Synthesis and Characterization of Graphene-Polymer Nanocomposites via Reversible Addition-Fragmentation Chain-Transfer Polymerization

Graphene has emerged as a subject of tremendous scientific interest due to its exceptional electrical, mechanical and thermal properties. When incorporated into a polymer matrix, graphene sheets can significantly improve the properties of the host polymer. However, the dispersion of pure graphene throughout a polymer matrix is not homogeneous, due to the strong van der Waals interactions between graphene sheets and the difference in surface compatabilities. To prevent agglomeration of these graphene sheets, surface functionalization is required. The goal of this thesis was to develop a facile approach for growing polymer chains from the surface of graphene sheets via reversible addition-fragmentation chain-transfer (RAFT) polymerization. Graphene oxide was synthesized by reacting graphite with potassium permanganate and concentrated sulfuric acid. The oxidation and exfoliation of graphite was investigated using FTIR, TEM, and AFM studies. For the methodology of growing polymers from graphene surfaces, polydopamine was coated on graphene oxide as a platform for subsequent “grafting from” RAFT polymerization. This was possible as polydopamine has available hydroxyl groups that can react with carboxylic groups of the RAFT agent via ester linkages. During the formation of polydopamine coating on graphene oxide, graphene oxide can be simultaneously reduced by the released electrons generated by self-polymerization of dopamine. The reduction of graphene oxide was determined by FTIR, UV/Vis, and XPS analysis. For growing the polymer chains from the graphene surface, the living radical polymerization methodology, RAFT polymerization, was investigated. The RAFT agent, S-dodecyl-S’-(α,α’-dimethyl-α’’-acetic acid)trithiocarbonate, having an available carboxyl group, was chosen to anchor onto the polydopamine coating and then grow chains of PS, PMMA, PNIPAM, and PtBA from this modified surface. The livingness of the polymerization was verified by GPC characterization. The additional free RAFT agents in the reaction system could enhance the control of the polymerization on PDA/RGO surface and in solution as measured by GPC. The polymer grafted polydopamine/reduced graphene oxide (PDA/RGO) nanocomposites showed excellent dispersibility in several organic solvents. The final polymer matrix dispersed of functionalized reduced graphene oxide showed higher maximum decomposition temperature measured by TGA, indicating better thermal stability

Design for Sustainability through a Life Cycle Assessment Conceptual Framework Integrated within Product Lifecycle Management

The need to include sustainable design principles during product realization poses several challenges in need of research. The demand for greener products has increased while competition has shortened product realization processes. Product Lifecycle Management (PLM) provides solutions in accelerating the development process and time to market by managing the information through a full life cycle of a product line. Life Cycle Assessment (LCA) provides a way to predict the environmental impacts that should be expected over the complete life cycle of a given product, but LCA methods are not well suited to efficient comparison of product alternatives during early design stages. Customers and other stakeholders demand products that not only comply with regulations and minimize environmental impacts, but also minimize costs and maximize certain performance objectives of a product. Thus, an approach is needed to unify validation of new products compliance with holistic consideration of environmental impacts along with other objectives over a complete life cycle for the selection of the optimal design concept in an efficient manner. This research addresses these matters by proposing the approach of integrating LCA software with a PLM system. A conceptual LCA framework- LCAatPLM (Life Cycle Assessment of assembly tree in PLM) is proposed that allows environmental assessment of assembly tree directly extracted from PLM. Firstly, relevant existing solutions are reviewed and several challenges are identified that prevent integration. By decomposing the structure of both PLM and LCA, a common foundation is identified for the integration. Then, a design methodology is developed to show the use of LCAatPLM within PLM environment. A charcoal grill design case study is detailed to show how evaluations can be made based on achievement of strategic goals, along with verification of compliance and the visibility of LCA and other results. Our findings show that design executions through LCA integrated with PLM reveal environmental criterion at early stages. It can be considered with other design criteria to identify and select optimal alternatives. This research transforms LCA as an evaluation tool used after a design is already completed to one that can guide designs earlier within the PLM environment

Chemoenzymatic Synthesis of Heparan Sulfate

Heparan sulfate (HS) participates in a variety of biological functions and has been exploited for its ability to be utilized as a HS-based drug. Chemical synthesis of HS remains extremely challenging. Previous research has proven the feasibility of using a HS enzyme-based approach to synthesize HS structures with unique biological activities. Our central hypothesis is that all subsequent modifications following N-sulfation during HS biosynthesis are governed by the number and position of the GlcNS residue. In this dissertation, a fluorous affinity tag-assisted chemoenzymatic synthesis technique has been developed to build a HS octasaccharide library with defined N-sulfo glucosamine (GlcNS) positions. The HS backbone was synthesized by heparosan biosynthetic enzymes. N-acetyl glucosaminyl transferase from E.coli K5 (KfiA) was used to transfer either GlcNAc or GlcNTFA (N-trifluoroacetylglucosamine) residues to the growing chain. Heparosan synthase from pasteurella (PmHS2) was used to transfer the GlcUA residues. A selective de-trifluoroacetylation was performed because under these conditions, the GlcNTFA is labile and will be converted to glucosamine (GlcNH2) while the GlcNAc residue remains intact. The resultant GlcNH2 is then converted to a GlcNS residue by N-sulfotransferase (NST). N-sulfo-6-O-sulfo HS backbones with different 6-O-sulfation patterns and different sizes were also prepared. Furthermore, we prepared oligosaccharide capable of binding to antithrombin (AT), which correlates to HS anticoagulant activity. In this study, an AT-binding dodecasaccharide was prepared and its structure was proven. The continuation of this dissertation will allow us to not only investigate enzymatic approaches to synthesize HS-based anticoagulant drugs, but also develop a general method for synthesizing structurally defined HS oligosaccharides that could aid in the discovery of novel HS-based therapeutic agents

2-[(Eth­oxy­carbonothio­yl)sulfan­yl]acetic acid

In the title compound, C5H8O3S2, the C—S and C—O bonds in the xanthate unit are shorter than those linked to it. In the crystal, inversion dimers linked by pairs of O—H⋯O hydrogen bonds occur