Polyorganosiloxanes oxidation

Of all the known elastomers, polyorganosiloxane elastomers are the most resistant to weather effect they are insensitive to oxidation with oxygen in air and ozone, as well as to UV rays. That is why they do not age even in veiy harsh conditions. E.g., if natural rubber decomposes under the influence of ozone within 5 minutes at 20 °C and within 6 seconds at 100 °C, polydimethylsiloxane elastomer does not decompose even after 60 minutes in ozone at 100 °C. If heated in air to 320 °C, elastomers based on polydimethylsiloxanes, polydimethyl(metylphenyl)siloxanes, etc. only slowly oxidise on the other hand, natural rubber and synthetic organic elastomers decompose at once. 

Polyorganosiloxanes are very stable chemically the siloxane chain is preserved in many chemical reactions, whereas the thermal oxidative destruction of the molecule is generally connected only with the detachment of lateral radicals. It is essential that the decomposition product is polymer (SiC>2)x, which keeps all its dielectric properties and some strength, unlike the decomposion products of organic polymers. E.g., at 200 °C the dielec-... 

The introduction of metals such as aluminium, cobalt, iron, nickel, and titanium, into the backbone chain of polyorganosiloxanes increases their thermal and thermal-oxidative stability because of both the termination of the kinetic chain of depolymerisation and to the formation of crosslinked rigid structures in the initial stages of the process. 

Polyorganosiloxanes possess great stability to oxidation and stability to the action of high temperatures. Polyorganosiloxanes, for example, polydimethylsiloxanes with a linear molecular structure, are depoly-... 

According to the mechanism cited, it is easy to understand why polyethylsiloxane is more easily destroyed than polymethylsiloxane the -CH2- group of the ethyl radical and the silicon atom is oxidized more readily than the CH3-group. This reaction mechanism permits us to predict the thermal stability of polyorganosiloxanes on the basis of the structure of the organic radical or group at the silicon atom. 

Abstract Different oligo-DNA surface functionalized polyorganosiloxane nanoparticles have been synthesized and characterized. The core-shell polyorganosiloxane nanoparticles possess a hydrodynamic radius of 14.1 (sample code CS1) and 12.1 nm (sample code CS2), respectively. Coupling of different short chain poly(ethylene oxide)s resulted in water soluble nanospheres. For CS2-PEO110, a number of approximately 500 PEO per siloxane nanosphere has been determined. Two different (partially lluorescently... 

---