RELATIONSHIP BETWEEN STRUCTURE AND ADHESION PROPERTIES OF AROMATIC POLYIMIDES

The adhesion properties of aromatic polyimide films on SiO2 and on various polyimides without any adhesion promoter were studied. Flexibility of the polyimide chains was found to be necessary for good adhesion. Polyimides with a flexible structure gave higher adhesion than those with a rigid structure for both substrate types. On SiO2, delamination occurred within 100 h on exposure to steam at 120-degrees-C. On polyimides, the adhesion depended on both the substrate and the coating, and the peel strength increased in the following order of coating/substrate combinations: rigid/rigid < flexible/rigid < rigid/flexible < flexible/flexible. For the case of a rigid polyimide substrate, the adhesive property was greatly improved when coatings were spun on partially imidized substrate. This suggests that the dominant factors affecting adhesion are the degree of freedom of the molecular chain, which will affect the interaction between polyimide and SiO2, and the diffusibility of the molecular chain at the polyimide/polyimide interface. The existence of a diffusion layer was observed at the polyimide/polyimide interface with energy-dispersive X-ray analysis/transmission electron microscopy.