Search results for "siloxane"
showing 10 items of 121 documents
On-fibre solid-phase microextraction coupled to conventional liquid chromatography versus in-tube solid-phase microextraction coupled to capillary li…
2006
This paper compares the advantages and disadvantages of two different configurations for the extraction of triazines from water samples: (1) on-fibre solid-phase microextraction (SPME) coupled to conventional liquid chromatography (LC); and (2) in-tube SPME coupled to capillary LC. In-tube SPME has been effected either with a packed column or with an open capillary column. A critical evaluation of the main parameters affecting the performance of each method has been carried out in order to select the most suitable approach according to the requirements of the analysis. In the on-fibre SPME configuration the fibre coating was polydimethylsiloxane (PDMS)-divinylbenzene (DVB). The limits of de…
Polydimethylsiloxane (silicone rubber) brooch as a personal passive air sampler for semi-volatile organic compounds
2018
Exposure assessments conducted using a personal sampler include the contribution of human activities to exposure that is neglected when using a stationary air sampler. This study evaluated the uptake characteristics and application of the polydimethylsiloxane (PDMS or silicone rubber) brooch as a personal passive air sampler (PPAS) for measuring concentrations of two groups of semi-volatile organic compounds (SVOCs), namely phthalates and organophosphate esters (OPEs), indoors in proximity to the breathing zone. Uptake rates of the PDMS brooch were calibrated against a personal low volume active air sampler (PLV-AAS) co-deployed on each of five study participants working in offices for 8 hs…
ORMOSIL thin films: Tuning mechanical properties via a nanochemistry approach
2006
The mechanical properties (hardness and elastic modulus) of organically modified silicate thin films can be finely tuned by varying the degree of alkylation and thus the fraction of six- and four-membered siloxane rings in the organosilica matrix. This opens the way to large tunability of parameters that are of crucial practical importance for films that are finding increasing application in numerous fields ranging from microelectronics to chemical sensing.
Development of a polydimethylsiloxane–thymol/nitroprusside composite based sensor involving thymol derivatization for ammonium monitoring in water sa…
2014
This report describes a polydimethylsiloxane (PDMS)-thymol/nitroprusside delivery composite sensor for direct monitoring of ammonium in environmental water samples. The sensor is based on a PDMS support that contains the Berthelot's reaction reagents. To prepare the PDMS-thymol/nitroprusside composite discs, thymol and nitroprusside have been encapsulated in the PDMS matrix, forming a reagent release support which significantly simplifies the analytical measurements, since it avoids the need to prepare derivatizing reagents and sample handling is reduced to the sampling step. When, the PDMS-thymol/nitroprusside composite was introduced in water samples spontaneous release of the chromophore…
Copper‐Promoted Formation of Vinylsiloxanes
2020
The metathesis reactions of chlorovinylsilanes with copper(I) oxide are reported. The process is catalyzed by HCl which can be in situ generated via hydrolysis of chlorosilanes by traces of water present in the system. An appearance of olefin/CuCl π‐intermediates can provide a stereoselectivity of the process and alter the pathway of siloxanes formation employing Cu2O as the source of oxygen. It was also shown that acetonitrile may be available as a solvent for construction of the systems with large preparative capabilities, including those based on the use atmospheric oxygen in siloxane synthesis.
Carboranyl Substituted Siloxanes and Octasilsesquioxanes: Synthesis, Characterization, and Reactivity
2008
Carboranyl-containing disiloxane, cyclic-siloxane and cage-like silsesquioxane have been prepared in high yields. Two routes are compared for their preparation, a classical hydrolytic process based on hydrolysis and condensation of the freshly prepared carboranylalkylchlorosilane and ethoxysilane precursors and a nonhydrolytic route based on the specific reactivity of chorosilane toward DMSO. Based on the typical reactivity of the carboranyl group toward nucleophiles, dianionic disiloxanes and octaanionic silsesquioxanes were obtained without modification of the siloxane bond. Products are fully characterized by FTIR, NMR and MALDI-TOF methods.
A continuous reaction system to investigate dispersion polymerization of vinyl monomers in supercritical carbon dioxide
2006
A laboratory-scale continuous reaction system using a stirred tank reac- tor was assembled in our laboratory to study the dispersion polymerization of vinyl monomers in supercritical carbon dioxide (scCO2). The apparatus was equipped with a suitable downstream separation section to collect solid particles entrained in the effluent stream from the reactor, whose monomer concentration could be measured online with a gas chromatograph. The dispersion polymerization of methyl methacry- late in scCO2 was selected as a model process to be investigated in the apparatus. The experiments were performed at 65 8C and 25 MPa with 2,2 0 -azobisisobutyroni- trile as the initiator and a reactive polysilox…
Accelerated laboratory weathering of polypropylene composites filled with synthetic silicon-based compounds
2019
Abstract Non-functionalized and n-alkyl functionalized polyhedral oligomeric silsesquioxanes (POSS), siloxane-silsesquioxane resins and the sol-gel silicas were for the first time examined as possible UV-stabilizers and/or antioxidants in polypropylene (PP). The obtained composites were subjected to the accelerated laboratory weathering tests. The influence of the weathering conditions on the structure and properties of the PP materials was evaluated on the basis of the results from Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) studies. It was found that weathering resistance of the PP materials was strongly de…
Development of standard operation procedures for the manufacture of n-octadecyl bonded silicas as packing material in certified reference columns for…
2004
The development of standard operation procedures for the manufacture of a n-octadecyl bonded spherical silica packing from partially condensed tetraethoxysilane as silica source is described. The synthesis comprises five intermediate products and six synthesis steps which were examined according to their reproducibility and robustness. The results led to the optimisation of the manufacturing process for a n-octadecyl bonded silica. Correlations were drawn between the dynamic viscosity of the poly(ethoxy)siloxane (PES), the synthesis parameters, the resulting pore structural properties and particle size distribution of the silicas. Validated procedures were developed to manufacture spherical…
Refractive index and equilibrium water content of conventional and silicone hydrogel contact lenses
2006
Prova tipográfica (In Press)