Surface characterization of a poly(styrene/p‐hydroxystyrene) copolymer series using x‐ray photoelectron spectroscopy, static secondary ion mass spectrometry, and chemical derivatization techniques

A series of poly(styrene/p‐hydroxystyrene) copolymers was examined by x‐ray photoelectron spectroscopy (XPS), static secondary ion mass spectrometry (SIMS), and chemical derivatization. Static SIMS distinguished polystyrene (PS) and poly(p‐hydroxystyrene) (PHS) on the basis of fragments, 107 D (C₇H₇O⁺) and 119–121 D {[M–H]⁺,, [M]⁺, and [M+H]⁺, where M is the hydroxystyrene (HS) monomer}, that were present in the positive ion spectrum of PHS. The negative ion spectrum of PHS was structurally less informative (C⁻ –C⁻₄, CH⁻–C₄H⁻, O⁻, OH⁻), with the exception of a peak at 119 D [M–H]⁻. While fluorinated fragments characteristic of trifluoroacetic anhydride (TFAA) (CF⁺₃, CF⁻₃, CF₃ CO⁻₂ ) were observed in both the positive and negative ion spectra of TFAA‐derivatized PHS, fragments characteristic of the derivatized polymer (C₇H₆F⁺ , C₇H₆CO₂CF⁺₃ ) were observed only in the positive ion spectrum of TFAA‐derivatized PHS. The quantitative relationship of positive ion intensities to XPS oxygen concentration for these copolymers was complicated by the absence of peaks unique to the styrene component. Quantitation based on normalization of unique hydroxystyrene peaks to total ion yield and peak ratio normalization of selected peaks was successful. Similarly, quantitative trends were observed for the TFAA‐derivatized copolymer series when the peak intensity of the C₇H₆CO₂CF⁺₃ ion was normalized to the total ion yield.