Remarkable enhancement of tracking resistance of addition-cure liquid silicone rubber by alkyl-disubstituted ureido siloxane immobilized on the silica filler surface

Abstract

It is urgent and significant to prepare silicone rubber with excellent tracking resistance in a harsh environment. In this work, alkyl-disubstituted ureido siloxane immobilized on silica (U-SiO2) was prepared by the dehydration condensation of hydrolysates of alkoxy groups in alkyl-disubstituted ureido siloxanes (US) and hydroxyl groups on the silica surface. The effect of U-SiO2 on the tracking resistance of addition-cure liquid silicone rubber (ALSR) was investigated by inclined-plane test (IP test). It was found that U-SiO2 could effectively enhance the tracking resistance of ALSR. Especially, diisopropylureidopropyltriethoxysilane and diisobutylureidopropyltriethoxysilane with isomeric substitution immobilized on silica (DIPUPES-SiO2 and DIBUPES-SiO2) performed the best. With less than 1.00 phr content, ALSR samples could reach 1A4.5 level. The erosion mass was only 0.40 % and 0.62%, respectively. Moreover, ALSR / DIPUPES-SiO2 had excellent water resistance. It could still reach 1A4.5 level and the erosion mass was almost unchanged after ALSR / DIPUPES-SiO2 was immersed in the water for five days. The results of plasma irradiation and thermal treatment showed that U-SiO2 could effectively inhibit the aggregation of platinum in Karstedt's catalyst, which could promote the crosslinking of ALSR chains under the elevated temperature to form a compact ceramic protected layer. It could not only isolate the oxygen and heat and suppress the thermal degradation of ALSR, but also resist the plasma bombardment. Therefore, the tracking resistance of ALSR was remarkably enhanced.