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- Acetobacter xylinum (1)
- Bacterial cellulose (1)
- C-13 NMR (1)
- CSA (1)
- Cellulose I (1)
- Cellulose II (1)
- Chemical shift anisotropy (1)
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- Graft copolymers (1)
The chemical shift anisotropies (CSAs) of cellulose I and I, the two crystalline constituents of bacterial cellulose produced by Acetobacter xylinum (DSM 14666), and regenerated cellulose II are reported for each of the spectroscopically resolved carbon resonances using the phase adjusted spinning sideband (PASS) experiment. The data are compared with experimental results using the recoupling of anisotropy information (RAI) technique and with theoretical calculations of the structure of cellulose, including the hydrogen bonding systems.
The nucleophilic substitution of fluorine of aromatic compounds with n-aminoalkyl trialkoxysilanes and consecutive sol-gel process have been used for the fabrication of various chromophoric sol-gel materials. The displacement of the fluoro substituent of an activated aromatic molecule occurs by a primary or secondary amino group of (CH3O)3Si-(CH2)3-NHR [R- = H-; CH3-, (CH3O)3Si-(CH2)3-] in tetraalkoxysilane or alcohol as solvent and the sol-gel process can be carried in the same vessel. The HF formed is trapped by a tertiary amine and simultaneously serves as the catalyst for the sol-gel process. Various aromatic compounds have been checked for this purpose: 1-(4-fluorophenyl)-2-nitroethylene, 1-(4-fluorophenyl)-2,2-dicyanoethylene, 4-fluorobenzonitrile, 4-fluoronitrobenzene, 4,4prime-difluorobenzophenone, 4,4prime-difluorobenzil, 7,7prime-difluorodibenzylideneacetone, tetrafluoro-p-benzoquinone, and 1,5-difluoro-2,4-dinitrobenzene. Mono and disubstitution has been studied by UV/Vis- and solid state NMR spectroscopy of the xerogels.
Two different radical polymerization techniques have been applied to covalently graft vinylformamide (VFA) onto silica particles. Grafting by the polymerization of VFA using an immobilized azo initiator on silica has been found less effective, because monomer conversion is limited in non-aqueous solvents and grafting yields are low in water. Radical copolymerization of VFA with vinyltriethoxysilane (VTS)-functionalized silica particles is suitable to produce poly(vinylformamide) (PVFA) silica hybrid particles in respectable yield. The VFA/VTS-silica ratio determines the degree of grafting. The PVFA-VTS-co-grafted silica particles can be acidically hydrolyzed into poly(vinylamine)-grafted silica particles. Molecular structures of the surface groups and grafted polymer chains have been confirmed by means of solid state 13C{1H} cross-polarization magic-angle spinning (CP MAS) NMR spectroscopy. Zeta potential measurements show the altering of the former silica particles surface charges arising from the introduction of basic groups on the surface.