Effect of siloxane segment length on the surface composition of poly(imidesiloxane) copolymers and its role in adhesion

A series of poly(imidesiloxane) (SIM) copolymers, based on α,ω-aminopropylpoly(dimethylsiloxane) (PDMS), 2,2-bis(4-[4-aminophenoxyl]phenyl)propane (BAPP), and 4,4′-oxydiphthalic anhydride (ODPA) was synthesized in our laboratories. We investigated the effect of siloxane segment length on the surface composition of the SIM copolymers and its role in adhesion. The aim is to elucidate the correlation between polymer structure, surface composition, and adhesion strength. Composition - depth profiles of the near surface region to approximately 100 Å depth were calculated using an algorithm to numerically model and simulate the deconvolution of angle-dependent electron spectroscopy for chemical analysis (ESCA) experiments. The simulated composition-depth profiles show that the topmost surface of the air (free) surface of the 75 μm thick SIM copolymer film consists of a siloxane-rich layer, even with the shortest siloxane segment. For a given siloxane bulk content, a longer siloxane segment gives a surface richer in siloxane. The peel strength of these films from adhesion to a standard Fe/Ni alloy-42 decreases with increasing thickness of the surface siloxane-rich layer, which corresponds to a longer siloxane segment length. However, all values of peel strength of the SIM copolymers are higher than that of pure polyimide.