Effects of pyromellitidiimide pattern on thermomechanical properties and thermal stability of silicone networks

Silicones are widely used in many industrial fields because of their operating temperature ranging from-40 degrees C to 200 degrees C. This range is limited at low temperature by a cold crystallization of high molar weight poly-dimethylsiloxane, and at high temperature their thermal degradation. To widen this operating temperature range, silicones have been associated with pyromellitidiimide (PYRO) patterns, commonly used for the synthesis of polyimides known for their high thermal stability. This unit has been introduced via hydrosilylation reactions up to 42 wt.% into silicone networks whose cross-linking node concentration varied from 1.36 10-4 to 22.42 10-4 mol/g. Thermal and thermomechanical properties of these materials were then characterized by DSC, TGA and DMTA, before and after isothermal ageing at 250 degrees C in air. While the presence of PYRO units reduced the cold crystallization phenomenon, surprisingly, the introduction of more than 10 wt.% PYRO units proportionally increased the mass loss of materials during their thermal ageing. However, the presence of PYRO patterns prevented the appearance of cracks and thus the breaking of the materials.