Doctoral Degrees (Chemistry and Polymer Science)

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Browsing Doctoral Degrees (Chemistry and Polymer Science) by Author "Akeroyd, Niels"

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    Click chemistry for the preparation of advanced macromolecular architectures
    (Stellenbosch : University of Stellenbosch, 2010-03) Akeroyd, Niels; Klumperman, Bert; University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science.
    ENGLISH ABSTRACT: Different click chemistry methods have been used together with Reversible Addition- Fragmentation chain Transfer (RAFT) mediated polymerization to synthesize macromolecular architectures. A new leaving group for RAFT was introduced. This triazole leaving group allows for easy conjugation of the RAFT agent to various substrates via the copperI catalyzed Huisgen 1,3-dipolar cycloaddition reaction. Subsequently monomer can be polymerized onto the substrate using the RAFT agent. This connects the polymer to the substrate via a hydrolytically stable 1,2,3-triazole. The Mitsunobu reaction was used to chain-end functionalize polymers. The Mitsunobu reaction allows for the substitution of primary and secondary alcohols with a nucleophile. The modification of polymer chain-ends was done in two ways. Firstly, thiol-functional chain-ends were used as the nucleophile in the Mitsunobu reaction using propargyl alcohol as the alcohol. This yielded alkyne-functional polymers. Thiol chain-end functional polymers were obtained by the aminolysis of polymers synthesized via RAFT. Secondly, alcohol-functional polymers were modified. In the case of poly(vinylpyrrolidone), the RAFT group was hydrolyzed and alcohols were obtained. Hydroxyl functional PEG was obtained commercially. The hydroxyl functionality was reacted in the Mitsunobu reaction using hydrazoic acid (HN3) as the nucleophile. Azide chain end functional polymers were obtained. These alkyne and azide chain end functional polymers were subsequently used in the copperI catalyzed Huisgen 1,3-dipolar cycloaddition reaction. Ultra Fast Hetero Diels-Alder click chemistry (UFHDA) was used to synthesizes norbornenelike structures (substituted 2-thiabicyclo[2.2.1]hept-5-ene moieties). Norbornene-like structures can be polymerized via Ring Opening Metathesis Polymerization (ROMP). Monomers were synthesized using phenethyl(diethoxyphosphoryl)dithioformate and cyclopentadiene. Macromonomers were obtained from the UFHDA of Polystyrene (PSTY) synthesized via RAFT, using phenethyl(diethoxyphosphoryl) dithioformate as the RAFT agent, and cyclopentadiene or cyclopentadienyl-terminated PEG as the dienes. The obtained (macro) monomers were homo- and copolymerized using Ring Opening Metathesis Polymerization (ROMP). For the ROMP, four different Grubbs type catalysts were tested.The ring-strain promoted Huisgen 1,3-dipolar cycloaddition reaction uses cyclooctynes as the alkyne. The ring-strain in this molecule allows for a fast reaction at room temperature. This reaction is potentially very interesting for biological applications because it doesn’t require the toxic copper catalyst. In this work three routes towards cyclooctynes are investigated. PEG was chain end functionalized with the obtained cyclooctyne derivatives. Overall, click chemistry methodologies were applied to synthesize different macromolecular architectures. Results include a new type of RAFT agent that allows for easy conjugation to substrates, reaction methods for chain end modification of polymers, and the synthesis of new monomers and polymers.