Reversible addition fragmentation chain transfer (RAFT) mediated polymerization of N-vinylpyrrolidone
Thesis (PhD (Chemistry and Polymer Science)--University of Stellenbosch, 2008.
Xanthate-mediated polymerization was investigated as a tool for the preparation of well-defined poly(N-vinylpyrrolidone) and copolymers of N-vinylpyrrolidone. Some results regarding the monomer vinyl acetate are included, mostly for comparison purposes. The structure of the leaving/reinitiating group of the xanthate mediating agent was tuned to match the monomer reactivity. This was achieved by studying the initialization behaviour of monomer-xanthate systems via in situ 1H-NMR spectroscopy. Additionally, the latter technique was valuable to identify side reactions affecting the monomer, xanthate and/or polymeric species. Subsequently, experimental conditions were defined, and used to optimize the level of control achieved during polymerization. Block copolymers were prepared from a xanthate end-functional poly(ethylene glycol) with both vinyl acetate and N-vinylpyrrolidone. Finally, the preparation of poly(N-vinylpyrrolidone) with a range of well-defined end groups was achieved via postpolymerization treatment of the xanthate end-functional polymerization product. 3 different routes were investigated, which lead to poly(N-vinylpyrrolidone) with 1) aldehyde or alcohol, 2) thiol or 3) unsaturated ω-chain-end functionality, in high yield, while the α-chain-end functionality is defined by the structure of the xanthate leaving group. The ω-aldehyde end-functional poly(N-vinylpyrrolidone) was successfully conjugated to the lysine residues of the model protein lysozyme via reductive amination. Particular attention was drawn to characterizing the polymerization products. NMR spectroscopy, liquid chromatographic and mass-spectroscopic techniques were used. The major achievements emerging from polymer analysis carried out in this study included the following: - a library of NMR chemical shifts for N-vinylpyrrolidone derivatives; - an estimation of the critical conditions for poly(N-vinylpyrrolidone) relevant for separation according to the polymer chain-ends; - conditions for the separation of block-copolymers comprising a poly(ethylene glycol) segment and a poly(N-vinylpyrrolidone) or poly(vinyl acetate) segment via liquid chromatography; - valuable results on matrix-assisted laser ionization-desorption time-of-flight mass spectroscopy (MALDI-ToF-MS) of poly(N-vinylpyrrolidone).