Sol-Gel-Derived Silicon-Boron Oxycarbide Glasses Containing Mixed Silicon Oxycarbide (SiCxO4−x) and Boron Oxycarbide (BCyO3−y) Units

The introduction of B atoms in SiOC glass networks has been achieved through the pyrolysis of sol-gel-derived polyborosiloxanes under an inert atmosphere. The starting gels were obtained from hydrolysis-condensation reactions of triethylborate (B(OEt)₃) and an organically modified trialkoxysilane (EtSi(OEt)₃). The resulting hybrid EtSiO_1.5-B₂O₃ gels showed a homogeneous dispersion of the B atoms in the siloxane network via ≡Si—O—B≦ bonds. The presence of such borosiloxane bridges prevents the formation of cyclic or cage siloxane entities and leads to relatively high ceramic yields (∼80%). The transformation of the polyborosiloxanes into amorphous SiBOC glasses was followed using Fourier transform infrared spectroscopy and multinuclear magic-angle spinning-nuclear magnetic resonance (MAS-NMR) (¹¹B, ¹³C, and ²⁹Si). An important change in the carbon, silicon, and boron environments occurs during pyrolysis. Interestingly, the ¹¹B MAS-NMR spectra suggest a progressive replacement of the B—O bonds by B—C bonds, which leads to a distribution of trigonal BC_xO_3−x sites in the glass that was pyrolyzed at 1000°C, with a residual amount of B(OSi)₃ sites. The resulting glasses can thus be described as silicon-boron oxycarbide networks that are based on SiC_xO_4−x and BC_yO_3−y mixed environments.     

Cationic photopolymerization of polyfunctional 1‐propenyl ether systems

The cationic photopolymerization of trimethylolpropane tripropenyl ether (TPE), initiated by a diaryl iodonium salt, has been investigated. The influence of the presence of different alcoholic additives on the rates of photopolymerization and on the properties of the networks obtained has been studied. New 1‐propenyl ethers (trimethylolpropane dipropenyl ether (DPE) and its acetyl ester) were synthesized and employed as modifying agents in TPE photopolymerization. The thermal and dynamic‐mechanical properties of the films obtained have been investigated and are correlated with the structure of the networks and to the mechanism of the curing reaction; a microheterogeneous structure of the network was shown by dynamic‐mechanical thermal analysis. © 2001 Society of Chemical Industry     

Piroxicam solid state studies after processing with SAS technique

Supercritical carbon dioxide (SCO₂) was used as anti-solvent to precipitate Piroxicam, a nonsteroidal anti-inflammatory drug, from different organic solvents (acetone, ethyl acetate and dichloromethane). Physicochemical properties of the samples were analyzed before and after the treatment to highlight possible changes in the form of the crystals. The solid state analysis of both products untreated and treated with CO₂, showed that the applied method choose a particle size reduction and transition to the pure α form resulting in needle-shaped crystals, regardless of the chosen solvent. In order to identify which process was responsible for the above results, Piroxicam was further precipitated from the same three solvents by traditional evaporation method (RV-samples).The dissolution profiles of Piroxicam processed in SCO₂ show a better dissolution performance of Piroxicam over their corresponding system obtained by traditional evaporation method.These results manifest that SAS technology is a controllable way to improve bioavailability of water-insoluble drugs.