High activity of an indium alkoxide complex toward ring opening polymerization of cyclic esters

An indium complex supported by a ferrocene-derived Schiff base ligand has an unprecedented high activity toward ε-caprolactone, δ-valerolactone, and β-butyrolactone. l-Lactide, d,l-lactide, and trimethylene carbonate polymerizations also showed moderate to high activity

Mixed solutions of an associating polymer with a cleavable surfactant

Mixtures of hydrophobically modified hydroxyethyl cellulose (HMHEC) and alkali-sensitive cleavable betaine ester surfactants have been studied by viscometry, H-1 NMR, absorbance measurements, and birefringence determinations. Before the hydrolysis, the surfactants behaved as conventional nondegradable surfactants in terms of the effect on the viscosity of increasing surfactant concentration. As the surfactants were hydrolyzed, systems with time-dependent viscosity were obtained. The viscosity either decreased monotonically or went through a maximum as a function of time, depending on the initial surfactant concentration. Different surfactant chain lengths gave rise to different viscosity profiles. The rate of hydrolysis, and thus the time-dependency of the surfactant concentration, could be controlled by changing the pH of the solution

NMR studies of aggregation and hydration of surfactants containing amide bonds

The consequences of including amide bonds into the structure of short-chain nonionic surfactants have been studied. Of particular interest were the possible effects of the hydrogen bonding ability of the amide group on the micellar shape. The aggregate structure and hydration of two different amide-containing surfactants, C7H15CO-NH-(CH2CH2O)(4)H and C7H15CO-(NH-C3H6-CO)(2)N(CH3)(2), were investigated using NMR diffusometry (pulsed gradient spin echo NMR) as the main technique. Data from experiments on the surfactants, the hydrophobic probe molecule hexamethyldisilane (HMDS), and water were interpreted to gain information about the solution structures, and the results were compared to those on a previously studied alcohol ethoxylate surfactant of similar size, C8E4. Both of the amide-containing surfactants form small micelles within the whole investigated concentration range. At the critical micelle concentration, the aggregates are most probably spherical, and with increasing surfactant concentration there are indications of either a minor aggregate growth or agglomeration of the micelles. In addition, it was found that the presence of amide groups in the surfactant inhibits the intermicellar transport of HMDS, which occurs in the C8E4 system. From measurements on water diffusion in the three surfactant systems, it could be concluded that the surfactant hydration is higher when amide bonds are present

Studies on the Formation of Organosilica Nanoparticles and Their Ability To Host Hydrophobic Substances

Water-dispersible organosilica nanoparticles were synthesized using microemulsions and micellar solutions. Octadecyltrimethoxysilane (OTMS) was used as the silica source resulting in particles having a hydrophobic interior with the ability to host oil. The diameters of the formed particles could be varied between 60 and 200 nm, depending on the amount of added oil and OTMS. The size of the particles was determined using dynamic light scattering and transmission electron microscopy. Exchange-coupled diffusion nuclear magnetic resonance experiments were performed to study the exchange rates between the particles and the surrounding media. Triethylamine and tributylamine were used as probe molecules, and it was shown that they had longer mean residence times in the particles compared with in the bulk. Moreover, it was found that the mean residence time of the probe molecules increased significantly when the particles contained oil. The results also showed that the mean residence time of tributylamine was longer than that of triethylamine. Furthermore, by the use of UV-vis spectrophotometry, it was shown that the particles were able to take up benzophenone from water solutions

Superparamagnetic Fe\u3csub\u3e3\u3c/sub\u3eO\u3csub\u3e4\u3c/sub\u3e/SiO\u3csub\u3e2\u3c/sub\u3e nanocomposites: Enabling the tuning of both the iron oxide load and the size of the nanoparticles

Using a water-in-oil microemulsion system, silica nanoparticles containing superparamagnetic iron oxide (SPIO) crystals have been prepared and characterized. With this method, the loading of iron oxide crystals, the thickness of the silica shells, and the overall particle sizes are tunable. Moving from low to high water concentration, within the microemulsion region, resulted in a gradual shift from larger particles, ca. 100 nm and fully loaded with SPIOs, to smaller particles, ca. 30 nm containing only one or a few SPIOs. By varying the amount of silica precursor, the thickness of the silica shell was altered. Field dependent magnetization measurements showed the magnetic properties of the SPIOs were preserved after the synthesis. © 2008 American Chemical Society