Preparation and stress relaxation properties of thermoplastic polysiloxane-block-polyimides

Three series of thermoplastic polysiloxane-block-polyimides were repared from 3, 3', 4, 4'-benzophenonetetracarboxylic dianhydride, aromatic diamines with four phenylene rings and diamine-terminated polydimethylsiloxane (<(M)over bar (w)> = 1240). The tensile modulus of their films was lowered and the coefficient of thermal expansion was increased with increasing polysiloxane composition. The copolyimides showed a good adherence onto silicon wafer even without adhesion promoter added. The adherence was maintained even after exposure to an environment of 23 degrees C and 78% RH for 72 h. The residual stress in the interface between the copolyimide coating and the silicon wafer was lowered according to the tensile modulus of coating materials, so the introduction of polysiloxane into aromatic polyimides can afford excellent adhesion and stress relaxation properties despite mismatching in thermal expansion between polymer and substrate.