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 alpha,omega-amin opropylpoly( dimethylsiloxane) (PDMS), 2,2-bis(4-[4-aminophenoxyl]phenyl)pr opane (BAPP), and 4,4'-oxydiphthalic anhydride (ODPA) was synthesized in ou r laboratories. We investigated the effect of siloxane segment length on th e surface composition of the SIM copolymers and its role in adhesion. The a im is to elucidate the correlation between polymer structure, surface compo sition, and adhesion strength. Composition-depth profiles of the near surfa ce region to approximately 100 Angstrom depth were calculated using an algo rithm to numerically model and simulate the deconvolution of angle-dependen t electron spectroscopy for chemical analysis (ESCA) experiments. The simul ated composition-depth profiles show that the topmost surface of the air (f ree) surface of the 75 mu m 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-4 2 decreases with increasing thickness of the surface siloxane-rich layer, w hich corresponds to a longer siloxane segment length. However, all values o f peel strength of the SIM copolymers are higher than that of pure polyimid e.