Investigation of the tracking and erosion resistance of cured liquid silicone rubber containing ureido-modified MQ silicone resin

Ureido-modified MQ silicone resin (DIPUPES-MQ) was prepared by the hydrolytic condensation of tetraethoxysilane (TEOS), (γ-diisopropylureidopropyl) triethoxysilane (DIPUPES), hexamethyldisiloxane and divinyltetramethyldisiloxane. Subsequently, DIPUPES-MQ was employed to improve the resistance to tracking and erosion of addition-cure liquid silicone rubber (ALSR), and it showed that DIPUPES-MQ could significantly enhance the tracking and erosion resistance as well as the mechanical properties of the ALSR. When the content of DIPUPES-MQ was 3.75 phr, all the test samples passed the inclined plane tracking and erosion (IP) test at 4.5 kV. The thermogravimetry (TG), thermogravimetry-Fourier transform infrared spectrometry (TG-FTIR) and FTIR results showed that the striking enhancement in the tracking and erosion resistance of the ALSR was probably ascribed to the decomposition of the ureido groups. In the pyrolysis process, the ureido groups of DIPUPES-MQ could generate isocyanic acid to hinder the “unzipping” depolymerization through reacting with Si-OH groups, so that the amount of cyclic dimethylsiloxanes inducing intense and continuous dry-band arcs was decreased.