SURFACE-COMPOSITION AND MORPHOLOGY OF POLYIMIDESILOXANE COPOLYMERS WITH SHORT POLYDIMETHYLSILOXANE SEGMENTS STUDIED BY ELECTRON-SPECTROSCOPY FOR CHEMICAL-ANALYSIS AND TIME-OF-FLIGHT SECONDARY-ION MASS-SPECTROMETRY

A series of polyimidesiloxane (STM) copolymers, based on alpha,omega-a minopropylpoly-(dimethylsiloxane) (PDMS), 2,2-bis(4-[4-aminophenoxyl]p henyl) propane and 4,4'- oxydiphthalicanhydride was synthesized in our laboratories. The effects of siloxane segment length (dimethylsiloxan e repeat units = 1, 2, 3, 4,5, and 9) and PDMS bulk content (1-30 wt % ) on the surface composition and free surface morphology of the copoly mers were investigated. Experimentally, angle-dependent electron spect roscopy for chemical analysis (ESCA) was used to acquire composition i nformation of the copolymer surface at various sampling depths. Time-o f-flight secondary ion mass spectrometry (TOF-SIMS) was used to descri be ion formation mechanism of bulk SIM copolymers with variation of bu lk composition or structure. In all cases, PDMS was segregated to the topmost 100 Angstrom of the air (free) surface of similar to 75 pm thi ck film, even with short siloxane segments and low PDMS contents. Angl e-dependent ESCA measurements show that the dominant factor in definin g the surface composition of these copolymers is not bulk composition, but in fact siloxane segment length. With the same PDMS content, a lo nger siloxane segment gives a surface richer in siloxane. For a given siloxane segment length, varying PDMS content does not significantly c hange the surface composition. TOF-SIMS measurements of bulk copolymer s simulated by solvent-cast thin films show that a longer siloxane seg ment gives higher relative ion yields of fragment ions from siloxane v ersus imide segments even with the same 10 wt % PDMS content in the co polymers. For a given average siloxane segment length of 9 dimethylsil oxane repeat units, a higher PDMS content in the copolymers yields hig her relative yields of fragment ions formed from siloxane versus imide Segments. (C) 1998 American Vacuum Society. [S0734-2101(98)04005-6].