Quantitative analysis of styrene-pentafluorostyrene random copolymers by ToF-SIMS and XPS

Poly(styrene) (PS), poly(2,3,4,5,6-pentafluorostyrene) (5FPS) and their random copolymers were prepared by bulk radical polymerization. The spin-cast polymer films of these polymers were analyzed using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The surface and bulk compositions of these copolymers were found to be same, implying that surface segregation did not occur. The detailed analysis of ToF-SIMS spectra indicated that the ion fragmentation mechanism is similar for both PS and 5FPS. ToF-SIMS quantitative analysis using absolute peak intensity showed that the SIMS intensities of positive styrene fragments, particularly C₇H⁷⁺, in the copolymers are higher than the intensities expected from a linear combination of PS and 5FPS, while the SIMS intensities of positive pentafluorostyrene fragments are smaller than expected. These results indicated the presence of matrix effects in ion formation process. However, the quantitative approach using relative peak intensity showed that ion intensity ratios are linearly proportional to the copolymer mole ratio when the characteristic ions of PS and 5FPS are selected. This suggests that quantitative analysis is still possible in this copolymer system.