easily use their organic chemistry knowledge—i.e. named organic reactions, functional group chemistry, and the retrosynthetic approach—to propose a research protocol; therefore, they used the database to substantiate their synthesis protocols and/or to find a method to synthesis the proposed starting materials. As a result of their exposure to their Ph.D. research, the graduates had become more proficient with using the database and developed heuristics to evaluate their searches, thereby allowing them to quickly evaluate the often times substantial amount of hits. Finally, the findings indicated that the graduate students were utilizing their CoP in different ways. For instance, the second-year and third-year graduate students would seek their advisor’s approval, whereas the sixth-year graduate students would seek their peers’ feedback regarding their protocols. Findings from my study can broadly be integrated into the information science field to… Advisors/Committee Members: Dr. Gautam Bhattacharyya, Committee Co-Chair, Dr. Gautam Bhattacharyya, Committee Co-Chair, Dr. Julie Martin, Dr. Rhett Smith, Dr. Michelle Cook.

Subjects/Keywords: Chemistry

…program at Clemson University and soon began my research endeavors under the guidance of Dr… 

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Cain, L. W. (2015). Understanding How Synthetic Organic Chemistry Graduate Students Navigate Scifinder. (Doctoral Dissertation). Clemson University. Retrieved from https://tigerprints.clemson.edu/all_dissertations/1679

Chicago Manual of Style (16th Edition):

Cain, Lindsey Whitfield. “Understanding How Synthetic Organic Chemistry Graduate Students Navigate Scifinder.” 2015. Doctoral Dissertation, Clemson University. Accessed November 28, 2020. https://tigerprints.clemson.edu/all_dissertations/1679.

MLA Handbook (7th Edition):

Cain, Lindsey Whitfield. “Understanding How Synthetic Organic Chemistry Graduate Students Navigate Scifinder.” 2015. Web. 28 Nov 2020.

Vancouver:

Cain LW. Understanding How Synthetic Organic Chemistry Graduate Students Navigate Scifinder. [Internet] [Doctoral dissertation]. Clemson University; 2015. [cited 2020 Nov 28]. Available from: https://tigerprints.clemson.edu/all_dissertations/1679.

Council of Science Editors:

Cain LW. Understanding How Synthetic Organic Chemistry Graduate Students Navigate Scifinder. [Doctoral Dissertation]. Clemson University; 2015. Available from: https://tigerprints.clemson.edu/all_dissertations/1679

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