Surface Organization of a Perfluorocarbon-Functionalized Polystyrene Homopolymer

We use the perfluorocarbon-functionalized polymer, poly(4-((1H,1H,2H,2H-perfluorodecyl)-oxycarbonyl)styrene) [PPFOCS], as a model system with both surface molecular segregation and molecular orientation to test the capabilities of a near-edge X-ray absorption fine structure (NEXAFS) spectroscopy analysis scheme for polymer surfaces. Both NEXAFS spectroscopy and angle-resolved X-ray photoelectron spectroscopy (XPS) show segregation of the -(CF2)(7)CF3 chain to the air/polymer interface with the styrenic portion underneath. Postedge analysis of the NEXAFS spectra indicates a low carbon atom density surface layer, of thickness 1.0-1.4 nm, due to the overlayer of perfluorocarbon chains. An analysis of the NEXAFS C is -> pi(C=C)* and C 1s -> sigma(C-F)* transitions accounting for the different depth distributions of the phenyl rings and fluorocarbon helices reveals strong orientational ordering with the orientational order parameter S-C=C for the phenyl ring equal to -0.27 and for the C-F bonds in the fluorocarbon helix SC-F equal to -0.13. The S-C=C and SC-F determined for the polymer with the ester-linked side chain are considerably higher than those reported previously (-0.039 and 0, respectively) for a polymer [poly(4-(1H,1H,2H,2H-perfluorodecyl)oxymethylstyrene)] with an identical side chain that was ether linked to the styrene phenyl ring.(1) We tentatively attribute the high orientation in the PPFOCS to the partial conjugation between the ester group and the phenyl ring providing a relatively stiff linkage between the perfluorocarbon helix and the phenyl ring.