Low Molecular Siloxanes Research Articles

Polymeric Composite Material for Medical Purposes

Polymeric composite materials (PСM) on the basis of low-molecular siloxane rubber which are supposed to be used as impression materials in stomatology are developed. As fillers for creation of PСM were used: amorphous aerosil; vegetable aerosil, received from waste of a rice peel; diatomite. Researches concerned definition influence of content of filler on working hours of siloxane compositions and a complex of properties of the developed impression materials.

A quantitative approach to dynamic and isothermal curing of an epoxy resin modified with oligomeric siloxanes

The reactivity of a system comprising commercial epoxy resin Epidian® 6 (E6) and triethylenetetramine (Z-1) hardener was studied. The system was modified with two low-molecular siloxane modifiers: 1,3-bis(glycidyloxypropyl)-1,1,3,3-tetramethyldisiloxane (DS1) and 1,3-bis(aminopropyl)-1,1,3,3-tetramethyldisiloxane (DS2). The modifiers replaced 10 mass% of E6 or Z-1, respectively. The systems E6/DS2 and DS1/Z-1 were also studied. Enthalpy of curing was determined for all systems in isothermal conditions and dynamically, i.e., in the range of 0–250 °C with linearly increasing temperature at the rate of 2, 5, 10, and 20 °C min−1. The activation energy of curing was determined using isoconversional methods by Friedman and Kissinger–Akahira–Sunose. The epoxy systems containing siloxane modifiers had generally lower activation energies than the reference E6/Z-1 system. The time to gelation measurements were taken using the temperature-modulated differential scanning calorimetry.

Various types of polysiloxanes studied by positron annihilation lifetime spectroscopy

In the work, linear poly(vinylsiloxanes) with regular distributions of vinyl groups along chains, the networks obtained by their hydrosilylation with various hydrogensiloxanes, products of pyrolysis of such networks as well as the networks prepared via reaction of low-molecular siloxanes have been studied by positron anihilation lifetime spectroscopy (PALS).Based on free volume sizes determined by this method, relations between cross-link densities in the investigated systems have been established. They have been compared with the results of swelling experiments conducted in the work and to efficiency of cross-linking reaction evaluated in our previous FTIR investigations of the systems. It has been found that PALS and swelling measurements lead to the same conclusions concerning cross-link densities in the networks prepared from low-molecular siloxanes. Discrepancies have been observed in the case of polymer-derived systems. Additionally, it is demonstrated that PALS is capable of revealing the presence of free carbon phase in SiCO materials formed upon pyrolysis of polysiloxane networks.

Hydrosilylation of low-molecular siloxanes in the presence of photactivated alkene and sulfoxide platinum(II) complexes

Hydrosilylation of tetramethyldivinyldisiloxane with pentamethyl-and tetramethyldisiloxane in the presence of photoactivated alkene and sulfoxide platinum(II) complexes was studied. The most active photoactivated catalysts are bis-sulfoxide platinum complexes; an additional photosensitive center, the oxalate ligand, enhances the effect of photoirradiation.

Separation of low molecular siloxanes for electronic application by liquid-liquid extraction

Silicone resins are widely used for electronic packaging as potting and encapsulating materials. Silicone resins have many advantages for electronic packaging applications such as superior electrical properties, thermal stability, low water absorption, etc. Furthermore, silicone resins are not only used as protective materials for integrated circuit (IC) devices but also as conducting materials for interconnection. However, silicone resins have two big drawbacks: low adhesion strength and low molecular weight creep. A simple liquid-liquid extraction method has been developed to purify silicone resins, which will improve adhesion strength and eliminate low molecular weight creep. This paper describes the results of the liquid-liquid extraction method to remove low molecular weight cyclic siloxanes. Fourier transform-infrared (FT-lR) spectroscopy was used to monitor the removal rate of low molecular weight cyclic siloxanes. Thermogravimetric analysis (TGA) was used to evaluate the purity of silicone resin. Gas chromatography-mass spectrometry (GC/MS) was used to identify the low molecular weight cyclic siloxanes. Thermomechanical analyzer (TMA), dynamic mechanical analyzer (DMA), and die shear test were used for evaluate the properties of silicone resin.

Thermal degradation of crosslinked polyorganosiloxanes

A study has been made of the thermal degradation of polyorganosiloxanes containing various organic radicals, prepared by alcoholysis of acetoxy-derivatives of the corresponding chlorosilanes. The kinetics of thermal degradation of the crosslinked polymers and the composition of the degradation products liberated at various stages up to 900° have been studied by dynamic and isothermal thermogravimetric analysis, and by volumetric gas analysis. It is shown that in thermal degradation of polymethylsiloxanes at 400–480° low-molecular siloxanes are eliminated, of composition identical with that of the original polymer. At higher temperatures all the polyorganosiloxanes studied begin simultaneously to evolve the appropriate hydrocarbon and form polysubstituted derivatives of that hydrocarbon, which form part of the charred residue. Hydrogen is evolved in the last stage of the reaction. An expression is proposed for determining the rate of thermal degradation of polyorganosiloxanes.

Modelle für Reaktionen zwischen organischen und mineralischen Substanzen im Boden

Low molecular siloxanes, silicagel, aluminium oxide, permutite, and perlite were dissolved by ammoniacal catechol solution. Silicagel was also dissolved by othero-diphenols. Low molecular silicon organic ester or complex compounds were crystallised from the reaction products of silicagel with catechol and 2,3-naphthalenediol. On orthoclase an insoluble brown cover was formed. The reaction ofo-diphenols with silicates may be important in soil formation.