Liquid dilicone tubber （LSR） due to its excellent mechanical properties and hydrophobicity

is widely used in the manufacture of insulation sheaths of transformers and arresters. By thermal aging in 200 ℃

it is found that tensile and tearing properties of LSR obviously decreased over time while its hardness had a slight increase. The crosslink density of LSR is measured by using equilibrium swelling method

and it is found that the total crosslink density and chemical crosslink density increases significantly over time

while physical crosslink density changes slightly. SEM

EDS and FTIR are applied to the micro-analysis of LSR

which shows slight change in its microstructure

elements ratio and functional group. The change of crosslink density and mechanical properties of LSR shows a significant correlation

indicating that the chemical cross linking reaction is the main factor that leads to the change of mechanical properties

and the crosslink density can effectively reflect the change of mechanical properties during thermo-aging process.