Monodisperse colloidal silica particles with diameters in the range 50-700 nm were prepared by hydrolysis of tetraethyl orthosilicate in water, ammonia, and ethanol. The 58-nm particles are either nonporous or only slightly porous, and they contain 6.0 mequiv/g of silanol and 1.03 mequiv/g of ethoxy groups. Assuming 6.3-10.0 µ /g of surface ethoxy and silanol groups, the interior of the bulk silica must contain 6.3-6.6 mequiv/g of (ethoxy + silanol) groups. The surfaces of the 58-nm particles were modified by reactions with (3-mercaptopropyl)trimethoxysilane, (3-aminopropyl)trimethoxysilane, and octadecyltrimethoxysilane. The surface modifications with mercaptopropyl and aminopropyl groups can be done in dimethylformamide. A more convenient, one-pot synthesis for preparation and surface modification of colloidal silica proceeds by reaction of the trimethoxysilane with colloidal silica in the original mixture of water, ammonia, and ethanol. With (mercaptopropyl)silica, this one-pot synthesis requires steric stabilization, which is accomplished by addition of an ABA block copolymer of polyethylene oxide) and poly(propylene oxide) to the reaction mixture. Octadecylsilica precipitates during the synthesis, providing an easy method to purify and transfer the octadecylsilica to a nonpolar solvent. 13C and 29Si NMR, BET surface area analysis, pycnometry, thermogravimetric analysis, mass spectrometry, and elemental analysis have been used to characterize the unmodified and modified colloidal silicas.
p‐Divinylbenzene (DVB) 13C‐labeled at the methine carbon of the vinyl group was copolymerized in suspension with styrene at 70, 70–95, and 135–155°C using 2,2′‐azobisisobutyronitrile (AIBN) as the initiator. The number of unreacted vinyl groups in each copolymer was determined by 13C CP–MAS NMR analysis of solid samples, direct polarization 13C‐NMR analysis of CDCl3‐swollen gels, and bromination. Results from the three methods agree methods agree qualitatively. Even the 1% DVB‐crosslinked networks contained 40% unreacted DVB‐vinyl groups when prepared by high conversion polymerization at 70°C and 16% unreacted DVB‐vinyl groups when polymerization was finished at 95°C. The analyses were also applied to some commercial crosslinked polystyrenes. Every sample examined contained pendent vinyl groups
Simple and complex aromatic hydrocarbons are conveniently prepared from aldehydes and ketones by tandem. phenylation-reduction. By this procedure benzyl alkoxides, generated in situ by phenylation, are reduced by lithium-ammonia-ammonium chloride to the corresponding aromatic hydrocarbons. Complex aldehydes and ketones, containing structural features or other functional groups which might not be compatible with the reaction conditions, were subjected to the phenylation-reduction sequence to explore the limits of this simple synthetic procedure as an efficient and selective synthesis of rather complex molecular structures. These structural features or functional groups included steric hindrance, terminal olefins, isolated double bonds, ,/3-unsaturated carbonyl systems, an a,/3,7,(5-unsaturated ketone system, ,/3-unsaturated aldehyde systems containing isolated double bonds, a cross-conjugated ketone, a cyclopropane ring, aromatic systems, and heterocycles.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.