Browsing by Author "Davis, TP"

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    Photochromic spirooxazines functionalized with oligomers: investigation of core-oligomer interactions and photomerocyanine isomer interconversion using NMR spectroscopy and DFT.
    (American Chemical Society, 2010-05-07) Yee, LH; Hanley, TL; Evans, RA; Davis, TP; Ball, GE
    Photochromic spirooxazines functionalized with poly(ethylene glycol) (PEG) and poly(dimethylsiloxane) (PDMS) oligomers were monitored using NMR spectroscopy at temperatures between 193 and 233 K before and after in situ exposure to UV irradiation. NOESY and ROESY experiments reveal the TTC (trans−s-trans−cis) isomer to be the dominant merocyanine isomer formed on photolysis, with some CTC (cis−s-trans−cis) isomer also present. Significant ROE cross peaks were observed between the “bulk” of the oligomeric units and protons across the entire photochromic core of the molecule, the intensity of these cross peaks suggesting that the interaction of the oligomer side chain and core of the molecule is significantly enhanced by the permanent attachment, especially with the PDMS side chain. The 2D NMR spectra indicate that there is exchange between the TTC and CTC isomers even at 193 K. This isomerization of the parent spirooxazine compounds, lacking the oligomeric side chains, was found to be acid-catalyzed, and DFT calculations support the strong possibility that it is the protonated merocyanine form that undergoes the facile isomerization process. Interconversion of the different merocyanine isomers is suggested to be fast on the NMR time scale under many experimental conditions, precluding the observation of different isomers using NMR spectroscopy at room temperature. © 2010, American Chemical Society
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    The use of SAXS and SANS to assist the design of block copolymers for ophthalmic applications
    (The Bragg Institute, Australian Nuclear Science and Technology Organisation, 2005-11-27) Saricilar, S; Davis, TP; Stenzel, M; Barner-Kowollik, C; Knott, RB
    The important properties of soft, extended-wear contact lenses include biocompatibility, oxygen permeability, wettability, material strength and stability. Significant overnight corneal swelling caused by low oxygen permeability limits the use of conventional hydrogels. The effect of molecular architecture on oxygen permeability is being investigated for a range of diblock copolymers based on monomers currently used in the contact lens industry. Diblock copolymers are synthesised via the controlled free radical polymerisation (RAFT) of 3-[tris(trimethyl silyoxy) silyl] propyl methacrylate (TRIS) with (i) methyl methacrylate (l\l|l\llA), and (ii) tert-butyl methacrylate (t-BuI\llA). The aim is to develop novel diblock copolymers with oxygen permeability (Dk) above 100 barrers in combination with superior hydration properties that will lead to materials suitable for extended-wear contact lenses. The molecular architecture of diblock copolymers has been determined using Small Angle X-ray and Neutron Scattering (SAXS and SANS), Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM), and the results correlated with oxygen permeability and hydration effects. © The Authors