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An optimized synthesis of nanometer silica particles via hydrolysis and condensation of tetraethylorthosilicate (TEOS) is described. At the optimum experimental conditions, homogeneous and stable silica nanoparticles with mean particles size of 7.1 ± 1.9 nm were obtained. The particle size is in a good agreement with primary particles. The size, size distribution (SD) and the yield of silica were controlled by the concentration of the reactants, ammonia feed rate, temperature and mixing mode. The increase in TEOS concentration resulted in bigger and multi-model distributed powder, while high temperature and magnetic agitation produced a highly aggregated powder. However, higher H2O/TEOS ratio and lower ammonia concentration at slower feed rate produced particles in the range of 10-14 nm. It was also found that the concentration of silanol group increased significantly with the decrease in particle size, especially below 40 nm. The optimized technique developed is simple and reproducible, affording a high yield of ∼75% of nanometer silica in a primary size range.

A structural study of epoxidized natural rubber (ENR-50) and its cyclic dithiocarbonate derivative was carried out using NMR spectroscopy techniques. The overlapping 1H-NMR signals of ENR-50 at δ 1.56, 1.68–1.70, 2.06, 2.15–2.17 ppm were successfully assigned. In this work, the 13C-NMR chemical shift assignments of ENR-50 were consistent to the previously reported work. A cyclic dithiocarbonate derivative of ENR-50 was synthesized from the reaction of purified ENR-50 with carbon disulfide (CS2), in the presence of 4-dimethylaminopyridine (DMAP) as catalyst at reflux temperature. The cyclic dithiocarbonate formation involved the epoxide ring opening of the ENR-50. This was followed by insertion of the C–S moiety of CS2 at the oxygen attached to the quaternary carbon and methine carbon of epoxidized isoprene unit, respectively. The bands due to the C=S and C–O were clearly observed in the FTIR spectrum while the 1H-NMR spectrum of the derivative revealed the peak attributed to the methylene protons had split. The 13C-NMR spectrum of the derivative further indicates two new carbon peaks arising from the >C=S and quaternary carbon of cyclic dithiocarbonate. All other 1H- and 13C-NMR chemical shifts of the derivative remain unchanged with respect to the ENR-50.

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Protonat ion ofBis[ 1,2-bis( diethyl phosphino)ethane] bis( din it rogen)molybdenum and -tungsten with Fluoroboric Acid-Diethyl Ether (1 / I ) in Benzene; Crystal and Molecular Structure of Bis[l,2bis( diet hyl phosp hino)ethane] f luoro [ hydrazido( 2-)]tungsten Tetraf luoro borate t J.

Anion electrolyte additives (ammonium salts) have been used for the first time to study the effect on the morphology development of nanometer, monodispersed silica particles by the sol-gel process. The phenomena can be explained by conductivity profile during the process as alternative to normally use zeta potential. Under experimental conditions where TEOS, water, EtOH and feed rate were fixed and without additives, unstable silica particles of ∼30 nm were formed at a ratio of TEOS/NH 3 ≥ 0.6, below that particles from 90 to 250 nm were obtained. However, upon the addition of small amount of anion electrolytes, monodispersed nanosilica powders with particles ranging from ∼20 to ∼34 nm were obtained depending on the type and concentration of anions added. It was found that all anions were able to reduce the particle size by 73-78%, among them, Br − and I − have the highest effect while Cl − has the least effect. The synthesized silica powder was free from cation impurities.

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A structural study of ring opening reaction of purified epoxidized natural rubber (ENR) with acetic acid was conducted using the NMR techniques and its thermal characteristic was evaluated with Thermal gravimetry/Differential Thermal Gravimetry (TG/DTG) and Differential Scanning Calorimetry (DSC) analyses. 1 H-NMR revealed that 19.56% of epoxide was ring-opened from the total amount of the epoxide unit in ENR-50 and this was supported by Fourier Transform Infrared (FTIR) spectroscopy. 13 C-NMR suggests the fixation of alkyl (R) i.e., acetate group to the epoxide carbon via ester linkage and formation of hydroxyl groups in the polymer chains. The attachment location of R occurred at both most (") and least (#) hindered carbons of the epoxide. The TG/DTG results of acid treated ENR-50 showed three decomposition steps at 235-338, 338-523, 523-627 8C due to the presence of the polymer chains mixture, i.e., ring-opened and intact epoxide of ENR-50. This increases the T g value of acid treated ENR-50 at 24.6 8C as compared to purified ENR-50 at 217.7 8C.