Degradation mechanism of silicone glues under UV irradiation and options for designing materials with increased stability

The degradation of silicone glues used, for example, in the assembly of solar modules for use in space, has been investigated and possible mechanisms which lead to colouration and possible embrittlement are analysed. Both effects are connected to the generation of radicals upon exposure to UV irradiation. As a follow up-reaction in vacuum, cross-linking and subsequently embrittlement and cracking due to shrinkage can occur. The degradation of the polymers via a radical mechanism can also lead to the formation of small metal clusters containing residues of the Karstedt catalyst and also silicon. Both types of nanoparticles contribute to colouration of the silicone glues. Possible ways to avoid this is the use of ultra-pure starting substances, a minimum amount of catalyst and a higher cross-link density of the silicone, minimizing the mobility of dangling chains formed upon UV-exposure and their tendency to form metal clusters.