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Title: RAFT dispersion polymerisation in silicone oil
Author: Rymaruk, Matthew
ISNI:       0000 0004 7651 3902
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2018
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The work described in this thesis involves reversible addition-fragmentation chain transfer (RAFT) dispersion polymerisation conducted primarily in silicone oil. This is an example of polymerisation-induced self-assembly (PISA), which provides a convenient and facile route to the reproducible synthesis of range of polymer nanoparticles. In Chapter 2, a silicone oil-soluble PDMS66 macromolecular chain transfer agent (macroCTA) is prepared via esterification of a carboxylic acid-based RAFT CTA with monohydroxyterminated PDMS66. This macro-CTA is then chain-extended with a range of methacrylic monomers directly in decamethylcyclopentasiloxane (D5). Spherical nanoparticles are obtained in all cases, except when using 2-(dimethylaminoethyl) methacrylate (DMA). In this case, spheres, worms or vesicles can be obtained in D5. In addition, PDMS-PDMA worms are also synthesised in three other solvents, hexadimethyldisiloxane, n-dodecane and octamethylcyclotetrasiloxane (D4). Furthermore, these PDMS-PDMA worms form soft freestanding gels at ambient temperature owing to multiple inter-worm contacts. This gelation behaviour is characterised by oscillatory and rotational rheometry, which suggests that PDMSPDMA worms may have potential application as thickeners for non-polar solvents, specifically silicone oil. When PDMS-PDMA worms are heated to 110 °C in D5, they undergo a worm-to-sphere transition. This is attributed to surface plasticisation of the nanoparticle core by the hot solvent. This transition is probed using 1H NMR, transmission electron microscopy, rheology and smallangle X-ray scattering. The effect of incorporating a cross-linking agent, 1,2bis(2- iodoethoxy)ethane (BIEE) into these PDMS-PDMA nanoparticles is also investigated. Covalent cross-linking has the most demonstrable effect on the worms: not only do they form significantly stronger gels, they are also no longer thermoresponsive. To produce spheres, worms or vesicles in D5 with a monomer other than DMA, a new silicone-containing macro-CTA is prepared via RAFT solution polymerisation of 3- [tris(trimethylsiloxy)silyl]propyl methacrylate (SiMA). The resulting PSiMA macro-CTA enables the formation of spheres, worms, or vesicles when chain-extended with benzyl methacrylate (BzMA) in D5. Two phase diagrams are constructed in order to facilitate the reproducible synthesis of these morphologies, with the copolymer concentration, PSiMA DP and PBzMA DP being important parameters. PSiMA-PBzMA spherical nanoparticles can also be prepared in a low molecular weight silicone oil with a viscosity of 5 cSt (DM5). The ability of such nanoparticles to stabilise oil-inDM5 Pickering emulsions is explored. A range of natural oils can be utilised for the dispersed phase, such as sunflower oil or castor oil, with the resulting emulsions stable for at least 2 months. Moreover, by statistically copolymerising lauryl methacrylate (LMA) with BzMA to form the nanoparticle cores, a much wider range of oils can be used as the dispersed phase. It is hypothesised that this is owing to the enhanced wettability of the resulting PSiMA-P(BzMA-statLMA) spherical nanoparticles by the various different vegetable oils examined. RAFT aqueous emulsion polymerisation is used to prepared to spherical nanoparticles with a semifluoronated core-forming block. Such nanoparticles have a relatively low refractive index, which can be matched to the aqueous phase by adding either sucrose or glycerol. Such isorefractive particles facilitate the production of highly transparent Pickering emulsions when an isorefractive oil (n-dodecane) is used as the dispersed phase. Finally, when these hydrophilic particles are used in conjunction with similar oil-dispersed particles comprising the same semifluorinated core-forming block, highly transparent Pickering double emulsions can be produced.
Supervisor: Armes, Steven Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available