Thermal imidization of poly(amic acid) precursors on glycidyl methacrylate (GMA) graft-polymerized aluminium and copper surfaces

A novel method was developed to achieve good adhesion of polyimides (PI, Kapton HN®) and fluorinated polyimides (FPI) on aluminium and copper surfaces via thermal imidization of the respective poly(amic acid) (PAA) and fluorinated poly(amic acid) (FPAA) precursors onto the glycidyl methacrylate (GMA) graft-polymerized aluminium and copper substrates. The properly cleaned surfaces of the aluminium and copper foils were first silanized with 3-aminopropy(triethoxysilane) (APS) (the APS–metal surface). The silanized aluminium and copper foils were pretreated with Ar plasma to generate the surface peroxides and hydroperoxides before been subjected to UV-induced graft polymerization with GMA (the GMA-g-APS–metal surface). The graft-polymerized metal surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The 180°-peel adhesion strength achieved with the use of GMA-g-APS–metal surface was about 10 N/cm, or about five times the value obtainable with the pristine metal surface. It was also found that the presence of fluorine-containing groups had negligible effect on the adhesion of the FPI to the present graft-modified metal substrates. The high adhesion strength was attributed to the synergistic effect of coupling the curing of epoxide functional groups of the grafted GMA chains with the imidization process of the PAA or FPAA, and the fact that the GMA chains were covalently tethered onto the metal surface. The XPS results revealed that the PI/GMA-g-APS–Cu laminate delaminated by cohesive failure inside the polyimide film.