Thermal imidization of fluorinated poly(amic acid) precursors on a glycidyl methacrylate graft-polymerized Si(100) surface

Abstract

A novel method was developed to achieve good adhesion of fluorinated polyimides (FPIs) on a Si(100) surface via thermal imidization of the fluorinated poly(amic acid) precursors (FPAAs) onto an argon plasma-pretreated and glycidyl methacrylate (GMA) graft-polymerized Si(100) (GMA-g-Si) surface. The FPI/GMA-g-Si laminates exhibited 180°-peel adhesion strengths as high as 8.0 N/cm, compared to negligible adhesion strength for the laminates prepared from thermal imidization of the FPAAs on pristine and argon plasma-treated Si(100) 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 FPAAs, and the fact that the GMA chains were covalently tethered on the Si(100) surface. The adhesion strength of the thermally imidized poly(amic acid) precursor of polyimide (PI, Kapton HN®) on the present graft-modified Si(100) surface was also investigated for comparison purpose. It was found that the presence of fluorine-containing groups, such as CF3, had negligible effect on the adhesion of the FPIs to the present graft-modified silicon substrates. The plasma-activated and graft-modified silicon surfaces were characterized by x-ray photoelectron spectroscopy (XPS) and atomic-force microscopy. The reaction and composition at the polymer–Si interphase were investigated by Fourier transform infrared spectroscopy and XPS. XPS results also revealed that the FPI/GMA-g-Si assembly delaminated by cohesive failure inside the polymer film.